Volume 46,Issue 3,2017 Table of Contents
1 The peg-nail structure selective laser modification of plasma sprayed YSZ thermal barrier coatings
2017, 46(3):577-584.
Abstract:
In this paper, yttria partially stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were deposited by air plasma spraying (APS) method on nickle-based superalloy with initially sprayed NiCoCrAlYTa bond coat. After that, the surface of the plasma sprayed TBCs was subjected to the peg-nail structure selective laser modification using a Nd:YAG pulsed laser. The microstructure and performance of the plasma sprayed and laser modified YSZ coatings were investigated. The results revealed that the peg-nail structure selective laser modification helped to reduce the surface roughness considerably, eliminate to surface porosities and produced a network of continuous cracks perpendicular to the surface. The microstructure of laser modified area consisted of columnar grains in the cross-section and equiaxed grains on the surface. XRD patterns showed that both as-sprayed and the peg-nail structure laser modified coatings consisted of nonequibrium tetragonal (T'') phase, however, monoclinic (M) phase disappeared and intensity of T'' phase slightly increased in the range of 72-76°（2θ) after the peg-nail structure laser modification. It has been found that the average bond strength YSZ coatings was enhanced from 7.3 MPa to 13.3 MPa after the peg-nail structure laser modification. Thermal insulation capability of the peg-nail structure laser modified TBCs, as compared to the as-sprayed TBCs, was decreased due to microstructure change in the ceramic top coat.
In this paper, yttria partially stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were deposited by air plasma spraying (APS) method on nickle-based superalloy with initially sprayed NiCoCrAlYTa bond coat. After that, the surface of the plasma sprayed TBCs was subjected to the peg-nail structure selective laser modification using a Nd:YAG pulsed laser. The microstructure and performance of the plasma sprayed and laser modified YSZ coatings were investigated. The results revealed that the peg-nail structure selective laser modification helped to reduce the surface roughness considerably, eliminate to surface porosities and produced a network of continuous cracks perpendicular to the surface. The microstructure of laser modified area consisted of columnar grains in the cross-section and equiaxed grains on the surface. XRD patterns showed that both as-sprayed and the peg-nail structure laser modified coatings consisted of nonequibrium tetragonal (T'') phase, however, monoclinic (M) phase disappeared and intensity of T'' phase slightly increased in the range of 72-76°（2θ) after the peg-nail structure laser modification. It has been found that the average bond strength YSZ coatings was enhanced from 7.3 MPa to 13.3 MPa after the peg-nail structure laser modification. Thermal insulation capability of the peg-nail structure laser modified TBCs, as compared to the as-sprayed TBCs, was decreased due to microstructure change in the ceramic top coat.
2017, 46(3):585-590.
Abstract:
Precursor powders of Bi2.1Sr1.96CaCuxO8 d (Bi-2212) high temperature superconductors with different nominal Cu content of x=2.0, 2.1, 2.2 and 2.4 were fabricated by modified co-precipitation process. The influences of Cu contents on the phase evolution process during sintering were investigated systematically. Bi-2212 thick films and single filament tapes were fabricated with dip-coating process and powder in tube process, respectively. Obvious influences of Cu contents on the phase compositions, microstructures and superconducting properties were systematically discussed. It was noticed that the initial Cu content can affect the thermodynamic properties of Bi-2212 phase, thus lead to the change of phase evolution process. With the increase of Cu content, the phase content of Bi-2201 decreased, while the content of AEC phase increased. The maximum critical current density was obtained on the x=2.2 film and tape simultaneously due to the proper phase composition and better texture structures.
Precursor powders of Bi2.1Sr1.96CaCuxO8 d (Bi-2212) high temperature superconductors with different nominal Cu content of x=2.0, 2.1, 2.2 and 2.4 were fabricated by modified co-precipitation process. The influences of Cu contents on the phase evolution process during sintering were investigated systematically. Bi-2212 thick films and single filament tapes were fabricated with dip-coating process and powder in tube process, respectively. Obvious influences of Cu contents on the phase compositions, microstructures and superconducting properties were systematically discussed. It was noticed that the initial Cu content can affect the thermodynamic properties of Bi-2212 phase, thus lead to the change of phase evolution process. With the increase of Cu content, the phase content of Bi-2201 decreased, while the content of AEC phase increased. The maximum critical current density was obtained on the x=2.2 film and tape simultaneously due to the proper phase composition and better texture structures.
2017, 46(3):591-595.
Abstract:
Yb:YAG and Nd:YAG nanocrystals were synthesized by ultrasound-microwave-assisted alkoxide hydrolysis precipitation method. The effect of reaction parameters including the microwave radiation power, microwave radiation time and calcination temperature on the composition of the products was investigated. The Yb:YAG and Nd:YAG nanocrystals were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectrum. The results show that the pure phase Yb:YAG and Nd:YAG nanocrystals can be obtained at microwave radiation power of 385W, microwave radiation time of 30 min and calcination temperature of 1100 C. The cooperative luminescent intensities of the Yb:YAG and Nd:YAG nanocrystals reached the maximum at the calcination temperature of 1100 C.
Yb:YAG and Nd:YAG nanocrystals were synthesized by ultrasound-microwave-assisted alkoxide hydrolysis precipitation method. The effect of reaction parameters including the microwave radiation power, microwave radiation time and calcination temperature on the composition of the products was investigated. The Yb:YAG and Nd:YAG nanocrystals were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectrum. The results show that the pure phase Yb:YAG and Nd:YAG nanocrystals can be obtained at microwave radiation power of 385W, microwave radiation time of 30 min and calcination temperature of 1100 C. The cooperative luminescent intensities of the Yb:YAG and Nd:YAG nanocrystals reached the maximum at the calcination temperature of 1100 C.
2017, 46(3):596-600.
Abstract:
By means of high energy shot peening (HESP) to a pure iron cylinder, a nanocrystalline surface layer without oxidation, porosity and contamination was obtained. The thickness of the nanocrystalline surface layer was more than 100μm and the average grain size was about 50nm. The pulse pressure diffusion (PPD) and constant pressure diffusion (CPD) were used to diffuse nickel into nanocrystalline iron at 850℃ on Gleebl 1500 . Experimental results showed that diffusivity of Ni in the nanocrystalline Fe is 1 orders of magnitude higher than that in coarse-grained Fe and 1 orders of magnitude higher than that using CPD. The enhanced diffusivity of Ni may originate from the following three reasons : (1) pulse pressure can break the metalic compound formed during diffusing which may block the diffusion of Ni to inner nanocrystalline Fe; (2) a considerable amount of triple junctions and (3) a large volume fraction of non-equilibrium grain boundarie(GBs) in the present nanocrystalline Fe sample processed by means of the HESP technique.
By means of high energy shot peening (HESP) to a pure iron cylinder, a nanocrystalline surface layer without oxidation, porosity and contamination was obtained. The thickness of the nanocrystalline surface layer was more than 100μm and the average grain size was about 50nm. The pulse pressure diffusion (PPD) and constant pressure diffusion (CPD) were used to diffuse nickel into nanocrystalline iron at 850℃ on Gleebl 1500 . Experimental results showed that diffusivity of Ni in the nanocrystalline Fe is 1 orders of magnitude higher than that in coarse-grained Fe and 1 orders of magnitude higher than that using CPD. The enhanced diffusivity of Ni may originate from the following three reasons : (1) pulse pressure can break the metalic compound formed during diffusing which may block the diffusion of Ni to inner nanocrystalline Fe; (2) a considerable amount of triple junctions and (3) a large volume fraction of non-equilibrium grain boundarie(GBs) in the present nanocrystalline Fe sample processed by means of the HESP technique.
2017, 46(3):601-605.
Abstract:
Nanostructured zirconia coating was prepared based on reasonable spraying technical parameters and corresponding thermal shock property of as-sprayed coating has been examined at 1100 篊. The structure and the surface morphology of coating have been analyzed using XRD, SEM and TEM. Experimental results show nanoparticles close to pre-existing microcracks or pores grow during thermal shock process. Based on the detailed analysis of the structure, a rational mechanism has been proposed for the failure of as-prepared coating suffered circular stress. That is, with the growth of most or all of the nanoparticles, the nanostructured zirconia coating correspondingly changes into the quasi-microstructured coating, then the thermal shock failure mode of the resulting coating can be interpreted as follows: the formation of cracks results in the propagation of cracks, which is followed by the spallation of coating, just as the failure mode of traditional micro coating.
Nanostructured zirconia coating was prepared based on reasonable spraying technical parameters and corresponding thermal shock property of as-sprayed coating has been examined at 1100 篊. The structure and the surface morphology of coating have been analyzed using XRD, SEM and TEM. Experimental results show nanoparticles close to pre-existing microcracks or pores grow during thermal shock process. Based on the detailed analysis of the structure, a rational mechanism has been proposed for the failure of as-prepared coating suffered circular stress. That is, with the growth of most or all of the nanoparticles, the nanostructured zirconia coating correspondingly changes into the quasi-microstructured coating, then the thermal shock failure mode of the resulting coating can be interpreted as follows: the formation of cracks results in the propagation of cracks, which is followed by the spallation of coating, just as the failure mode of traditional micro coating.
2017, 46(3):606-611.
Abstract:
Ti-5Al-5Mo-5V-1Fe-1Cr Ti matrix composites reinforced with different weight fractions of TiB and TiC are fabricated via a consumable vacuum arc-remelting furnace. The reinforcements can significantly refine β phase during heat treatment. However, the extent of the microstructure refinement decreases gradually with the increase of the reinforcements. It is revealed that the microstructural phenomenon is associated with Zener dragging force exerted by the reinforcements. The rate of increase of the dragging force tends to decrease with the increase of the reinforcements. Additionally, the effects of the reinforcements on the spheroidization of α are also investigated. The spheroidization rate of α fluctuates somewhat with increasing the trace reinforcements during heat treatment. Nevertheless, the reinforcements accelerate the spheroidization of α lath in the Widmannstatten structure obviously during isothermal compression. The effects of the reinforcements during isothermal compression are different from those during heat treatment. In addition to accelerating the diffusion significantly, the trace reinforcements also contribute to the spheroidization of α by accelerating interface transformation during isothermal compression.
Ti-5Al-5Mo-5V-1Fe-1Cr Ti matrix composites reinforced with different weight fractions of TiB and TiC are fabricated via a consumable vacuum arc-remelting furnace. The reinforcements can significantly refine β phase during heat treatment. However, the extent of the microstructure refinement decreases gradually with the increase of the reinforcements. It is revealed that the microstructural phenomenon is associated with Zener dragging force exerted by the reinforcements. The rate of increase of the dragging force tends to decrease with the increase of the reinforcements. Additionally, the effects of the reinforcements on the spheroidization of α are also investigated. The spheroidization rate of α fluctuates somewhat with increasing the trace reinforcements during heat treatment. Nevertheless, the reinforcements accelerate the spheroidization of α lath in the Widmannstatten structure obviously during isothermal compression. The effects of the reinforcements during isothermal compression are different from those during heat treatment. In addition to accelerating the diffusion significantly, the trace reinforcements also contribute to the spheroidization of α by accelerating interface transformation during isothermal compression.
2017, 46(3):612-616.
Abstract:
In order to solve the wear repair problem of large steam turbine rotor shaft journal, the material of steam turbine rotor shaft as substrate and the self-made special laser cladding remanufacturing powder as experimental material, the experiments were carried out by laser cladding remanufacturing method based on laser cladding remanufacturing system with coaxial powder feeder. Focusing on effect of different width of laser cladding layers on total indicated runout (TIR) of steam turbine rotor, the experiment research and mechanism simulation verification were performed, and the influence mechanism of different factors were analyzed. The results show that the data results of total indicated runout are closely related to probe diameter and laser cladding layer width. The width of cladding layer determines the turbine rotor surface magnetic, eddy current density and magnetic flux density distribution. Due to the interference of matrix magnetic field and eddy current density of surface, the magnetic flux density suddenly changes in the laser cladding layer edge when the laser cladding layer width is less than 8mm.The measurement results are too large caused by the comprehensive effect of substrate and laser cladding layer. According to the numerical simulation of magnetic flux density distribution of measured metal body surface, the critical value of laser cladding width is 9.82mm.
In order to solve the wear repair problem of large steam turbine rotor shaft journal, the material of steam turbine rotor shaft as substrate and the self-made special laser cladding remanufacturing powder as experimental material, the experiments were carried out by laser cladding remanufacturing method based on laser cladding remanufacturing system with coaxial powder feeder. Focusing on effect of different width of laser cladding layers on total indicated runout (TIR) of steam turbine rotor, the experiment research and mechanism simulation verification were performed, and the influence mechanism of different factors were analyzed. The results show that the data results of total indicated runout are closely related to probe diameter and laser cladding layer width. The width of cladding layer determines the turbine rotor surface magnetic, eddy current density and magnetic flux density distribution. Due to the interference of matrix magnetic field and eddy current density of surface, the magnetic flux density suddenly changes in the laser cladding layer edge when the laser cladding layer width is less than 8mm.The measurement results are too large caused by the comprehensive effect of substrate and laser cladding layer. According to the numerical simulation of magnetic flux density distribution of measured metal body surface, the critical value of laser cladding width is 9.82mm.
2017, 46(3):617-621.
Abstract:
Field emission characteristics of metals-doped nano-diamond on titanium substrate are studied, wherein metals—Ti and Hf are mixed with nano-diamond separately, and cathode samples are prepared by electrophoresis. Then the structures and morphologies of cathode samples are characterized by SEM and XRD, finally, field emission test is conducted. Results show that the morphology of 5 mg Ti-doped sample is more uniform and dense, but the morphologies of Hf-doped samples become worse. Meanwhile, compared with undoped sample, field emission characteristics of Ti-doped samples improve, Hf-doped samples decrease. Compared between Ti-doped samples, it is found that the amount of Ti mixed with nano-diamond should not be too much, mixing a moderate amount of Ti can make field emission characteristics of nano-diamond on Ti substrate improve. Analysis shows that this is determined by the nature of metal Ti and Hf, which influences the bonding reaction between nano-diamond and substrate Ti, therefore, field emission characteristics of doped nano-diamond on Ti substrate are influenced.
Field emission characteristics of metals-doped nano-diamond on titanium substrate are studied, wherein metals—Ti and Hf are mixed with nano-diamond separately, and cathode samples are prepared by electrophoresis. Then the structures and morphologies of cathode samples are characterized by SEM and XRD, finally, field emission test is conducted. Results show that the morphology of 5 mg Ti-doped sample is more uniform and dense, but the morphologies of Hf-doped samples become worse. Meanwhile, compared with undoped sample, field emission characteristics of Ti-doped samples improve, Hf-doped samples decrease. Compared between Ti-doped samples, it is found that the amount of Ti mixed with nano-diamond should not be too much, mixing a moderate amount of Ti can make field emission characteristics of nano-diamond on Ti substrate improve. Analysis shows that this is determined by the nature of metal Ti and Hf, which influences the bonding reaction between nano-diamond and substrate Ti, therefore, field emission characteristics of doped nano-diamond on Ti substrate are influenced.
9 Mechanical properties and formability of ultrasonic treated twin roll casting magnesium alloy sheet
2017, 46(3):622-626.
Abstract:
The effects of ultrasonic treatment on the microstructure and properties of twin roll casting Mg-3wt%Al-1%Zn-0.8?-0.3%Mn alloy strip were studied in this investigation. The results show that the ultrasonic treatment contributes to the improvement of strength, elongation and limiting drawing ratio of alloy strip. The highest limiting drawing ratio of the sheet is 2.16 at 250℃. The improvement of properties is attributed to the refinement of α-Mg grains and the modification of Mg17(Al,Zn)12 and AlCeMn phases by ultrasonic treatment during the twin roll casting process. The grain size of the twin roll casting strip is refined from 150 μm to less than 30 μm with the ultrasonic treatment power of 800 W, and the needle-like shape of the AlCeMn phase is modified to a globular shape.
The effects of ultrasonic treatment on the microstructure and properties of twin roll casting Mg-3wt%Al-1%Zn-0.8?-0.3%Mn alloy strip were studied in this investigation. The results show that the ultrasonic treatment contributes to the improvement of strength, elongation and limiting drawing ratio of alloy strip. The highest limiting drawing ratio of the sheet is 2.16 at 250℃. The improvement of properties is attributed to the refinement of α-Mg grains and the modification of Mg17(Al,Zn)12 and AlCeMn phases by ultrasonic treatment during the twin roll casting process. The grain size of the twin roll casting strip is refined from 150 μm to less than 30 μm with the ultrasonic treatment power of 800 W, and the needle-like shape of the AlCeMn phase is modified to a globular shape.
2017, 46(3):627-633.
Abstract:
In this study, Ti-Al-Si-Cu-N nanocomposite films with different Cu contents were deposited on AISI-304 stainless steel by DC reactive magnetron sputtering. Both Ti-Al-Si-N and Ti-Al-Si-Cu-N nanocomposite films were oxidized at 800℃ to investigate the influence of Cu content on the microsturcture and high temperature oxidation resistance by means of scanning electron microscope(SEM), energy disperse spectroscopy(EDS), X-ray diffraction(XRD), nanoindentation tester and a home-made indentation system. The results indicated that with increasing copper content in the films, the micropores disappeared from the surface of Ti-Al-Si-N nanocomposite film and the compact films were obtained. A reduction of the grain size and a change of the (111) preferred orientation to (110) were observed. The microhardness of films increased from 14.76 GPa to 19.42 GPa. The elasticity modulus of Ti-Al-Si-Cu-N films with 1.72 at.% Cu content had the minimum value of 104.5 GPa. The incorporation of copper at high temperature had two effects, one was that the diffusion rate of Al element was advanced another was the crack of oxide layer was induced and the micropores were produced. Ti-Al-Si-N films had a better oxidation resistance than that of the films added Cu element.
In this study, Ti-Al-Si-Cu-N nanocomposite films with different Cu contents were deposited on AISI-304 stainless steel by DC reactive magnetron sputtering. Both Ti-Al-Si-N and Ti-Al-Si-Cu-N nanocomposite films were oxidized at 800℃ to investigate the influence of Cu content on the microsturcture and high temperature oxidation resistance by means of scanning electron microscope(SEM), energy disperse spectroscopy(EDS), X-ray diffraction(XRD), nanoindentation tester and a home-made indentation system. The results indicated that with increasing copper content in the films, the micropores disappeared from the surface of Ti-Al-Si-N nanocomposite film and the compact films were obtained. A reduction of the grain size and a change of the (111) preferred orientation to (110) were observed. The microhardness of films increased from 14.76 GPa to 19.42 GPa. The elasticity modulus of Ti-Al-Si-Cu-N films with 1.72 at.% Cu content had the minimum value of 104.5 GPa. The incorporation of copper at high temperature had two effects, one was that the diffusion rate of Al element was advanced another was the crack of oxide layer was induced and the micropores were produced. Ti-Al-Si-N films had a better oxidation resistance than that of the films added Cu element.
2017, 46(3):634-639.
Abstract:
This paper analyzed the microstructure of Ti6Al4V titanium alloy after different heat treatments. The tensile experiment and instrumented impact test were done. It was studied that the microstructure, mechanical properties and impact toughness of Ti6Al4V titanium alloy were affected by the solution and aging treatment. The relationship among the microstructure, impact fracture characteristic and mechanical properties was analyzed by metallurgical mi-croscope and environment scanning electron microscope (ESEM). The results showed that the yield strength and ul-timate tensile strength were improved remarkably. The ductile increased firstly, then it decreased. The good compre-hensive properties can be gotten when the Ti6Al4V titanium alloy was treated in the condition of 960 ℃×1h WQ and 500 ℃×4h AC. The σ0.2 is 1050 MPa. The σb is 1120 MPa and Ak is 46.22 J. The microstructure of the tita-nium alloy after solution and aging treatment was consisted of the β matrix and the precipitation of the α-phase. The lamellar β-phase and the α-phase structure of the small needle plexiform can enhance comprehensive properties.
This paper analyzed the microstructure of Ti6Al4V titanium alloy after different heat treatments. The tensile experiment and instrumented impact test were done. It was studied that the microstructure, mechanical properties and impact toughness of Ti6Al4V titanium alloy were affected by the solution and aging treatment. The relationship among the microstructure, impact fracture characteristic and mechanical properties was analyzed by metallurgical mi-croscope and environment scanning electron microscope (ESEM). The results showed that the yield strength and ul-timate tensile strength were improved remarkably. The ductile increased firstly, then it decreased. The good compre-hensive properties can be gotten when the Ti6Al4V titanium alloy was treated in the condition of 960 ℃×1h WQ and 500 ℃×4h AC. The σ0.2 is 1050 MPa. The σb is 1120 MPa and Ak is 46.22 J. The microstructure of the tita-nium alloy after solution and aging treatment was consisted of the β matrix and the precipitation of the α-phase. The lamellar β-phase and the α-phase structure of the small needle plexiform can enhance comprehensive properties.
2017, 46(3):640-645.
Abstract:
Magnesium alloys AZ31B plates and pure titanium TA2 plates were bonded successfully through explosive welding. The microstructure and composition of the interface were examined by means of optical microscope (OM), scanning electron microscopy (SEM) and energy dispersive spectroscope (EDS). To explore the process of element diffusion between AZ31B and TA2, the composite plates were annealed at different temperature. Furthermore, the mechanical behavior of the composite plates was evaluated. The results show that straight and wavy interface coexisted on the bonding area. The degree of the element diffusion became obvious when heating at 450?C and 490?C for 4h and 8h. The hardness of AZ31B and TA2 was increased significantly due to the plastic deformation and the strain hardening. The mechanical properties of the composite plates were found significantly improved compared to that of base plate AZ31B.
Magnesium alloys AZ31B plates and pure titanium TA2 plates were bonded successfully through explosive welding. The microstructure and composition of the interface were examined by means of optical microscope (OM), scanning electron microscopy (SEM) and energy dispersive spectroscope (EDS). To explore the process of element diffusion between AZ31B and TA2, the composite plates were annealed at different temperature. Furthermore, the mechanical behavior of the composite plates was evaluated. The results show that straight and wavy interface coexisted on the bonding area. The degree of the element diffusion became obvious when heating at 450?C and 490?C for 4h and 8h. The hardness of AZ31B and TA2 was increased significantly due to the plastic deformation and the strain hardening. The mechanical properties of the composite plates were found significantly improved compared to that of base plate AZ31B.
2017, 46(3):646-650.
Abstract:
The effects of thermal exposure on microstructure of an experimental third generation single crystal superalloy were investigated. The alloy was exposed at 1100℃ for 100-800 h. The γ′ particles in dendrite core gradually had coarsened and became very irregular by γ′ precipitates dissolving resulting from elements diffusion with increasing exposure time. The γ′ precipitates in interdendritic region varied from cuboidal morphology, fusing together, and rafting with the increase of exposure time. The various γ′ particles behaviors between dendritic core and interdendritic region were attributed to the segregation of refractory elements. After 300h a small amount of needle-shaped TCP phases were found in dendrite core and the mount of TCP phases increased with increasing exposure time. There was no TCP phase in interdendritic region until 800h. TEM and EDX measurements showed that TCP phases observed in these samples were identified as σ phase enriched Re and W elements.
The effects of thermal exposure on microstructure of an experimental third generation single crystal superalloy were investigated. The alloy was exposed at 1100℃ for 100-800 h. The γ′ particles in dendrite core gradually had coarsened and became very irregular by γ′ precipitates dissolving resulting from elements diffusion with increasing exposure time. The γ′ precipitates in interdendritic region varied from cuboidal morphology, fusing together, and rafting with the increase of exposure time. The various γ′ particles behaviors between dendritic core and interdendritic region were attributed to the segregation of refractory elements. After 300h a small amount of needle-shaped TCP phases were found in dendrite core and the mount of TCP phases increased with increasing exposure time. There was no TCP phase in interdendritic region until 800h. TEM and EDX measurements showed that TCP phases observed in these samples were identified as σ phase enriched Re and W elements.
2017, 46(3):651-656.
Abstract:
The influences of B element on the microstructure and property of AlCoCrFeNiBx high entropy alloys (x denotes the atomic fraction of B element 0, 0.1, 0.25, 0.5, 0.75 and 1.0) were investigated. The AlCoCrFeNi high entropy alloy exhibit equiaxed grain morphology, then turns to dendrite structure when B content, x=0.1. The spinodal decomposition microstructure can be clearly observed in equiaxed grains. When x>0.1, both of the dendrite and the spinodal decomposition microstructure gradually disappeared, but much borides formed instead. The transformation is attributed to the high negative mixing enthalpy of Cr-B and Co-B. The microstructures of AlCoCrFeNiBx high entropy alloys changed from B2 BCC structures to B2 BCC FCC structures, finally formed B2 BCC FCC and borides mixing structures with the increased B elements. And the hardness declined from HV486.0 to HV460.7, then rose to HV615.7 as the addition of B element. The lowest hardness value is obtained when x=0.1. The compressive fracture strength shows a distinct decrease with B addition. The maximum compression strength is 2227MPa when x=0.25. But when x reached 0.75, the samples fractured during the elastic deformation due to the formation of hard and brittle borides. The coercive forces and the specific saturation magnetizations of the alloys decrease as the contents B element increase. The decreasing coercive forces show a better soft magnetic behavior.
The influences of B element on the microstructure and property of AlCoCrFeNiBx high entropy alloys (x denotes the atomic fraction of B element 0, 0.1, 0.25, 0.5, 0.75 and 1.0) were investigated. The AlCoCrFeNi high entropy alloy exhibit equiaxed grain morphology, then turns to dendrite structure when B content, x=0.1. The spinodal decomposition microstructure can be clearly observed in equiaxed grains. When x>0.1, both of the dendrite and the spinodal decomposition microstructure gradually disappeared, but much borides formed instead. The transformation is attributed to the high negative mixing enthalpy of Cr-B and Co-B. The microstructures of AlCoCrFeNiBx high entropy alloys changed from B2 BCC structures to B2 BCC FCC structures, finally formed B2 BCC FCC and borides mixing structures with the increased B elements. And the hardness declined from HV486.0 to HV460.7, then rose to HV615.7 as the addition of B element. The lowest hardness value is obtained when x=0.1. The compressive fracture strength shows a distinct decrease with B addition. The maximum compression strength is 2227MPa when x=0.25. But when x reached 0.75, the samples fractured during the elastic deformation due to the formation of hard and brittle borides. The coercive forces and the specific saturation magnetizations of the alloys decrease as the contents B element increase. The decreasing coercive forces show a better soft magnetic behavior.
2017, 46(3):657-662.
Abstract:
A series of barium doped nano-magnesia supports (Ba-MgO) modified with EDTA were prepared by chemical co-precipitation with ultrasonic method and were used as supports to prepare Ru-based catalysts. The surface texture and the matter phase of the supports and Ru catalysts were characterized by X-ray diffraction, scanning electron microscope, N2 physical-adsorption, H2 temperature-programmed reduction and inductively coupled plasma-atomic emission spectrometry respectively. The results showed that modification of EDTA increased the amount of barium promoter into the support and controlled the formation state of barium in support. The effects of barium promoter content and surface texture in support achieved an equilibrium state when the molar ratio of EDTA to Ba was 1/2, and the highest activity of Ru/Ba-MgO catalyst was 69.31 mmol g-1h-1 under the reaction conditions of 10 MPa, 10 000 h-1 and 698 K.
A series of barium doped nano-magnesia supports (Ba-MgO) modified with EDTA were prepared by chemical co-precipitation with ultrasonic method and were used as supports to prepare Ru-based catalysts. The surface texture and the matter phase of the supports and Ru catalysts were characterized by X-ray diffraction, scanning electron microscope, N2 physical-adsorption, H2 temperature-programmed reduction and inductively coupled plasma-atomic emission spectrometry respectively. The results showed that modification of EDTA increased the amount of barium promoter into the support and controlled the formation state of barium in support. The effects of barium promoter content and surface texture in support achieved an equilibrium state when the molar ratio of EDTA to Ba was 1/2, and the highest activity of Ru/Ba-MgO catalyst was 69.31 mmol g-1h-1 under the reaction conditions of 10 MPa, 10 000 h-1 and 698 K.
2017, 46(3):663-668.
Abstract:
The influence of microstructure homogeneity on crack intiation behavior under high-cycle fatigue (HCF) test at room temperature was studied in Ti-55531 alloy with lamellar microstructure by TEM and SEM methods. The results show that the HCF strength of Ti-55531 alloy could be as high as 639 MPa. However, a small amount of grain boundary (GB) α and a large number of inhomogenious regions in microstructure significantly effect the HCF behavior of lamellar Ti-55531 alloy. Fatigue microcracks mainly initiated at interfaces between αs and β phases owing to their different structure and properties. Moreover, small amount of microcracks initiated at GB α and αs phases during fatigue.
The influence of microstructure homogeneity on crack intiation behavior under high-cycle fatigue (HCF) test at room temperature was studied in Ti-55531 alloy with lamellar microstructure by TEM and SEM methods. The results show that the HCF strength of Ti-55531 alloy could be as high as 639 MPa. However, a small amount of grain boundary (GB) α and a large number of inhomogenious regions in microstructure significantly effect the HCF behavior of lamellar Ti-55531 alloy. Fatigue microcracks mainly initiated at interfaces between αs and β phases owing to their different structure and properties. Moreover, small amount of microcracks initiated at GB α and αs phases during fatigue.
2017, 46(3):669-674.
Abstract:
Ultrafine grained commercially pure Ti with different grain size was prepared by Equal Channel Angular Pressing (ECAP). The mechanical properties of commercially pure Ti were investigated by the nanoindentation technique. The effects of loading strain rate and grain size on the nanoindentation measurement of commercially pure Ti were discussed. Strain hardening capacity and residual stress of commercially pure Ti were analyzed. The results show that the hardness of commercially pure Ti increases with the loading strain rate increasing and grain size decreasing. The hardness-dislocation curves exhibit the Indentation Size Effect (ISE) with the incorporated hardening effect. The indentation morphology shows that commercially pure Ti processed by ECAP has little strain hardening capacity and compressive residual stress compared to coarse-grained sample.
Ultrafine grained commercially pure Ti with different grain size was prepared by Equal Channel Angular Pressing (ECAP). The mechanical properties of commercially pure Ti were investigated by the nanoindentation technique. The effects of loading strain rate and grain size on the nanoindentation measurement of commercially pure Ti were discussed. Strain hardening capacity and residual stress of commercially pure Ti were analyzed. The results show that the hardness of commercially pure Ti increases with the loading strain rate increasing and grain size decreasing. The hardness-dislocation curves exhibit the Indentation Size Effect (ISE) with the incorporated hardening effect. The indentation morphology shows that commercially pure Ti processed by ECAP has little strain hardening capacity and compressive residual stress compared to coarse-grained sample.
2017, 46(3):675-679.
Abstract:
The Friction and wear performance of Ti-12Mo alloy fabricated by powder injection molding (PIM) were investigated. It is compared with that of as-PMed Ti and TC4 alloy and as-casted TC4 alloy, which are the most widely used in the dental materials field. The results show that the Ti-12Mo alloy exhibits higher wear resistance than the as-PMed Ti and TC4 alloy, close to the as-casted TC4 alloy under the same sliding friction conditions. The Ti-Mo alloy exhibit a typical Widmanstatten structure, consisting of β-Ti and α-Ti phases. The micro hardness of Ti-12Mo alloy is about 310HV, and the friction coefficient is stabilized at about 0.43, which are lower than the three other alloys. The wear mechanisms of Ti-12Mo alloy(PIM) is dominated by abrasive wear.
The Friction and wear performance of Ti-12Mo alloy fabricated by powder injection molding (PIM) were investigated. It is compared with that of as-PMed Ti and TC4 alloy and as-casted TC4 alloy, which are the most widely used in the dental materials field. The results show that the Ti-12Mo alloy exhibits higher wear resistance than the as-PMed Ti and TC4 alloy, close to the as-casted TC4 alloy under the same sliding friction conditions. The Ti-Mo alloy exhibit a typical Widmanstatten structure, consisting of β-Ti and α-Ti phases. The micro hardness of Ti-12Mo alloy is about 310HV, and the friction coefficient is stabilized at about 0.43, which are lower than the three other alloys. The wear mechanisms of Ti-12Mo alloy(PIM) is dominated by abrasive wear.
2017, 46(3):680-686.
Abstract:
The effect of SO2 in simulated furnace atmosphere on the corrosion behaviors of CoCrFeNiTi0.5 anti-alkali metal sulphate was investigated by means of XRD, SEM (EDS) and EMPA. The results show that the corrosion kinetic curve of the alloy in 0.75%SO2 follows the parabolic law and is similar to that in 0% SO2. The corrosion products are mainly composed of Ti，Cr，Fe oxides, minor compound oxides with spinals structure as well as (Fe,Ni)xSy. Adding 0.75%SO2 in simulated furnace atmosphere increases significantly the oxide films in thickness as well as the pore densities occurring in the corrosion affected zone, and accelerates the spalling of the oxide films off the surface of the alloy. It is concluded that the corrosion of CoCrFeNiTi0.5 high-entropy alloy in 0% SO2 is attributed to the formation of the protective oxide layers and to the basic fluxing of Cr2O3 in molten Na2SO4 induced by low melting point eutectic，however，the high temperature corrosion of CoCrFeNiTi0.5 in 0.75%SO2 is contributed to the oxidation of the alloy, the sulfate salinization of metallic oxide and the formation of ternary composed alkali metal sulfate as well as the dissolution of Fe in melted salt. Moreover, the sulfidition of Fe,Ni occurring in the corrosion affected zone is also contributed to the corrosion.
The effect of SO2 in simulated furnace atmosphere on the corrosion behaviors of CoCrFeNiTi0.5 anti-alkali metal sulphate was investigated by means of XRD, SEM (EDS) and EMPA. The results show that the corrosion kinetic curve of the alloy in 0.75%SO2 follows the parabolic law and is similar to that in 0% SO2. The corrosion products are mainly composed of Ti，Cr，Fe oxides, minor compound oxides with spinals structure as well as (Fe,Ni)xSy. Adding 0.75%SO2 in simulated furnace atmosphere increases significantly the oxide films in thickness as well as the pore densities occurring in the corrosion affected zone, and accelerates the spalling of the oxide films off the surface of the alloy. It is concluded that the corrosion of CoCrFeNiTi0.5 high-entropy alloy in 0% SO2 is attributed to the formation of the protective oxide layers and to the basic fluxing of Cr2O3 in molten Na2SO4 induced by low melting point eutectic，however，the high temperature corrosion of CoCrFeNiTi0.5 in 0.75%SO2 is contributed to the oxidation of the alloy, the sulfate salinization of metallic oxide and the formation of ternary composed alkali metal sulfate as well as the dissolution of Fe in melted salt. Moreover, the sulfidition of Fe,Ni occurring in the corrosion affected zone is also contributed to the corrosion.
2017, 46(3):687-692.
Abstract:
A series of tensile tests for Zr-Sn-Nb alloy strip was carried out at 25℃, 200℃ and 400℃. The effect of texture on the mechanical properties of zirconium alloy was studied by Electron Backscatter Diffraction (EBSD). The results show that Zr-Sn-Nb alloy strip possessed typical basal texture with twin peaks, and [0002] basal poles (in TD-ND plane) tilted ±30° in TD. The larger grains mostly belonged to the {0001} < > and {0001} < > texture while the smaller grains were in the {0001} < > orientation. Due to the texture, the strip presented mechanical anisotropy. The σs was highest in TD and lowest in RD; the σb was highest in RD and lowest in 45° direction. With the increase of temperature, both σs and σb decreased. Besides, Δσs and Δσb decreased too, but Δσs decreased more obviously. The elongation of strip increased with the temperature increasing. However, the elongation of strip at 400℃ was smaller than that at 200℃,which may be induced by the decrease of grain boundary strength and dynamic strain aging phenomenon.
A series of tensile tests for Zr-Sn-Nb alloy strip was carried out at 25℃, 200℃ and 400℃. The effect of texture on the mechanical properties of zirconium alloy was studied by Electron Backscatter Diffraction (EBSD). The results show that Zr-Sn-Nb alloy strip possessed typical basal texture with twin peaks, and [0002] basal poles (in TD-ND plane) tilted ±30° in TD. The larger grains mostly belonged to the {0001} < > and {0001} < > texture while the smaller grains were in the {0001} < > orientation. Due to the texture, the strip presented mechanical anisotropy. The σs was highest in TD and lowest in RD; the σb was highest in RD and lowest in 45° direction. With the increase of temperature, both σs and σb decreased. Besides, Δσs and Δσb decreased too, but Δσs decreased more obviously. The elongation of strip increased with the temperature increasing. However, the elongation of strip at 400℃ was smaller than that at 200℃,which may be induced by the decrease of grain boundary strength and dynamic strain aging phenomenon.
2017, 46(3):693-698.
Abstract:
The Ni60 coatings was prepared by means of supersonic plasma spraying on 45 # steel substrate, and it was subsequently treated by the induction remelting and induction remelting forced cooling, respectively.The microstructure, microhardness distribution and friction-wear properties were analyzed by OM, SEM, XRD, microhardness tester and pin-on-diskSfriction wearStester to investigate the evolutionScharacteristic of microstructure of Ni60 alloy coatings and its properties.The results showed that the three kinds of coating have greater different microstructures, the remelted treatment only by high-frequencySinduction make the microstructures refining of the coating,and the coating remelted by induction remelting forced cooling form directionalScrystal structure which show epitaxial growth. The hardness of spraying coating appeared a downward trend from inside to outside, and the other two coatings were slightly increased from inside to outside, so, despite the higher the average hardness of spray coating, but the surface hardness is lower than the other two kinds of coating. The three kinds of coating have all good wear resistance, but subsequent treatment make the friction coefficient of the coating increase obviously, and wear-resisting performance are significantly enhanced. The coating added forced cooling shows more excellent wear resistance especially, and its average wear rate is lower about 8.5 times than the spraying coating and about 2 times than induction remelting coating,respectively.
The Ni60 coatings was prepared by means of supersonic plasma spraying on 45 # steel substrate, and it was subsequently treated by the induction remelting and induction remelting forced cooling, respectively.The microstructure, microhardness distribution and friction-wear properties were analyzed by OM, SEM, XRD, microhardness tester and pin-on-diskSfriction wearStester to investigate the evolutionScharacteristic of microstructure of Ni60 alloy coatings and its properties.The results showed that the three kinds of coating have greater different microstructures, the remelted treatment only by high-frequencySinduction make the microstructures refining of the coating,and the coating remelted by induction remelting forced cooling form directionalScrystal structure which show epitaxial growth. The hardness of spraying coating appeared a downward trend from inside to outside, and the other two coatings were slightly increased from inside to outside, so, despite the higher the average hardness of spray coating, but the surface hardness is lower than the other two kinds of coating. The three kinds of coating have all good wear resistance, but subsequent treatment make the friction coefficient of the coating increase obviously, and wear-resisting performance are significantly enhanced. The coating added forced cooling shows more excellent wear resistance especially, and its average wear rate is lower about 8.5 times than the spraying coating and about 2 times than induction remelting coating,respectively.
2017, 46(3):699-703.
Abstract:
High strength and high conductivity Cu-Nb microcomposites are with nano-structured Nb fibers and pure Cu matrix. Strength size effect has been observed. The rule of strength changing with the size of Nb filaments was analyzed by stress-strain curves. The characteristics of elastic modulus and nano-indention hardness varying with the thickness of Nb filaments are investigated by nanoindentation. It is shown that the measured value of strength is considerably higher than that obtained by ROM and the UTS of Cu-Nb increases exponentially with the decreasing of dNb. Moreover, the nano-indention hardness of Nb filaments also increases greatly as the size dreased. It is believed that electronic interface scattering associated with the mean free path of the electrons is the main factor of Cu-Nb conductivity.
High strength and high conductivity Cu-Nb microcomposites are with nano-structured Nb fibers and pure Cu matrix. Strength size effect has been observed. The rule of strength changing with the size of Nb filaments was analyzed by stress-strain curves. The characteristics of elastic modulus and nano-indention hardness varying with the thickness of Nb filaments are investigated by nanoindentation. It is shown that the measured value of strength is considerably higher than that obtained by ROM and the UTS of Cu-Nb increases exponentially with the decreasing of dNb. Moreover, the nano-indention hardness of Nb filaments also increases greatly as the size dreased. It is believed that electronic interface scattering associated with the mean free path of the electrons is the main factor of Cu-Nb conductivity.
2017, 46(3):704-710.
Abstract:
The ultrafine/nanostructured WC-10Co-4Cr composite powder was synthesized by reduction and carburization reactions, the composite powder was agglomerated to prepare the composite powder feeding that was used in spraying, then the ultrafine/nanostructured WC-10Co-4Cr coating was prepared by high velocity oxygen fuel (HVOF). The phases, elemental distribution and microstructure of the coating were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM), and then the wear resistance and corrosion resistance of the coating were tested. The results show that the main phases of the coating is WC , binding phase of amorphous structure is Co(Cr), and there is a little W2C phase of hexagonal crystal structure and W2C Co(Cr) multiphase of amorphous coexisting. The change rule of WC grain were obtained from phase boundary to eutectic area to Co area by the quantitative analysis of distribution of Co and Cr element in coating. Combined WC-10Co-4Cr composite powder and process characteristics of HVOF, explain the causes of Cr in the WC-10Co-4Cr coating distribution, and discusses the impact on the coating performance.
The ultrafine/nanostructured WC-10Co-4Cr composite powder was synthesized by reduction and carburization reactions, the composite powder was agglomerated to prepare the composite powder feeding that was used in spraying, then the ultrafine/nanostructured WC-10Co-4Cr coating was prepared by high velocity oxygen fuel (HVOF). The phases, elemental distribution and microstructure of the coating were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM), and then the wear resistance and corrosion resistance of the coating were tested. The results show that the main phases of the coating is WC , binding phase of amorphous structure is Co(Cr), and there is a little W2C phase of hexagonal crystal structure and W2C Co(Cr) multiphase of amorphous coexisting. The change rule of WC grain were obtained from phase boundary to eutectic area to Co area by the quantitative analysis of distribution of Co and Cr element in coating. Combined WC-10Co-4Cr composite powder and process characteristics of HVOF, explain the causes of Cr in the WC-10Co-4Cr coating distribution, and discusses the impact on the coating performance.
2017, 46(3):711-715.
Abstract:
By in situ tension for the N18 zircaloy, which had been charged hydrogen by electrolytic hydrogenation method, the crack initiating and developing inside of hydrides were observed with SEM. The effects of hydrides on the tensile properties and the fracture behaviours were investigated. The results show that, necking in tension occurs, and many dimples exist on matrix fracture surface, which means that ductile fracture happened during in situ tension, and that the N18 zircaloy has ductility. The cracks are naturally initiated from strip hydrides clusters and propagate rapidly inside of hydrides, but are blunted by plastic matrix, and become to holes. There are many secondary cracks between matrix and brittle hydrides on the fracture surface. Both the shape and distribution of the secondary cracks are similar to those of hydrides. The holes and secondary cracks reduce the ductility of the N18 zircaloy with hydrogen.
By in situ tension for the N18 zircaloy, which had been charged hydrogen by electrolytic hydrogenation method, the crack initiating and developing inside of hydrides were observed with SEM. The effects of hydrides on the tensile properties and the fracture behaviours were investigated. The results show that, necking in tension occurs, and many dimples exist on matrix fracture surface, which means that ductile fracture happened during in situ tension, and that the N18 zircaloy has ductility. The cracks are naturally initiated from strip hydrides clusters and propagate rapidly inside of hydrides, but are blunted by plastic matrix, and become to holes. There are many secondary cracks between matrix and brittle hydrides on the fracture surface. Both the shape and distribution of the secondary cracks are similar to those of hydrides. The holes and secondary cracks reduce the ductility of the N18 zircaloy with hydrogen.
2017, 46(3):716-721.
Abstract:
The microstructures evolution of the Mg-6Gd-2Y alloy were investigated deeply during homogenizing and then aging treatment by OM,SEM, EDS, XRD, HRTEM in this paper. It was found that the microstructure of the as-cast alloy mainly consisted of α(Mg) equiaxed grains and eutectic compound Mg5(Gd,Y) with some non-equilibrium particles Mg2(Gd,Y). With the solution time prolonging, the α(Mg) grains did not significantly grow. The size of semi-continuous Mg5(Gd,Y) eutectic compound was shrinked gradually, and disappeared finally. And many fine RE-rich particles (Mg (Gd,Y) 2) with fcc structure were formed in the grain boundaries, which prevented the growth of α(Mg) grains. Age-hardening of the alloy at 175℃ was most obvious. β" phase was precipitated from α(Mg) matrix in the early-aging period(4-32h). β'' phase was formed in the rapid-aging precipitation period(32-100h). β" and β'' phase were mainly precipitation in the α(Mg) at the peak-aging stage(100h). β'' phase was transitioned to β1 ,which was transformed to stable β phase gradually at the over-aging stage (after 100h).
The microstructures evolution of the Mg-6Gd-2Y alloy were investigated deeply during homogenizing and then aging treatment by OM,SEM, EDS, XRD, HRTEM in this paper. It was found that the microstructure of the as-cast alloy mainly consisted of α(Mg) equiaxed grains and eutectic compound Mg5(Gd,Y) with some non-equilibrium particles Mg2(Gd,Y). With the solution time prolonging, the α(Mg) grains did not significantly grow. The size of semi-continuous Mg5(Gd,Y) eutectic compound was shrinked gradually, and disappeared finally. And many fine RE-rich particles (Mg (Gd,Y) 2) with fcc structure were formed in the grain boundaries, which prevented the growth of α(Mg) grains. Age-hardening of the alloy at 175℃ was most obvious. β" phase was precipitated from α(Mg) matrix in the early-aging period(4-32h). β'' phase was formed in the rapid-aging precipitation period(32-100h). β" and β'' phase were mainly precipitation in the α(Mg) at the peak-aging stage(100h). β'' phase was transitioned to β1 ,which was transformed to stable β phase gradually at the over-aging stage (after 100h).
2017, 46(3):722-727.
Abstract:
The temperature change history of AZ3lB Mg alloy was measured under different rolling conditions. An in situ measurement method through inlaid thermocouples was used. The results show the whole temperature variation process consisted of deformation process(0.02~0.08s) and subsequent temperature homogenizing process(0.8~1.2s). The temperature rises in these two stages both increased with either increased reduction or decreased initial rolling temperature. Those two temperature rises reached 80℃ and 35℃, respectively, for 45% rolling at 200℃. On this basis, two empirical formulas were established to predict temperature rises. The deformation induced temperature rise significantly affected the microstructure and recrystallization behavior of rolled sheet.
The temperature change history of AZ3lB Mg alloy was measured under different rolling conditions. An in situ measurement method through inlaid thermocouples was used. The results show the whole temperature variation process consisted of deformation process(0.02~0.08s) and subsequent temperature homogenizing process(0.8~1.2s). The temperature rises in these two stages both increased with either increased reduction or decreased initial rolling temperature. Those two temperature rises reached 80℃ and 35℃, respectively, for 45% rolling at 200℃. On this basis, two empirical formulas were established to predict temperature rises. The deformation induced temperature rise significantly affected the microstructure and recrystallization behavior of rolled sheet.
2017, 46(3):728-734.
Abstract:
The microstructure of Mg-8.07Al-0.53Zn-1.36Nd magnesium alloy was characterized and analysed by using XRD, SEM, TEM and EDS. The effect of microstructure on the behavior of crack initiation and propagation was investigated by in situ tensile testing. Results show that the microstructure consists of α-Mg matrix, β-Mg17Al12, eutectic phase α β, needle-like Al11Nd3 and particle Al2Nd phase while the 1.36 wt.%Nd added in AZ91 alloy. The twin structure of the Al2Nd phase was observed, and the twin plane is {11-1}. Moreover, a continuous concave and convex interface structure of the Al11Nd3 has been found. In situ tensile testing of the alloy at room temperature shows that the crack initiation mainly occured in the β-Mg17Al12phase, and the crack propagation modes includes of intergranular and transgranular expansion. Crack transgranular expansion is due to the strong binding ability between of Al11Nd3 or Al2Nd phases and surrounding organization, and the continuous concave and convex interface structure of the Al11Nd3 provides a significant meshing effect on the matrix and eutectic structure.
The microstructure of Mg-8.07Al-0.53Zn-1.36Nd magnesium alloy was characterized and analysed by using XRD, SEM, TEM and EDS. The effect of microstructure on the behavior of crack initiation and propagation was investigated by in situ tensile testing. Results show that the microstructure consists of α-Mg matrix, β-Mg17Al12, eutectic phase α β, needle-like Al11Nd3 and particle Al2Nd phase while the 1.36 wt.%Nd added in AZ91 alloy. The twin structure of the Al2Nd phase was observed, and the twin plane is {11-1}. Moreover, a continuous concave and convex interface structure of the Al11Nd3 has been found. In situ tensile testing of the alloy at room temperature shows that the crack initiation mainly occured in the β-Mg17Al12phase, and the crack propagation modes includes of intergranular and transgranular expansion. Crack transgranular expansion is due to the strong binding ability between of Al11Nd3 or Al2Nd phases and surrounding organization, and the continuous concave and convex interface structure of the Al11Nd3 provides a significant meshing effect on the matrix and eutectic structure.
2017, 46(3):735-739.
Abstract:
The appropriate ground states of the Al-La and Al-Y binary alloy are calculated by using the first-principles method based on density functional theory, the solubility of La and Y elements in Al are discussed, as well as the mechanical properties of the RE precipitates. The results show that the most stable phase of Al-La and Al-Y is Al2RE compound. For three of the priority precipitates (Al3Y(R-3M), Al3Y(PM-3M) and Al11La3(IMMM)), Al3Y(R-3M) has the highest stability and strengthening capability, and the difference of the calculated solubility for La and Y in Al indicates that Y has a high solubility limit. A comprehensive elastic modulus and solubility calculations, it can be concluded that Y is the better candidate as a potential addition to enhance the Al alloy matrix.
The appropriate ground states of the Al-La and Al-Y binary alloy are calculated by using the first-principles method based on density functional theory, the solubility of La and Y elements in Al are discussed, as well as the mechanical properties of the RE precipitates. The results show that the most stable phase of Al-La and Al-Y is Al2RE compound. For three of the priority precipitates (Al3Y(R-3M), Al3Y(PM-3M) and Al11La3(IMMM)), Al3Y(R-3M) has the highest stability and strengthening capability, and the difference of the calculated solubility for La and Y in Al indicates that Y has a high solubility limit. A comprehensive elastic modulus and solubility calculations, it can be concluded that Y is the better candidate as a potential addition to enhance the Al alloy matrix.
2017, 46(3):740-746.
Abstract:
The CuW/ZL101A integrated materials were prepared by the solid/liquid diffusion bonding process, the microstructures and formation mechanism of the diffusion solution layer (DSL) were investigated. The results showed that a good bonding interface was obtained at 690-705 ℃ for 60 min. With the growth direction perpendicular to the interface, the interfacial DSL mainly consists of planar DSL, columnar DSL, eutectic DSL. The phase composition was analyzed by SEM and XRD. The microstructure evolution and formation mechanism of the DSL obtained at 705 ℃ for 60 min can be explained as follows: the nucleation occurred at the W-Cu interface, the lateral growth firstly along the interface and the subsequent connection resulted in the formation of the small planar DSL, and then the longitudinal growth resulted in the formation of the columnar DSL. The eutectic DSL consists of lamellar pseudoeutectic and net divorced eutectic structures with the composition closing to or far from the Al-Cu eutectic point. With the increase of bonding time at 690 ℃, the DSL showed the similar morphology but different thickness. In addition, the formation of new phase was not observed.
The CuW/ZL101A integrated materials were prepared by the solid/liquid diffusion bonding process, the microstructures and formation mechanism of the diffusion solution layer (DSL) were investigated. The results showed that a good bonding interface was obtained at 690-705 ℃ for 60 min. With the growth direction perpendicular to the interface, the interfacial DSL mainly consists of planar DSL, columnar DSL, eutectic DSL. The phase composition was analyzed by SEM and XRD. The microstructure evolution and formation mechanism of the DSL obtained at 705 ℃ for 60 min can be explained as follows: the nucleation occurred at the W-Cu interface, the lateral growth firstly along the interface and the subsequent connection resulted in the formation of the small planar DSL, and then the longitudinal growth resulted in the formation of the columnar DSL. The eutectic DSL consists of lamellar pseudoeutectic and net divorced eutectic structures with the composition closing to or far from the Al-Cu eutectic point. With the increase of bonding time at 690 ℃, the DSL showed the similar morphology but different thickness. In addition, the formation of new phase was not observed.
2017, 46(3):747-753.
Abstract:
In order to further comparatively investigate microstructure and mechanical property of biomedical β-type titanium alloys with different compositions, ultrafine-grained β-type Ti28Nb2Zr8Sn bulk alloys with high strength and low elastic modulus were fabricated by mechanical alloying and spark plasma sintering in this work. XRD and SEM examinations indicate that the fabricated ultrafine-grained bulk alloys are fully bcc β-Ti structure by spark plasma sintering of 60h-milled alloy powders. Further TEM analysis proves that the grains of bcc β-Ti are equiaxed and their sizes are approximately 500-1000nm in the fabricated ultrafine-grained bulk alloys, which is far smaller than several micron-sized grains of similar titanium alloys prepared by casting method. In addition, mechanical property tests show that compressive strength increases and elastic modulus decreases gradually for the fabricated ultrafine-grained bulk alloys with the increased heating rate and decreased holding time. Under sintering temperature of 900℃, the heating rate of 150℃/min and no holding, the fabricated ultrafine-grained bulk alloy has the smallest grain size of bcc β-Ti,and thus the largest ultimate strength of 2675MPa, and the highest fracture strain of 0.54 along with lowest elastic modulus of 31.6GPa. Meanwhile, its work-hardening exponent 0.073 is far higher than that of Ti6Al4V alloy, indicating its excellent work-hardening ability and plastic deformation ability. This suggests that the fabricated ultrafine-grained bulk alloy can withstand high load and large deformation, and consequently can be an excellent candidate metallic material used as biomedical applications.
In order to further comparatively investigate microstructure and mechanical property of biomedical β-type titanium alloys with different compositions, ultrafine-grained β-type Ti28Nb2Zr8Sn bulk alloys with high strength and low elastic modulus were fabricated by mechanical alloying and spark plasma sintering in this work. XRD and SEM examinations indicate that the fabricated ultrafine-grained bulk alloys are fully bcc β-Ti structure by spark plasma sintering of 60h-milled alloy powders. Further TEM analysis proves that the grains of bcc β-Ti are equiaxed and their sizes are approximately 500-1000nm in the fabricated ultrafine-grained bulk alloys, which is far smaller than several micron-sized grains of similar titanium alloys prepared by casting method. In addition, mechanical property tests show that compressive strength increases and elastic modulus decreases gradually for the fabricated ultrafine-grained bulk alloys with the increased heating rate and decreased holding time. Under sintering temperature of 900℃, the heating rate of 150℃/min and no holding, the fabricated ultrafine-grained bulk alloy has the smallest grain size of bcc β-Ti,and thus the largest ultimate strength of 2675MPa, and the highest fracture strain of 0.54 along with lowest elastic modulus of 31.6GPa. Meanwhile, its work-hardening exponent 0.073 is far higher than that of Ti6Al4V alloy, indicating its excellent work-hardening ability and plastic deformation ability. This suggests that the fabricated ultrafine-grained bulk alloy can withstand high load and large deformation, and consequently can be an excellent candidate metallic material used as biomedical applications.
2017, 46(3):754-759.
Abstract:
The effects of aluminum content on microstructure and compressive properties of TiAl alloy were investigated, and the failure mechanism was also discussed. It is interesting to find that the content of aluminum remarkably influence the microstructure of TiAl alloys fabricated by Induction Skull Melting techniques. The microstructrue of Ti-46Al(at%) alloy was fully lamellar, and the γ/α2 lamellar clonies exhibit the characteristics of columnar crystals. The microstructrue of Ti-50Al(at%) alloy was duplex, which contains γ/α2 lamellar clonies and γ phase with 3D net structure. The microstructrue of Ti-50Al(at%) alloy is much finner than that of Ti-46Al(at%) alloy. Investigations on mechanical properties show that compared with Ti-50Al(at%) alloy, Ti-46Al(at%) alloy exhibits higher yield strength, lower ultimate compressive strength, and lower ductility under both quasi-static compression and dynamic compression. Failure analysis after quasi-static compression shows that in Ti-46Al(at%) alloy, micro-porous initiate in α2 phase of γ/α2 lamellar clonies. In Ti-50Al(at%) alloy, micro-porous initiate in both α2 phase of γ/α2 lamellar clonies and γ phase with 3D net structure. Thus, the failure mechanisms of both Ti-46Al(at%) alloy and Ti-50Al(at%) alloy is micro-porous coalescence fracture under quasi-static compression. Failure analysis after dynamic compression shows that in Ti-46Al(at%) alloy, micro-cracks intiated in phase boundary between γ phase and α2 phase. In Ti-50Al(at%) alloy, micro-cracks intiate in both phase boundary of γ/α2 lamellar clonies and γ phase with 3D net structure. With the increasing strain, the micro-cracks propagate rapidly, and lead to the failure of the alloys under dynamic compression.
The effects of aluminum content on microstructure and compressive properties of TiAl alloy were investigated, and the failure mechanism was also discussed. It is interesting to find that the content of aluminum remarkably influence the microstructure of TiAl alloys fabricated by Induction Skull Melting techniques. The microstructrue of Ti-46Al(at%) alloy was fully lamellar, and the γ/α2 lamellar clonies exhibit the characteristics of columnar crystals. The microstructrue of Ti-50Al(at%) alloy was duplex, which contains γ/α2 lamellar clonies and γ phase with 3D net structure. The microstructrue of Ti-50Al(at%) alloy is much finner than that of Ti-46Al(at%) alloy. Investigations on mechanical properties show that compared with Ti-50Al(at%) alloy, Ti-46Al(at%) alloy exhibits higher yield strength, lower ultimate compressive strength, and lower ductility under both quasi-static compression and dynamic compression. Failure analysis after quasi-static compression shows that in Ti-46Al(at%) alloy, micro-porous initiate in α2 phase of γ/α2 lamellar clonies. In Ti-50Al(at%) alloy, micro-porous initiate in both α2 phase of γ/α2 lamellar clonies and γ phase with 3D net structure. Thus, the failure mechanisms of both Ti-46Al(at%) alloy and Ti-50Al(at%) alloy is micro-porous coalescence fracture under quasi-static compression. Failure analysis after dynamic compression shows that in Ti-46Al(at%) alloy, micro-cracks intiated in phase boundary between γ phase and α2 phase. In Ti-50Al(at%) alloy, micro-cracks intiate in both phase boundary of γ/α2 lamellar clonies and γ phase with 3D net structure. With the increasing strain, the micro-cracks propagate rapidly, and lead to the failure of the alloys under dynamic compression.
2017, 46(3):760-764.
Abstract:
The samples of TC18 titanium alloy were produced by electron beam rapid manufacturing(EBRM). The effect of different wire feeding modes on microstructure and tensile properties of TC18 by EBRM were studied. The typical macrostructure of TC18 exhibit large columnar β grains nucleated at the substrate after EBRM, and the size of single wire is finer than that of double wire. However, both processes leads to flake primary α phase, β transformation microstructure and grain boundary α phase. While the amount of primary α phase of single wire is larger than that of double wire, the interlamellar spacing of single wire is smaller than double wire. The plasticity and stability of single wire are higher, and the strength is slightly lower than the double wire.
The samples of TC18 titanium alloy were produced by electron beam rapid manufacturing(EBRM). The effect of different wire feeding modes on microstructure and tensile properties of TC18 by EBRM were studied. The typical macrostructure of TC18 exhibit large columnar β grains nucleated at the substrate after EBRM, and the size of single wire is finer than that of double wire. However, both processes leads to flake primary α phase, β transformation microstructure and grain boundary α phase. While the amount of primary α phase of single wire is larger than that of double wire, the interlamellar spacing of single wire is smaller than double wire. The plasticity and stability of single wire are higher, and the strength is slightly lower than the double wire.
2017, 46(3):765-769.
Abstract:
The micro-arc oxidation method is employed to make the highly hardness ceramic layer on the surface of TC4 titanium alloy. The Al2TiO5 is the main crystal phase of the layer. The hardness of the ceramic layer is raised to 1150 HV0.05 and decreased subsequently from interface to surface. It is indicate that the compact layer could protect the substrate effectively in fretting wear test. At the initiate state, loose coating start to break and the severe wear will be occurred in friction pair. While it is stable, the abrasive dust which produced through mashed fruiting body of loose coating will be expelled from the wear zone and the sliding wear turns to be the main style as the compact layer replace loose coating gradually. At the stable state, the metal material transferred from the friction pair to compact layer for the wearability of it. Thus, the compact layer of ceramic layer fabricated by micro-arc oxidation could protect the substrate effectively in fretting wear test.
The micro-arc oxidation method is employed to make the highly hardness ceramic layer on the surface of TC4 titanium alloy. The Al2TiO5 is the main crystal phase of the layer. The hardness of the ceramic layer is raised to 1150 HV0.05 and decreased subsequently from interface to surface. It is indicate that the compact layer could protect the substrate effectively in fretting wear test. At the initiate state, loose coating start to break and the severe wear will be occurred in friction pair. While it is stable, the abrasive dust which produced through mashed fruiting body of loose coating will be expelled from the wear zone and the sliding wear turns to be the main style as the compact layer replace loose coating gradually. At the stable state, the metal material transferred from the friction pair to compact layer for the wearability of it. Thus, the compact layer of ceramic layer fabricated by micro-arc oxidation could protect the substrate effectively in fretting wear test.
2017, 46(3):770-776.
Abstract:
The morphology and element distribution of the bonding interface were investigated by means of SEM and EDS to evaluate the interface bonding property of titanium/aluminum/titanium with three layers prepared by one-step explosive bonding method. Besides, the tensile property and the bending property were also investigated. The results indicated that the linear and wavy bonding interface coexisted and element diffusion occurred in the interfacial zone. Meanwhile, the tensile and bending test results showed that as-prepared Ti/Al/Ti laminates had a high strength and excellent bonding property and could endure a large secondary plastic deformation.
The morphology and element distribution of the bonding interface were investigated by means of SEM and EDS to evaluate the interface bonding property of titanium/aluminum/titanium with three layers prepared by one-step explosive bonding method. Besides, the tensile property and the bending property were also investigated. The results indicated that the linear and wavy bonding interface coexisted and element diffusion occurred in the interfacial zone. Meanwhile, the tensile and bending test results showed that as-prepared Ti/Al/Ti laminates had a high strength and excellent bonding property and could endure a large secondary plastic deformation.
2017, 46(3):777-782.
Abstract:
The phase composition, interface structure, microstructure evolution and mechanical behavior of the Nb-35Ti-4C alloy before and after heat-treatment are comprehensively investigated using x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The results show that as cast and heat treated Nb-35Ti-4C alloy consists of Niobium solid solution (Nbss) and carbide of (Nb, Ti)C.The numerous secondary (Nb, Ti)C with the sizes of several nanometers precipitates from Nbss matrix during heat treatment. Furthermore, the secondary Nbss with a reticular structure distribution also precipitates from carbide, the phase transformation of the carbide can be summarized as (Nb, Ti)C→(Nb, Ti)C Nbss. the secondary Nbss nucleates along the close-packed surface (111) of fcc (Nb, Ti)C at the early state of heat-treatment, and the strip secondary Nbss and the (Nb, Ti)C matrix adopt a well-defined orientation relationship (OR): ， . The hard carbide has a strong bonding with the Nbss, and the eutectoid transformation of the large sized carbide after heat treatment leads to less possibility for the forming of cracks on the carbide surface, which in turn improves the toughness.
The phase composition, interface structure, microstructure evolution and mechanical behavior of the Nb-35Ti-4C alloy before and after heat-treatment are comprehensively investigated using x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The results show that as cast and heat treated Nb-35Ti-4C alloy consists of Niobium solid solution (Nbss) and carbide of (Nb, Ti)C.The numerous secondary (Nb, Ti)C with the sizes of several nanometers precipitates from Nbss matrix during heat treatment. Furthermore, the secondary Nbss with a reticular structure distribution also precipitates from carbide, the phase transformation of the carbide can be summarized as (Nb, Ti)C→(Nb, Ti)C Nbss. the secondary Nbss nucleates along the close-packed surface (111) of fcc (Nb, Ti)C at the early state of heat-treatment, and the strip secondary Nbss and the (Nb, Ti)C matrix adopt a well-defined orientation relationship (OR): ， . The hard carbide has a strong bonding with the Nbss, and the eutectoid transformation of the large sized carbide after heat treatment leads to less possibility for the forming of cracks on the carbide surface, which in turn improves the toughness.
2017, 46(3):783-789.
Abstract:
Ti-6Al-4V(TC4)has been the most highly used titanium alloy, and it is the world leading in the applications of titanium alloys. In this paper, mechanical alloying is adopted to prepare Ti-6Al-4V alloy powder, the experimental results show that: mechanical alloying can prepare nanocrystalline Ti-6Al-4V alloy powder, the reaction mechanism dominated by diffusion, and the solid-state reaction is the result of defects in energy and interaction of the collision energy. With increasing milling time, substitution solid solution Ti(V)formed in the process, there is no intermediate phase generated in milling process. After milling for 40h can obtain nanocrystalline, nanocrystalline and polycrystalline mixtures obtained for 60 hour. The grain sizes are less than 60nm and little change in grain size after milling for 60h. After milling, the atomic ratio of Ti, Al, V is near to 90:6:4, which is consistent with the Ti-6Al-4V elemental composition.
Ti-6Al-4V(TC4)has been the most highly used titanium alloy, and it is the world leading in the applications of titanium alloys. In this paper, mechanical alloying is adopted to prepare Ti-6Al-4V alloy powder, the experimental results show that: mechanical alloying can prepare nanocrystalline Ti-6Al-4V alloy powder, the reaction mechanism dominated by diffusion, and the solid-state reaction is the result of defects in energy and interaction of the collision energy. With increasing milling time, substitution solid solution Ti(V)formed in the process, there is no intermediate phase generated in milling process. After milling for 40h can obtain nanocrystalline, nanocrystalline and polycrystalline mixtures obtained for 60 hour. The grain sizes are less than 60nm and little change in grain size after milling for 60h. After milling, the atomic ratio of Ti, Al, V is near to 90:6:4, which is consistent with the Ti-6Al-4V elemental composition.
2017, 46(3):790-795.
Abstract:
The composite coatings of Ni-P chemical deposition and Ni-Co-Mn electroplating were made by the process of first Chemical deposition and last electroplating, and the mechanical properties and hot-corrosion resistance of the coatings were studied through the methods of metallographic observation, nanoindentation, nano-scratch, SEM, and EDS. The results show that the elastic modulus and nano-hardness of the coatings are similar with the electroplating, slightly lower than the chemical deposition. The coatings and substrate is combined well, and the two layers, chemical deposition and electroplating also with good binding force exceeds the maximum measurement value of nano-scratch, while larger than the one between a single electroplating and substrate. The tissue density of the chemical deposition and the electroplating is higher than the substrate, also the anti-hot corrosion resistance and oxidation resistance, and chemical deposition shows better than electroplating. First chemical deposition and last electroplating process is with better binding force than single electroplating process before and after hot corrosion, and is with faster coating growth rate than single chemical plating.
The composite coatings of Ni-P chemical deposition and Ni-Co-Mn electroplating were made by the process of first Chemical deposition and last electroplating, and the mechanical properties and hot-corrosion resistance of the coatings were studied through the methods of metallographic observation, nanoindentation, nano-scratch, SEM, and EDS. The results show that the elastic modulus and nano-hardness of the coatings are similar with the electroplating, slightly lower than the chemical deposition. The coatings and substrate is combined well, and the two layers, chemical deposition and electroplating also with good binding force exceeds the maximum measurement value of nano-scratch, while larger than the one between a single electroplating and substrate. The tissue density of the chemical deposition and the electroplating is higher than the substrate, also the anti-hot corrosion resistance and oxidation resistance, and chemical deposition shows better than electroplating. First chemical deposition and last electroplating process is with better binding force than single electroplating process before and after hot corrosion, and is with faster coating growth rate than single chemical plating.
2017, 46(3):796-801.
Abstract:
Effect of pre-recovery solid solution-T652 treatment and solid solution-T652 treatment on microstructure and properties of Al-11.5Zn-3.5Mg-2.3Cu-0.24Zr-0.0025Sr aluminum alloy extrusion were studied by means of micro-hardness tester and electrical conductivity test, tensile test, intergranular and exfoliation corrosion experiment, scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD). The results show that pre-recovery-annealing treatment can restrain recrystallization effectively, refine the grain size, and reduce the average angle of grain boundaries, increase the percentage of low angle grain boundaries significantly. Pre-annealing can improve the yield strength and the corrosion resistance performance, and maintain the same tensile strength. The increase of the yield strength is attributed to dislocation strengthening and low angel grain boundaries strengthening.
Effect of pre-recovery solid solution-T652 treatment and solid solution-T652 treatment on microstructure and properties of Al-11.5Zn-3.5Mg-2.3Cu-0.24Zr-0.0025Sr aluminum alloy extrusion were studied by means of micro-hardness tester and electrical conductivity test, tensile test, intergranular and exfoliation corrosion experiment, scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD). The results show that pre-recovery-annealing treatment can restrain recrystallization effectively, refine the grain size, and reduce the average angle of grain boundaries, increase the percentage of low angle grain boundaries significantly. Pre-annealing can improve the yield strength and the corrosion resistance performance, and maintain the same tensile strength. The increase of the yield strength is attributed to dislocation strengthening and low angel grain boundaries strengthening.
2017, 46(3):802-806.
Abstract:
Gd3 and Ga3 co-doped garnet-type Yb3-xGdxAl5-xGaxO12 solid solution (x=0.0,0.1,0.2,0.3,0.4,0.5;YGAGO) ceramic materials were synthesized by citric acid sol-gel method. XRD results demonstrate that all the Yb3-xGdxAl5-xGaxO12 compositions are comprised of the pure garnet Yb3Al5O12 phase. Increasing the Gd3 and Ga3 doping fractions leads to a shift of the X-ray spectrum to lower 2θ values. SEM morphology shows that microstructure is composed of nano-sized crystal grains and high densed grain boundary. The substitution of larger Gd3 and Ga3 in smaller Yb3 and Al6 sites, respectively, not only can lower the thermal conductivity, but also jontly facilitate higher coefficients of thermal expansion (CET), which is due to the relaxation of distored Yb3-xGdxAl5-xGaxO12 structure with substitutional point defects. The phonon mean free path of Yb3-xGdxAl5-xGaxO12 ceramics decreases with increasing Gd3 and Ga3 fraction at identical temperature levels, which is due to the lattice distortion and local imperfection scaling generated by incorporating large dopant Gd3 and Ga3 cations. Gd3 and Ga3 co-doped garnet-type Yb3-xGdxAl5-xGaxO12 composition showed a minimum thermal conductivity value (λ=1.67W/m.K,T=1273K) and a maximum CET (ɑl=11.71×10-6 K-1,T=1273K) at the composition Yb2.5Gd0.5Al4.5Ga0.5O12.
Gd3 and Ga3 co-doped garnet-type Yb3-xGdxAl5-xGaxO12 solid solution (x=0.0,0.1,0.2,0.3,0.4,0.5;YGAGO) ceramic materials were synthesized by citric acid sol-gel method. XRD results demonstrate that all the Yb3-xGdxAl5-xGaxO12 compositions are comprised of the pure garnet Yb3Al5O12 phase. Increasing the Gd3 and Ga3 doping fractions leads to a shift of the X-ray spectrum to lower 2θ values. SEM morphology shows that microstructure is composed of nano-sized crystal grains and high densed grain boundary. The substitution of larger Gd3 and Ga3 in smaller Yb3 and Al6 sites, respectively, not only can lower the thermal conductivity, but also jontly facilitate higher coefficients of thermal expansion (CET), which is due to the relaxation of distored Yb3-xGdxAl5-xGaxO12 structure with substitutional point defects. The phonon mean free path of Yb3-xGdxAl5-xGaxO12 ceramics decreases with increasing Gd3 and Ga3 fraction at identical temperature levels, which is due to the lattice distortion and local imperfection scaling generated by incorporating large dopant Gd3 and Ga3 cations. Gd3 and Ga3 co-doped garnet-type Yb3-xGdxAl5-xGaxO12 composition showed a minimum thermal conductivity value (λ=1.67W/m.K,T=1273K) and a maximum CET (ɑl=11.71×10-6 K-1,T=1273K) at the composition Yb2.5Gd0.5Al4.5Ga0.5O12.
2017, 46(3):807-811.
Abstract:
The nano and micro WC-17Co coatings were fabricated on the 0Cr13Ni5Mo stainless steel by supersonic plasma spraying method. The porosity, adhesive strength, hardness and wear resistance of both coatings were compared. The results indicate that the porosity and adhesive strength of nano-coating (i.e., 0.56% and over 69.2 MPa) are higher than those of micro-coating. The hardness of nano-coating and micro-coating are 3.9 and 3.8 times more than that of matrix, respectively. The hardness of both coating will gradually increase from its top to bottom. The wear mechanisms of matrix were adhesive wear, abrasive wear and delamination, while the coatings only suffered adhesive wear. The lower porosity, higer hardness and stonger compressive resistance of nano-coating result in its excellent wear resistance.
The nano and micro WC-17Co coatings were fabricated on the 0Cr13Ni5Mo stainless steel by supersonic plasma spraying method. The porosity, adhesive strength, hardness and wear resistance of both coatings were compared. The results indicate that the porosity and adhesive strength of nano-coating (i.e., 0.56% and over 69.2 MPa) are higher than those of micro-coating. The hardness of nano-coating and micro-coating are 3.9 and 3.8 times more than that of matrix, respectively. The hardness of both coating will gradually increase from its top to bottom. The wear mechanisms of matrix were adhesive wear, abrasive wear and delamination, while the coatings only suffered adhesive wear. The lower porosity, higer hardness and stonger compressive resistance of nano-coating result in its excellent wear resistance.
2017, 46(3):812-817.
Abstract:
Ni60-Y2O3 alloy layers were prepared on the surface of 6063 aluminum alloy by using laser additive manufacturing. The effects of rare earth Y2O3 addition on microstructure, phase structure and corrosion resistance of bonding interface between Ni60-Y2O3 alloy layers and substrate were investigated by means of OM, XRD,SEM and electrochemical corrosion tester. The results show that an excellent bonding between the alloy layers and the substrate was ensued by a strong metallurgical interface. Ni60-Y2O3 alloy layers have less of cracks, holes and porosity, more refined grain size than Ni60 alloy layers which without adding rare earth. The main phase structures of Ni60 alloy layers are β-NiAl (Cr), Al3Ni, AlNi3, Al , etc. After adding rare earth Y2O3, the diffraction peaks of Y2O3、YAl3、AlNiY、Ni17Y2 are found in the Ni60-Y2O3 alloy layers. Electrochemical corrosion tests show that the corrosion resistance of Ni60- Y2O3 alloy layer is 4.07 times as that of Ni60 alloy layer in 1mol/L H2SO4 solution, In 3.5% NaCl solution, the corrosion resistance of Ni60-Y2O3 alloy layer is 4.3 times as that of Ni60 alloy layer; In 1mol/L NaOH solution, the corrosion resistance of Ni60- Y2O3 alloy layer is 2.3 times as that of Ni60 alloy layer. It is visible that adding rare earth Y2O3 make Ni60 alloy layer grain refinement, organizational improvement, and significantly improve the corrosion resistance of the alloy layer.
Ni60-Y2O3 alloy layers were prepared on the surface of 6063 aluminum alloy by using laser additive manufacturing. The effects of rare earth Y2O3 addition on microstructure, phase structure and corrosion resistance of bonding interface between Ni60-Y2O3 alloy layers and substrate were investigated by means of OM, XRD,SEM and electrochemical corrosion tester. The results show that an excellent bonding between the alloy layers and the substrate was ensued by a strong metallurgical interface. Ni60-Y2O3 alloy layers have less of cracks, holes and porosity, more refined grain size than Ni60 alloy layers which without adding rare earth. The main phase structures of Ni60 alloy layers are β-NiAl (Cr), Al3Ni, AlNi3, Al , etc. After adding rare earth Y2O3, the diffraction peaks of Y2O3、YAl3、AlNiY、Ni17Y2 are found in the Ni60-Y2O3 alloy layers. Electrochemical corrosion tests show that the corrosion resistance of Ni60- Y2O3 alloy layer is 4.07 times as that of Ni60 alloy layer in 1mol/L H2SO4 solution, In 3.5% NaCl solution, the corrosion resistance of Ni60-Y2O3 alloy layer is 4.3 times as that of Ni60 alloy layer; In 1mol/L NaOH solution, the corrosion resistance of Ni60- Y2O3 alloy layer is 2.3 times as that of Ni60 alloy layer. It is visible that adding rare earth Y2O3 make Ni60 alloy layer grain refinement, organizational improvement, and significantly improve the corrosion resistance of the alloy layer.
2017, 46(3):818-823.
Abstract:
The AZO films were deposited on glass substrates by DC coupled RF magnetron sputtering at low temperature with a AZO ceramic target(2 wt % Al2O3) , and then AZO films were etched by the mass fraction of 0.5% HCl solution to obtain textured structures. Crystal phase structure, surface morphology, optical, electrical properties and the textured structure of AZO films mainly influenced by working pressure were characterized by XRD, SEM, spectrophotometer, hall effect test system and photoelectric haze instrument respectively. The results show that AZO thin films with excellent performance can be prepared by DC coupled RF magnetron sputtering at low temperatures. With the decrease of working pressure, the compactness of AZO films is increased, and their photoelectric performance improves, and textured structures with good light trapping effect can be obtained by post etching. Under working pressure of 0.5 Pa, the resistivity of AZO thin films prepared at low temperature is 3.55?0-4 Ω?cm, and the transmittance at visible light is 88.36%. After etching, their resistivity and transmittance at visible light are 4.19?0-4 Ω?cm and 89.59% respectively, and the haze reaches to 24.7%.
The AZO films were deposited on glass substrates by DC coupled RF magnetron sputtering at low temperature with a AZO ceramic target(2 wt % Al2O3) , and then AZO films were etched by the mass fraction of 0.5% HCl solution to obtain textured structures. Crystal phase structure, surface morphology, optical, electrical properties and the textured structure of AZO films mainly influenced by working pressure were characterized by XRD, SEM, spectrophotometer, hall effect test system and photoelectric haze instrument respectively. The results show that AZO thin films with excellent performance can be prepared by DC coupled RF magnetron sputtering at low temperatures. With the decrease of working pressure, the compactness of AZO films is increased, and their photoelectric performance improves, and textured structures with good light trapping effect can be obtained by post etching. Under working pressure of 0.5 Pa, the resistivity of AZO thin films prepared at low temperature is 3.55?0-4 Ω?cm, and the transmittance at visible light is 88.36%. After etching, their resistivity and transmittance at visible light are 4.19?0-4 Ω?cm and 89.59% respectively, and the haze reaches to 24.7%.
2017, 46(3):824-828.
Abstract:
Porous MnCo2O4.5 was prepared by the self-sacrificial template method. That is, the precursor with a plate-like morphology was firstly synthesized via a hydrothermal method, using MnSO4 and CoSO4 as raw materials and H2C2O4 as precipitator, respectively. Then porous MnCo2O4.5 well preserved the plate-like morphology, was in situ obtained by calcining the precursor. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and N2 adsorption-desorption were used to characterize the phases, morphologies and pore structures of the samples. Differential scanning calorimetry (DSC) was employed to evaluate the catalytic performance of these porous MnCo2O4.5 microsplates for thermal decomposition of ammonium perchlorate (AP). The result shows that the as-obtained porous MnCo2O4.5 exhibites excellent catalytic performance. Adding 2% (wt) porous MnCo2O4.5 into AP decreases the high-temperature exothermic peak by 128 癈 and the apparent decomposition heat increases by 557 J/g, respectively.
Porous MnCo2O4.5 was prepared by the self-sacrificial template method. That is, the precursor with a plate-like morphology was firstly synthesized via a hydrothermal method, using MnSO4 and CoSO4 as raw materials and H2C2O4 as precipitator, respectively. Then porous MnCo2O4.5 well preserved the plate-like morphology, was in situ obtained by calcining the precursor. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and N2 adsorption-desorption were used to characterize the phases, morphologies and pore structures of the samples. Differential scanning calorimetry (DSC) was employed to evaluate the catalytic performance of these porous MnCo2O4.5 microsplates for thermal decomposition of ammonium perchlorate (AP). The result shows that the as-obtained porous MnCo2O4.5 exhibites excellent catalytic performance. Adding 2% (wt) porous MnCo2O4.5 into AP decreases the high-temperature exothermic peak by 128 癈 and the apparent decomposition heat increases by 557 J/g, respectively.
2017, 46(3):829-834.
Abstract:
With the raw material of the precision forging M42 spray formed high speed steel, the orthogonal experiment under different parameters was used to optimize the technology of heat treatment and analyze the material’s microstructure, hardness, and flexural strength and the evolution law of carbide in different heat treatment systems. Results show that the best preservation temperature for quenching was 1180℃, and the temperature for temper which should be repeated 3 times and 1h for each time was 540℃. In this system, Rockwell hardness of M42 can reach to 67.2HRC, while flexural strength can be 315MPa.During the process of heat treatment, M6C carbide was largely affected by the change of quenching preservation temperature. When the quenching temperature was 1190℃, M6C carbide fully melted, and dispersedly separated after tempering.
With the raw material of the precision forging M42 spray formed high speed steel, the orthogonal experiment under different parameters was used to optimize the technology of heat treatment and analyze the material’s microstructure, hardness, and flexural strength and the evolution law of carbide in different heat treatment systems. Results show that the best preservation temperature for quenching was 1180℃, and the temperature for temper which should be repeated 3 times and 1h for each time was 540℃. In this system, Rockwell hardness of M42 can reach to 67.2HRC, while flexural strength can be 315MPa.During the process of heat treatment, M6C carbide was largely affected by the change of quenching preservation temperature. When the quenching temperature was 1190℃, M6C carbide fully melted, and dispersedly separated after tempering.
2017, 46(3):835-840.
Abstract:
W-based alloys were fabricated at 1500℃ under a pressure of 25 MPa by high-energy ball milling and hot pressing，where the CNTs and Ti were used as the dopants．The influence of different dopants on the sintering density，morphologies and mechanical properties of sintered W-based materials was investigated. The microstructure was characterized by scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). The fracture strength and toughness were measured by three-point bending and single-edge notched beams tests, respectively. Density measurements indicated that both CNTs and Ti can effectively enhance the sintering behavior. The W-0.1CNTs and W-5Ti exhibited a high relative density of 95.8％ and 96.5％, but their grain size is large. In case of W-5Ti-0.1CNTs alloy, the density is high and the addition of CNTs and Ti can refrain the grain size. W-5Ti-0.1CNTs alloy showed the excellent mechanical properties. The microhardness, fracture strength and fracture toughness of W-5Ti-0.1CNTs alloy are 7.32GPa, 654.3MPa, 10.13MPa?m1/2. The microstructure analysis of fracture surface revealed that the intergranular fracture is the main mode for the W-0.1CNTs and W-5Ti alloys, but the W-5Ti-0.1CNTs fractured in a mixture mode of intergranular and transgranular fracture. These results demonstrated that both the addition of CNTs and Ti can refine the microstructure and enhance the strength and fracture toughness of W-based alloys.
W-based alloys were fabricated at 1500℃ under a pressure of 25 MPa by high-energy ball milling and hot pressing，where the CNTs and Ti were used as the dopants．The influence of different dopants on the sintering density，morphologies and mechanical properties of sintered W-based materials was investigated. The microstructure was characterized by scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). The fracture strength and toughness were measured by three-point bending and single-edge notched beams tests, respectively. Density measurements indicated that both CNTs and Ti can effectively enhance the sintering behavior. The W-0.1CNTs and W-5Ti exhibited a high relative density of 95.8％ and 96.5％, but their grain size is large. In case of W-5Ti-0.1CNTs alloy, the density is high and the addition of CNTs and Ti can refrain the grain size. W-5Ti-0.1CNTs alloy showed the excellent mechanical properties. The microhardness, fracture strength and fracture toughness of W-5Ti-0.1CNTs alloy are 7.32GPa, 654.3MPa, 10.13MPa?m1/2. The microstructure analysis of fracture surface revealed that the intergranular fracture is the main mode for the W-0.1CNTs and W-5Ti alloys, but the W-5Ti-0.1CNTs fractured in a mixture mode of intergranular and transgranular fracture. These results demonstrated that both the addition of CNTs and Ti can refine the microstructure and enhance the strength and fracture toughness of W-based alloys.
2017, 46(3):841-846.
Abstract:
The carbon-supported fuel cell platinum catalysts 20%Pt/C were prepared by one-step microwave-colloidal method. The influence of different factors, such as the concentration of nitric acid used in carbon powder catalyst carrier, the microwave reaction time of preparation for the catalysts and the dosage of ethylene glycol reductant on the catalyst electric catalytic activity was compared here. It is found that the activity is the best when the concentration of nitric acid is 40% and the microwave reaction time is 70 second during both anode and cathode reaction. Interestingly, when the catalyst is used for methanol oxidation, lower dosage of EG leads to higher activity, while for oxygen reduction higher dosage of EG is better instead. X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) and cyclic voltammetry (CV) etc, revealed that the structure, crystal structure and the particle size did not change much by different preparation conditions whereas the electrochemical special surface area and electric catalytic activity have a significant influence.
The carbon-supported fuel cell platinum catalysts 20%Pt/C were prepared by one-step microwave-colloidal method. The influence of different factors, such as the concentration of nitric acid used in carbon powder catalyst carrier, the microwave reaction time of preparation for the catalysts and the dosage of ethylene glycol reductant on the catalyst electric catalytic activity was compared here. It is found that the activity is the best when the concentration of nitric acid is 40% and the microwave reaction time is 70 second during both anode and cathode reaction. Interestingly, when the catalyst is used for methanol oxidation, lower dosage of EG leads to higher activity, while for oxygen reduction higher dosage of EG is better instead. X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) and cyclic voltammetry (CV) etc, revealed that the structure, crystal structure and the particle size did not change much by different preparation conditions whereas the electrochemical special surface area and electric catalytic activity have a significant influence.
2017, 46(3):847-852.
Abstract:
A preparation method of TiO2 nanotubes grown on the pore surface of foamed titanium and the growth mechanism of the TiO2 nanotubes were studied in this paper. A kind of porous foamed Ti-Ni alloy was prepared by vacuum sintering method that is similar to the preparation method of porous ceramics. The porous foamed alloy was modified: an anodic oxidation method was used to generate a layer of TiO2 nanotubes on the surface of the porous foamed Ti-Ni alloy. Besides, the growth mechanism of TiO2 nanotubes was researched through scanning electronic microscopy (SEM) method, and the influences both of the anode oxidation voltage and the time on the TiO2 nanotube structure were also investigated.
A preparation method of TiO2 nanotubes grown on the pore surface of foamed titanium and the growth mechanism of the TiO2 nanotubes were studied in this paper. A kind of porous foamed Ti-Ni alloy was prepared by vacuum sintering method that is similar to the preparation method of porous ceramics. The porous foamed alloy was modified: an anodic oxidation method was used to generate a layer of TiO2 nanotubes on the surface of the porous foamed Ti-Ni alloy. Besides, the growth mechanism of TiO2 nanotubes was researched through scanning electronic microscopy (SEM) method, and the influences both of the anode oxidation voltage and the time on the TiO2 nanotube structure were also investigated.
2017, 46(3):853-856.
Abstract:
Diamond/copper composites were successfully fabricated by hot isostatic pressing(HIP) at a temperature of 900 ℃ and a pressure of 110 MPa for 1 h, and their microstructure and thermal properties were also studied. The results show that diamond particles are dispersed homogeneously in the copper matrix without evident graphitization. With increasing volume fraction of diamond, the relative density, thermal conductivity and coefficient of thermal expansion of the composites decrease. The maximum relative density and thermal conductivity of these samples are up to 98.5% and 305 W/mK, respectively. The diamond/copper composites prepared by HIP can achieve equal or even higher thermal conductivity than those fabricated by hot pressing(HP) and spark plasma sintering(SPS). Obviously, HIP shows great potential in preparing diamond/copper composites.
Diamond/copper composites were successfully fabricated by hot isostatic pressing(HIP) at a temperature of 900 ℃ and a pressure of 110 MPa for 1 h, and their microstructure and thermal properties were also studied. The results show that diamond particles are dispersed homogeneously in the copper matrix without evident graphitization. With increasing volume fraction of diamond, the relative density, thermal conductivity and coefficient of thermal expansion of the composites decrease. The maximum relative density and thermal conductivity of these samples are up to 98.5% and 305 W/mK, respectively. The diamond/copper composites prepared by HIP can achieve equal or even higher thermal conductivity than those fabricated by hot pressing(HP) and spark plasma sintering(SPS). Obviously, HIP shows great potential in preparing diamond/copper composites.
2017, 46(3):857-863.
Abstract:
Dense metallic membranes are primarily used for high-purity hydrogen separation from a mixture of gases, and especially hydrogen-permeable metallic membranes made of palladium-silver alloys being used for industrial application. However, palladium-silver alloy membranes have limited industrial application due to their high cost, and alternative to these and less expensive are non-palladium alloys. Vanadium-based alloy membranes are considered to be one of the most promising metallic membranes due to their higher permeabilities than palladium-silver and greater resistance to embrittlement as compared to pure vanadium. This paper will review metallic membranes permeation mechanism, V-based alloy membrane research status, the effect of catalyst layer on hydrogen-permeability, and vanadium-based alloy membrane fabrication.
Dense metallic membranes are primarily used for high-purity hydrogen separation from a mixture of gases, and especially hydrogen-permeable metallic membranes made of palladium-silver alloys being used for industrial application. However, palladium-silver alloy membranes have limited industrial application due to their high cost, and alternative to these and less expensive are non-palladium alloys. Vanadium-based alloy membranes are considered to be one of the most promising metallic membranes due to their higher permeabilities than palladium-silver and greater resistance to embrittlement as compared to pure vanadium. This paper will review metallic membranes permeation mechanism, V-based alloy membrane research status, the effect of catalyst layer on hydrogen-permeability, and vanadium-based alloy membrane fabrication.
2017, 46(3):864-868.
Abstract:
The Heusler alloy Ni2MnGa with ferromagnetic shape memory effect has the development potential. It has attracted much attention in the research of new intelligent materials. In this paper, the research progresses of the tetragonal distortions, phonon softening, magnetic properties and other aspects in Ni2MnGa alloys which were calculated by first-principles method are summarized; at the same time, discuss the site preference of Ni, Ti, Co doping elements in Ni2MnGa alloy and the influences of the doping elements on the electronic structure, martensitic transformation temperature TM and the Curie temperature TC.
The Heusler alloy Ni2MnGa with ferromagnetic shape memory effect has the development potential. It has attracted much attention in the research of new intelligent materials. In this paper, the research progresses of the tetragonal distortions, phonon softening, magnetic properties and other aspects in Ni2MnGa alloys which were calculated by first-principles method are summarized; at the same time, discuss the site preference of Ni, Ti, Co doping elements in Ni2MnGa alloy and the influences of the doping elements on the electronic structure, martensitic transformation temperature TM and the Curie temperature TC.
