Volume 45,Issue 11,2016 Table of Contents
1 Effect of Zn on microstructure and properties of Mg-Zn alloys prepared by powder metallurgy method
2016, 45(11):2757-2762.
Abstract:
Mg-Zn alloys were prepared by powder metallurgy method using Mg powder and Zn powder as initial materials. The effects of the Zn content on sintering density, microstructure, phase composition, bending properties and micro-hardness of the Mg-Zn alloys were studied. The corrosion resistance of the Mg-Zn alloys was also measured. The function mechanism of Zn element during the powder metallurgy process was analyzed. It is shown that the sintered compacts have finer grain size and higher sintered density upon Zn addition. The density of the sintered products increases with increasing Zn contents. XRD analysis shows the Mg-3 wt% Zn alloy is mainly composed of α-Mg phase. When the content of Zn is 4 wt%, the Mg-Zn alloys are composed of α-Mg and MgZn2 phases. With the increase of the Zn content, the bending strength of the Mg-Zn alloys first increases and then decreases, but the micro-hardness of Mg-Zn alloys always increases. The bending strength and micro-hardness of Mg-3 wt% Zn alloys are 123.6 MPa and 101.7 HV, respectively, which are 58% and 45% higher than those of pure Mg samples. Corrosion resistance measurements show that the corrosion rate of the Mg-Zn alloys decreases with the addition of Zn element, with the Mg-3 wt% Zn alloy showing the lowest corrosion rate and best corrosion resistance.
Mg-Zn alloys were prepared by powder metallurgy method using Mg powder and Zn powder as initial materials. The effects of the Zn content on sintering density, microstructure, phase composition, bending properties and micro-hardness of the Mg-Zn alloys were studied. The corrosion resistance of the Mg-Zn alloys was also measured. The function mechanism of Zn element during the powder metallurgy process was analyzed. It is shown that the sintered compacts have finer grain size and higher sintered density upon Zn addition. The density of the sintered products increases with increasing Zn contents. XRD analysis shows the Mg-3 wt% Zn alloy is mainly composed of α-Mg phase. When the content of Zn is 4 wt%, the Mg-Zn alloys are composed of α-Mg and MgZn2 phases. With the increase of the Zn content, the bending strength of the Mg-Zn alloys first increases and then decreases, but the micro-hardness of Mg-Zn alloys always increases. The bending strength and micro-hardness of Mg-3 wt% Zn alloys are 123.6 MPa and 101.7 HV, respectively, which are 58% and 45% higher than those of pure Mg samples. Corrosion resistance measurements show that the corrosion rate of the Mg-Zn alloys decreases with the addition of Zn element, with the Mg-3 wt% Zn alloy showing the lowest corrosion rate and best corrosion resistance.
2016, 45(11):2763-2767.
Abstract:
Lead-free piezoelectric ceramics (KxNa1?x)1-yLiyNb0.80Ta0.20O3 ( x=0.40–0.60 when y=0.030, 0.035, 0.040 ) were prepared by conventional solid-state reaction method to investigate the thermal stability of piezoelectric properties. It has been found that samples in the researched compositional range have high piezoelectric constant of d33=250 pC/N and kp=50%, respectively. In the thermal aging test up to the Curie temperature of approximately 325oC, d33 and kp of the ceramics remain almost unchanged although there existing the polymorphic phase transition (PPT) near room temperature. Moreover, ceramics presents the very good piezoelectric temperature stability and kp show the weak temperature dependence over a wide measured temperature range from -50oC to 120oC. The excellent thermal stability was discussed from the aspect of temperature range of phase coexistance.
Lead-free piezoelectric ceramics (KxNa1?x)1-yLiyNb0.80Ta0.20O3 ( x=0.40–0.60 when y=0.030, 0.035, 0.040 ) were prepared by conventional solid-state reaction method to investigate the thermal stability of piezoelectric properties. It has been found that samples in the researched compositional range have high piezoelectric constant of d33=250 pC/N and kp=50%, respectively. In the thermal aging test up to the Curie temperature of approximately 325oC, d33 and kp of the ceramics remain almost unchanged although there existing the polymorphic phase transition (PPT) near room temperature. Moreover, ceramics presents the very good piezoelectric temperature stability and kp show the weak temperature dependence over a wide measured temperature range from -50oC to 120oC. The excellent thermal stability was discussed from the aspect of temperature range of phase coexistance.
2016, 45(11):2768-2773.
Abstract:
A bi-layered Ir/W metallic coating was successfully deposited onto the Mo network via the magnetron sputtering method. The sputtering W bond-coat was proved able to enhance the binding energy between the sputtering Ir coating and the Mo substrate, and virtually neither delamination nor peeling off was observed for the as-prepared coating. In addition, the interdiffusion between the W bond-coat and the Ir coating or the Mo substrate was not apparent. The dense and adherent Ir coating was identified to have a polycrystalline structure with (111) orientation. According to the three zone model suggested by Movchan and Demchishin for sputtering metallic coatings, the microstructure of the bi-layered metallic coating was consistent with the Zone 1 features. In fact, the bi-layered coating had very low lateral strength and inclined to crack under tension.
A bi-layered Ir/W metallic coating was successfully deposited onto the Mo network via the magnetron sputtering method. The sputtering W bond-coat was proved able to enhance the binding energy between the sputtering Ir coating and the Mo substrate, and virtually neither delamination nor peeling off was observed for the as-prepared coating. In addition, the interdiffusion between the W bond-coat and the Ir coating or the Mo substrate was not apparent. The dense and adherent Ir coating was identified to have a polycrystalline structure with (111) orientation. According to the three zone model suggested by Movchan and Demchishin for sputtering metallic coatings, the microstructure of the bi-layered metallic coating was consistent with the Zone 1 features. In fact, the bi-layered coating had very low lateral strength and inclined to crack under tension.
2016, 45(11):2774-2778.
Abstract:
The fatigue property of Al-5Zn-2Mg aluminum alloy Metal-Inert Gas (MIG) welding joints used in high-speed train are studied by fatigue machine. Scanning electron microscopy (SEM) is used to observe the fatigue fracture and the surface damage. Results shows that uniaxial ratcheting behavior take place in the welding zone (WZ) when the stress is higher than 0.5σb. There is obvious plastic deformation in the WZ and a lot of slip band on the surface, which reduces the fatigue life of the sample. The uniaxial ratcheting behavior take place mainly in the first cycle and the finally failure stage of the fatigue process. When the stress is lower than 0.5σb, the fatigue samples crack in the heat affected zone (HAZ). The fatigue fracture of the WZ and the fusion zone (FZ) is typical ductile fracture pattern while that of the HAZ and the base metal (BM) is quasi-cleavage fracture. The fatigue life of the BM is much longer than the HAZ.
The fatigue property of Al-5Zn-2Mg aluminum alloy Metal-Inert Gas (MIG) welding joints used in high-speed train are studied by fatigue machine. Scanning electron microscopy (SEM) is used to observe the fatigue fracture and the surface damage. Results shows that uniaxial ratcheting behavior take place in the welding zone (WZ) when the stress is higher than 0.5σb. There is obvious plastic deformation in the WZ and a lot of slip band on the surface, which reduces the fatigue life of the sample. The uniaxial ratcheting behavior take place mainly in the first cycle and the finally failure stage of the fatigue process. When the stress is lower than 0.5σb, the fatigue samples crack in the heat affected zone (HAZ). The fatigue fracture of the WZ and the fusion zone (FZ) is typical ductile fracture pattern while that of the HAZ and the base metal (BM) is quasi-cleavage fracture. The fatigue life of the BM is much longer than the HAZ.
2016, 45(11):2779-2783.
Abstract:
Titania nanotube arrays decorated with WO3 (WTN) were fabricated by a chemical bath deposition (CBD) technique in combination with a pyrolysis process. The products were uniform and the amount of tungsten can be easily adjusted by the deposition time. The resultant hybrid nanotubes arrays were characterized by SEM, EDX and XRD. Results show that titania nanotubes with an internal diameter of the tubes 90~120 nm, an external diameter 120~160 nm, wall thickness in the range of 30~60 nm and a length of 39 μm are grown on titanium substrate by anodizing. The tungsten trioxide is i decorated on the titania nanotubes, which enhances the photocatalytic activity of the WTN, as indicated by the efficient removal of C.I. Sulphur Red 14. The resultant composite films show better photocatalytic activity than the non-decorated nanotube arrays (TN) under visible light illumination.
Titania nanotube arrays decorated with WO3 (WTN) were fabricated by a chemical bath deposition (CBD) technique in combination with a pyrolysis process. The products were uniform and the amount of tungsten can be easily adjusted by the deposition time. The resultant hybrid nanotubes arrays were characterized by SEM, EDX and XRD. Results show that titania nanotubes with an internal diameter of the tubes 90~120 nm, an external diameter 120~160 nm, wall thickness in the range of 30~60 nm and a length of 39 μm are grown on titanium substrate by anodizing. The tungsten trioxide is i decorated on the titania nanotubes, which enhances the photocatalytic activity of the WTN, as indicated by the efficient removal of C.I. Sulphur Red 14. The resultant composite films show better photocatalytic activity than the non-decorated nanotube arrays (TN) under visible light illumination.
2016, 45(11):2784-2789.
Abstract:
An agitation leaching method was used for gold extraction from Aghdareh mine samples. Mineralogical study showed that 58% of the gold particles were finer than 10 μm. In addition 3% of the grade in the sample was related to refractory gold. Experiments results showed that at the optimum condition gold recovery was 91.8% and silver, and mercury recoveries were 41.5%, and 10.2%, respectively. After performing cyanidation tests for 6 different fractions, it was concluded that the most unleached gold particles exist in the fraction size finer than 25 μm and about 5% of gold particles in the fraction size larger than 25 μm was not leached. Therefore, further comminution was applied which increased by about 3.57% of gold recovery and about 5% of silver recovery. Further comminution did not affect the recovery of mercury. In order to increase the mercury recovery and prevent from amalgamation of gold by mercury particles, Knelson gravity concentrator was used. The tailing of gravity method was examined using cyanidation tests by considering the optimum conditions. According to the final results, using the combination of these methods, gold recovery is increased to 93.3% and the recovery of mercury increased to 42.1% while the recovery of silver is 42.17%, without noticeable change.
An agitation leaching method was used for gold extraction from Aghdareh mine samples. Mineralogical study showed that 58% of the gold particles were finer than 10 μm. In addition 3% of the grade in the sample was related to refractory gold. Experiments results showed that at the optimum condition gold recovery was 91.8% and silver, and mercury recoveries were 41.5%, and 10.2%, respectively. After performing cyanidation tests for 6 different fractions, it was concluded that the most unleached gold particles exist in the fraction size finer than 25 μm and about 5% of gold particles in the fraction size larger than 25 μm was not leached. Therefore, further comminution was applied which increased by about 3.57% of gold recovery and about 5% of silver recovery. Further comminution did not affect the recovery of mercury. In order to increase the mercury recovery and prevent from amalgamation of gold by mercury particles, Knelson gravity concentrator was used. The tailing of gravity method was examined using cyanidation tests by considering the optimum conditions. According to the final results, using the combination of these methods, gold recovery is increased to 93.3% and the recovery of mercury increased to 42.1% while the recovery of silver is 42.17%, without noticeable change.
2016, 45(11):2790-2792.
Abstract:
Rare-earth doped phosphors with tunable optical properties have potential applications in solid state lighting such as display panels and fluorescent lamps. Herein, trivalent Eu3 , Tb3 activated Y2O3 phosphors have been successfully synthesized by solid state process. The structural studies have been performed by the measurements of X-ray diffraction profiles. The pure phase of Y2O3 is obtained and RE ions is not shown any effect on the structural properties. Single RE ions activated Y2O3 phosphors exhibit their characteristic emission. As Tb3 doped in Y2O3, a bright green emission is obtained and while Eu3 is introduced into the material Y2O3: Tb3 , the emission color can be adjusted to white light. The calculated CIE chromaticity coordinates of RE ions activated Y2O3 phosphors confirmed the green and white emissions.
Rare-earth doped phosphors with tunable optical properties have potential applications in solid state lighting such as display panels and fluorescent lamps. Herein, trivalent Eu3 , Tb3 activated Y2O3 phosphors have been successfully synthesized by solid state process. The structural studies have been performed by the measurements of X-ray diffraction profiles. The pure phase of Y2O3 is obtained and RE ions is not shown any effect on the structural properties. Single RE ions activated Y2O3 phosphors exhibit their characteristic emission. As Tb3 doped in Y2O3, a bright green emission is obtained and while Eu3 is introduced into the material Y2O3: Tb3 , the emission color can be adjusted to white light. The calculated CIE chromaticity coordinates of RE ions activated Y2O3 phosphors confirmed the green and white emissions.
2016, 45(11):2793-2797.
Abstract:
High purity rare earth metals, such as samarium, ytterbium and thulium, have been prepared by vacuum reduction-distillation of each rare earth oxide with lanthanum metal. The rare earth metals of samarium and ytterbium with 4N-purity are prepared by direct vacuum reduction-distillation, and the purity of above metals is 99.99 wt.% and 99.993 wt.% respectively with respect to 75 impurities; there is a high concentration of reductant in thulium metal due to the higher reaction temperature and lower distillation velocity ratio of metallic thulium to lanthanum, so that the sublimation purification with lower temperature and high vacuum has been conducted, the purified thulium can be reach a high purity of 99.995 wt.% with respect to 75 impurities; the experimental results indicates that, the preparation of high purity reductant of lanthanum metal, especially of total amount control of metallic impurities, is the key step to obtain 4N-purity rare earth metallic samarium, ytterbium and thulium.
High purity rare earth metals, such as samarium, ytterbium and thulium, have been prepared by vacuum reduction-distillation of each rare earth oxide with lanthanum metal. The rare earth metals of samarium and ytterbium with 4N-purity are prepared by direct vacuum reduction-distillation, and the purity of above metals is 99.99 wt.% and 99.993 wt.% respectively with respect to 75 impurities; there is a high concentration of reductant in thulium metal due to the higher reaction temperature and lower distillation velocity ratio of metallic thulium to lanthanum, so that the sublimation purification with lower temperature and high vacuum has been conducted, the purified thulium can be reach a high purity of 99.995 wt.% with respect to 75 impurities; the experimental results indicates that, the preparation of high purity reductant of lanthanum metal, especially of total amount control of metallic impurities, is the key step to obtain 4N-purity rare earth metallic samarium, ytterbium and thulium.
2016, 45(11):2798-2803.
Abstract:
In situ 5wt.%Al3Zr/6063Al composites were fabricated by direct melt reaction method (DMR) and then processed by deformation pretreatment. Process of the pretreatment is forging of 70% deformation at 450℃ and friction stir processing (FSP). The high strain rate superplasticity of the composites was studied by modern analytic determination methods. The results show that the average grain size of the composites is less than 10 μm after forging and FSP. The composites exhibited superplasticity at the temperature of 350℃ to 500℃ and initial strain rate of 1.0×10-3s-1 to 1.0×10-1s-1. The elongation reached 330% and the sensitive index (m value) is 0.45 at the initial strain rate of 1.0×10-2s-1 and the temperature of 500 ℃. The dominant mechanisms of superplastic deformation were grain boundary sliding and dislocation slip which synergized with moderate grain growth and dynamic continuous recrystallization.
In situ 5wt.%Al3Zr/6063Al composites were fabricated by direct melt reaction method (DMR) and then processed by deformation pretreatment. Process of the pretreatment is forging of 70% deformation at 450℃ and friction stir processing (FSP). The high strain rate superplasticity of the composites was studied by modern analytic determination methods. The results show that the average grain size of the composites is less than 10 μm after forging and FSP. The composites exhibited superplasticity at the temperature of 350℃ to 500℃ and initial strain rate of 1.0×10-3s-1 to 1.0×10-1s-1. The elongation reached 330% and the sensitive index (m value) is 0.45 at the initial strain rate of 1.0×10-2s-1 and the temperature of 500 ℃. The dominant mechanisms of superplastic deformation were grain boundary sliding and dislocation slip which synergized with moderate grain growth and dynamic continuous recrystallization.
2016, 45(11):2804-2808.
Abstract:
In the present work, the effect of heat treatment at 773 K for 48h on microstructure and mechanical properties of as-cast Mg94Zn2Y4 (at.%) alloy has been investigated. The results showed that block shaped and laths structures 18R long period stacking ordered (LPSO) phase forms directly from the melt. After heat treatment, vast majority of the block shaped and laths structures LPSO phase changed into fine lamellar or needle-like shaped 14H. During heat treatment, a great fraction of LPSO phase was transformed from 18R structure to 14H type. Both 18R and 14H can co-exist within the α-Mg matrix after solution treatment. As a result, with grain sizes of 14-24 μm (the average grain size is about 19 μm), the co-existence of the block shaped and laths structures phase and needle-like shaped phase helps to improve the ultimate tensile strength, yield strength and elongation from 182 MPa, 135 Mpa and 10.2% in as-cast alloy to 245 MPa, 157 MPa and 13.8%, respectively.
In the present work, the effect of heat treatment at 773 K for 48h on microstructure and mechanical properties of as-cast Mg94Zn2Y4 (at.%) alloy has been investigated. The results showed that block shaped and laths structures 18R long period stacking ordered (LPSO) phase forms directly from the melt. After heat treatment, vast majority of the block shaped and laths structures LPSO phase changed into fine lamellar or needle-like shaped 14H. During heat treatment, a great fraction of LPSO phase was transformed from 18R structure to 14H type. Both 18R and 14H can co-exist within the α-Mg matrix after solution treatment. As a result, with grain sizes of 14-24 μm (the average grain size is about 19 μm), the co-existence of the block shaped and laths structures phase and needle-like shaped phase helps to improve the ultimate tensile strength, yield strength and elongation from 182 MPa, 135 Mpa and 10.2% in as-cast alloy to 245 MPa, 157 MPa and 13.8%, respectively.
2016, 45(11):2809-2813.
Abstract:
First-principles calculations are performed to investigate the electronic structure of the Bi2Se3 single-QL thin film and the films doped with Pb. Their band structures and densities of states are explored. The results show that the main composition of the valence band and conduction band of these films is p-states, and their band-gap type can change from the direct to the indirect as Bi2Se3 from block to film. In BiPbSe3 film, The newly appeared Se(1／) layer caused by the doped Pb has an significant impact on the electronic structures of the film, but in the Pb0.25Bi1.75Se3 thin film with the concentration of Pb ～5%, there is the similar band structure to the pristine film. This paper also discusses the modulation of Bi 6s orbital states at the valence band maximum and the concentration of carriers in doped films.
First-principles calculations are performed to investigate the electronic structure of the Bi2Se3 single-QL thin film and the films doped with Pb. Their band structures and densities of states are explored. The results show that the main composition of the valence band and conduction band of these films is p-states, and their band-gap type can change from the direct to the indirect as Bi2Se3 from block to film. In BiPbSe3 film, The newly appeared Se(1／) layer caused by the doped Pb has an significant impact on the electronic structures of the film, but in the Pb0.25Bi1.75Se3 thin film with the concentration of Pb ～5%, there is the similar band structure to the pristine film. This paper also discusses the modulation of Bi 6s orbital states at the valence band maximum and the concentration of carriers in doped films.
2016, 45(11):2814-2817.
Abstract:
The samples of La(Fe1-xCox)11.2Si1.8 (x = 0, 0.02, 0.04, 0.06) have been prepared by ball-milling with elemental powder and LaSi cast master alloys. After sintering at 1423 K for 30 minutes followed by a quenching in water, an almost NaZn13 type single phase has been obtained. The study of magnetic properties revealed that the Curie temperature increases with Co content from x=0 to 0.06 whereas the magnetic entropy change decreases. The alloy of LaFe11.2Si1.8 has a maximum magnetic entropy change △Sm of 6.5 J/kg K near its Curie temperature under a magnetic field of 0-1.5T, while the maximum magnetic entropy change is about 2.1 J/kg K with x=0.06. Furthermore, the magnetization of ball-milled samples exhibits a second-order magnetic transition, which is interesting for magnetocaloric applications.
The samples of La(Fe1-xCox)11.2Si1.8 (x = 0, 0.02, 0.04, 0.06) have been prepared by ball-milling with elemental powder and LaSi cast master alloys. After sintering at 1423 K for 30 minutes followed by a quenching in water, an almost NaZn13 type single phase has been obtained. The study of magnetic properties revealed that the Curie temperature increases with Co content from x=0 to 0.06 whereas the magnetic entropy change decreases. The alloy of LaFe11.2Si1.8 has a maximum magnetic entropy change △Sm of 6.5 J/kg K near its Curie temperature under a magnetic field of 0-1.5T, while the maximum magnetic entropy change is about 2.1 J/kg K with x=0.06. Furthermore, the magnetization of ball-milled samples exhibits a second-order magnetic transition, which is interesting for magnetocaloric applications.
2016, 45(11):2818-2822.
Abstract:
To improve the corrosion resistance of steel wires, a uniform thin layer of bulk metallic glass alloy with different compositions of (Zr41.2Ti13.8Cu12.5Ni10Be22.5)100-xNbx (x=0, 3, 5, 8 at. %) was coated on the surface of Q 195 steel wires by a newly developed continuous coating process. Phase analysis results show that the coating is mainly composed of metallic glass alloy and some other intermetallics. The potentiodynamic polarization tests show that the steel wires with metallic glass coating show passivation behavior, and have higher pitting potential and lower corrosion current density than Q 195 steel wires. With the increment of Nb content, passivation region of the metallic glass-coated steel wires become wider while pitting potential is increased. As shown in composition analysis results, it may be attributed to the addition of Nb which has properties of easy passivation and stabilizing the passivation elements of Zr and Ti.
To improve the corrosion resistance of steel wires, a uniform thin layer of bulk metallic glass alloy with different compositions of (Zr41.2Ti13.8Cu12.5Ni10Be22.5)100-xNbx (x=0, 3, 5, 8 at. %) was coated on the surface of Q 195 steel wires by a newly developed continuous coating process. Phase analysis results show that the coating is mainly composed of metallic glass alloy and some other intermetallics. The potentiodynamic polarization tests show that the steel wires with metallic glass coating show passivation behavior, and have higher pitting potential and lower corrosion current density than Q 195 steel wires. With the increment of Nb content, passivation region of the metallic glass-coated steel wires become wider while pitting potential is increased. As shown in composition analysis results, it may be attributed to the addition of Nb which has properties of easy passivation and stabilizing the passivation elements of Zr and Ti.
2016, 45(11):2823-2826.
Abstract:
Anand constitutive model of SnAgCuFe solder joints was studied, and the nine parameters was determined based on tensile testing. And the model was incorporated in finite element code for analyze the stress-strain response of SnAgCuFe solder joints in WLCSP30 device. The results indicate that the maximum stress concentrates on the top surface of corner solder joints, and the stress-strain of SnAgCuFe solder joints is lower than that of SnAgCu solder joints. Based on the fatigue life model, the addition of Fe can enhance the fatigue life of SnAgCu solder joints, therefore, the SnAgCuFe solders can replace the traditional SnPb to be used in electronic packaging.
Anand constitutive model of SnAgCuFe solder joints was studied, and the nine parameters was determined based on tensile testing. And the model was incorporated in finite element code for analyze the stress-strain response of SnAgCuFe solder joints in WLCSP30 device. The results indicate that the maximum stress concentrates on the top surface of corner solder joints, and the stress-strain of SnAgCuFe solder joints is lower than that of SnAgCu solder joints. Based on the fatigue life model, the addition of Fe can enhance the fatigue life of SnAgCu solder joints, therefore, the SnAgCuFe solders can replace the traditional SnPb to be used in electronic packaging.
2016, 45(11):2827-2834.
Abstract:
The interaction and synergetic effects of the four corrosive anions (Cl-, HPO42-, HCO3-, and SO42-) on the degradation behavior of the Mg-3Zn-0.5Zr alloy were investigated using some electrochemical tests, such as potentiodynamic polarization, open circuit potential evolution, and electrochemical impedance spectroscopy (EIS). We found that chloride ions induce porous pitting corrosion on the alloy. The corrosion pits expanded on the surface and much deeper. Hydrogen phosphate ions inhibited the degradation rate and restrained the pitting corrosion. The degradation rate of the Mg-3Zn-0.5Zr alloy was accelerated at early time point during immersed in solutions containing hydrogen carbonate ions. However, precipitation of the magnesium carbonate resulted in passivation and the corrosion products totally inhibited the pitting corrosion. Sulfate ions could also corrode the Mg-3Zn-0.5Zr alloy, but for its low concentration in the physiological environment, the effects of sulfate on the degradation rate and corrosion morphology were limited. All of these results develop our knowledge on the degradation mechanism of Mg-3Zn-0.5Zr alloy in the physiological environment.
The interaction and synergetic effects of the four corrosive anions (Cl-, HPO42-, HCO3-, and SO42-) on the degradation behavior of the Mg-3Zn-0.5Zr alloy were investigated using some electrochemical tests, such as potentiodynamic polarization, open circuit potential evolution, and electrochemical impedance spectroscopy (EIS). We found that chloride ions induce porous pitting corrosion on the alloy. The corrosion pits expanded on the surface and much deeper. Hydrogen phosphate ions inhibited the degradation rate and restrained the pitting corrosion. The degradation rate of the Mg-3Zn-0.5Zr alloy was accelerated at early time point during immersed in solutions containing hydrogen carbonate ions. However, precipitation of the magnesium carbonate resulted in passivation and the corrosion products totally inhibited the pitting corrosion. Sulfate ions could also corrode the Mg-3Zn-0.5Zr alloy, but for its low concentration in the physiological environment, the effects of sulfate on the degradation rate and corrosion morphology were limited. All of these results develop our knowledge on the degradation mechanism of Mg-3Zn-0.5Zr alloy in the physiological environment.
2016, 45(11):2835-2840.
Abstract:
Abstract：By means of creep properties measurement and microstructure observation, an investigation has been made into the microstructure and creep properties of as-cast TiAl-Nb alloy in the temperature ranges of 800--910篊. Results show that the microstructure of as-cast TiAl-Nb alloy consists of r/a2 phases with the lamellar feature. The boundaries with the irregular jagged configuration are located in between the different oriented lamellar phases, and the single r is distributed in the region near the boundaries. The creep lifetime of as-cast TiAl-Nb alloy is measured to be 237 h under the applied stress of 120 MPa at 900 篊, and the creep lifetime of the alloy is measured to be 307 h under the applied stress of 220 MPa at 800篊. The deformation mechanism of alloy during creep is dislocation slipping within the lamellar r/a2 phases, and the boundaries between the lamellar r/a2 phases may hinder dislocation slipping. During steady state creep, the lamellar r/a2 phases in the alloy may be contorted due to the double orientation slipping of dislocations. In the latter stage of the creep, the micro-crack may be initiated and propagated along the grain boundaries being perpendicular or at about 45?angles relative to the stress axis, under the action of maximum shear stress, up to the occurrence of creep fracture, which is thought to be the fracture mechanism of alloy during creep.
Abstract：By means of creep properties measurement and microstructure observation, an investigation has been made into the microstructure and creep properties of as-cast TiAl-Nb alloy in the temperature ranges of 800--910篊. Results show that the microstructure of as-cast TiAl-Nb alloy consists of r/a2 phases with the lamellar feature. The boundaries with the irregular jagged configuration are located in between the different oriented lamellar phases, and the single r is distributed in the region near the boundaries. The creep lifetime of as-cast TiAl-Nb alloy is measured to be 237 h under the applied stress of 120 MPa at 900 篊, and the creep lifetime of the alloy is measured to be 307 h under the applied stress of 220 MPa at 800篊. The deformation mechanism of alloy during creep is dislocation slipping within the lamellar r/a2 phases, and the boundaries between the lamellar r/a2 phases may hinder dislocation slipping. During steady state creep, the lamellar r/a2 phases in the alloy may be contorted due to the double orientation slipping of dislocations. In the latter stage of the creep, the micro-crack may be initiated and propagated along the grain boundaries being perpendicular or at about 45?angles relative to the stress axis, under the action of maximum shear stress, up to the occurrence of creep fracture, which is thought to be the fracture mechanism of alloy during creep.
2016, 45(11):2841-2846.
Abstract:
Microstructures morphology and phases of Ti-35V-15Cr-xSi-yC alloy after different annealing and solution treatments were studied using different analysis methods. The results show the amount of grain-boundary small grain increases but their sizes shows little change for the specimen annealing below 900℃. The microstructure morphology shows little different for different annealing specimen below 900℃.When the annealing temperature is above 900 ℃，the small grain at grain-boundary growth obviously and the microstructure morphology shows visible change. Tere are four precipitations in the alloy microstructure, they are spherical particle precipitation of Ti2C, “chicken feet” type precipitation of (TiV)C, dot particle precipitation of Ti5Si3 and needle-like precipitation of α. The solvus temperature for precipitation of (TiV)C and Ti5Si3 in Ti-35V-15Cr-xSi-yC are separately in temperature range form 950℃ to 1000℃ and 1000℃ to 1050℃. When the solution temperature increase to 1200℃，there is only partial solution of Ti2C.
Microstructures morphology and phases of Ti-35V-15Cr-xSi-yC alloy after different annealing and solution treatments were studied using different analysis methods. The results show the amount of grain-boundary small grain increases but their sizes shows little change for the specimen annealing below 900℃. The microstructure morphology shows little different for different annealing specimen below 900℃.When the annealing temperature is above 900 ℃，the small grain at grain-boundary growth obviously and the microstructure morphology shows visible change. Tere are four precipitations in the alloy microstructure, they are spherical particle precipitation of Ti2C, “chicken feet” type precipitation of (TiV)C, dot particle precipitation of Ti5Si3 and needle-like precipitation of α. The solvus temperature for precipitation of (TiV)C and Ti5Si3 in Ti-35V-15Cr-xSi-yC are separately in temperature range form 950℃ to 1000℃ and 1000℃ to 1050℃. When the solution temperature increase to 1200℃，there is only partial solution of Ti2C.
2016, 45(11):2847-2850.
Abstract:
Abstract:Quasi-static and dynamic mechanical properties of Ni-Ti shape memory alloy bar have been investigated by using electronic universal testing machine (INSTRON5985) and Split-Hopkinson Pressure Bar (SHPB), and analyze the microstructure under different condition through microscopic analysis methods such as XRD, OM and SEM. The experimental results show that Ni-Ti alloy original organizations consist of B2 austenitic phase, B19’ martensite phase , Ni3Ti4 phase and with small equiaxed grains; quasi-static and dynamic compression all occur stress induced martensite phase transformation, but dynamic compression stress-strain curve does not appear yield platform and presents strain rate hardening effect; within a certain range of strain rate, the striped organizations increase with the increase of strain rate, and the degree of stress induced martensite phase transformation increases.
Abstract:Quasi-static and dynamic mechanical properties of Ni-Ti shape memory alloy bar have been investigated by using electronic universal testing machine (INSTRON5985) and Split-Hopkinson Pressure Bar (SHPB), and analyze the microstructure under different condition through microscopic analysis methods such as XRD, OM and SEM. The experimental results show that Ni-Ti alloy original organizations consist of B2 austenitic phase, B19’ martensite phase , Ni3Ti4 phase and with small equiaxed grains; quasi-static and dynamic compression all occur stress induced martensite phase transformation, but dynamic compression stress-strain curve does not appear yield platform and presents strain rate hardening effect; within a certain range of strain rate, the striped organizations increase with the increase of strain rate, and the degree of stress induced martensite phase transformation increases.
2016, 45(11):2851-2856.
Abstract:
The stress distribution and its evolution，after repeated thermal shock, in NiCrAlY coatings/YSZ diffusion barrier /René N5 substrate were studied using the finite element method, as well as the effect of peak value on stress. The results showed that higher shear and tensile stresses existed in the outer edge and the alumina layer, where cracks were easier to initiate and propagate, after 75 times- thermal shock. With the increasing number of thermal shock, the stresses in YSZ active diffusion barrier coating system increased. Moreover, the peak stress increasement was observed in the alumina layer, and the optimum peak value (A) was 3 μm.
The stress distribution and its evolution，after repeated thermal shock, in NiCrAlY coatings/YSZ diffusion barrier /René N5 substrate were studied using the finite element method, as well as the effect of peak value on stress. The results showed that higher shear and tensile stresses existed in the outer edge and the alumina layer, where cracks were easier to initiate and propagate, after 75 times- thermal shock. With the increasing number of thermal shock, the stresses in YSZ active diffusion barrier coating system increased. Moreover, the peak stress increasement was observed in the alumina layer, and the optimum peak value (A) was 3 μm.
2016, 45(11):2857-2860.
Abstract:
The thermodilatometry was used to study αZr→αZr βZ phase transformation kinetics at various heating rates in Zr-1Nb-0.01Cu alloy. The results show that the relationship between the start transformation temperature of αZr→αZr βZr and the heating rates is as follows: Tα→α β=744.4 9.4ln(RH), and the heating rates show lower influence on the transformation temperatures compared with that of E110 alloy. The active energy of αZr→αZr βZr is 149.1kJ/mol which is calculated from JMA model, and it is smaller than that of Zr-4 and M5 alloys.The continuous heating transformation diagram (CHT) of αZr→αZr βZr is given according to phase transformation curves of the alloy.
The thermodilatometry was used to study αZr→αZr βZ phase transformation kinetics at various heating rates in Zr-1Nb-0.01Cu alloy. The results show that the relationship between the start transformation temperature of αZr→αZr βZr and the heating rates is as follows: Tα→α β=744.4 9.4ln(RH), and the heating rates show lower influence on the transformation temperatures compared with that of E110 alloy. The active energy of αZr→αZr βZr is 149.1kJ/mol which is calculated from JMA model, and it is smaller than that of Zr-4 and M5 alloys.The continuous heating transformation diagram (CHT) of αZr→αZr βZr is given according to phase transformation curves of the alloy.
2016, 45(11):2861-2866.
Abstract:
In this study, effect and mechanism of different stacking structures of LPSO phase on microstructures and mechanical properties of Mg-2.0Zn-0.3Zr-5.8Y under different extrusion temperatures were studied. The results showed that the average grain size of the alloy containing 18R and 14H LPSO phases reached 9.5±3.0μm under the extrusion temperature of 390℃, and the tensile strength and elongation reached 280MPa and 18.7%, respectively. When the extrusion temperature increased to 420℃, the 18R LPSO phase transformed to 14H structure, the grain size was refined significantly, and the tensile strength and elongation increased to 330MPa and 20.8%, respectively. With the increasing of extrusion temperature (over 420℃), the grain size increased and the tensile strength and elongation decreased. The variation of texture intensity under different deformation temperatures, the transformation of stacking structure and shape of LPSO phase and grain refinement are the main reasons caused the variation of mechanical properties of extruded alloy.
In this study, effect and mechanism of different stacking structures of LPSO phase on microstructures and mechanical properties of Mg-2.0Zn-0.3Zr-5.8Y under different extrusion temperatures were studied. The results showed that the average grain size of the alloy containing 18R and 14H LPSO phases reached 9.5±3.0μm under the extrusion temperature of 390℃, and the tensile strength and elongation reached 280MPa and 18.7%, respectively. When the extrusion temperature increased to 420℃, the 18R LPSO phase transformed to 14H structure, the grain size was refined significantly, and the tensile strength and elongation increased to 330MPa and 20.8%, respectively. With the increasing of extrusion temperature (over 420℃), the grain size increased and the tensile strength and elongation decreased. The variation of texture intensity under different deformation temperatures, the transformation of stacking structure and shape of LPSO phase and grain refinement are the main reasons caused the variation of mechanical properties of extruded alloy.
2016, 45(11):2867-2872.
Abstract:
Scanning Kelvin probe (SKP) and electron backscatter diffraction（EBSD）testing techniques, combined with high temperature and pressure immersion test were used to investigate the electrochemical corrosion behavior of C-type ring made by 690 alloy with different degrees of deformation. The results show that the corrosion products on the 690 alloy are composed of oxide particles which are rich in Fe、Ni and Cr. EBSD test statistics analysis shows that the proportion of Σ3 grain boundaries in 690 alloy with 25% deformation is 10% more than that of 690 alloy with 50% deformation, and both kinds of 690 alloy have mild but different texture. The SKP measurement results display that Ekp of C-type ring samples after immersion has a significant rise, reaching -3.5mV for 690 alloy with 25% deformation and -29.2mV for 690 alloy with 50% deformation respectively, which also indicates the corrosion products film on 690 alloy with 25% deformation plays a better protective role as it results in a higher Ekp (26mV higher than that of 690 alloy with 50% deformation).
Scanning Kelvin probe (SKP) and electron backscatter diffraction（EBSD）testing techniques, combined with high temperature and pressure immersion test were used to investigate the electrochemical corrosion behavior of C-type ring made by 690 alloy with different degrees of deformation. The results show that the corrosion products on the 690 alloy are composed of oxide particles which are rich in Fe、Ni and Cr. EBSD test statistics analysis shows that the proportion of Σ3 grain boundaries in 690 alloy with 25% deformation is 10% more than that of 690 alloy with 50% deformation, and both kinds of 690 alloy have mild but different texture. The SKP measurement results display that Ekp of C-type ring samples after immersion has a significant rise, reaching -3.5mV for 690 alloy with 25% deformation and -29.2mV for 690 alloy with 50% deformation respectively, which also indicates the corrosion products film on 690 alloy with 25% deformation plays a better protective role as it results in a higher Ekp (26mV higher than that of 690 alloy with 50% deformation).
2016, 45(11):2873-2877.
Abstract:
Fe40Al60 alloy was prepared by laster ignition induced self-propagating high-temperature synthesis. By means of XRD, microscopic test, hardness test to analyze the microstructure and macroscopic properities of the sintered alloy about different areas. According to finite element method, the temperature field of Fe40Al60 was simulated by finite element analysis software ANSYS. Contour maps of temperature field and path map were obtained after sintering 10s. The experiment result shows that: The main phases of the alloy upper surface was FeAl, Al2O3. the middle layer of the alloy were Fe3Al, FeAl, Al2O3. the buttom layer of the alloy was Fe3Al, Al2O3 and Fe . The microstructure of the upper surface was strip, the median surface was celluar, the buttom surface was fine needle, hardness highest to 1005 HV of the middle layer, 901 HV to the surface layer, 965HV to the buttom layer.The simulation result shows that: At 10s, the temperature of the direct laster sintering surface up to 1150K, the buttom surface up to 820.979K and the temperature of median surface was 894.033K.The results show that the experimental results are consistent with the simulation results.
Fe40Al60 alloy was prepared by laster ignition induced self-propagating high-temperature synthesis. By means of XRD, microscopic test, hardness test to analyze the microstructure and macroscopic properities of the sintered alloy about different areas. According to finite element method, the temperature field of Fe40Al60 was simulated by finite element analysis software ANSYS. Contour maps of temperature field and path map were obtained after sintering 10s. The experiment result shows that: The main phases of the alloy upper surface was FeAl, Al2O3. the middle layer of the alloy were Fe3Al, FeAl, Al2O3. the buttom layer of the alloy was Fe3Al, Al2O3 and Fe . The microstructure of the upper surface was strip, the median surface was celluar, the buttom surface was fine needle, hardness highest to 1005 HV of the middle layer, 901 HV to the surface layer, 965HV to the buttom layer.The simulation result shows that: At 10s, the temperature of the direct laster sintering surface up to 1150K, the buttom surface up to 820.979K and the temperature of median surface was 894.033K.The results show that the experimental results are consistent with the simulation results.
2016, 45(11):2878-2883.
Abstract:
ABSTRACT: Ribbons of the Fe53Nd37Al10 alloy with different cooling rates, 40 m/s and 20 m/s, were prepared by melt spinning method. The magnetic behavior, magnetic viscosity behavior and microstructure of the ribbons were investigated. The remanent magnetization Mr of the ribbons with the cooling rate of 40 m/s and 20 m/s is 33.50 Am2/kg and 36.05 Am2/kg, and the coercivity Hci is 62.00 kA/m and 121.50 kA/m, respectively. The fluctuation field Hf, activation volume Va and activation diameter Da of the ribbons with the cooling rate of 40 m/s are 2.47 mT, 3.90?0-18cm3 and 19.53 nm, respectively. The Hf, Va, and Da of the ribbons with the cooling rate of 20 m/s are 2.73 mT, 3.53?0-18cm3 and 18.89 nm, respectively. The size of nanoclusters in the ribbons with the cooling rate of 40 m/s is less than 5 nm. However, the size of nanoclusters in the ribbons with the cooling rate of 20 m/s is 5-10 nm and there are more nanoclusters in the ribbons. The hard magnetic property of the ribbons melt-spun at 40 m/s and 20 m/s would be due to the exchange coupling interactions and pinning effect. the size and amount of nanoclusters and the interactive units composed by many nanoclusters mostly affect the coercivity of the ribbons of Fe-Nd-Al amorphous alloy.
ABSTRACT: Ribbons of the Fe53Nd37Al10 alloy with different cooling rates, 40 m/s and 20 m/s, were prepared by melt spinning method. The magnetic behavior, magnetic viscosity behavior and microstructure of the ribbons were investigated. The remanent magnetization Mr of the ribbons with the cooling rate of 40 m/s and 20 m/s is 33.50 Am2/kg and 36.05 Am2/kg, and the coercivity Hci is 62.00 kA/m and 121.50 kA/m, respectively. The fluctuation field Hf, activation volume Va and activation diameter Da of the ribbons with the cooling rate of 40 m/s are 2.47 mT, 3.90?0-18cm3 and 19.53 nm, respectively. The Hf, Va, and Da of the ribbons with the cooling rate of 20 m/s are 2.73 mT, 3.53?0-18cm3 and 18.89 nm, respectively. The size of nanoclusters in the ribbons with the cooling rate of 40 m/s is less than 5 nm. However, the size of nanoclusters in the ribbons with the cooling rate of 20 m/s is 5-10 nm and there are more nanoclusters in the ribbons. The hard magnetic property of the ribbons melt-spun at 40 m/s and 20 m/s would be due to the exchange coupling interactions and pinning effect. the size and amount of nanoclusters and the interactive units composed by many nanoclusters mostly affect the coercivity of the ribbons of Fe-Nd-Al amorphous alloy.
2016, 45(11):2884-2888.
Abstract:
The initial corrosion behavior of SiCp/Al composites in Cl- containing solution was inverstigated by using immersion test and Scanning Kelvin probe (SKP) technique. The results show that the initial corrosion is preferential to occur at the interface between SiC particles and Al matrix of SiCp/Al composites in Cl- containing solution. Cl- and interfacial phase is responsible for the development of initial corrosion. The passive film formed in the initial stage, while the surface potential of SiCp/Al composites moved positively. When the corrosion process continued, the passive film finally breakdowned, resulting in the negative shift of the surface potential. The main corrosion products are Al(OH)3, Al2O3 and AlCl3.
The initial corrosion behavior of SiCp/Al composites in Cl- containing solution was inverstigated by using immersion test and Scanning Kelvin probe (SKP) technique. The results show that the initial corrosion is preferential to occur at the interface between SiC particles and Al matrix of SiCp/Al composites in Cl- containing solution. Cl- and interfacial phase is responsible for the development of initial corrosion. The passive film formed in the initial stage, while the surface potential of SiCp/Al composites moved positively. When the corrosion process continued, the passive film finally breakdowned, resulting in the negative shift of the surface potential. The main corrosion products are Al(OH)3, Al2O3 and AlCl3.
2016, 45(11):2889-2894.
Abstract:
By means of performance testing, microstructure and differential thermal analysis, the hardness-time curves, TEM microstructures, TTT curves and precipitate activation energy of β″ phase for Al-Mg-Si-Zr-XEr alloy were investigated, and kinetics expressions and TTT expressions of β″ phase were acquired. The results show that the addition of Er element accelerates the dispersively precipitation of the β″ phase, and the fine and uniform β″ phase of Al-Mg-Si-Zr-0.3Er alloy precipitate dispersively after the solution treatment at 540 ℃ for 1 h and aging at 180 ℃ for 5 h. As the element Er content increases, hardening rate of alloy is significantly accelerated, softening rate of alloy is decreased, precipitate activation energy of β″ phase for alloy is decreased, and the values are 96.3, 93.6 and 84.9 kJ/mol. The kinetics expressions are obtained as follows, YEr0.1=1-exp[-1.534×1013t1.5exp(-17382.7/T)], YEr0.2=1-exp[-5.865×1012t1.5exp(-16895.3/T)], YEr0.3=1-exp[-2.965×1011t1.5exp(-15324.9/ T)]. The TTT expressions are obtained as follows, TEr0.1=17382.7/[30.4 1.5lnt-lnln(1-Y)-1], TEr0.2=16895.3/[29.4 1.5lnt-lnln(1-Y)-1], TEr0.3=15324.9/[26.4 1.5lnt-lnln(1-Y)-1].
By means of performance testing, microstructure and differential thermal analysis, the hardness-time curves, TEM microstructures, TTT curves and precipitate activation energy of β″ phase for Al-Mg-Si-Zr-XEr alloy were investigated, and kinetics expressions and TTT expressions of β″ phase were acquired. The results show that the addition of Er element accelerates the dispersively precipitation of the β″ phase, and the fine and uniform β″ phase of Al-Mg-Si-Zr-0.3Er alloy precipitate dispersively after the solution treatment at 540 ℃ for 1 h and aging at 180 ℃ for 5 h. As the element Er content increases, hardening rate of alloy is significantly accelerated, softening rate of alloy is decreased, precipitate activation energy of β″ phase for alloy is decreased, and the values are 96.3, 93.6 and 84.9 kJ/mol. The kinetics expressions are obtained as follows, YEr0.1=1-exp[-1.534×1013t1.5exp(-17382.7/T)], YEr0.2=1-exp[-5.865×1012t1.5exp(-16895.3/T)], YEr0.3=1-exp[-2.965×1011t1.5exp(-15324.9/ T)]. The TTT expressions are obtained as follows, TEr0.1=17382.7/[30.4 1.5lnt-lnln(1-Y)-1], TEr0.2=16895.3/[29.4 1.5lnt-lnln(1-Y)-1], TEr0.3=15324.9/[26.4 1.5lnt-lnln(1-Y)-1].
2016, 45(11):2895-2901.
Abstract:
W-Y binary alloy has potential applications in the first wall material for nuclear fusion device. Mechanical properties have important effects on material processing and application. However, the mechanical properties of W-Y alloy are rarely reported in the literature. In this paper, the effect of yttrium contents on the fundamental mechanical properties of W-Y alloys has been studied by using first-principles method based on the density functional theory. The mechanical constants of W1-xYx (x=0.0625,0.125,0.25,0.5) alloys were calculated for different compositions in solid solution model. According to the calculated mechanical constants, the mechanical properties are analyzed. Our results show that the elastic constants, bulk modulus, Young’s modulus and shear modulus of W-Y alloys decrease non-monotonically with the increase of Y concentration, indicating that the doped Y decreases the mechanical strength of W materials. Based on the mechanical characteristic, such as B/G, Poisson’s ratio ν and Cauchy pressure C", the ductility and toughness of the W-Y alloys are significantly improved with the increase of Y concentration. When the Y contents reaches 0.25, the resistant and ductility of W-Y alloy are largely enhanced. Through the analysis of the density of states, W-Y alloy metallic properties begin decreases and then increases as the concentration of Y increases.
W-Y binary alloy has potential applications in the first wall material for nuclear fusion device. Mechanical properties have important effects on material processing and application. However, the mechanical properties of W-Y alloy are rarely reported in the literature. In this paper, the effect of yttrium contents on the fundamental mechanical properties of W-Y alloys has been studied by using first-principles method based on the density functional theory. The mechanical constants of W1-xYx (x=0.0625,0.125,0.25,0.5) alloys were calculated for different compositions in solid solution model. According to the calculated mechanical constants, the mechanical properties are analyzed. Our results show that the elastic constants, bulk modulus, Young’s modulus and shear modulus of W-Y alloys decrease non-monotonically with the increase of Y concentration, indicating that the doped Y decreases the mechanical strength of W materials. Based on the mechanical characteristic, such as B/G, Poisson’s ratio ν and Cauchy pressure C", the ductility and toughness of the W-Y alloys are significantly improved with the increase of Y concentration. When the Y contents reaches 0.25, the resistant and ductility of W-Y alloy are largely enhanced. Through the analysis of the density of states, W-Y alloy metallic properties begin decreases and then increases as the concentration of Y increases.
2016, 45(11):2902-2906.
Abstract:
Both deformation temperature and strain rate are important factors for the damage behavior of Csf/Mg composites in the liquid-solid state. In present paper, Zener-Hollomon parameter, which incorporates a combined effect of temperature and strain rate, was introduced to Cockroft–Latham fracture criterion as a correlation coefficient. The correlation coefficient, which equals facture strain under uniaxial tensile stress state, was determined by a series of tensile tests of Csf/Mg composites in the high temperature solid state and semi-solid state, and fitted into a nonliner function of lnZ, thereby obtaining a modified Cockroft–Latham fracture criterion. Furthermore, the modified Cockroft–Latham fracture criterion was applied to the simulation of liquid-solid extrusion, and the predicted results show a good agreement with experimental observations in both the direction and length of surface cracks.
Both deformation temperature and strain rate are important factors for the damage behavior of Csf/Mg composites in the liquid-solid state. In present paper, Zener-Hollomon parameter, which incorporates a combined effect of temperature and strain rate, was introduced to Cockroft–Latham fracture criterion as a correlation coefficient. The correlation coefficient, which equals facture strain under uniaxial tensile stress state, was determined by a series of tensile tests of Csf/Mg composites in the high temperature solid state and semi-solid state, and fitted into a nonliner function of lnZ, thereby obtaining a modified Cockroft–Latham fracture criterion. Furthermore, the modified Cockroft–Latham fracture criterion was applied to the simulation of liquid-solid extrusion, and the predicted results show a good agreement with experimental observations in both the direction and length of surface cracks.
2016, 45(11):2907-2911.
Abstract:
Factors influencing the heater power consumption on 22inch hotzone in TDR-95A-ZJS Czochrolaski crystal growth furnace for photovoltaic application are analyzed by means of numerical modeling and simulations. Based on numerical simulation results, hotzone optimization through structure and graphite insulator layout modifications targeted for heater power reduction is proposed. Physical crystal growthexperiments show that the heater power consumption is reduced by 29% after hotzone optimization while the crystal quality remains very similar to the ones obtained by original hotzone.
Factors influencing the heater power consumption on 22inch hotzone in TDR-95A-ZJS Czochrolaski crystal growth furnace for photovoltaic application are analyzed by means of numerical modeling and simulations. Based on numerical simulation results, hotzone optimization through structure and graphite insulator layout modifications targeted for heater power reduction is proposed. Physical crystal growthexperiments show that the heater power consumption is reduced by 29% after hotzone optimization while the crystal quality remains very similar to the ones obtained by original hotzone.
2016, 45(11):2912-2917.
Abstract:
Based on the section of the junction of two metal fibers which is different oval-oval geometry structure in different direction, the oval-oval model for the sintering crunode of two metal fibers is established by surface diffusion in every section. The model is numerically solved by using level set method to achieve the numerical simulation of the growth process of the sintering crunode in different sections. The three dimensional numerical simulation of the growth process of the sintering crunode is achieved by reconstituting the numerical simulation results in these sections. For two metal fibers with the fiber angle 60? the three-dimensional numerical simulation of the growth process of the sintering crunode is implemented, and the growth rates of sintering neck are discussed in different sections. The numerical simulation results show that the closer to the bisector of acute angle the direction is, the faster the growth rate of sintering neck is. The initial local geometrical structure in each section plays a key role in the sintering neck formation.
Based on the section of the junction of two metal fibers which is different oval-oval geometry structure in different direction, the oval-oval model for the sintering crunode of two metal fibers is established by surface diffusion in every section. The model is numerically solved by using level set method to achieve the numerical simulation of the growth process of the sintering crunode in different sections. The three dimensional numerical simulation of the growth process of the sintering crunode is achieved by reconstituting the numerical simulation results in these sections. For two metal fibers with the fiber angle 60? the three-dimensional numerical simulation of the growth process of the sintering crunode is implemented, and the growth rates of sintering neck are discussed in different sections. The numerical simulation results show that the closer to the bisector of acute angle the direction is, the faster the growth rate of sintering neck is. The initial local geometrical structure in each section plays a key role in the sintering neck formation.
31 Anti-corrosion Mechanism of Al-Ti-Si-RE Coating in the Pressure Environment of Simulated Deep Sea
2016, 45(11):2918-2924.
Abstract:
In this paper, the anticorrosion mechanism of Al-Ti-Si-RE coating in the environment of simulated deep sea was investigated using electrochemical measurement and micro-analysis. The result showed that Al-Ti-Si-RE coating performed better corrosion resistance at hydrostatic pressure than that at atmospheric pressure. After 480 h of immersion at 3 MPa, the anode of potentiodynamic polarization curve represented a linear because corrosion products blocked the corrosion channels. At the same time, at hydrostatic pressure, electrochemical impedance spectroscopy (EIS) indicated that Al passive film dissolved in the 6 h of immersion, then the coating tended to be stable, was hardly changed between 300 h and 480 h. To further analyze the original corrosion process, electrochemical noise (EN) of 0~64 ks at 0.1 MPa and 3 MPa was measured, which quantificationally represented the corrosion process from passive film dissolving to corrosion product fast-forming to stabilization. From morphology observation and X-Ray diffraction (XRD) analysis, the rich Ti phase (Ti-Al intermetallics etc.) of the coating with good corrosion resistance was cellular, whose construction could fix the Al oxide inside the coating, and made the coating thick in order to inhibit the corrosion.
In this paper, the anticorrosion mechanism of Al-Ti-Si-RE coating in the environment of simulated deep sea was investigated using electrochemical measurement and micro-analysis. The result showed that Al-Ti-Si-RE coating performed better corrosion resistance at hydrostatic pressure than that at atmospheric pressure. After 480 h of immersion at 3 MPa, the anode of potentiodynamic polarization curve represented a linear because corrosion products blocked the corrosion channels. At the same time, at hydrostatic pressure, electrochemical impedance spectroscopy (EIS) indicated that Al passive film dissolved in the 6 h of immersion, then the coating tended to be stable, was hardly changed between 300 h and 480 h. To further analyze the original corrosion process, electrochemical noise (EN) of 0~64 ks at 0.1 MPa and 3 MPa was measured, which quantificationally represented the corrosion process from passive film dissolving to corrosion product fast-forming to stabilization. From morphology observation and X-Ray diffraction (XRD) analysis, the rich Ti phase (Ti-Al intermetallics etc.) of the coating with good corrosion resistance was cellular, whose construction could fix the Al oxide inside the coating, and made the coating thick in order to inhibit the corrosion.
2016, 45(11):2925-2931.
Abstract:
The equilibrium precipitation phases and the process of non-equilibrium solidification for GH141 Ni-based superalloy were studied by Thermo-Calc software. The main precipitation phases include γ、γ''、σ、μ and carbides (MC,M6C and M23C6). Significant positive segregation of Mo and Ti may occur during solidification based on the calculation, which would decrease the initial melting points of GH141 Ni-based superalloy. The contents of Al and Ti can strongly influence the solvus temperature and the maximum mass fraction of γ'' phase. C is the main control element about the maximum mass fraction of carbides (MC, M6C and M23C6) and the enriched elements of MC, M6C and M23C6 are Ti, Mo and Cr respectively. Research results can provide theoretical basis for composition design and heat treatment.
The equilibrium precipitation phases and the process of non-equilibrium solidification for GH141 Ni-based superalloy were studied by Thermo-Calc software. The main precipitation phases include γ、γ''、σ、μ and carbides (MC,M6C and M23C6). Significant positive segregation of Mo and Ti may occur during solidification based on the calculation, which would decrease the initial melting points of GH141 Ni-based superalloy. The contents of Al and Ti can strongly influence the solvus temperature and the maximum mass fraction of γ'' phase. C is the main control element about the maximum mass fraction of carbides (MC, M6C and M23C6) and the enriched elements of MC, M6C and M23C6 are Ti, Mo and Cr respectively. Research results can provide theoretical basis for composition design and heat treatment.
2016, 45(11):2932-2936.
Abstract:
The Strength(σb, σ0.2), ductility(δ, ψ)and impact toughness (ak)of TC4 alloy annealed in 940℃, 960℃, 980℃ and cooled in different cooling rate after 980℃annealed were tested by means of Tensile Test in room temperature and Impact Test in room temperature. Combined with metallography and fractography, the influence of annealing temperature and cooling rate were studied. The results show that the strength, ductility and impact toughness decrease with the increasing of annealing temperature, the strength increases, but the ductility and impact toughness decrease with the increasing of cooling rate.
The Strength(σb, σ0.2), ductility(δ, ψ)and impact toughness (ak)of TC4 alloy annealed in 940℃, 960℃, 980℃ and cooled in different cooling rate after 980℃annealed were tested by means of Tensile Test in room temperature and Impact Test in room temperature. Combined with metallography and fractography, the influence of annealing temperature and cooling rate were studied. The results show that the strength, ductility and impact toughness decrease with the increasing of annealing temperature, the strength increases, but the ductility and impact toughness decrease with the increasing of cooling rate.
2016, 45(11):2937-2941.
Abstract:
The fatigue crack propagation rate of different lamellar microstructure in TC4-DT titanium alloy was studied in the paper. Different lamellar microstructures were obtained by different heat treatment process, effect of lamellar microstructure parameter on fatigue crack growth rate is researched, and crack growth fractographs were observed. The results reveal that: the thinner lamellar structure showed higher crack growth resistance. Lamellar structure under multi-heat treatment showed higher crack propagation rate than double-heat treatment , which owes the secondary alpha phase.
The fatigue crack propagation rate of different lamellar microstructure in TC4-DT titanium alloy was studied in the paper. Different lamellar microstructures were obtained by different heat treatment process, effect of lamellar microstructure parameter on fatigue crack growth rate is researched, and crack growth fractographs were observed. The results reveal that: the thinner lamellar structure showed higher crack growth resistance. Lamellar structure under multi-heat treatment showed higher crack propagation rate than double-heat treatment , which owes the secondary alpha phase.
2016, 45(11):2942-2947.
Abstract:
With the development of domestic civil high bypass ratio turbofan engine, the research on the forming technology of large titanium wide-chord hollow fan blade has important significance currently. The titanium wide-chord hollow fan blade is characteristic by unique building structure. The surface skin is an equal-thickness shell. Inside the entity, weight-reduction chambers and reinforcement ribbons arranged alternatively. When the blade blank subjects to the torque movement during the forming process, instability occurs on the skin, inducing the appearance of local sinkage. In order to solve this problem, a creep method was proposed for the repairing of skin defects. The repairing work was performed by gas loading at elevated temperature. The creep test of base material experienced twice heat cycle was carried out and the creep formula was modeled. The numerical method was used to investigate the effects of different dwell pressure and time on the result. Based on the FEM result, the best set of parameters was selected and used to conduct the skin repairing experiment. The result shows that the gas loading creep repair method proves to be effective in repairing skin groove of the titanium TC4 wide-chord hollow fan blade. It can be used to assist the manufacture of this kind of component.
With the development of domestic civil high bypass ratio turbofan engine, the research on the forming technology of large titanium wide-chord hollow fan blade has important significance currently. The titanium wide-chord hollow fan blade is characteristic by unique building structure. The surface skin is an equal-thickness shell. Inside the entity, weight-reduction chambers and reinforcement ribbons arranged alternatively. When the blade blank subjects to the torque movement during the forming process, instability occurs on the skin, inducing the appearance of local sinkage. In order to solve this problem, a creep method was proposed for the repairing of skin defects. The repairing work was performed by gas loading at elevated temperature. The creep test of base material experienced twice heat cycle was carried out and the creep formula was modeled. The numerical method was used to investigate the effects of different dwell pressure and time on the result. Based on the FEM result, the best set of parameters was selected and used to conduct the skin repairing experiment. The result shows that the gas loading creep repair method proves to be effective in repairing skin groove of the titanium TC4 wide-chord hollow fan blade. It can be used to assist the manufacture of this kind of component.
Chen Haisheng
,
Luo Jinhua
,
Wangwensheng
,
Sunxiaoping
,
Liu Xianghong
,
Feng Yong
,
Zhang Pingxiang
,
Fu Hengzhi
2016, 45(11):2948-2952.
Abstract:
Ti-6321 titanium alloy billets have been heated in (α β) phase region and forged at the deformation range of 50%~80% and undergone conventional annealing, we can find that the microtructure types of original billets have not been changed, but the elongated α phase structure have been crushed obviously.With the increasing of deformation, the degree of grain refinement is improved gradually, the strength of bars increased and the impact toughness of bars decreased. The bars with 45 mm diameter have been heat treated by conventional annealing, dual annealing, β annealing, and solution annealing and aging, the result shows that the microstructure and properties of Ti-6321 alloy bars are sensitive to heat treatment process and the optimum heat treatment method should be chosen to achieve a appropriate combination of strength, plasticity and toughness according to the special requirements.
Ti-6321 titanium alloy billets have been heated in (α β) phase region and forged at the deformation range of 50%~80% and undergone conventional annealing, we can find that the microtructure types of original billets have not been changed, but the elongated α phase structure have been crushed obviously.With the increasing of deformation, the degree of grain refinement is improved gradually, the strength of bars increased and the impact toughness of bars decreased. The bars with 45 mm diameter have been heat treated by conventional annealing, dual annealing, β annealing, and solution annealing and aging, the result shows that the microstructure and properties of Ti-6321 alloy bars are sensitive to heat treatment process and the optimum heat treatment method should be chosen to achieve a appropriate combination of strength, plasticity and toughness according to the special requirements.
2016, 45(11):2953-2958.
Abstract:
In this paper, the dynamic mechanical properties and sensitivity of adiabatic shear banding of TC21 alloy was investigated. The lamellar microstructures with different thicknesses of lamellar α were obtained via different heat treatments. The dynamic compression properties and sensitivity of adiabatic shear banding behavior of TC21 alloys having lamellar microstructures were tested on the Split Hopkinson Pressure Bar. The results showed that the thickness of lamellar α increased from 0.57μm to 6.49μm with the decreasing of the cooling rate. Under dynamic compression experiments, the dynamic strength decreased as the thickness of lamellar α increased; while the dynamic strain exhibited an opposite trend. Under forced shearing experiments, on the one hand, the sensitivity of adiabatic shear banding increased with the decreasing of the thickness of lamellar α at the same impact velocity; on the other hand, the sensitivity of adiabatic shear banding increased for the same microstructure with the increasing of impact velocity.
In this paper, the dynamic mechanical properties and sensitivity of adiabatic shear banding of TC21 alloy was investigated. The lamellar microstructures with different thicknesses of lamellar α were obtained via different heat treatments. The dynamic compression properties and sensitivity of adiabatic shear banding behavior of TC21 alloys having lamellar microstructures were tested on the Split Hopkinson Pressure Bar. The results showed that the thickness of lamellar α increased from 0.57μm to 6.49μm with the decreasing of the cooling rate. Under dynamic compression experiments, the dynamic strength decreased as the thickness of lamellar α increased; while the dynamic strain exhibited an opposite trend. Under forced shearing experiments, on the one hand, the sensitivity of adiabatic shear banding increased with the decreasing of the thickness of lamellar α at the same impact velocity; on the other hand, the sensitivity of adiabatic shear banding increased for the same microstructure with the increasing of impact velocity.
2016, 45(11):2959-2964.
Abstract:
Under the complex environment，Titanium alloy not only has decent wear-resisting performance, but also the ability to resist the corrosion of acidic medium. This article studies the electrochemical properties and immersing-corrosion resistance of the Titanium sample, whose surface was Hydrogen-free carburized, in HCl and H2SO4 solution by using the method of electrochemistry and eroding. The result shows that after being Hydrogen-free carburized, the corrosion-resisting performance of Titanium sample which was immersed in HCl and H2SO4 solution is significantly improved.
Under the complex environment，Titanium alloy not only has decent wear-resisting performance, but also the ability to resist the corrosion of acidic medium. This article studies the electrochemical properties and immersing-corrosion resistance of the Titanium sample, whose surface was Hydrogen-free carburized, in HCl and H2SO4 solution by using the method of electrochemistry and eroding. The result shows that after being Hydrogen-free carburized, the corrosion-resisting performance of Titanium sample which was immersed in HCl and H2SO4 solution is significantly improved.
2016, 45(11):2965-2969.
Abstract:
Quaternary Ni-Co-Cu-P coatings were synthesized on 45 steel substrates by electroless deposition. The chemical composition, crystal structures and corrosion properties of the coatings were investigated by EDX, XRD, SEM, salt spray tests and Tafel polarization curves. The results indicated that Ni-Co-Cu-P coatings were amorphous with the content of 32.66 wt.% Ni, 47.19 wt.% Co and 15.28 wt.% Cu. Spherical clusters with the diameter of 240 ~ 500 nm were distributed uniformly on the coating surfaces and some clusters contained nano-sized poles. The coatings showed visible red rust points after 156 h and were totally failed after 192 h in neutral salt spray tests. Moreover, corrosion resistance of the coatings was much better than that of the 45 steel substrates and Ni-Co-P coatings. In 1.0 wt.% H2SO4 solution, corrosion potential and corrosion current density of the coatings were -0.26 V and 19.17 μA?cm-2 respectively. By increasing the potential, numerous microcracks emerged on the coating surfaces. In 3.5 wt.% NaCl solution, the coatings exhibited an active-passive-transpassive behavior with passive films penetrated by Clˉ and resulted with pin-holes.
Quaternary Ni-Co-Cu-P coatings were synthesized on 45 steel substrates by electroless deposition. The chemical composition, crystal structures and corrosion properties of the coatings were investigated by EDX, XRD, SEM, salt spray tests and Tafel polarization curves. The results indicated that Ni-Co-Cu-P coatings were amorphous with the content of 32.66 wt.% Ni, 47.19 wt.% Co and 15.28 wt.% Cu. Spherical clusters with the diameter of 240 ~ 500 nm were distributed uniformly on the coating surfaces and some clusters contained nano-sized poles. The coatings showed visible red rust points after 156 h and were totally failed after 192 h in neutral salt spray tests. Moreover, corrosion resistance of the coatings was much better than that of the 45 steel substrates and Ni-Co-P coatings. In 1.0 wt.% H2SO4 solution, corrosion potential and corrosion current density of the coatings were -0.26 V and 19.17 μA?cm-2 respectively. By increasing the potential, numerous microcracks emerged on the coating surfaces. In 3.5 wt.% NaCl solution, the coatings exhibited an active-passive-transpassive behavior with passive films penetrated by Clˉ and resulted with pin-holes.
2016, 45(11):2970-2974.
Abstract:
W-ZrC composite powders were prepared by sol-heterogeneous precipitation-spray drying thermal reduction technology. W-ZrC material was prepared by high temperature sintering under hydrogen atmosphere. Effect of ZrC content on the microstructure and properties were investigated. The results show that the relative density of W-ZrC material is greatly improved compared with that of pure W, the room temperature tensile strength of W-ZrC material is twofold of pure W , which is 290MPa. And the strain of the material is increased from 1.7% to3.5%. The second phase particles of ZrC can effectively prevent the migration of grain boundary. The grain is refined from 100μm to 10-15μm. The fracture morphology of pure W is mainly intergranular fracture, but W-ZrC materials is visible in transgranular brittle fracture. ZrC can effectively enhance the strength of the grain boundary of W, and has good effect in fine grain strengthening and dispersion strengthening.
W-ZrC composite powders were prepared by sol-heterogeneous precipitation-spray drying thermal reduction technology. W-ZrC material was prepared by high temperature sintering under hydrogen atmosphere. Effect of ZrC content on the microstructure and properties were investigated. The results show that the relative density of W-ZrC material is greatly improved compared with that of pure W, the room temperature tensile strength of W-ZrC material is twofold of pure W , which is 290MPa. And the strain of the material is increased from 1.7% to3.5%. The second phase particles of ZrC can effectively prevent the migration of grain boundary. The grain is refined from 100μm to 10-15μm. The fracture morphology of pure W is mainly intergranular fracture, but W-ZrC materials is visible in transgranular brittle fracture. ZrC can effectively enhance the strength of the grain boundary of W, and has good effect in fine grain strengthening and dispersion strengthening.
2016, 45(11):2975-2980.
Abstract:
Cu-xat.%Ni (x = 18,32,52,72) alloy were smelted by cold crucible induction levitation melting, and tapes with a final thickness of 80μm were obtained after forging, hot rolling, cold rolling and recrystallization annealing. The recrystallization texture and microstructure of alloy tapes were characterized by electron backscatter diffraction technology (EBSD) and high resolution transmission electron microscopy (HRTEM) respectively. The results showed that the deformation texture of these Cu-Ni alloys are similar, but with the increase of Ni content, the volume fraction of cube texture in alloy tapes decreased after recrystallization annealing, the grain orientation became scattered, and grain size significantly became larger. In the alloys with a composition of 52-72at.%Ni, spinodal decomposition occurred at recovery stage is the main cause of scattered recrystallization texture; single-phase solid solution of Cu-Ni alloy is the key element in obtaining cube texture after recrystallization.
Cu-xat.%Ni (x = 18,32,52,72) alloy were smelted by cold crucible induction levitation melting, and tapes with a final thickness of 80μm were obtained after forging, hot rolling, cold rolling and recrystallization annealing. The recrystallization texture and microstructure of alloy tapes were characterized by electron backscatter diffraction technology (EBSD) and high resolution transmission electron microscopy (HRTEM) respectively. The results showed that the deformation texture of these Cu-Ni alloys are similar, but with the increase of Ni content, the volume fraction of cube texture in alloy tapes decreased after recrystallization annealing, the grain orientation became scattered, and grain size significantly became larger. In the alloys with a composition of 52-72at.%Ni, spinodal decomposition occurred at recovery stage is the main cause of scattered recrystallization texture; single-phase solid solution of Cu-Ni alloy is the key element in obtaining cube texture after recrystallization.
2016, 45(11):2981-2986.
Abstract:
Abstract: To achieve the aim that reducing the brazing temperature of tungsten and CuCrZr alloy applied in the ITER equipment, Continuous and uniform amorphous ribbon with dimensional sizes of 10 mm in width and 80μm in thickness was prepared by melt-spinning a Cu47Ti33Zr11Ni8Si1 (at.%) alloy. The application of the amorphous foil as a new brazing filler for joint of tungsten and CuCrZr alloy have been investigated. The microstructures and mechanical properties of the joints obtained at different brazing temperatures were examined using optical microscopy, scanning electron microscopy, X-ray diffarction and microhardness indentation. Comparison of the microstructures and mechanical properties of the joints indicates that high quality interface bonding can be realized at an optimal barzing temperature of 900℃, and the joint zone thus formed is microcrack-free and the heat affected zone is fine-grained, exhibiting the highest microharness; the application of the amorphous foil as a new brazing filler can reduce the temperature for joint of tungsten and CuCrZr alloy effectively.
Abstract: To achieve the aim that reducing the brazing temperature of tungsten and CuCrZr alloy applied in the ITER equipment, Continuous and uniform amorphous ribbon with dimensional sizes of 10 mm in width and 80μm in thickness was prepared by melt-spinning a Cu47Ti33Zr11Ni8Si1 (at.%) alloy. The application of the amorphous foil as a new brazing filler for joint of tungsten and CuCrZr alloy have been investigated. The microstructures and mechanical properties of the joints obtained at different brazing temperatures were examined using optical microscopy, scanning electron microscopy, X-ray diffarction and microhardness indentation. Comparison of the microstructures and mechanical properties of the joints indicates that high quality interface bonding can be realized at an optimal barzing temperature of 900℃, and the joint zone thus formed is microcrack-free and the heat affected zone is fine-grained, exhibiting the highest microharness; the application of the amorphous foil as a new brazing filler can reduce the temperature for joint of tungsten and CuCrZr alloy effectively.
2016, 45(11):2987-2991.
Abstract:
Sn nanoparticles were prepared by the method of DC arc plasma and introduced into the AZ31 magnesium alloy melt by stir casting. Influence of the different addition proportion of Sn nanoparticles on as-cast microstructures and mechanical properties of AZ31 magnesium alloy were investigated by metallography, scanning electron microscopy (SEM) and tensile tests. The results show that, the eutectic phases which were precipitated in the shape of lamellar will be inhibited, but the amount of β-Mg17Al12 distributed at the grain boundary in the shape of bone will be promoted with the addition of Sn nanoparticles. Importantly, it is observed that Sn nanoparticles were generated to nano-sized Mg2Sn particles in the magnesium alloy matrix, but mainly existed in the form of particle clusters. With the excessive addition of Sn nanoparticles, a more severe Mg2Sn nanoparticle clusters and a reduction of the mechanical properties will be observed. In the present study, the most superior mechanical properties of the AZ31 magnesium alloy can be achieved when the proportion of Sn nanoparticles was about 1wt.%.
Sn nanoparticles were prepared by the method of DC arc plasma and introduced into the AZ31 magnesium alloy melt by stir casting. Influence of the different addition proportion of Sn nanoparticles on as-cast microstructures and mechanical properties of AZ31 magnesium alloy were investigated by metallography, scanning electron microscopy (SEM) and tensile tests. The results show that, the eutectic phases which were precipitated in the shape of lamellar will be inhibited, but the amount of β-Mg17Al12 distributed at the grain boundary in the shape of bone will be promoted with the addition of Sn nanoparticles. Importantly, it is observed that Sn nanoparticles were generated to nano-sized Mg2Sn particles in the magnesium alloy matrix, but mainly existed in the form of particle clusters. With the excessive addition of Sn nanoparticles, a more severe Mg2Sn nanoparticle clusters and a reduction of the mechanical properties will be observed. In the present study, the most superior mechanical properties of the AZ31 magnesium alloy can be achieved when the proportion of Sn nanoparticles was about 1wt.%.
2016, 45(11):2992-2998.
Abstract:
To overcome these shortcomings of the blowing agent, which is used too much as the foaming agent for fabricating aluminum foams in melt foaming processing, as high cost, poor dispersion, difficult to match the foaming process and degrade the performance of the material, a new vacuum foaming processing was employed to prepare AlSi12 alloy foams. The processes that related to the initial pores and the cell structure of the vacuum foamed AlSi12 foams were studied. The results showed that: (1) Well-distribution, fine initial pores were obtained by the processing parameters: melting AlSi12 alloy at 620℃ for 1h, adding 1%SiC and 2% Ca into the melt and stirring the melt for 10min with stirring speed 2000r/mm to increasing the melt viscosity, then adding a few of TiH2 (0.02%) into the melt and stirring the melt for 6min with stirring speed 2000r/min; (2) AlSi12 alloy foams with uniform cell structure, average pore diameter 2.4mm and porosity 83.7% were obtained by the vacuum foaming processing: foaming the melt for 10s with vacuum degree of 5Pa, and cooling the melt foams for 6min in vacuum surroundings; (3) The bobble nucleation of the initial pores in the AlSi12 alloy melt were heterogeneous nucleation, and these phases, SiC, Al2O3, SiO2, etc., acted as the nuclei of the heterogeneous nucleation.
To overcome these shortcomings of the blowing agent, which is used too much as the foaming agent for fabricating aluminum foams in melt foaming processing, as high cost, poor dispersion, difficult to match the foaming process and degrade the performance of the material, a new vacuum foaming processing was employed to prepare AlSi12 alloy foams. The processes that related to the initial pores and the cell structure of the vacuum foamed AlSi12 foams were studied. The results showed that: (1) Well-distribution, fine initial pores were obtained by the processing parameters: melting AlSi12 alloy at 620℃ for 1h, adding 1%SiC and 2% Ca into the melt and stirring the melt for 10min with stirring speed 2000r/mm to increasing the melt viscosity, then adding a few of TiH2 (0.02%) into the melt and stirring the melt for 6min with stirring speed 2000r/min; (2) AlSi12 alloy foams with uniform cell structure, average pore diameter 2.4mm and porosity 83.7% were obtained by the vacuum foaming processing: foaming the melt for 10s with vacuum degree of 5Pa, and cooling the melt foams for 6min in vacuum surroundings; (3) The bobble nucleation of the initial pores in the AlSi12 alloy melt were heterogeneous nucleation, and these phases, SiC, Al2O3, SiO2, etc., acted as the nuclei of the heterogeneous nucleation.
2016, 45(11):2999-3003.
Abstract:
The microstructure, annealing strengthen and compressive deformation mechanism of Mg-5.3Nd alloy were investigated by using of OM, XRD, SEM/EDS and room temperature compression test, the results showed that the main second phase on as-casting Mg-5.3Nd alloy was Mg12Nd and the optimal solution treatment was 550 ℃×8 h for eliminating the second phases. Not subsequent unload and recompression but annealling treatment between pre-compression and recompression could markedly increase the compression strength of pre-deformed Mg-5.3Nd solid solution and the optimal annealing process was 180℃×4 h to reach the strength increament of 47MPa. The in-situ optical micrographs indicated that the preformed twins in the pre-compressed Mg-5.3Nd alloy untreated by annealing obviously grew up during the subsequent compression, whereas after annealing treatment the second compression deformation proceeded by the initiation of the new twins rather than the growth of the prefromed ones for the diffusion segregation of Nd element in the twin grainboudary during annealing process.
The microstructure, annealing strengthen and compressive deformation mechanism of Mg-5.3Nd alloy were investigated by using of OM, XRD, SEM/EDS and room temperature compression test, the results showed that the main second phase on as-casting Mg-5.3Nd alloy was Mg12Nd and the optimal solution treatment was 550 ℃×8 h for eliminating the second phases. Not subsequent unload and recompression but annealling treatment between pre-compression and recompression could markedly increase the compression strength of pre-deformed Mg-5.3Nd solid solution and the optimal annealing process was 180℃×4 h to reach the strength increament of 47MPa. The in-situ optical micrographs indicated that the preformed twins in the pre-compressed Mg-5.3Nd alloy untreated by annealing obviously grew up during the subsequent compression, whereas after annealing treatment the second compression deformation proceeded by the initiation of the new twins rather than the growth of the prefromed ones for the diffusion segregation of Nd element in the twin grainboudary during annealing process.
2016, 45(11):3004-3009.
Abstract:
The effects of Ce-rich Rare Earth (RE) on modification of eutectic silicon, formation of RE compound, and mechanical properties of Al-20Si-2Cu-1Ni high silicon aluminum alloy have been studied by use of optical microscope (OM), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). The mechanism was also discussed. The results show that, RE can modify eutectic silicon effectively which show better modification with increasing amounts of RE. While it also cause formation of needle-like RE compounds which increase with increasing amounts of RE. The mechanism of eutectic silicon modification is that the growth of eutectic silicon is hindered by the RE elements enriched at solidification front. But the excess RE will lead to form acicular Al2Si2RE compound containing a few solution of Cu and Ni elements which can offset part of the improvement of mechanical properties contributed by eutectic silicon modification. As a result, the mechanical performances of this alloy decrease with more acicular Al2Si2RE compound formation. With addition of 0.6% RE to the melt, the tensile strength and elongation of casted high silicon aluminum alloy reach maximum values which improve by 33% and 230% respectively, compared to the case without RE.
The effects of Ce-rich Rare Earth (RE) on modification of eutectic silicon, formation of RE compound, and mechanical properties of Al-20Si-2Cu-1Ni high silicon aluminum alloy have been studied by use of optical microscope (OM), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). The mechanism was also discussed. The results show that, RE can modify eutectic silicon effectively which show better modification with increasing amounts of RE. While it also cause formation of needle-like RE compounds which increase with increasing amounts of RE. The mechanism of eutectic silicon modification is that the growth of eutectic silicon is hindered by the RE elements enriched at solidification front. But the excess RE will lead to form acicular Al2Si2RE compound containing a few solution of Cu and Ni elements which can offset part of the improvement of mechanical properties contributed by eutectic silicon modification. As a result, the mechanical performances of this alloy decrease with more acicular Al2Si2RE compound formation. With addition of 0.6% RE to the melt, the tensile strength and elongation of casted high silicon aluminum alloy reach maximum values which improve by 33% and 230% respectively, compared to the case without RE.
2016, 45(11):3010-3014.
Abstract:
Abastract: The nanosized In2O3 was synthesized via the reverse microemulsion method. The hot-wire semiconductor metal oxide gas sensor was fabricated based on the In2O3. A dense layer of SiO2 on the surface of the sensitive element was formed by chemical vapor deposition of diethoxydimethylsilane (DEMS). The SiO2 functioned as molecular sieve, thereby the diffusion of reducing gases with large molecular diameter into sensing layer, except for H2, was restricted, resulting in high selectivity and response to H2. The effect of environmental humidity on the sensor response was reduced by the compensation of reference element, and the underlying reason of reduction was discussed by gas-sensing mechanism model. The sensor had high selectivity and response to H2, low ambient temperature and humidity dependence, excellent long term stability and low power consumption.
Abastract: The nanosized In2O3 was synthesized via the reverse microemulsion method. The hot-wire semiconductor metal oxide gas sensor was fabricated based on the In2O3. A dense layer of SiO2 on the surface of the sensitive element was formed by chemical vapor deposition of diethoxydimethylsilane (DEMS). The SiO2 functioned as molecular sieve, thereby the diffusion of reducing gases with large molecular diameter into sensing layer, except for H2, was restricted, resulting in high selectivity and response to H2. The effect of environmental humidity on the sensor response was reduced by the compensation of reference element, and the underlying reason of reduction was discussed by gas-sensing mechanism model. The sensor had high selectivity and response to H2, low ambient temperature and humidity dependence, excellent long term stability and low power consumption.
2016, 45(11):3015-3022.
Abstract:
Abstract: The two-stage homogenization process of 2055 Al-Li alloy was investigated by OM,DSC and SEM. The results show that the suitable two-stage homogenization process of 2055 Al-Li alloy is 470℃/8h 530~535℃/22~24h. The dendritic structure of as-cast alloys is obvious,the intermetallic phases in as-cast alloy consist of Cu ,Ag,Mg ,Zn,Fe and Mn enriched eutectic aluminides，Cu enriched eutectic aluminides: Al2Cu and AlCuFeMn second phase. The overburnt temperature of the alloy is 522.7℃.During the first homogenization process, firstly,Cu ,Mg and Zn enriched eutectic aluminides dissolve into matrix,then Cu enriched non-equilibrium aluminides Al2Cu gradually dissolve into matrix,except a small amount of Al-Cu-Fe-Mn phases, the size of residual phases is about 15μｍ.The second homogenization process agrees well with the results of homogenization kinetic analysis.
Abstract: The two-stage homogenization process of 2055 Al-Li alloy was investigated by OM,DSC and SEM. The results show that the suitable two-stage homogenization process of 2055 Al-Li alloy is 470℃/8h 530~535℃/22~24h. The dendritic structure of as-cast alloys is obvious,the intermetallic phases in as-cast alloy consist of Cu ,Ag,Mg ,Zn,Fe and Mn enriched eutectic aluminides，Cu enriched eutectic aluminides: Al2Cu and AlCuFeMn second phase. The overburnt temperature of the alloy is 522.7℃.During the first homogenization process, firstly,Cu ,Mg and Zn enriched eutectic aluminides dissolve into matrix,then Cu enriched non-equilibrium aluminides Al2Cu gradually dissolve into matrix,except a small amount of Al-Cu-Fe-Mn phases, the size of residual phases is about 15μｍ.The second homogenization process agrees well with the results of homogenization kinetic analysis.
49 Preparation and Electrochemical Performance of Lithium Vanadium Phosphate with Double Carbon Sources
2016, 45(11):3023-3029.
Abstract:
Using glucose as main carbon source and ascorbic acid (AA) as accessory carbon source, carbon coated lithium vanadium phosphate (LVP/C-AA) with high-rate performance was successfully synthesized by a solid-state reaction. The phases, morphologies, structures and electrochemical performance of samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), charging and discharging measurements, cyclic voltammogram (CV) testing and electrochemical impedance spectra (EIS). The results show that using ascorbic acid as accessory carbon source has no effect on the crystal structure of Li3V2(PO4)3, but enhances the high-rate performance. The LVP/C-AA electrode delivers an initial capacity as high as 162.4 mAh g-1 at 5 C, and shows an excellent capacity retention ration of 80.4% even after 100 cycles.
Using glucose as main carbon source and ascorbic acid (AA) as accessory carbon source, carbon coated lithium vanadium phosphate (LVP/C-AA) with high-rate performance was successfully synthesized by a solid-state reaction. The phases, morphologies, structures and electrochemical performance of samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), charging and discharging measurements, cyclic voltammogram (CV) testing and electrochemical impedance spectra (EIS). The results show that using ascorbic acid as accessory carbon source has no effect on the crystal structure of Li3V2(PO4)3, but enhances the high-rate performance. The LVP/C-AA electrode delivers an initial capacity as high as 162.4 mAh g-1 at 5 C, and shows an excellent capacity retention ration of 80.4% even after 100 cycles.
2016, 45(11):3030-3036.
Abstract:
Ferritic Stainless Steels (FSS) can be applied as interconnects of solid oxide fuel cells due at reduced operating temperatures due to their high thermo conductivities, suitable coefficients of thermal expansion and low price, However, practical application is still facing veraous challenges, such as low oxidation resistances, high volatility of chromium oxides etc. These issues could be minimized by coating technique. In this review, the application and effects of rare element oxide coatings(REOs)、perovskite coatings and spinel coatings are compared and discussed.
Ferritic Stainless Steels (FSS) can be applied as interconnects of solid oxide fuel cells due at reduced operating temperatures due to their high thermo conductivities, suitable coefficients of thermal expansion and low price, However, practical application is still facing veraous challenges, such as low oxidation resistances, high volatility of chromium oxides etc. These issues could be minimized by coating technique. In this review, the application and effects of rare element oxide coatings(REOs)、perovskite coatings and spinel coatings are compared and discussed.
