Volume 50,Issue 10,2021 Table of Contents
1 Influence of Hot Corrosion on Precipitation of δ Phase and Tensile Properties of GH4169 Superalloy
2021, 50(10):3427-3436.
DOI: 10.12442/j.issn.1002-185X.E20200039
Abstract:
The hot corrosion behavior of the superalloy GH4169 were analyzed in the salt mixture of 75Na2SO4+ 25NaCl (wt%) at 650, 750 and 850 °C for 50, 75 and 100 h. Then the precipitation of δ phase and tensile properties of the superalloy at ambient temperature were investigated. Results show that with increasing the heat treatment temperature, the ultimate tensile strength (UTS) and yield strength (YS) of the alloy exhibit a drastic degradation while elongation improves significantly. The needle-shaped δ phase precipitated at the grain boundaries can enhance the strength of the superalloy, and cause intergranular brittle fracture. As a result, the ductility of the superalloy is reduced after exposure at 750 °C. The corrosion mechanism of the alloy conforms to type-II hot corrosion at 650 and 750 °C while to type-I hot corrosion at 850 °C. Both kinds of corrosion can form a corrosion layer and promote the δ phase precipitation.
The hot corrosion behavior of the superalloy GH4169 were analyzed in the salt mixture of 75Na2SO4+ 25NaCl (wt%) at 650, 750 and 850 °C for 50, 75 and 100 h. Then the precipitation of δ phase and tensile properties of the superalloy at ambient temperature were investigated. Results show that with increasing the heat treatment temperature, the ultimate tensile strength (UTS) and yield strength (YS) of the alloy exhibit a drastic degradation while elongation improves significantly. The needle-shaped δ phase precipitated at the grain boundaries can enhance the strength of the superalloy, and cause intergranular brittle fracture. As a result, the ductility of the superalloy is reduced after exposure at 750 °C. The corrosion mechanism of the alloy conforms to type-II hot corrosion at 650 and 750 °C while to type-I hot corrosion at 850 °C. Both kinds of corrosion can form a corrosion layer and promote the δ phase precipitation.
2021, 50(10):3437-3445.
DOI: 10.12442/j.issn.1002-185X.20210170
Abstract:
The influence of different cumulative rolling processes on the distribution of thermal parameters of sheet was simulated using DEFORM commercial finite element software. The dynamic globularization process of TA15 titanium alloy after thermal compression and cumulative rolling was simulated by the cellular automata. The result shows that during the accumulative roll bonding (ARB) process, the microstructure and properties of TA15 titanium alloy can be effectively improved by reducing the deformation of single pass and rolling speed as well as maintaining a certain temperature. A reasonable dynamic globularization cellular automata (CA) model was imported into Deform-3D commercial finite element simulation software and the microstructure evolution was simulated in the process of thermal compression and accumulative rolling-bonding.
The influence of different cumulative rolling processes on the distribution of thermal parameters of sheet was simulated using DEFORM commercial finite element software. The dynamic globularization process of TA15 titanium alloy after thermal compression and cumulative rolling was simulated by the cellular automata. The result shows that during the accumulative roll bonding (ARB) process, the microstructure and properties of TA15 titanium alloy can be effectively improved by reducing the deformation of single pass and rolling speed as well as maintaining a certain temperature. A reasonable dynamic globularization cellular automata (CA) model was imported into Deform-3D commercial finite element simulation software and the microstructure evolution was simulated in the process of thermal compression and accumulative rolling-bonding.
2021, 50(10):3446-3453.
DOI: 10.12442/j.issn.1002-185X.20200597
Abstract:
The mechanical behavior and texture evolution of extruded AZ31 magnesium alloy during the axial tension-compression process at room temperature were simulated by a modified viscoplastic self-consistent model considering slip and twin plastic deformation mechanisms. On the basis of EBSD experiment and simulation, the mechanism of tension-compression asymmetry caused by different deformation mechanisms and the texture evolution in the process of plastic deformation were analyzed. Results show that basal slip is the main deformation mode in the early stage of axial tension deformation, but the orientation factor of basal slip is low and has a hard orientation, resulting in higher yield stress. With the increase in strain, prismatic slip becomes the main deformation mechanism, and the strain hardening rate is low, so the stress-strain curve is smooth. In the early stage of axial compression, tension twinning has a high activity due to its low critical shear stress, leading to lower yield stress. As the relative activity decreases rapidly with the tension twinning, the hardening rate increases at the same time. In the later stage, with the activation of compression twinning, its relative activity increases rapidly; the accumulated stress during plastic deformation can be released, and the hardening rate decreases. In addition, the less twin volume fraction in the ED direction was explained by the color and the twin trace of typical grain.
The mechanical behavior and texture evolution of extruded AZ31 magnesium alloy during the axial tension-compression process at room temperature were simulated by a modified viscoplastic self-consistent model considering slip and twin plastic deformation mechanisms. On the basis of EBSD experiment and simulation, the mechanism of tension-compression asymmetry caused by different deformation mechanisms and the texture evolution in the process of plastic deformation were analyzed. Results show that basal slip is the main deformation mode in the early stage of axial tension deformation, but the orientation factor of basal slip is low and has a hard orientation, resulting in higher yield stress. With the increase in strain, prismatic slip becomes the main deformation mechanism, and the strain hardening rate is low, so the stress-strain curve is smooth. In the early stage of axial compression, tension twinning has a high activity due to its low critical shear stress, leading to lower yield stress. As the relative activity decreases rapidly with the tension twinning, the hardening rate increases at the same time. In the later stage, with the activation of compression twinning, its relative activity increases rapidly; the accumulated stress during plastic deformation can be released, and the hardening rate decreases. In addition, the less twin volume fraction in the ED direction was explained by the color and the twin trace of typical grain.
2021, 50(10):3454-3461.
DOI: 10.12442/j.issn.1002-185X.20210483
Abstract:
Friction stir processing (FSP) was applied to process a 2 mm thick Al-Mg-Si (6061-T6) alloy plate. The influence of the FSP with the same speed ratio on microstructure evolution, microhardness distribution, tensile properties and corrosion performances of the stirred zone (SZ) in the 6061-T6 alloy was investigated. Results show that there are obvious differences in the microstructure, such as grain morphologies, mean grain size, grain boundary distributions and precipitate distributions of the SZ prepared using the FSP with different processing speeds, which in turn affects the mechanical properties and corrosion resistance. The mean grain size of the equiaxed recrystallized grains of the SZ sample prepared by high speed (8000 r/min, 800 mm/min) is 9.5 μm, which is significantly refined compared to 23.2 μm of the conventional speed (1000 r/min, 100 mm/min) and 13.6 μm of the as-received 6061-T6 alloy. In addition, the distribution characteristics of the precipitates are more similar to that of the as-received 6061-T6 alloy. As a result, in addition to the slight change in corrosion resistance, the SZ sample prepared using the high speed FSP exhibits excellent mechanical properties. The maximum tensile strength and elongation of the SZ sample are 281.5 MPa and 34.8%, which are 86.3% and 122.1% of that of the as-received 6061-T6 alloy, respectively.
Friction stir processing (FSP) was applied to process a 2 mm thick Al-Mg-Si (6061-T6) alloy plate. The influence of the FSP with the same speed ratio on microstructure evolution, microhardness distribution, tensile properties and corrosion performances of the stirred zone (SZ) in the 6061-T6 alloy was investigated. Results show that there are obvious differences in the microstructure, such as grain morphologies, mean grain size, grain boundary distributions and precipitate distributions of the SZ prepared using the FSP with different processing speeds, which in turn affects the mechanical properties and corrosion resistance. The mean grain size of the equiaxed recrystallized grains of the SZ sample prepared by high speed (8000 r/min, 800 mm/min) is 9.5 μm, which is significantly refined compared to 23.2 μm of the conventional speed (1000 r/min, 100 mm/min) and 13.6 μm of the as-received 6061-T6 alloy. In addition, the distribution characteristics of the precipitates are more similar to that of the as-received 6061-T6 alloy. As a result, in addition to the slight change in corrosion resistance, the SZ sample prepared using the high speed FSP exhibits excellent mechanical properties. The maximum tensile strength and elongation of the SZ sample are 281.5 MPa and 34.8%, which are 86.3% and 122.1% of that of the as-received 6061-T6 alloy, respectively.
2021, 50(10):3462-3469.
DOI: 10.12442/j.issn.1002-185X.20200586
Abstract:
In order to improve the wear resistance of titanium alloy, and to prevent the deformation of thin-walled components, taking Ti6Al4V alloy as the object, the effect of shot peening pretreatment on the low-temperature nitriding of titanium alloy was studied. The results show that the pretreatment of shot peening (SP) can effectively promote the plasma nitriding process at low temperature. Under the test conditions of 500 °C, with the increase of shot peening strength, nitriding efficiency of pretreated samples increases gradually, and the surface hardness, load-bearing capacity and the wear resistance of nitrided layer increase gradually. Compared with unpretreated nitrided samples (Ti6Al4V-PN), when the shot strength increases to 0.25 mmA, the surface hardness of the pretreated nitrided samples (SP(0.25)-PN) increases by 32.7% and the wear rate decreases by 42.3%. The goal of shot peening pretreatment to promote low-temperature plasma nitriding of Ti6Al4V alloy is well achieved.
In order to improve the wear resistance of titanium alloy, and to prevent the deformation of thin-walled components, taking Ti6Al4V alloy as the object, the effect of shot peening pretreatment on the low-temperature nitriding of titanium alloy was studied. The results show that the pretreatment of shot peening (SP) can effectively promote the plasma nitriding process at low temperature. Under the test conditions of 500 °C, with the increase of shot peening strength, nitriding efficiency of pretreated samples increases gradually, and the surface hardness, load-bearing capacity and the wear resistance of nitrided layer increase gradually. Compared with unpretreated nitrided samples (Ti6Al4V-PN), when the shot strength increases to 0.25 mmA, the surface hardness of the pretreated nitrided samples (SP(0.25)-PN) increases by 32.7% and the wear rate decreases by 42.3%. The goal of shot peening pretreatment to promote low-temperature plasma nitriding of Ti6Al4V alloy is well achieved.
2021, 50(10):3470-3476.
DOI: 10.12442/j.issn.1002-185X.20200623
Abstract:
The high-temperature stress rupture properties of K417G superalloy with various Mn contents (0.09wt%~0.35wt%) were studied and the existence form and distribution of Mn were evaluated as well. The results show that Mn is solid-dissolved in γ matrix and enriched in γ'-depleted matrix in front of γ+γ' eutectic cap. Mn elements promote the segregation of Al and Ti to interdendrite zone, thus increasing the volume fraction of γ+γ' eutectic in interdendrite zone and decreasing the size of γ' phase in dendrite core. With the increase of Mn content, the stress rupture life and the plasticity decrease greatly under the condition of 950 °C/235 MPa. The alloy with the minimal Mn content shows the optimal high-temperature stress rupture properties.
The high-temperature stress rupture properties of K417G superalloy with various Mn contents (0.09wt%~0.35wt%) were studied and the existence form and distribution of Mn were evaluated as well. The results show that Mn is solid-dissolved in γ matrix and enriched in γ'-depleted matrix in front of γ+γ' eutectic cap. Mn elements promote the segregation of Al and Ti to interdendrite zone, thus increasing the volume fraction of γ+γ' eutectic in interdendrite zone and decreasing the size of γ' phase in dendrite core. With the increase of Mn content, the stress rupture life and the plasticity decrease greatly under the condition of 950 °C/235 MPa. The alloy with the minimal Mn content shows the optimal high-temperature stress rupture properties.
2021, 50(10):3477-3484.
DOI: 10.12442/j.issn.1002-185X.E20200036
Abstract:
Four alloy rods of Al-Zn-Mg-Cu-Zr-xEr (x=0, 0.1, 0.2, 0.5, wt%) were prepared by directional solidification. The microstructure and second phase morphology of alloys were investigated by optical microscopy (OM), electron probe micro-analysis (EPMA), energy dispersive spectrometer (EDS) and other methods. The results indicate that Er element can increase the number of dendrites in the directional solidification structure of Al-Zn-Mg-Cu-Zr alloy, and reduce the primary dendrite arm spacing and secondary dendrite arm spacing of the alloy. A proper amount of Er element can reduce the content of second phase in the alloy and increase the tendency to form round second phase. The formation of Al8Cu4Er phase can reduce the Cu content in the T phase (AlZnMgCu phase), which plays a role of rounding the boundary of the T phase, and can change the morphology and internal structure of the T phase. The Al8Cu4Er phase serves as the nucleation position of the T phase, and part of the T phase grows around this phase. The addition of Er can improve the microhardness of the alloy.
Four alloy rods of Al-Zn-Mg-Cu-Zr-xEr (x=0, 0.1, 0.2, 0.5, wt%) were prepared by directional solidification. The microstructure and second phase morphology of alloys were investigated by optical microscopy (OM), electron probe micro-analysis (EPMA), energy dispersive spectrometer (EDS) and other methods. The results indicate that Er element can increase the number of dendrites in the directional solidification structure of Al-Zn-Mg-Cu-Zr alloy, and reduce the primary dendrite arm spacing and secondary dendrite arm spacing of the alloy. A proper amount of Er element can reduce the content of second phase in the alloy and increase the tendency to form round second phase. The formation of Al8Cu4Er phase can reduce the Cu content in the T phase (AlZnMgCu phase), which plays a role of rounding the boundary of the T phase, and can change the morphology and internal structure of the T phase. The Al8Cu4Er phase serves as the nucleation position of the T phase, and part of the T phase grows around this phase. The addition of Er can improve the microhardness of the alloy.
2021, 50(10):3485-3494.
DOI: 10.12442/j.issn.1002-185X.20200610
Abstract:
Hydrogenated amorphous TiO2 nanotube arrays (H@am-TNAs) with different tube diameter, length and wall thickness were prepared through the modified two-step electrochemical anodization and electrochemical hydrogenation method. Results show that the electrochemical hydrogenation has almost no effect on the topology of TiO2 nanotube arrays. After electrochemical hydrogenation, the nanotubes have a specific capacitance of 4.05 mF·cm-2 at 100 mV·s-1 that is 20 times larger than that of the corresponding one without hydrogenation with the same tube length and diameter. The capacitance of the nanotube is not only related to the tube length but also influenced by tube diameter. The aspect ratio of the nanotubes shows a linear relationship if fitted by an exponential function. The areal capacitance/aspect ratio reaches 0.056, which is almost equivalent to that of the anatase phase TiO2 nanotubes. The nanotubes anodized for 2 h own the smallest charge transfer resistance, the best ion diffusion/transportation kinetics, and the highest areal capacity. Furthermore, to study the wettability in the electrochemical properties of the H@am-TNAs, the same H@am-TNAs electrode was soaked in the electrolyte for different hours before C-V and C-P testing, and the results show that the capacitance decreases with increasing the soaking time.
Hydrogenated amorphous TiO2 nanotube arrays (H@am-TNAs) with different tube diameter, length and wall thickness were prepared through the modified two-step electrochemical anodization and electrochemical hydrogenation method. Results show that the electrochemical hydrogenation has almost no effect on the topology of TiO2 nanotube arrays. After electrochemical hydrogenation, the nanotubes have a specific capacitance of 4.05 mF·cm-2 at 100 mV·s-1 that is 20 times larger than that of the corresponding one without hydrogenation with the same tube length and diameter. The capacitance of the nanotube is not only related to the tube length but also influenced by tube diameter. The aspect ratio of the nanotubes shows a linear relationship if fitted by an exponential function. The areal capacitance/aspect ratio reaches 0.056, which is almost equivalent to that of the anatase phase TiO2 nanotubes. The nanotubes anodized for 2 h own the smallest charge transfer resistance, the best ion diffusion/transportation kinetics, and the highest areal capacity. Furthermore, to study the wettability in the electrochemical properties of the H@am-TNAs, the same H@am-TNAs electrode was soaked in the electrolyte for different hours before C-V and C-P testing, and the results show that the capacitance decreases with increasing the soaking time.
2021, 50(10):3495-3503.
DOI: 10.12442/j.issn.1002-185X.20200638
Abstract:
Regular porous titanium specimens with different porosities was fabricated to investigate the overall and local failure characteristics of porous metals. Dynamic compression tests were implemented using the split Hopkinson pressure bar system at the strain rates from 600 s-1 to 2100 s-1. Results show that the specimens with different porosities exhibit two typical deformation modes: compression deformation mode and connected fracture mode. The compression deformation mode mainly occurs in the specimens with low porosity, and the characteristic is that the cell walls of outer surface of the specimen exhibit local collapse. However, the connected fracture mode mostly occurs in the specimens with high porosity, and usually shows connected fracture in one or more pore layers. Moreover, the local pores of two deformation modes present different characteristics during compression, and the stress concentration occurs at the position with the minimum curvature of the pores. Microstructural analysis indicates that shear band appearing in the intercellular walls is the main failure mechanism of the specimens. Dimples and ductile stripes of fracture surface reveal that the collapse of the intercellular wall is a process of ductile fracture. Meanwhile, the softening failure of the cell walls and the strain hardening of the matrix material can affect the mechanical response of porous titanium. Additionally, with the increase of porosity, the greater the stress concentration factor, the easier the failure of porous metals.
Regular porous titanium specimens with different porosities was fabricated to investigate the overall and local failure characteristics of porous metals. Dynamic compression tests were implemented using the split Hopkinson pressure bar system at the strain rates from 600 s-1 to 2100 s-1. Results show that the specimens with different porosities exhibit two typical deformation modes: compression deformation mode and connected fracture mode. The compression deformation mode mainly occurs in the specimens with low porosity, and the characteristic is that the cell walls of outer surface of the specimen exhibit local collapse. However, the connected fracture mode mostly occurs in the specimens with high porosity, and usually shows connected fracture in one or more pore layers. Moreover, the local pores of two deformation modes present different characteristics during compression, and the stress concentration occurs at the position with the minimum curvature of the pores. Microstructural analysis indicates that shear band appearing in the intercellular walls is the main failure mechanism of the specimens. Dimples and ductile stripes of fracture surface reveal that the collapse of the intercellular wall is a process of ductile fracture. Meanwhile, the softening failure of the cell walls and the strain hardening of the matrix material can affect the mechanical response of porous titanium. Additionally, with the increase of porosity, the greater the stress concentration factor, the easier the failure of porous metals.
2021, 50(10):3504-3511.
DOI: 10.12442/j.issn.1002-185X.20200636
Abstract:
The effects of cold deformation on the evolution of the microstructure and mechanical properties of pure nickel N6 were investigated. Samples of pure nickel N6 were deformed by cold rolling (CR) to different thickness reductions (20%, 30%, 50%, 70%, 90%). Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), microhardness measurements, and tensile tests were used to characterize the microstructure and mechanical properties of the cold-rolled samples. The results show that the grains of pure nickel N6 are refined, and the grain with irregular orientation transforms into a strip-like grain with a preferred orientation parallel to the rolling direction. Micro- and nano-grains of pure nickel N6 are obtained under CR reduction of 90%, at which the grain diameter is mainly below 10 μm, accounting for 94% of the entire grain size. The distribution of low-angle grain boundaries (LAGBs) in the rolled samples is uniform, with a relatively high fraction of misorientation angles of 10° from neighboring points. Upon increasing the cold rolling reductions, the tensile strength and microhardness increase, but the elongation decreases. At a CR thickness reduction of 90%, the tensile strength is 837 MPa, and the microhardness is 2479 MPa, which are 2.32 and 2.7 times higher than those in the unrolled condition, respectively. The fracture morphology of pure nickel N6 at various CR reductions include equiaxed dimples, ridges, and a step morphology, which indicate ductile fracture.
The effects of cold deformation on the evolution of the microstructure and mechanical properties of pure nickel N6 were investigated. Samples of pure nickel N6 were deformed by cold rolling (CR) to different thickness reductions (20%, 30%, 50%, 70%, 90%). Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), microhardness measurements, and tensile tests were used to characterize the microstructure and mechanical properties of the cold-rolled samples. The results show that the grains of pure nickel N6 are refined, and the grain with irregular orientation transforms into a strip-like grain with a preferred orientation parallel to the rolling direction. Micro- and nano-grains of pure nickel N6 are obtained under CR reduction of 90%, at which the grain diameter is mainly below 10 μm, accounting for 94% of the entire grain size. The distribution of low-angle grain boundaries (LAGBs) in the rolled samples is uniform, with a relatively high fraction of misorientation angles of 10° from neighboring points. Upon increasing the cold rolling reductions, the tensile strength and microhardness increase, but the elongation decreases. At a CR thickness reduction of 90%, the tensile strength is 837 MPa, and the microhardness is 2479 MPa, which are 2.32 and 2.7 times higher than those in the unrolled condition, respectively. The fracture morphology of pure nickel N6 at various CR reductions include equiaxed dimples, ridges, and a step morphology, which indicate ductile fracture.
2021, 50(10):3512-3519.
DOI: 10.12442/j.issn.1002-185X.20210253
Abstract:
Cu-Ni-P alloys with different atomic ratios of Ni:P (2:1, 3:1, 4:1 and 5:1) were designed, and the microstructure characteristics and phase extraction treatments of ingots and melt-spun ribbons were discussed. Results show that Cu-xNi-4.5P ingots are composed of Cu and multiple Ni-P phases, including Ni5P4, Ni12P5 and Ni3P. With melt-spun process, the phosphides mainly exist in the form of Ni12P5 and Ni3P compounds. Meanwhile, further increasing nickel concentration of alloys can cause the structure-coarsening of phosphides in some degree. By controlling the solidification behavior and phase extraction process, Ni-P particles with multistage pore structure can be obtained, in which the pores are formed due to the etching of Cu dendrites and Cu existing in eutectic structure and solid solution region. Thus, phase extraction from metallic alloys provides a new controllable method to synthesize functional multistage porous phosphides.
Cu-Ni-P alloys with different atomic ratios of Ni:P (2:1, 3:1, 4:1 and 5:1) were designed, and the microstructure characteristics and phase extraction treatments of ingots and melt-spun ribbons were discussed. Results show that Cu-xNi-4.5P ingots are composed of Cu and multiple Ni-P phases, including Ni5P4, Ni12P5 and Ni3P. With melt-spun process, the phosphides mainly exist in the form of Ni12P5 and Ni3P compounds. Meanwhile, further increasing nickel concentration of alloys can cause the structure-coarsening of phosphides in some degree. By controlling the solidification behavior and phase extraction process, Ni-P particles with multistage pore structure can be obtained, in which the pores are formed due to the etching of Cu dendrites and Cu existing in eutectic structure and solid solution region. Thus, phase extraction from metallic alloys provides a new controllable method to synthesize functional multistage porous phosphides.
2021, 50(10):3520-3526.
DOI: 10.12442/j.issn.1002-185X.E20200041
Abstract:
Porous magnesium (Mg) scaffolds are beneficial to biological implantation, but because of the high activity of Mg, the degradation rate after implantation is too fast, which is not conducive to the formation of new bone. In order to effectively control the degradation of Mg scaffolds, three different surface coatings, magnesium oxide (MgO), calcium hydrogen phosphate (DCPD) and stearic acid (SA) on the porous Mg scaffolds was prepared and their effects on the scaffolds were investigated. The surface composition of the uncoated scaffold and the coatings was confirmed to be pure Mg, MgO, DCPD and SA by energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and Fourier transforms infrared spectra (FTIR). The results show that SA coating is smoother and more compact in surface morphology. In vitro degradation in simulated body fluid (SBF) indicates that surface coatings can effectively slow down the scaffold degradation, while DCPD coating and SA coating are better than MgO coating in resisting the degradation. The degradation rate of the scaffolds with DCPD and SA coating soaked in SBF is 70% at the 15th week, which provides a certain period of time for the growth of new bone.
Porous magnesium (Mg) scaffolds are beneficial to biological implantation, but because of the high activity of Mg, the degradation rate after implantation is too fast, which is not conducive to the formation of new bone. In order to effectively control the degradation of Mg scaffolds, three different surface coatings, magnesium oxide (MgO), calcium hydrogen phosphate (DCPD) and stearic acid (SA) on the porous Mg scaffolds was prepared and their effects on the scaffolds were investigated. The surface composition of the uncoated scaffold and the coatings was confirmed to be pure Mg, MgO, DCPD and SA by energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and Fourier transforms infrared spectra (FTIR). The results show that SA coating is smoother and more compact in surface morphology. In vitro degradation in simulated body fluid (SBF) indicates that surface coatings can effectively slow down the scaffold degradation, while DCPD coating and SA coating are better than MgO coating in resisting the degradation. The degradation rate of the scaffolds with DCPD and SA coating soaked in SBF is 70% at the 15th week, which provides a certain period of time for the growth of new bone.
2021, 50(10):3527-3531.
DOI: 10.12442/j.issn.1002-185X.20200629
Abstract:
The CuPSn brazing filler metal was prepared on the basis of Cu93P brazing filler metal by hot-dip tinning. The interface morphology of tin coating was observed by scanning electron microscope. The tensile strength, microhardness, melting temperature and wettability of the brazing filler metal were investigated by universal mechanical testing machine, micro-hardness tester, differential thermal analyzer, resistance furnace and stereomicroscope. The results indicate that the liquid tin reacts with the brazing filler metal to form Cu6Sn5 intermetallic compound during hot-dip tinning, which means that the brazing filler metal and tin coating form good metallurgical bonding. The tensile strength and microhardness of brazing filler metal decrease with the increase of hot-dipping temperature and time. The decrease of tensile strength is due to the formation of Cu6Sn5 brittle compound and pores at the interface, and the decrease of microhardness is due to the stress-relieving annealing effect of hot-dip. Hot-dip tinning can reduce the melting temperature and improve the wettability of the brazing filler metal. The wetting area of brazing filler metal increases by about 43.15% compared with that of the matrix when 5.20wt% tin is hot dipped in it, and the Cu88.16P6.64Sn5.20 brazing filler metal possesses a good wettability.
The CuPSn brazing filler metal was prepared on the basis of Cu93P brazing filler metal by hot-dip tinning. The interface morphology of tin coating was observed by scanning electron microscope. The tensile strength, microhardness, melting temperature and wettability of the brazing filler metal were investigated by universal mechanical testing machine, micro-hardness tester, differential thermal analyzer, resistance furnace and stereomicroscope. The results indicate that the liquid tin reacts with the brazing filler metal to form Cu6Sn5 intermetallic compound during hot-dip tinning, which means that the brazing filler metal and tin coating form good metallurgical bonding. The tensile strength and microhardness of brazing filler metal decrease with the increase of hot-dipping temperature and time. The decrease of tensile strength is due to the formation of Cu6Sn5 brittle compound and pores at the interface, and the decrease of microhardness is due to the stress-relieving annealing effect of hot-dip. Hot-dip tinning can reduce the melting temperature and improve the wettability of the brazing filler metal. The wetting area of brazing filler metal increases by about 43.15% compared with that of the matrix when 5.20wt% tin is hot dipped in it, and the Cu88.16P6.64Sn5.20 brazing filler metal possesses a good wettability.
2021, 50(10):3532-3537.
DOI: 10.12442/j.issn.1002-185X.E20200038
Abstract:
The deformation microstructures of two Ni-based superalloys with different Co contents after creep tests at 650 °C/630 MPa, 725 °C/630 MPa and 760 °C/630 MPa were investigated by transmission electron microscopy (TEM), in order to study the influence of temperature and stacking fault energy (SFE) on the creep deformation mechanisms. The results show that the improvement in temperature enhances the creep mechanism transition from stacking faults to micro-twinning for the experimental single crystal alloys, suggesting that the formation of micro-twins is dependent on temperature. Moreover, increasing Co content as well as lowering SFE allow stacking faults or micro-twins to extend through the γ matrix and γ′ precipitates, which improve the creep resistance and prolong the creep life of the alloys.
The deformation microstructures of two Ni-based superalloys with different Co contents after creep tests at 650 °C/630 MPa, 725 °C/630 MPa and 760 °C/630 MPa were investigated by transmission electron microscopy (TEM), in order to study the influence of temperature and stacking fault energy (SFE) on the creep deformation mechanisms. The results show that the improvement in temperature enhances the creep mechanism transition from stacking faults to micro-twinning for the experimental single crystal alloys, suggesting that the formation of micro-twins is dependent on temperature. Moreover, increasing Co content as well as lowering SFE allow stacking faults or micro-twins to extend through the γ matrix and γ′ precipitates, which improve the creep resistance and prolong the creep life of the alloys.
2021, 50(10):3538-3542.
DOI: 10.12442/j.issn.1002-185X.20200616
Abstract:
The microstructure and mechanical property of gold cladding silver composite bonding wire under different true strains were characterized by metallographic microscope, double beam electron microscope, high-low temperature tensile tester and nano-indentor. The results show that the silver alloy core of gold cladding silver composite bonding wire evolves from cellular dendrite to fiber structure along the drawing direction. The gold cladding layer is uniform and continuous and the transition layer near the interface always keeps fine equiaxed or spherical grains during the deformation process. Inconsistent size change among each component is observed during deformation, and the fitted size change constant is not proportional to the change of wire diameter. Microhardness, tensile strength and elongation increase with the increase of deformation amount. During the uniaxial drawing process, the unidirectional tensile strain becomes a complex two-dimensional stress state due to the interaction between each component of the composite wire. Thus the plasticity and toughness of the material can be improved because the alternating stress inhibits the nucleation of crack.
The microstructure and mechanical property of gold cladding silver composite bonding wire under different true strains were characterized by metallographic microscope, double beam electron microscope, high-low temperature tensile tester and nano-indentor. The results show that the silver alloy core of gold cladding silver composite bonding wire evolves from cellular dendrite to fiber structure along the drawing direction. The gold cladding layer is uniform and continuous and the transition layer near the interface always keeps fine equiaxed or spherical grains during the deformation process. Inconsistent size change among each component is observed during deformation, and the fitted size change constant is not proportional to the change of wire diameter. Microhardness, tensile strength and elongation increase with the increase of deformation amount. During the uniaxial drawing process, the unidirectional tensile strain becomes a complex two-dimensional stress state due to the interaction between each component of the composite wire. Thus the plasticity and toughness of the material can be improved because the alternating stress inhibits the nucleation of crack.
2021, 50(10):3543-3549.
DOI: 10.12442/j.issn.1002-185X.20200587
Abstract:
Graded Ti-6Al-4V alloys were produced by selective laser melting (SLM). Regulation of laser power and scanning speed was applied separately on each sample along the building direction. The microstructure transformation and phase transition in the graded Ti-6Al-4V were investigated. Results show that due to the rapid cooling rate of the SLM process, the microstructure of Ti-6Al-4V is mainly acicular α′ martensite in prior β column grains. The β column grains are enlarged with the increase of laser power or the decrease of scanning speed. The preferential orientation of α′ grains changes due to the variation of laser power and scanning speed. Moreover, the ascending scanning speed or descending scanning speed during the process may lead to two different defects.
Graded Ti-6Al-4V alloys were produced by selective laser melting (SLM). Regulation of laser power and scanning speed was applied separately on each sample along the building direction. The microstructure transformation and phase transition in the graded Ti-6Al-4V were investigated. Results show that due to the rapid cooling rate of the SLM process, the microstructure of Ti-6Al-4V is mainly acicular α′ martensite in prior β column grains. The β column grains are enlarged with the increase of laser power or the decrease of scanning speed. The preferential orientation of α′ grains changes due to the variation of laser power and scanning speed. Moreover, the ascending scanning speed or descending scanning speed during the process may lead to two different defects.
17 Evolution law of directional solidification structure of Nb42Ti21Co37 ternary quasiperitectic alloy
Wang Jinhua
,
闫二虎
,
Di Chongbo
,
Chen Yuncan
,
Liu Wei
,
Wang Hao
,
Ge Xiaoyu
,
Cheng Jian
,
Huang Renjun
,
Sun Lixian
2021, 50(10):3577-3584.
DOI: 10.12442/j.issn.1002-185X.20200786
Abstract:
The quasiperitecticcoated transformation has the dual characteristics of eutectic transformation and peritectic transformation, and it exists in many industrial alloys. However, a relatively complete theoretical model of peritectic solidification has not been established so far, and there are few related studies on its solidification mechanism. Based on this, this article carried out directional solidification experiments at different drawing speeds (v=1, 3, 5, 15, 30, 70 μm/s) for the Nb42Ti21Co37 quasiperitectic alloy, aiming to study the alloy"s performance at different drawing speeds. Microstructure evolution law, and build the corresponding solidification mechanism. The research results show that the conventional as-cast and directional solidification structures of Nb42Ti21Co37 quasiperitectic alloy contain α-Nb,Co6Nb7 and TiCo+Co6Nb7 quasiperitectic phases. With the gradual increase of the drawing rate, the primary α-Nb phase undergoes a spherical shape →petal-like →cluster-like →dendrite-like transformation; along with the above process, the quenched interface has undergone the transformation from cellular interface to cellular dendrite-like interface, and at the pulling rate v=70 μm/s, solid/liquid The interface disappears; secondly, the quasiperitectic structure in the steady-state growth zone of directional solidification is gradually refined, and the interlayer spacing has an exponential linear relationship with the growth rate, that is, λ=1＋5×e2.5V;when the pulling rate is lower than 5μm/s the directional solidification process of the alloy is similar to equilibrium solidification; in addition, the growth mechanism of each phase in the stable growth zone is symbiotic growth. With the increase of the pulling rate, the directional arrangement of the quasiperitectic structure gradually deteriorates.
The quasiperitecticcoated transformation has the dual characteristics of eutectic transformation and peritectic transformation, and it exists in many industrial alloys. However, a relatively complete theoretical model of peritectic solidification has not been established so far, and there are few related studies on its solidification mechanism. Based on this, this article carried out directional solidification experiments at different drawing speeds (v=1, 3, 5, 15, 30, 70 μm/s) for the Nb42Ti21Co37 quasiperitectic alloy, aiming to study the alloy"s performance at different drawing speeds. Microstructure evolution law, and build the corresponding solidification mechanism. The research results show that the conventional as-cast and directional solidification structures of Nb42Ti21Co37 quasiperitectic alloy contain α-Nb,Co6Nb7 and TiCo+Co6Nb7 quasiperitectic phases. With the gradual increase of the drawing rate, the primary α-Nb phase undergoes a spherical shape →petal-like →cluster-like →dendrite-like transformation; along with the above process, the quenched interface has undergone the transformation from cellular interface to cellular dendrite-like interface, and at the pulling rate v=70 μm/s, solid/liquid The interface disappears; secondly, the quasiperitectic structure in the steady-state growth zone of directional solidification is gradually refined, and the interlayer spacing has an exponential linear relationship with the growth rate, that is, λ=1＋5×e2.5V;when the pulling rate is lower than 5μm/s the directional solidification process of the alloy is similar to equilibrium solidification; in addition, the growth mechanism of each phase in the stable growth zone is symbiotic growth. With the increase of the pulling rate, the directional arrangement of the quasiperitectic structure gradually deteriorates.
2021, 50(10):3585-3590.
DOI: 10.12442/j.issn.1002-185X.20200799
Abstract:
The influence of two cold rolling processes of unidirectional rolling and cross rolling on the microstructure, mechanical properties and texture of TC4 alloy plate was studied in this paper. The research results show that the grains of the two rolling processes are all refined. The microstructure of the unidirectional rolling still has a band structure, and the α grains elongated with rolling direction. The microstructure of the cross rolling is a uniform composition of equiaxed α grains and intercrystalline β. The plasticity of the cross rolling process is significantly better than that of the unidirectional rolling, and the strength is slightly lower than that of the unidirectional cold rolling. But the difference between the RD and TD directions of the plate is significantly reduced. The original cold-rolled plate mainly has (-12-10)<10-10> pyramid texture with strong intensity. Unidirectional cold rolling inherits the texture components of the original plate. Cross rolling promotes strong basal texture of (0001) diffuse to the ND-TD surface and the RD-TD surface, and which deflected a certain angle. The intensity of the pyramid texture is effectively decreased, which improves the anisotropy of the plate. Crossing rolling process promotes redistribution of texture components and weakens anisotropy.
The influence of two cold rolling processes of unidirectional rolling and cross rolling on the microstructure, mechanical properties and texture of TC4 alloy plate was studied in this paper. The research results show that the grains of the two rolling processes are all refined. The microstructure of the unidirectional rolling still has a band structure, and the α grains elongated with rolling direction. The microstructure of the cross rolling is a uniform composition of equiaxed α grains and intercrystalline β. The plasticity of the cross rolling process is significantly better than that of the unidirectional rolling, and the strength is slightly lower than that of the unidirectional cold rolling. But the difference between the RD and TD directions of the plate is significantly reduced. The original cold-rolled plate mainly has (-12-10)<10-10> pyramid texture with strong intensity. Unidirectional cold rolling inherits the texture components of the original plate. Cross rolling promotes strong basal texture of (0001) diffuse to the ND-TD surface and the RD-TD surface, and which deflected a certain angle. The intensity of the pyramid texture is effectively decreased, which improves the anisotropy of the plate. Crossing rolling process promotes redistribution of texture components and weakens anisotropy.
2021, 50(10):3591-3599.
DOI: 10.12442/j.issn.1002-185X.20200832
Abstract:
A cold rolled Zr-4 alloy sheet of 3.6mm thickness with a typical bimodal texture was applied. Texture evolution was characterized by electron backscattering diffraction (EBSD) technique. Visco-plastic self-consistent (VPSC) model was analyzed to evaluate deformation mechanism of Zr-4 alloy sheet during cold rolling. Effects of rolling pass number, reduction per pass and total deformation on texture were predicted with the VPSC model. Results show that the texture of Zr-4 alloy sheet maintained a typical basal bimodal texture during the cold rolling process. Rolling pass number and reduction per pass had little influence on the texture evolution and deformation mechanism. However, total rolling deformation had significant effect on the texture evolution. With the decrease of deformation, the C-axis of most grains rotated from the normal direction to the transverse direction; When the rolling deformation is less than the critical deformation which is 39%, the Kearn factors of normal direction (Fn) rises rapidly with the increased deformation, and prismatic slip quickly decreases.When the deformation exceeds 39%, only slight increase of Kearns factor was observed, and prismatic slip becomes stable.
A cold rolled Zr-4 alloy sheet of 3.6mm thickness with a typical bimodal texture was applied. Texture evolution was characterized by electron backscattering diffraction (EBSD) technique. Visco-plastic self-consistent (VPSC) model was analyzed to evaluate deformation mechanism of Zr-4 alloy sheet during cold rolling. Effects of rolling pass number, reduction per pass and total deformation on texture were predicted with the VPSC model. Results show that the texture of Zr-4 alloy sheet maintained a typical basal bimodal texture during the cold rolling process. Rolling pass number and reduction per pass had little influence on the texture evolution and deformation mechanism. However, total rolling deformation had significant effect on the texture evolution. With the decrease of deformation, the C-axis of most grains rotated from the normal direction to the transverse direction; When the rolling deformation is less than the critical deformation which is 39%, the Kearn factors of normal direction (Fn) rises rapidly with the increased deformation, and prismatic slip quickly decreases.When the deformation exceeds 39%, only slight increase of Kearns factor was observed, and prismatic slip becomes stable.
2021, 50(10):3600-3608.
DOI: 10.12442/j.issn.1002-185X.20200843
Abstract:
Three directional forging textures and their non-uniformity under different conditions were simulated to explain the formation of forging texture in forged TC18 titanium alloy bars. Firstly, finite element method is used to simulate the non-uniform distributions of temperature, effective stress and effective strain in forged bars. Then the textures in b-phase with BCC structure are simulated using visco-plastic self-consistent model(VPSC) under different initial conditions. Results show that during three directional forging the textures in center region changes more apparently than in edge region. The compressive cube texture {100}<001> and brass type texture {110}<112> generally develop in center region, whereas weak compressive {100} and {111} texture are involved. Initial texture plays important role. By random initial texture, the third step compression often determines the final texture. By weak initial texture the final texture is also weak. In contrast, when strong initial texture exists, three directional forging can’t change its influence with characteristic feature of its initial state. Finally the influences of different combinations of strain amounts in three directions are simulated and special condition for large difference in textures is determined. The texture changes along axial and radical directions are also simulated.
Three directional forging textures and their non-uniformity under different conditions were simulated to explain the formation of forging texture in forged TC18 titanium alloy bars. Firstly, finite element method is used to simulate the non-uniform distributions of temperature, effective stress and effective strain in forged bars. Then the textures in b-phase with BCC structure are simulated using visco-plastic self-consistent model(VPSC) under different initial conditions. Results show that during three directional forging the textures in center region changes more apparently than in edge region. The compressive cube texture {100}<001> and brass type texture {110}<112> generally develop in center region, whereas weak compressive {100} and {111} texture are involved. Initial texture plays important role. By random initial texture, the third step compression often determines the final texture. By weak initial texture the final texture is also weak. In contrast, when strong initial texture exists, three directional forging can’t change its influence with characteristic feature of its initial state. Finally the influences of different combinations of strain amounts in three directions are simulated and special condition for large difference in textures is determined. The texture changes along axial and radical directions are also simulated.
WANG Wei
,
WANG Meng
,
CAI Jun
,
ZHANG Haoze
,
SHI Yaming
,
ZHANG Xiaofeng
,
HUANG Haiguang
,
WANG Kuaishe
2021, 50(10):3609-3620.
DOI: 10.12442/j.issn.1002-185X.20200852
Abstract:
The thermal simulation compression experiment is used to study the thermal deformation behavior of EB furnace smelting TC4 titanium alloy at a strain rate of 0.01 s-1-10 s-1 and a deformation temperature of 800 ℃-1100 ℃, and calculate the strain rate of the alloy under different deformation conditions Sensitivity index m, and based on the DMNR model to establish a dual multivariate nonlinear regression constitutive equation for EB furnace smelting TC4 titanium alloy. The results show that at the beginning of deformation, work hardening is dominant, and the flow stress increases with the increase of strain. When the peak stress is reached, the softening effect is more obvious, the dislocations begin to slip and climb, and the flow stress increases with the strain. Increase and decrease. The value of m is larger under low temperature and small strain rate, and smaller under high temperature and large strain rate. The larger the value of m, the more uniform the corresponding microstructure. The established nonlinear regression constitutive equation can better predict the flow stress of EB furnace smelting TC4 titanium alloy. The average absolute relative error between the predicted value and the measured value is 5.83%, and the correlation coefficient is 0.98.
The thermal simulation compression experiment is used to study the thermal deformation behavior of EB furnace smelting TC4 titanium alloy at a strain rate of 0.01 s-1-10 s-1 and a deformation temperature of 800 ℃-1100 ℃, and calculate the strain rate of the alloy under different deformation conditions Sensitivity index m, and based on the DMNR model to establish a dual multivariate nonlinear regression constitutive equation for EB furnace smelting TC4 titanium alloy. The results show that at the beginning of deformation, work hardening is dominant, and the flow stress increases with the increase of strain. When the peak stress is reached, the softening effect is more obvious, the dislocations begin to slip and climb, and the flow stress increases with the strain. Increase and decrease. The value of m is larger under low temperature and small strain rate, and smaller under high temperature and large strain rate. The larger the value of m, the more uniform the corresponding microstructure. The established nonlinear regression constitutive equation can better predict the flow stress of EB furnace smelting TC4 titanium alloy. The average absolute relative error between the predicted value and the measured value is 5.83%, and the correlation coefficient is 0.98.
Yongnan Chen
,
Ziwei Guo
,
Zehui Yang
,
Qinyang Zhao
,
Long Zhang
,
Yiku Xu
,
Jianmin Hao
,
Haifei Zhan
,
Yongqing Zhao
2021, 50(10):3621-3626.
DOI: 10.12442/j.issn.1002-185X.20200144
Abstract:
Self-sealing pore is one of the important technologies to improve the antifriction and corrosion resistance of micro-arc oxidation coating. In order to solve the problem that the stability and expansion effect of sealing agent of physical sealing pore coating limited the service time. This paper uses the electrical property of graphene oxide to control the pore structure of ceramic coatings and to prepare GO/TiO2 self-sealing pore ceramic coatings with antifriction effect. The effect of graphene oxide concentration on pore structure and antifriction of ceramic coating were discussed. The result show that the conductivity of electrolyte was changed by graphene oxide to affect the reaction process, which contributed to control the pore structure of the GO/TiO2 coating. The self-sealing pore coating with the porosity, pore size and average friction coefficient of 3.6%, 2.5μm and 0.1 was prepared at the graphene oxide concentration of 5g/L, which decreased by 83.2%,78.4% and 87.5% respectively compared with traditional coatings. It is believed that the pore structure of micro-arc oxidation coating can be controlled by the concentration of graphene oxide, which provides a new idea for the preparation of antifriction self-sealing pore coating.
Self-sealing pore is one of the important technologies to improve the antifriction and corrosion resistance of micro-arc oxidation coating. In order to solve the problem that the stability and expansion effect of sealing agent of physical sealing pore coating limited the service time. This paper uses the electrical property of graphene oxide to control the pore structure of ceramic coatings and to prepare GO/TiO2 self-sealing pore ceramic coatings with antifriction effect. The effect of graphene oxide concentration on pore structure and antifriction of ceramic coating were discussed. The result show that the conductivity of electrolyte was changed by graphene oxide to affect the reaction process, which contributed to control the pore structure of the GO/TiO2 coating. The self-sealing pore coating with the porosity, pore size and average friction coefficient of 3.6%, 2.5μm and 0.1 was prepared at the graphene oxide concentration of 5g/L, which decreased by 83.2%,78.4% and 87.5% respectively compared with traditional coatings. It is believed that the pore structure of micro-arc oxidation coating can be controlled by the concentration of graphene oxide, which provides a new idea for the preparation of antifriction self-sealing pore coating.
Chen Fenghua
,
Shi Xiangdong
,
Liang Weiwei
,
Yang Maosen
,
Chen Qingtao
,
Jiang Liying
,
Zhang yonghui
2021, 50(10):3627-3633.
DOI: 10.12442/j.issn.1002-185X.20210076
Abstract:
Polyaniline was firstly grown on carbon cloth by in-situ polymerization. The final composite material of CC/PANI/ TiO2 was then successfully synthesized via solvothermal method, during which TiO2 nanosheets was formed on the prepared carbon cloth/polyaniline (CC/PANI) composite material. The synthesized photocatalysts were characterized using SEM, XRD, UV, FTIR,XPS and so on. The photocatalytic degradation performances of RhB over the prepared CC/PANI/TiO2 and the pure TiO2 were compared. The results indicated that CC/PANI/TiO2 composite material had better photocatalytic activity than TiO2 under UV-vis irradiation. PL showed that the luminescence intensity of CC/PANI/TiO2 was much weaker than that of pure TiO2, which inhibited the electron-hole pair recombination effectively. Transient photocurrent response and EIS curves verified that CC/PANI/TiO2 catalyst showed more efficient photocarrier separation and transfer efficiency, beneficial to the improvement of photocatalytic activity. The capture of active pieces experiments indicated that the free .OH radicals and .O2- radicals were the main active oxidizing species involved in the RhB photoreaction process of CC/PANI/TiO2. Moreover, CC/PANI/TiO2 catalyst still had high catalytic activity after 6 times of recycling, showing its good application prospects in the field of sewage treatment.
Polyaniline was firstly grown on carbon cloth by in-situ polymerization. The final composite material of CC/PANI/ TiO2 was then successfully synthesized via solvothermal method, during which TiO2 nanosheets was formed on the prepared carbon cloth/polyaniline (CC/PANI) composite material. The synthesized photocatalysts were characterized using SEM, XRD, UV, FTIR,XPS and so on. The photocatalytic degradation performances of RhB over the prepared CC/PANI/TiO2 and the pure TiO2 were compared. The results indicated that CC/PANI/TiO2 composite material had better photocatalytic activity than TiO2 under UV-vis irradiation. PL showed that the luminescence intensity of CC/PANI/TiO2 was much weaker than that of pure TiO2, which inhibited the electron-hole pair recombination effectively. Transient photocurrent response and EIS curves verified that CC/PANI/TiO2 catalyst showed more efficient photocarrier separation and transfer efficiency, beneficial to the improvement of photocatalytic activity. The capture of active pieces experiments indicated that the free .OH radicals and .O2- radicals were the main active oxidizing species involved in the RhB photoreaction process of CC/PANI/TiO2. Moreover, CC/PANI/TiO2 catalyst still had high catalytic activity after 6 times of recycling, showing its good application prospects in the field of sewage treatment.
Zhang Jiexin
,
Kang Shenglin
,
Zhao Xuetong
,
Sun Jianjie
,
Liang Jie
,
Chen Han
,
Yang Lijun
,
Liao Ruijin
2021, 50(10):3634-3639.
DOI: 10.12442/j.issn.1002-185X.20210157
Abstract:
ZnO ceramics were fabricated via spark plasma sintering (SPS) technology. The role of acetic acid solution on the SPS was mainly investigated. The results indicated that, with the addition of liquid phase (2 mol/L acetic acid solution) during SPS, the shrinkage and densification of ZnO ceramic samples were activated at 52 oC and 115 oC, respectively. The density of ZnO ceramic samples can be achieved to the value of more than 95% and then fully densified when the sintering temperature was further increased to 160 oC and 200 oC. The grain grows from 200 nm of the raw particle to 600 nm after sintering at 250 oC for 5 min. The X-ray diffraction results show that no obvious impurity phase can be observed, and the grain growth present a clear anisotropic orientation, preferentially growing along the vertical direction of applied pressure. With assistance of liquid phase in SPS, the grain growth activation energy was determined at only 78.8 kJ/mol, a third as large as that sintered in the conventional SPS. Impedance of ZnO ceramic samples was measured at room temperature. It was found that the grain boundary resistance decreases from 9.82×106 W to 2.75×103 W with the increasing sintering temperature from 120 oC to 250 oC.
ZnO ceramics were fabricated via spark plasma sintering (SPS) technology. The role of acetic acid solution on the SPS was mainly investigated. The results indicated that, with the addition of liquid phase (2 mol/L acetic acid solution) during SPS, the shrinkage and densification of ZnO ceramic samples were activated at 52 oC and 115 oC, respectively. The density of ZnO ceramic samples can be achieved to the value of more than 95% and then fully densified when the sintering temperature was further increased to 160 oC and 200 oC. The grain grows from 200 nm of the raw particle to 600 nm after sintering at 250 oC for 5 min. The X-ray diffraction results show that no obvious impurity phase can be observed, and the grain growth present a clear anisotropic orientation, preferentially growing along the vertical direction of applied pressure. With assistance of liquid phase in SPS, the grain growth activation energy was determined at only 78.8 kJ/mol, a third as large as that sintered in the conventional SPS. Impedance of ZnO ceramic samples was measured at room temperature. It was found that the grain boundary resistance decreases from 9.82×106 W to 2.75×103 W with the increasing sintering temperature from 120 oC to 250 oC.
2021, 50(10):3640-3647.
DOI: 10.12442/j.issn.1002-185X.20210206
Abstract:
AlCoCrFeNiSix (x=0, 0.2, 0.5, 0.8, 1.0) high entropy alloys were prepared by vacuum arc melting. The effects of Si addition and its content on the hot corrosion behavior of AlCoCrFeNi alloys at 950℃ in mixed salt of 75% Na2SO4 + 25% NaCl (mass fraction) were investigated. The results showed that the surface phase composition of the alloys changed from BCC to FCC due to selective oxidation of Al after 100h hot corrosion. A single Al2O3 scale could be formed preferentially on the surface of the alloy by adding proper amount of Si, and the hot corrosion resistance of the alloy can be improved significantly. However, the mixed oxides scales mainly composed of Al2O3 and Cr-Fe-Co-Si enriched spinel oxides formed on the surfaces of the alloys with the increase of Si content. Under the synergistic action of the growth stress of mixed oxides scale and the multi-element corrosion medium (oxidization-vulcanization-chlorination), the oxide scales were loose and easy to fall off, and serious internal oxidation and vulcanization were observed in the alloys.
AlCoCrFeNiSix (x=0, 0.2, 0.5, 0.8, 1.0) high entropy alloys were prepared by vacuum arc melting. The effects of Si addition and its content on the hot corrosion behavior of AlCoCrFeNi alloys at 950℃ in mixed salt of 75% Na2SO4 + 25% NaCl (mass fraction) were investigated. The results showed that the surface phase composition of the alloys changed from BCC to FCC due to selective oxidation of Al after 100h hot corrosion. A single Al2O3 scale could be formed preferentially on the surface of the alloy by adding proper amount of Si, and the hot corrosion resistance of the alloy can be improved significantly. However, the mixed oxides scales mainly composed of Al2O3 and Cr-Fe-Co-Si enriched spinel oxides formed on the surfaces of the alloys with the increase of Si content. Under the synergistic action of the growth stress of mixed oxides scale and the multi-element corrosion medium (oxidization-vulcanization-chlorination), the oxide scales were loose and easy to fall off, and serious internal oxidation and vulcanization were observed in the alloys.
2021, 50(10):3648-3656.
DOI: 10.12442/j.issn.1002-185X.20210280
Abstract:
The characteristics of superalloy powders used for the gradient integral turbine blisk by the hyper-transient solidified additive manufacturing are investigated. According to the temperature capacity of the alloy and the phase equilibrium diagram calculated by JMatPro, GH4169 and K418 alloys are selected as the disk hub and rim materials respectively, whereas DZ4125 is selected as the blade material for integral turbine blisk. The superalloy powder are prepared by vacuum induction melting and argon gas atomization (VIGA) and sieved to the particle size range of 53-105μm. The differential scanning calorimeter (DSC), field emission scanning electron microscope (FESEM), electron probe x-ray micro-analyzer (EPMA), laser diffraction particle size analyzer, dynamic image analysis system and comprehensive powder property analyzer are used to systematically characterize the phase change temperatures, microstructure, element segregation, particle size and shape, apparent density, tap density and flowability of the selected superalloy powders. The results show that the liquidus and solidus temperature range of K418 alloy is smaller than that of the GH4169 alloy. The onset precipitated temperature of γ′and MC carbides of K418 alloy is higher than that of GH4169. The precipitation temperatures of the main strengthening phases of the (GH4169+K418) hybrid composition alloy in the transition zone are between that of the GH4169 and K418 alloys. The morphology of GH4169 and K418 alloy powders is mainly spherical and nearly spherical. The surface and cross-section microstructures are mainly dendritic structure. For the selected alloy powders, the elements Ti, Nb, Zr and Mo, which is rich in the interdendritic region, exhibit strong segregation tendency, while the elements with weak segregation tendency include Ni, Cr, Fe and Al. The element segregation type of superalloy powder is similar to the cast Ni-based superalloys, however the powders possess finer and uniform microstructure than that of the cast superalloy. The particle size distribution of powders measured by laser diffraction and dynamic image analysis methods are similar. The D50 value of GH4169 is 79.1μm and 76.2μm, and the D50 of K418 is 67.8μm and 65.6μm, respectively. The dynamic image analysis result shows that the two alloys both possess good sphericity, and the SPHT mean values of GH4169 and K418 are 0.91 and 0.90, respectively. The GH4169 and K418 superalloy powders have similar apparent density, tap density and flowablity. In addition, the apparent density and tap density of the two alloy powders can reach 50% and 60% of the theoretical density of the alloy respectively. Furthermore, the GH4169 and K418 superalloy powders both have good compressibility (13.3~15.5%) and flowability of 18.5~20.4 s?(50 g)-1.
The characteristics of superalloy powders used for the gradient integral turbine blisk by the hyper-transient solidified additive manufacturing are investigated. According to the temperature capacity of the alloy and the phase equilibrium diagram calculated by JMatPro, GH4169 and K418 alloys are selected as the disk hub and rim materials respectively, whereas DZ4125 is selected as the blade material for integral turbine blisk. The superalloy powder are prepared by vacuum induction melting and argon gas atomization (VIGA) and sieved to the particle size range of 53-105μm. The differential scanning calorimeter (DSC), field emission scanning electron microscope (FESEM), electron probe x-ray micro-analyzer (EPMA), laser diffraction particle size analyzer, dynamic image analysis system and comprehensive powder property analyzer are used to systematically characterize the phase change temperatures, microstructure, element segregation, particle size and shape, apparent density, tap density and flowability of the selected superalloy powders. The results show that the liquidus and solidus temperature range of K418 alloy is smaller than that of the GH4169 alloy. The onset precipitated temperature of γ′and MC carbides of K418 alloy is higher than that of GH4169. The precipitation temperatures of the main strengthening phases of the (GH4169+K418) hybrid composition alloy in the transition zone are between that of the GH4169 and K418 alloys. The morphology of GH4169 and K418 alloy powders is mainly spherical and nearly spherical. The surface and cross-section microstructures are mainly dendritic structure. For the selected alloy powders, the elements Ti, Nb, Zr and Mo, which is rich in the interdendritic region, exhibit strong segregation tendency, while the elements with weak segregation tendency include Ni, Cr, Fe and Al. The element segregation type of superalloy powder is similar to the cast Ni-based superalloys, however the powders possess finer and uniform microstructure than that of the cast superalloy. The particle size distribution of powders measured by laser diffraction and dynamic image analysis methods are similar. The D50 value of GH4169 is 79.1μm and 76.2μm, and the D50 of K418 is 67.8μm and 65.6μm, respectively. The dynamic image analysis result shows that the two alloys both possess good sphericity, and the SPHT mean values of GH4169 and K418 are 0.91 and 0.90, respectively. The GH4169 and K418 superalloy powders have similar apparent density, tap density and flowablity. In addition, the apparent density and tap density of the two alloy powders can reach 50% and 60% of the theoretical density of the alloy respectively. Furthermore, the GH4169 and K418 superalloy powders both have good compressibility (13.3~15.5%) and flowability of 18.5~20.4 s?(50 g)-1.
2021, 50(10):3657-3663.
DOI: 10.12442/j.issn.1002-185X.20200671
Abstract:
Abstract: Using Ti foil with thickness of 0.1 mm as the interlayer, SiCp/6061-T6 Al MMCs was welded by employing low-power laser-TIG hybrid welding. After welding experiment, the macro morphology, microstructure, phase, resistivity, tensile strength and fracture morphology of the joint were analyzed. The results showed that laser power had significant influence on the formability of welding seam. Ti foil can basically suppress the formation of needle-like Al4C3 in weld seam. Meanwhile, some new phases such as TiC reinforcement phase and strip-like TiAl3 were generated in welding seam. The morphology of weld zone and fusion zone were characterized by equiaxed crystal and columnar crystal, respectively. The microstructure in heat-affected zone did not change obviously. The joint resistivity increased with the increasing of laser power and the value of joint resistivity was significantly higher than that in base material. The joint tensile strength achieved 196.98 MPa, which was equal to 54.71% of base material, when laser power of 554 W was applied. There were almost no pores in joint fracture and the second phase particle in dimple was mainly composed of TiC. The joint displayed the characteristics of brittle-ductile mixed fracture which was dominated by brittle fracture.
Abstract: Using Ti foil with thickness of 0.1 mm as the interlayer, SiCp/6061-T6 Al MMCs was welded by employing low-power laser-TIG hybrid welding. After welding experiment, the macro morphology, microstructure, phase, resistivity, tensile strength and fracture morphology of the joint were analyzed. The results showed that laser power had significant influence on the formability of welding seam. Ti foil can basically suppress the formation of needle-like Al4C3 in weld seam. Meanwhile, some new phases such as TiC reinforcement phase and strip-like TiAl3 were generated in welding seam. The morphology of weld zone and fusion zone were characterized by equiaxed crystal and columnar crystal, respectively. The microstructure in heat-affected zone did not change obviously. The joint resistivity increased with the increasing of laser power and the value of joint resistivity was significantly higher than that in base material. The joint tensile strength achieved 196.98 MPa, which was equal to 54.71% of base material, when laser power of 554 W was applied. There were almost no pores in joint fracture and the second phase particle in dimple was mainly composed of TiC. The joint displayed the characteristics of brittle-ductile mixed fracture which was dominated by brittle fracture.
Hao Fang
,
Du Yuxuan
,
Mao Youchua
,
Chen Jun
,
Xin Shewei
,
Chen Haisheng
,
Wang Kaixuan
,
Liu Xianghong
,
Feng Yong
2021, 50(10):3664-3669.
DOI: 10.12442/j.issn.1002-185X.20210653
Abstract:
The adiabatic shear characteristics of a typical near α-type Ti-6Al-2Zr-1Mo-1V Ti alloy at different strain rates have been investigated by hat shaped specimen. The results show that the dynamic stress-strain curve can be divided into three typical stages, which correspond to strain hardening, heat softening and shear localization, respectively, and finally develops into mature ASB；Close to the shear band，the primary α and second α distorted or even fractured in the transition zone，and showing the characteristics of twin deformation；In the near shear zone, the Kernel average misorientation(KAM) increases, α phase which is favorable to dislocation slip/twin orientation has a preferential plastic deformation, forming substructure, grain fragmentation and dynamic recrystallization. With the increase of strain rate, the width of shear band extended, and the vortex structure is supplemented by the coordination and adaptive deformation. The elastic modulus and microhardness of α-phase and β-phase of ASB ,near ASB and matrix were analyzed by nano indentation test, the results show that the adiabatic shear band of the this alloy is a softening band, and the width of the heat-affected zone is about 30μm around ASB.
The adiabatic shear characteristics of a typical near α-type Ti-6Al-2Zr-1Mo-1V Ti alloy at different strain rates have been investigated by hat shaped specimen. The results show that the dynamic stress-strain curve can be divided into three typical stages, which correspond to strain hardening, heat softening and shear localization, respectively, and finally develops into mature ASB；Close to the shear band，the primary α and second α distorted or even fractured in the transition zone，and showing the characteristics of twin deformation；In the near shear zone, the Kernel average misorientation(KAM) increases, α phase which is favorable to dislocation slip/twin orientation has a preferential plastic deformation, forming substructure, grain fragmentation and dynamic recrystallization. With the increase of strain rate, the width of shear band extended, and the vortex structure is supplemented by the coordination and adaptive deformation. The elastic modulus and microhardness of α-phase and β-phase of ASB ,near ASB and matrix were analyzed by nano indentation test, the results show that the adiabatic shear band of the this alloy is a softening band, and the width of the heat-affected zone is about 30μm around ASB.
2021, 50(10):3670-3676.
DOI: 10.12442/j.issn.1002-185X.20200792
Abstract:
Nanoporous tin with nanosheet arrays and nanoparticle were successfully prepared by dealloying in corrosion medium using Mg89Sn11 as precursor alloy. The morphology and structure of nanoporous tin and the process of dealloying were investigated by adjusting the corrosion medium and corrosion time. The results show that in acidic corrosive medium it can obtain a bicontinuous nanoporous tin structure. Among them, the pore walls are constituted by discontinuous nano-spherical particles in the 0.1% H3PO4 solution, while in the 0.1 mol/L HCl and neutral NaCl solution the pore walls are the nanosheet structure, forming a nanosheet array of porous tin. With the extension of the dealloying time, the porous morphology changes from a uniform nanosheet array porous to a cluster-like nanoporous morphology in 5% NaCl solution. The porous structure on the surface grows from uniform nanosheet array to discontinuous clusters with the corrosion time from 1h to 6h, and finally evolved into a continuous undulating sheet-like nanoporous structure with the average pore size of 50nm. Nano-porous tin structures with different morphologies were prepared by adjusting the dealloying process.
Nanoporous tin with nanosheet arrays and nanoparticle were successfully prepared by dealloying in corrosion medium using Mg89Sn11 as precursor alloy. The morphology and structure of nanoporous tin and the process of dealloying were investigated by adjusting the corrosion medium and corrosion time. The results show that in acidic corrosive medium it can obtain a bicontinuous nanoporous tin structure. Among them, the pore walls are constituted by discontinuous nano-spherical particles in the 0.1% H3PO4 solution, while in the 0.1 mol/L HCl and neutral NaCl solution the pore walls are the nanosheet structure, forming a nanosheet array of porous tin. With the extension of the dealloying time, the porous morphology changes from a uniform nanosheet array porous to a cluster-like nanoporous morphology in 5% NaCl solution. The porous structure on the surface grows from uniform nanosheet array to discontinuous clusters with the corrosion time from 1h to 6h, and finally evolved into a continuous undulating sheet-like nanoporous structure with the average pore size of 50nm. Nano-porous tin structures with different morphologies were prepared by adjusting the dealloying process.
2021, 50(10):3677-3683.
DOI: 10.12442/j.issn.1002-185X.20200794
Abstract:
During loss of coolant accident, the oxidation can cause burst of the cladding tube in high temperature steam, which lead to the leakage of the nuclear fuel. At present work, the oxidation behaviors of a Zr-Sn-Nb alloy were investigated in 1000~1250℃ steam. The weight gains per area were calculated by the weight gain method. The microscopic morphology, thickness of the alloy were measured by a scanning electron microscope. The oxidation kinetics of the alloy was characterized by weight gain and the thickness increase of α-Zr (O) and ZrO2 layers. The results show that the parabolic weight gain curves and ZrO2 layer growth kinetics curves become to be linear in 1000℃ steam for about 1500s, while α-Zr (O) growth kinetics always follow the parabolic law. Meanwhile, a large number of cracks are formed in the ZrO2 layers. The weight gain kinetics curves and α-Zr (O) and ZrO2 layers growth kinetics curves all follow the parabolic law in 1100~1250℃ steam,and the ZrO2 layer is almost intact. The oxidation resistance of Zr-Sn-Nb alloy is higher than that of Zr-4 alloy. The growth rate of ZrO2 layer and α-Zr (O) layer is slower than that of Zr-4 alloy.
During loss of coolant accident, the oxidation can cause burst of the cladding tube in high temperature steam, which lead to the leakage of the nuclear fuel. At present work, the oxidation behaviors of a Zr-Sn-Nb alloy were investigated in 1000~1250℃ steam. The weight gains per area were calculated by the weight gain method. The microscopic morphology, thickness of the alloy were measured by a scanning electron microscope. The oxidation kinetics of the alloy was characterized by weight gain and the thickness increase of α-Zr (O) and ZrO2 layers. The results show that the parabolic weight gain curves and ZrO2 layer growth kinetics curves become to be linear in 1000℃ steam for about 1500s, while α-Zr (O) growth kinetics always follow the parabolic law. Meanwhile, a large number of cracks are formed in the ZrO2 layers. The weight gain kinetics curves and α-Zr (O) and ZrO2 layers growth kinetics curves all follow the parabolic law in 1100~1250℃ steam,and the ZrO2 layer is almost intact. The oxidation resistance of Zr-Sn-Nb alloy is higher than that of Zr-4 alloy. The growth rate of ZrO2 layer and α-Zr (O) layer is slower than that of Zr-4 alloy.
2021, 50(10):3684-3692.
DOI: 10.12442/j.issn.1002-185X.20200802
Abstract:
Inconel 718 alloy samples with different densities were prepared by selective laser melting technology. The influence of processing parameters including laser power and scanning speed on the density of alloy samples was studied. The formation causes of micro pore defects and its effect on the tensile property were analyzed. The mechanical properties of alloys with different densities were studied by SIDA heat treatmet. The results showed that the interaction mode between laser and powder was determined by processing parameters. The "keyhole" mode occurred under the condition of high laser power and low scanning speed, which resulted in the decrease of density. When the power decreased or the scanning speed increased, the "keyhole" mode would change to the "heat conduction" mode, and the density would increase. However, when the laser power was too small or the scanning speed was too large, the unfused pore defects would occur, which would greatly reduce the density of the sample. The strength of the selective laser melting Inconel 718 alloy sample did not increase in a strictly monotonic manner with increasing the density. The morphology, quantity and size of the micro pore defects also had an effect on the tensile properties of the samples. SIDA heat treatment can greatly improve the microhardness and tensile strength of selective laser melting formed Inconel 718 alloy, but the plasticity is significantly reduced.
Inconel 718 alloy samples with different densities were prepared by selective laser melting technology. The influence of processing parameters including laser power and scanning speed on the density of alloy samples was studied. The formation causes of micro pore defects and its effect on the tensile property were analyzed. The mechanical properties of alloys with different densities were studied by SIDA heat treatmet. The results showed that the interaction mode between laser and powder was determined by processing parameters. The "keyhole" mode occurred under the condition of high laser power and low scanning speed, which resulted in the decrease of density. When the power decreased or the scanning speed increased, the "keyhole" mode would change to the "heat conduction" mode, and the density would increase. However, when the laser power was too small or the scanning speed was too large, the unfused pore defects would occur, which would greatly reduce the density of the sample. The strength of the selective laser melting Inconel 718 alloy sample did not increase in a strictly monotonic manner with increasing the density. The morphology, quantity and size of the micro pore defects also had an effect on the tensile properties of the samples. SIDA heat treatment can greatly improve the microhardness and tensile strength of selective laser melting formed Inconel 718 alloy, but the plasticity is significantly reduced.
2021, 50(10):3693-3697.
DOI: 10.12442/j.issn.1002-185X.20200804
Abstract:
Inconel625 has excellent corrosion resistance and high temperature mechanical properties, which is widely used in aerospace, petrochemical, nuclear industry etc. Porous materials are widely used as filter materials because of its light weight and excellent permeability. The purpose of this paper is to prepare a filter material with good corrosion resistance. Porous Inconel625 alloy with its own characteristics and functionality was prepared by molding-atmosphere sintering process with 100~200 μm alloy powder. The morphology and properties of the alloy are characterized and evaluated at different sintering temperatures. The results show that the sintered neck is well developed and the degree of pore spheroidization is high at 1240 ℃. At this time, the air permeability can satisfy the requirements of service performance, and can be used as high temperature gas-liquid filter material. At 1240 ℃ sintering temperature, the shear performance of the alloy reaches the best, and the maximum shear force is 51.0 kN, which also provides a reference for further research.
Inconel625 has excellent corrosion resistance and high temperature mechanical properties, which is widely used in aerospace, petrochemical, nuclear industry etc. Porous materials are widely used as filter materials because of its light weight and excellent permeability. The purpose of this paper is to prepare a filter material with good corrosion resistance. Porous Inconel625 alloy with its own characteristics and functionality was prepared by molding-atmosphere sintering process with 100~200 μm alloy powder. The morphology and properties of the alloy are characterized and evaluated at different sintering temperatures. The results show that the sintered neck is well developed and the degree of pore spheroidization is high at 1240 ℃. At this time, the air permeability can satisfy the requirements of service performance, and can be used as high temperature gas-liquid filter material. At 1240 ℃ sintering temperature, the shear performance of the alloy reaches the best, and the maximum shear force is 51.0 kN, which also provides a reference for further research.
2021, 50(10):3698-3706.
DOI: 10.12442/j.issn.1002-185X.20200809
Abstract:
Improving the degradation rate and bioactivity of magnesium in physiological environment is helpful to its application in biomedical field. Alloying treatment and surface modification are two effective ways. In the present study, a novel surface modification strategy, i.e. graphene oxide / hydroxyapatite / magnesium hydroxide (GO/HA/Mg(OH)2) composite coating constructed on the surface of magnesium-calcium alloy by the combination of hydrothermal treatment, electrophoretic deposition and electrochemical deposition, was proposed for magnesium-calcium alloy (ZQ). Scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis confirmed that the surface of the coating sample (ZQ-HEP) was composed of outer nano-sheet HA, middle flocculent-lamellae GO and inner Mg (OH)2 nano-sheet. The electrochemical corrosion resistance test in vitro showed that comparing with the untreated ZQ, ZQ-HEP had higher corrosion resistance in phosphate buffer solution (PBS). A rabbit femoral condyle fracture model was constructed to evaluate the fracture repair effect of ZQ samples before and after surface modification. Postoperative gross observation, radiograph and histological analysis confirmed that comparing with the untreated ZQ, ZQ-HEP screws could decrease the hydrogen release obviously and thus the subcutaneous emphysema after implantation into the body. Meanwhile, due to its higher corrosion resistance and bioactivity, ZQ-HEP screw could maintain its integrity better than the ZQ one at 4 weeks postoperatively, and induce more new bone growth. Therefore, more rapid fracture healing was observed on ZQ-HEP than ZQ. In conclusion, the multi-functional coating construction strategy proposed in current study could have good prospect of clinical application. It can not only regulate the degradation rate of medical magnesium metals, but also significantly improve their osteogenic ability.
Improving the degradation rate and bioactivity of magnesium in physiological environment is helpful to its application in biomedical field. Alloying treatment and surface modification are two effective ways. In the present study, a novel surface modification strategy, i.e. graphene oxide / hydroxyapatite / magnesium hydroxide (GO/HA/Mg(OH)2) composite coating constructed on the surface of magnesium-calcium alloy by the combination of hydrothermal treatment, electrophoretic deposition and electrochemical deposition, was proposed for magnesium-calcium alloy (ZQ). Scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis confirmed that the surface of the coating sample (ZQ-HEP) was composed of outer nano-sheet HA, middle flocculent-lamellae GO and inner Mg (OH)2 nano-sheet. The electrochemical corrosion resistance test in vitro showed that comparing with the untreated ZQ, ZQ-HEP had higher corrosion resistance in phosphate buffer solution (PBS). A rabbit femoral condyle fracture model was constructed to evaluate the fracture repair effect of ZQ samples before and after surface modification. Postoperative gross observation, radiograph and histological analysis confirmed that comparing with the untreated ZQ, ZQ-HEP screws could decrease the hydrogen release obviously and thus the subcutaneous emphysema after implantation into the body. Meanwhile, due to its higher corrosion resistance and bioactivity, ZQ-HEP screw could maintain its integrity better than the ZQ one at 4 weeks postoperatively, and induce more new bone growth. Therefore, more rapid fracture healing was observed on ZQ-HEP than ZQ. In conclusion, the multi-functional coating construction strategy proposed in current study could have good prospect of clinical application. It can not only regulate the degradation rate of medical magnesium metals, but also significantly improve their osteogenic ability.
2021, 50(10):3707-3713.
DOI: 10.12442/j.issn.1002-185X.20200817
Abstract:
In this paper, a series of new Cr-Mn-Fe-V-Cu high-entropy alloys with high ductility were prepared by arc melting and suction casting. It was found that with the addition of Cu, the structure of the alloys evolved from BCC+BCC1 phases (CrFeMnV alloy) to BCC + FCC phases (CrFeMnxVCu0.2xalloys). Formation of the Cu-Mn-rich FCC phase was caused by immiscibility of Cu with V, Cr and Fe. With increase of Cu, the volume fraction of FCC phase increased, and the morphology of the FCC phase transformed from granular particles to long strips and blocks. The five Cr-Mn-Fe-V-Cu HEAs present a great balance between strength and ductility. The CrFeMn0.3VCu0.06 alloy with granular FCC particles exhibits highest compressive yield strength (1273 MPa) and excellent ductility (εf = 50.7%). The dislocation and precipitate strengthening are responsible for high strength of the CrFeMn0.3VCu0.06 alloy. Therefore, the dislocation density and distribution of FCC phase are the crucial factors influencing both microstructures and mechanical properties of the HEAs.
In this paper, a series of new Cr-Mn-Fe-V-Cu high-entropy alloys with high ductility were prepared by arc melting and suction casting. It was found that with the addition of Cu, the structure of the alloys evolved from BCC+BCC1 phases (CrFeMnV alloy) to BCC + FCC phases (CrFeMnxVCu0.2xalloys). Formation of the Cu-Mn-rich FCC phase was caused by immiscibility of Cu with V, Cr and Fe. With increase of Cu, the volume fraction of FCC phase increased, and the morphology of the FCC phase transformed from granular particles to long strips and blocks. The five Cr-Mn-Fe-V-Cu HEAs present a great balance between strength and ductility. The CrFeMn0.3VCu0.06 alloy with granular FCC particles exhibits highest compressive yield strength (1273 MPa) and excellent ductility (εf = 50.7%). The dislocation and precipitate strengthening are responsible for high strength of the CrFeMn0.3VCu0.06 alloy. Therefore, the dislocation density and distribution of FCC phase are the crucial factors influencing both microstructures and mechanical properties of the HEAs.
2021, 50(10):3714-3719.
DOI: 10.12442/j.issn.1002-185X.20200819
Abstract:
The mechanical shot peening technology is applied to study the surface strengthening of tungsten plasma facing materials for fusion device. The strengthening effect of tungsten after shot peening was discussed in detail, which included micro morphology, grain refinement, surface roughness, surface hardness and surface residual compressive stress. And the shot peening process parameters were also optimized. The results indicate that it is the optimum shot peening parameters for the brittle and hard tungsten that air pressure of 0.3 MPa, ceramic pellet with the diameter of 0.4 mm and 100 mm pellet distance, which induces the performance enhancement of tungsten plasma facing material. The surface grain refinement phenomenon is obvious. The surface hardness increasement of about 53.5% is obtained, and the residual compressive stress is increased by 8.3 times. And the influence of shot peening technology on surface roughness is not obvious. The maximum roughness is about 1.5μm.
The mechanical shot peening technology is applied to study the surface strengthening of tungsten plasma facing materials for fusion device. The strengthening effect of tungsten after shot peening was discussed in detail, which included micro morphology, grain refinement, surface roughness, surface hardness and surface residual compressive stress. And the shot peening process parameters were also optimized. The results indicate that it is the optimum shot peening parameters for the brittle and hard tungsten that air pressure of 0.3 MPa, ceramic pellet with the diameter of 0.4 mm and 100 mm pellet distance, which induces the performance enhancement of tungsten plasma facing material. The surface grain refinement phenomenon is obvious. The surface hardness increasement of about 53.5% is obtained, and the residual compressive stress is increased by 8.3 times. And the influence of shot peening technology on surface roughness is not obvious. The maximum roughness is about 1.5μm.
2021, 50(10):3720-3728.
DOI: 10.12442/j.issn.1002-185X.20200820
Abstract:
The materials used in the hydrogen/oxygen catalytic combustion heat exchanger are gradually developed to the high strength and high conductivity copper alloy, and the brazing of the fins and separators of the heat exchanger is important to the thermal efficiency, service safety and reliability of the heat exchanger.The brazing of Cu-3Ag-0.5Zr alloy fins and baffles is studied in this paper.A Cu-3Ag-0.5Zr alloy was brazed at 840 ℃-900 ℃ brazing temperature for 5 min-20 min using 37.5Ag-48.8Cu-5.5Zn-8.2Mn braze filler that hadbeen produced into differern thickness.Solid-liquid interface morphology of the brazing joint at the insulation stage quenched by water was studied,which pointed that brazing joint structure has experienced the dissolution of the base material into the brazing filler metal area, the isothermal solidification of the Cu-rich phase, and the cooling and solidificationthree stages.Structures of the joints and shear fracture of joints were studied by scanning electron microscope(SEM) and energy dispersive spectrometers(EDS),which proved three kind of microstructures exist in joints which included Ag-rich phase distributing in a network between the base metal and the Cu-rich phase, AgCu eutectic structure in joint gap, and the filler zone structure consisted of AgCu eutectic and copper-rich phase constitute.And integrating these kinds of microstructures with shear strength datas of joints showed that CuZr in the brazing joint structure relatively weakens the joint shear strength,meanwhile Mn element strengthens the joint shear performance.shear strength of joint was effected in the way that brazing temperature,holding time and filler thickness control CuZr forming and Mn concentration in filler area of joints.The maximum shear strength value,308.29 MPa, was got at 100μm filler thickness,840℃ brazing temperature and 5 min holding time condition.
The materials used in the hydrogen/oxygen catalytic combustion heat exchanger are gradually developed to the high strength and high conductivity copper alloy, and the brazing of the fins and separators of the heat exchanger is important to the thermal efficiency, service safety and reliability of the heat exchanger.The brazing of Cu-3Ag-0.5Zr alloy fins and baffles is studied in this paper.A Cu-3Ag-0.5Zr alloy was brazed at 840 ℃-900 ℃ brazing temperature for 5 min-20 min using 37.5Ag-48.8Cu-5.5Zn-8.2Mn braze filler that hadbeen produced into differern thickness.Solid-liquid interface morphology of the brazing joint at the insulation stage quenched by water was studied,which pointed that brazing joint structure has experienced the dissolution of the base material into the brazing filler metal area, the isothermal solidification of the Cu-rich phase, and the cooling and solidificationthree stages.Structures of the joints and shear fracture of joints were studied by scanning electron microscope(SEM) and energy dispersive spectrometers(EDS),which proved three kind of microstructures exist in joints which included Ag-rich phase distributing in a network between the base metal and the Cu-rich phase, AgCu eutectic structure in joint gap, and the filler zone structure consisted of AgCu eutectic and copper-rich phase constitute.And integrating these kinds of microstructures with shear strength datas of joints showed that CuZr in the brazing joint structure relatively weakens the joint shear strength,meanwhile Mn element strengthens the joint shear performance.shear strength of joint was effected in the way that brazing temperature,holding time and filler thickness control CuZr forming and Mn concentration in filler area of joints.The maximum shear strength value,308.29 MPa, was got at 100μm filler thickness,840℃ brazing temperature and 5 min holding time condition.
2021, 50(10):3729-3738.
DOI: 10.12442/j.issn.1002-185X.20200825
Abstract:
10 wt% Nano-Al2O3 / 7075 aluminum matrix composites were prepared by powder metallurgy and hot extrusion. The effects of sintering temperature and extrusion ratio on microstructure, density, elastic modulus, hardness and compressive strength of the composites were studied. The results show that: with the increase of sintering temperature, the hardness of the composites with extrusion ratio of 4:1 and 8:1 increases at first and then decreases, and the overall hardness of the composites increases obviously; the compactness of the composites after extrusion is more than 98%; the compactness of the composites after extrusion is 4:1, the sintering temperature is 620 ℃, 630 ℃ When the extrusion ratio is 8:1, the compressive strength of the composite increases by 33.2%, 34.1% and 31.1%, which increases first and then decreases with temperature. In conclusion, the elastic modulus of the composites has little change.
10 wt% Nano-Al2O3 / 7075 aluminum matrix composites were prepared by powder metallurgy and hot extrusion. The effects of sintering temperature and extrusion ratio on microstructure, density, elastic modulus, hardness and compressive strength of the composites were studied. The results show that: with the increase of sintering temperature, the hardness of the composites with extrusion ratio of 4:1 and 8:1 increases at first and then decreases, and the overall hardness of the composites increases obviously; the compactness of the composites after extrusion is more than 98%; the compactness of the composites after extrusion is 4:1, the sintering temperature is 620 ℃, 630 ℃ When the extrusion ratio is 8:1, the compressive strength of the composite increases by 33.2%, 34.1% and 31.1%, which increases first and then decreases with temperature. In conclusion, the elastic modulus of the composites has little change.
38 Controllable and Large-scale Preparation of High-purity Nanosilicon and Electrochemical Performance
2021, 50(10):3739-3744.
DOI: 10.12442/j.issn.1002-185X.20200827
Abstract:
Silicon（Si） has become one of the hot spots in the research of anode materials in lithium-ion batteries (LIBs) for its highest lithium intercalation capacity among known elements. However, the large volume expansion (~300%) of Si due to the lithium intercalation restricts its application in LIBs. Nano-crystalized is an effective solution to resolve the volume expansion. Nano-Si was prepared by high-energy electron beam and mechanical grinding method, using metallurgical Si. According to scanning electron microscopy (SEM) observation, the molten Si was deposited into Si nanofibers with a linear diameter of about 40nm after evaporation under the action of high-energy electron beam, and then gathered into Si nanobundles, and the size distribution of nano-Si particles after mechanical grinding is uniform. The results of electrochemical tests show that the first reversible capacity is 1292.4mAh/g, and the charge transfer impedance fitting value is 51.36Ω, under the condition of the nano-Si purity reaches more than 99.96% and the discharge density is 100mAh/g. The experimental results indicates that this method can be applied to controllable and large-scale prepare nano-Si, and gives a guidance that how to scalable use Si in LIBs industry.
Silicon（Si） has become one of the hot spots in the research of anode materials in lithium-ion batteries (LIBs) for its highest lithium intercalation capacity among known elements. However, the large volume expansion (~300%) of Si due to the lithium intercalation restricts its application in LIBs. Nano-crystalized is an effective solution to resolve the volume expansion. Nano-Si was prepared by high-energy electron beam and mechanical grinding method, using metallurgical Si. According to scanning electron microscopy (SEM) observation, the molten Si was deposited into Si nanofibers with a linear diameter of about 40nm after evaporation under the action of high-energy electron beam, and then gathered into Si nanobundles, and the size distribution of nano-Si particles after mechanical grinding is uniform. The results of electrochemical tests show that the first reversible capacity is 1292.4mAh/g, and the charge transfer impedance fitting value is 51.36Ω, under the condition of the nano-Si purity reaches more than 99.96% and the discharge density is 100mAh/g. The experimental results indicates that this method can be applied to controllable and large-scale prepare nano-Si, and gives a guidance that how to scalable use Si in LIBs industry.
2021, 50(10):3745-3750.
DOI: 10.12442/j.issn.1002-185X.20200828
Abstract:
In this paper, Ni-coated carbon fiber was prepared by electroplating process, and continuous carbon fiber reinforced Al matrix (Cf/Al) composite plate was successfully prepared via twin-roll casting and short process forming process, and the effect of pouring temperature on the microstructure, interface characteristics, fracture morphology and mechanical properties of the Cf/Al composites was investigated. The results indicate that the Cf/Al composite plate with smooth and no obvious surface defects were fabricated under the conditions of pouring temperature of 963-983K, rolling speed of 2.7m/min and roll gap of 2.0mm; Among them, when the pouring temperature is 973K, the interface between the carbon fiber and the Al-matrix is ??well bonded; Ni-coated on the surface of fiber significantly improves the wettability between carbon fiber and aluminum matrix, and also effectively inhibits the formation of Al4C3 brittle phase, which greatly improves the mechanical properties of Cf/Al composite strip. The tensile strength of the Cf/Al composite plate at a pouring temperature of 973K increased by 87.4% compared with the initial 38.2MPa.
In this paper, Ni-coated carbon fiber was prepared by electroplating process, and continuous carbon fiber reinforced Al matrix (Cf/Al) composite plate was successfully prepared via twin-roll casting and short process forming process, and the effect of pouring temperature on the microstructure, interface characteristics, fracture morphology and mechanical properties of the Cf/Al composites was investigated. The results indicate that the Cf/Al composite plate with smooth and no obvious surface defects were fabricated under the conditions of pouring temperature of 963-983K, rolling speed of 2.7m/min and roll gap of 2.0mm; Among them, when the pouring temperature is 973K, the interface between the carbon fiber and the Al-matrix is ??well bonded; Ni-coated on the surface of fiber significantly improves the wettability between carbon fiber and aluminum matrix, and also effectively inhibits the formation of Al4C3 brittle phase, which greatly improves the mechanical properties of Cf/Al composite strip. The tensile strength of the Cf/Al composite plate at a pouring temperature of 973K increased by 87.4% compared with the initial 38.2MPa.
2021, 50(10):3751-3756.
DOI: 10.12442/j.issn.1002-185X.20200837
Abstract:
Ti(C,N)-based cermets containing 18 wt% and 38 wt% Ni–xCr (wt%, x=0, 10, 20, 30) were prepared by powder metallurgy, in order to study the effect of the composition and content of Ni–xCr binders on microstructure and mechanical properties of Ti(C,N)-based cermets. Ni-based binder phase and Ti-based carbonitride ceramic grains were observed in the other cermets, except that high-Mo and high-Cr white microstructure was also observed in cermet containing 38 wt% Ni–30Cr binder. There were often very fine white speckles in black core of ceramic grains for cermets with Cr-containing binder, especially at 38 wt% binder, and grey outer rim of ceramic grains became thicker when Cr content was high in binders. Regardless of binder content, hardness of cermets increased with increasing Cr content in binders, and the increase in hardness was more obvious at 38 wt% binder. At 18 wt% binder, transverse rupture strength and fracture toughness of cermets decreased with increasing Cr content in binders, however, at 38 wt% binder, they increased and then decreased with increasing Cr content in binders, and reached the peak at Ni–10Cr binder. Ceramic grain refinement led to the increase in the probability of intergranular fracture, and the synergistic effect of ceramic grain refinement, crack deflection, crack bridging, micro-crack toughening, etc., significantly improved transverse rupture strength and fracture toughness of Ti(C,N)-based cermets.
Ti(C,N)-based cermets containing 18 wt% and 38 wt% Ni–xCr (wt%, x=0, 10, 20, 30) were prepared by powder metallurgy, in order to study the effect of the composition and content of Ni–xCr binders on microstructure and mechanical properties of Ti(C,N)-based cermets. Ni-based binder phase and Ti-based carbonitride ceramic grains were observed in the other cermets, except that high-Mo and high-Cr white microstructure was also observed in cermet containing 38 wt% Ni–30Cr binder. There were often very fine white speckles in black core of ceramic grains for cermets with Cr-containing binder, especially at 38 wt% binder, and grey outer rim of ceramic grains became thicker when Cr content was high in binders. Regardless of binder content, hardness of cermets increased with increasing Cr content in binders, and the increase in hardness was more obvious at 38 wt% binder. At 18 wt% binder, transverse rupture strength and fracture toughness of cermets decreased with increasing Cr content in binders, however, at 38 wt% binder, they increased and then decreased with increasing Cr content in binders, and reached the peak at Ni–10Cr binder. Ceramic grain refinement led to the increase in the probability of intergranular fracture, and the synergistic effect of ceramic grain refinement, crack deflection, crack bridging, micro-crack toughening, etc., significantly improved transverse rupture strength and fracture toughness of Ti(C,N)-based cermets.
2021, 50(10):3757-3764.
DOI: 10.12442/j.issn.1002-185X.20200839
Abstract:
LiNi0.8Co0.1Mn0.1O2 cathode materials were prepared by a high-temperature solid-phase reaction method with Four different lithium salts (LiOH.H2O, Li2CO3, LiNO3, CH3COOLi) as lithium sources. The microstructure of the LiNi0.8Co0.1Mn0.1O2 materials was characterized by X-ray powder diffraction (XRD) and field emission electron microscopy (FESEM). The results demonstrated that the size of all the four synthesized LiNi0.8Co0.1Mn0.1O2 samples were micrometers size, with a layered structure (R-3m space group). The electrochemical test results showed that the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 samples prepared with different lithium sources is very different. Among them, the LiNi0.8Co0.1Mn0.1O2 sample prepared with LiOH?H2O as lithium source (pre-sintering at 500 °C for 6 h and sintering at 800 °C for 16 h) exhibited the lowest degree of lithium-nickel mixing and the best electrochemical performance. For example, its reversible specific capacity is as high as 206.2 mA.h/g at a rate of 0.1 C (1 C=180 mA/g), and its reversible specific capacity remains 80.9 mA.h/g at a rate of 10 C; During 100 charge-discharge cycles at a rate of 0.5 C, the highest specific discharge capacity was 176.2 mA.h/g, and the average specific discharge capacity was 140.1 mA.h/g. The analysis of kinetics and electrode stability revealled that the LiNi0.8Co0.1Mn0.1O2 sample prepared with LiOH?H2O as lithium source possessed the best electrochemical reversibility, highest Li+ diffusion coefficient, and superior structural stability during charge-discharge cycling.
LiNi0.8Co0.1Mn0.1O2 cathode materials were prepared by a high-temperature solid-phase reaction method with Four different lithium salts (LiOH.H2O, Li2CO3, LiNO3, CH3COOLi) as lithium sources. The microstructure of the LiNi0.8Co0.1Mn0.1O2 materials was characterized by X-ray powder diffraction (XRD) and field emission electron microscopy (FESEM). The results demonstrated that the size of all the four synthesized LiNi0.8Co0.1Mn0.1O2 samples were micrometers size, with a layered structure (R-3m space group). The electrochemical test results showed that the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 samples prepared with different lithium sources is very different. Among them, the LiNi0.8Co0.1Mn0.1O2 sample prepared with LiOH?H2O as lithium source (pre-sintering at 500 °C for 6 h and sintering at 800 °C for 16 h) exhibited the lowest degree of lithium-nickel mixing and the best electrochemical performance. For example, its reversible specific capacity is as high as 206.2 mA.h/g at a rate of 0.1 C (1 C=180 mA/g), and its reversible specific capacity remains 80.9 mA.h/g at a rate of 10 C; During 100 charge-discharge cycles at a rate of 0.5 C, the highest specific discharge capacity was 176.2 mA.h/g, and the average specific discharge capacity was 140.1 mA.h/g. The analysis of kinetics and electrode stability revealled that the LiNi0.8Co0.1Mn0.1O2 sample prepared with LiOH?H2O as lithium source possessed the best electrochemical reversibility, highest Li+ diffusion coefficient, and superior structural stability during charge-discharge cycling.
2021, 50(10):3765-3770.
DOI: 10.12442/j.issn.1002-185X.20200841
Abstract:
In the present work, Nd-Fe-B base magnets with 0.5% and 0.25% (Al+Cu) were treated by Dy grain boundary diffusion process and the coercivity distribution, Dy content distribution and microstructure were analyzed. By comparing the composition and properties of the two types of magnets, it was found that the coercivity increment of high (Al + Cu) magnet is 37 kA/m ~ 43kA/m higher than that of low (Al + Cu) magnet in spite of the same Dy increment. Further gradient analysis of composition and coercivity showed that the change of (Al + Cu) content does not change Dy distribution versus to the diffusion depth, but the coercivity increments of high (Al+Cu) magnet slices were 40kA/m~ 80kA/m higher than those of low (Al+Cu) slices. The subsequent EPMA Dy mapping images showed that Dy-rich shells were distributed more clearly and continuously at the high (Al+Cu) magnet, and the TEM EDX analysis results also showed Dy concentration near the grain boundary region is higher in the high (Al+Cu) magnet. With the increase of (Al + Cu) content, the fluidity of grain boundary phase is enhanced and Dy-rich shell wraps the main phase grains more continuously, which further enhances the coercivity with the same Dy increment.
In the present work, Nd-Fe-B base magnets with 0.5% and 0.25% (Al+Cu) were treated by Dy grain boundary diffusion process and the coercivity distribution, Dy content distribution and microstructure were analyzed. By comparing the composition and properties of the two types of magnets, it was found that the coercivity increment of high (Al + Cu) magnet is 37 kA/m ~ 43kA/m higher than that of low (Al + Cu) magnet in spite of the same Dy increment. Further gradient analysis of composition and coercivity showed that the change of (Al + Cu) content does not change Dy distribution versus to the diffusion depth, but the coercivity increments of high (Al+Cu) magnet slices were 40kA/m~ 80kA/m higher than those of low (Al+Cu) slices. The subsequent EPMA Dy mapping images showed that Dy-rich shells were distributed more clearly and continuously at the high (Al+Cu) magnet, and the TEM EDX analysis results also showed Dy concentration near the grain boundary region is higher in the high (Al+Cu) magnet. With the increase of (Al + Cu) content, the fluidity of grain boundary phase is enhanced and Dy-rich shell wraps the main phase grains more continuously, which further enhances the coercivity with the same Dy increment.
2021, 50(10):3771-3776.
DOI: 10.12442/j.issn.1002-185X.20200847
Abstract:
In this paper, the linear friction welding test was carried out on TC17 titanium alloy by several different welding parameters. The distribution of the interface temperature during the welding process, was measured by embedding the thermol couple, and the OM and SEM technology was applied to analyze the typical welding defects of the joint, the distribution of the joints’ microhardness under two different parameters was measured. The results showed that a sound welded joint cannot be obtained on account of the insufficient heat input in a=1mm. The interface temperature could reach around the phase transition point in a lower amplitude, however, it can reach up to 1170℃ under a=3mm. Additionally, there were welding defects at the interface, such as holes, residual wear particles, oxide layers and inclusions, local unbonded, at a=1mm. The result of the micro-hardness test showed that the microhardness of the joint weld center under a=3mm was the lowest, whereas it reached the maximum value under a=1mm due to the presence of residual oxides and inclusions.
In this paper, the linear friction welding test was carried out on TC17 titanium alloy by several different welding parameters. The distribution of the interface temperature during the welding process, was measured by embedding the thermol couple, and the OM and SEM technology was applied to analyze the typical welding defects of the joint, the distribution of the joints’ microhardness under two different parameters was measured. The results showed that a sound welded joint cannot be obtained on account of the insufficient heat input in a=1mm. The interface temperature could reach around the phase transition point in a lower amplitude, however, it can reach up to 1170℃ under a=3mm. Additionally, there were welding defects at the interface, such as holes, residual wear particles, oxide layers and inclusions, local unbonded, at a=1mm. The result of the micro-hardness test showed that the microhardness of the joint weld center under a=3mm was the lowest, whereas it reached the maximum value under a=1mm due to the presence of residual oxides and inclusions.
2021, 50(10):3550-3561.
DOI: 10.12442/j.issn.1002-185X.20210168
Abstract:
The oxidation of Al and Ti in the electroslag remelting process causes an uneven axial composition of the electroslag ingot, which adversely affects its performance, including corrosion resistance and mechanical properties. To control the uniformity of Al and Ti content in electroslag ingots, it is necessary to clarify the change in Al and Ti content during the high-temperature electroslag remelting and to reduce the oxidation of Al and Ti in the alloy by optimizing the slag system ratio and smelting conditions. The research status of Al and Ti element control in the electroslag remelting process was reviewed based on the existing literature, taking the low-fluorine slag CaF2-CaO-Al2O3-MgO-TiO2 and Incoloy 825 alloy as examples. The ion and molecular coexistence theory of slag (IMCT) was used along with FactSage software to summarize the thermodynamic and kinetic research methods. The effects of temperature and components of slag on the equilibrium Al and Ti contents in the alloy were discussed. Based on the film-penetration theory, a kinetics model for predicting Al and Ti contents in the alloy was proposed, and the mathematical equation of the Al and Ti contents vs time in the electroslag process and the slag-metal reaction rate-limiting method were obtained. Results show that the optimum TiO2 addition during the electroslag remelting for Incoloy 825 alloy is determined to be approximately 10%. The slag-metal equilibrium experimental results were compared and analyzed using IMCT and FactSage. It is found that the FactSage calculation results are more accurate than the IMCT calculation results. The higher the TiO2 content, the smaller the deviation between the calculated and experimental results.
The oxidation of Al and Ti in the electroslag remelting process causes an uneven axial composition of the electroslag ingot, which adversely affects its performance, including corrosion resistance and mechanical properties. To control the uniformity of Al and Ti content in electroslag ingots, it is necessary to clarify the change in Al and Ti content during the high-temperature electroslag remelting and to reduce the oxidation of Al and Ti in the alloy by optimizing the slag system ratio and smelting conditions. The research status of Al and Ti element control in the electroslag remelting process was reviewed based on the existing literature, taking the low-fluorine slag CaF2-CaO-Al2O3-MgO-TiO2 and Incoloy 825 alloy as examples. The ion and molecular coexistence theory of slag (IMCT) was used along with FactSage software to summarize the thermodynamic and kinetic research methods. The effects of temperature and components of slag on the equilibrium Al and Ti contents in the alloy were discussed. Based on the film-penetration theory, a kinetics model for predicting Al and Ti contents in the alloy was proposed, and the mathematical equation of the Al and Ti contents vs time in the electroslag process and the slag-metal reaction rate-limiting method were obtained. Results show that the optimum TiO2 addition during the electroslag remelting for Incoloy 825 alloy is determined to be approximately 10%. The slag-metal equilibrium experimental results were compared and analyzed using IMCT and FactSage. It is found that the FactSage calculation results are more accurate than the IMCT calculation results. The higher the TiO2 content, the smaller the deviation between the calculated and experimental results.
2021, 50(10):3562-3576.
DOI: 10.12442/j.issn.1002-185X.20200595
Abstract:
The application of ultrasonic surface rolling process (USRP) to obtain gradient nanostructured materials is presented with comprehensive researches. Concept and description of USRP treatment which has been proved to be able to create gradient nanostructured layers and induce residual compressive stress were depicted. Meanwhile, the microstructural evolutions and surface characteristics which critically depend on processing regimes were discussed. On this basis, it is found that the improvement of mechanical properties, i.e. hardness, strength, wear and fatigue performances, is obtained by USRP treatment while the corrosion/oxidation behavior depends on the composition and structure, surface integrity and stress, solution and service environment. In addition, some possible addresses for future research in this field were drawn and underlined.
The application of ultrasonic surface rolling process (USRP) to obtain gradient nanostructured materials is presented with comprehensive researches. Concept and description of USRP treatment which has been proved to be able to create gradient nanostructured layers and induce residual compressive stress were depicted. Meanwhile, the microstructural evolutions and surface characteristics which critically depend on processing regimes were discussed. On this basis, it is found that the improvement of mechanical properties, i.e. hardness, strength, wear and fatigue performances, is obtained by USRP treatment while the corrosion/oxidation behavior depends on the composition and structure, surface integrity and stress, solution and service environment. In addition, some possible addresses for future research in this field were drawn and underlined.
TIAN Haoliang
,
WANG Hao
,
JIN Guo
,
ZHANG Baosen
,
WANG Changliang
,
GUO Mengqiu
,
DU Xiuxin
,
Wang Tianying
,
ZHANG Ang
,
XIAO Chenbing
2021, 50(10):3777-3785.
DOI: 10.12442/j.issn.1002-185X.20210142
Abstract:
Intelligent temperature sensitive coating is a new kind of functional coating, which has the function of real-time detection of temperature changes, can achieve the timely detection and treatment of abnormal temperature in the process of coating use. The measurement error of external temperature measuring device and the inconvenience of temperature measurement are reduced. In this paper, the research status of aeroengine temperature detection is introduced in detail, and the principle of up conversion luminescence used in rare earth ion temperature detection is introduced. The advantage of temperature measurement lies in real-time detection, no external temperature measurement and other methods on the shape and size of the workpiece requirements, no temperature delay. However, the temperature range of different rare earth ions is quite different, which can not take into account all the temperature ranges. The application principle of temperature sensitive TBC based on rare earth fluorescent ions is also introduced. The coating has great advantages in the application of aeroengine temperature measurement and TBC performance testing. This paper summarizes the different material systems and their temperature detection range studied by scholars at home and abroad, and analyzes the current application status and future development trend of temperature sensitive thermal barrier coatings.
Intelligent temperature sensitive coating is a new kind of functional coating, which has the function of real-time detection of temperature changes, can achieve the timely detection and treatment of abnormal temperature in the process of coating use. The measurement error of external temperature measuring device and the inconvenience of temperature measurement are reduced. In this paper, the research status of aeroengine temperature detection is introduced in detail, and the principle of up conversion luminescence used in rare earth ion temperature detection is introduced. The advantage of temperature measurement lies in real-time detection, no external temperature measurement and other methods on the shape and size of the workpiece requirements, no temperature delay. However, the temperature range of different rare earth ions is quite different, which can not take into account all the temperature ranges. The application principle of temperature sensitive TBC based on rare earth fluorescent ions is also introduced. The coating has great advantages in the application of aeroengine temperature measurement and TBC performance testing. This paper summarizes the different material systems and their temperature detection range studied by scholars at home and abroad, and analyzes the current application status and future development trend of temperature sensitive thermal barrier coatings.
2021, 50(10):3786-3796.
DOI: 10.12442/j.issn.1002-185X.20200791
Abstract:
Owing to their unique mechanical properties compared to conventional materials, mechanical metamaterials have attracted a lot of attention. This unique and novel characteristic is closely related to the microstructure and geometry of mechanical metamaterials, rather than material composition. In addition, many special mechanical properties can also be obtained by designing and preparing various materials and structures. In this paper, the research progress of several mechanical metamaterials properties is reviewed, including: Strong-ultralight, negative Poisson’s ratio, negative compressibility, negative thermal expansion, and meta-fluids. In addition, the restrictive factors of the development of mechanical composite materials are summarized, and the research and development directions in this field is put forward.
Owing to their unique mechanical properties compared to conventional materials, mechanical metamaterials have attracted a lot of attention. This unique and novel characteristic is closely related to the microstructure and geometry of mechanical metamaterials, rather than material composition. In addition, many special mechanical properties can also be obtained by designing and preparing various materials and structures. In this paper, the research progress of several mechanical metamaterials properties is reviewed, including: Strong-ultralight, negative Poisson’s ratio, negative compressibility, negative thermal expansion, and meta-fluids. In addition, the restrictive factors of the development of mechanical composite materials are summarized, and the research and development directions in this field is put forward.
2021, 50(10):3797-3808.
DOI: 10.12442/j.issn.1002-185X.20200797
Abstract:
TiAl alloys have broad application prospects in aerospace and automobile engines, which is due to its excellent properties, such as high melting point, low density, high specific strength, good high temperature oxidation resistance, and creep resistance. Powder hot isostatic pressing can realize the integral forming of TiAl alloy parts with complex shapes, and the obtained parts have small grain size, uniform composition and excellent mechanical properties. In this paper, the principle of powder preparation by atomizing and powder hot isostatic pressing of TiAl alloys are introduced. The research states of microstructures and properties in TiAl alloys after atomization process, powder hot isostatic pressing and heat treatments are summarized. It also analyzes some problems of TiAl alloys’ powder hot isostatic pressing technology in the current, and puts forward prospects for the future development.
TiAl alloys have broad application prospects in aerospace and automobile engines, which is due to its excellent properties, such as high melting point, low density, high specific strength, good high temperature oxidation resistance, and creep resistance. Powder hot isostatic pressing can realize the integral forming of TiAl alloy parts with complex shapes, and the obtained parts have small grain size, uniform composition and excellent mechanical properties. In this paper, the principle of powder preparation by atomizing and powder hot isostatic pressing of TiAl alloys are introduced. The research states of microstructures and properties in TiAl alloys after atomization process, powder hot isostatic pressing and heat treatments are summarized. It also analyzes some problems of TiAl alloys’ powder hot isostatic pressing technology in the current, and puts forward prospects for the future development.
2021, 50(10):3809-3813.
DOI: 10.12442/j.issn.1002-185X.20210094
Abstract:
A large number of tellurium nanowires were prepared on quartz substrates coated with Au sol by thermal evaporation method in a vacuum tube furnace with Bi2Te3 as the source at 560 °C for 2h. The microstructure and morphology of tellurium nanowires were characterized by XRD, SEM and HRTEM. The results showed that the as prepared tellurium nanowires were cubic single crystal tellurium nanowires oriented along the (101) direction with diameters ranging from 40 to 100 nm. The growth mechanism conforms to the VLS growth mechanism .The evaporation source material and Au sol were the key factors for the preparation of tellurium nanowires by thermal evaporation.
A large number of tellurium nanowires were prepared on quartz substrates coated with Au sol by thermal evaporation method in a vacuum tube furnace with Bi2Te3 as the source at 560 °C for 2h. The microstructure and morphology of tellurium nanowires were characterized by XRD, SEM and HRTEM. The results showed that the as prepared tellurium nanowires were cubic single crystal tellurium nanowires oriented along the (101) direction with diameters ranging from 40 to 100 nm. The growth mechanism conforms to the VLS growth mechanism .The evaporation source material and Au sol were the key factors for the preparation of tellurium nanowires by thermal evaporation.
2021, 50(10):3814-3818.
DOI: 10.12442/j.issn.1002-185X.20210173
Abstract:
For rapid breakthrough, acquire the key manufacturing technology and accomplish key data accumulation, CFHI had manufactured a large-section Ni-base trial forging for 700 ℃ advanced USC powder plant. We successfully manufactured the rotor trial forging with a diameter of 660mm after several times of upsetting and drawing. Grain size of Ni-base alloy forging was 4-6 class and 1~2 class after heat treatment. The room temperature tensile strength can reach 1000MPa, yield strength can reach 600MPa, the impact energy is beyond 45J at different positions after heat treatment. The tensile strength can reach 800MPa, yield strength can reach 500MPa at 700℃.Tthe plasticity is more than20% at room temperature and 700℃.We realized the homogeneous manufacture of large section nickel base alloy forging.
For rapid breakthrough, acquire the key manufacturing technology and accomplish key data accumulation, CFHI had manufactured a large-section Ni-base trial forging for 700 ℃ advanced USC powder plant. We successfully manufactured the rotor trial forging with a diameter of 660mm after several times of upsetting and drawing. Grain size of Ni-base alloy forging was 4-6 class and 1~2 class after heat treatment. The room temperature tensile strength can reach 1000MPa, yield strength can reach 600MPa, the impact energy is beyond 45J at different positions after heat treatment. The tensile strength can reach 800MPa, yield strength can reach 500MPa at 700℃.Tthe plasticity is more than20% at room temperature and 700℃.We realized the homogeneous manufacture of large section nickel base alloy forging.
