Volume 41,Issue 7,2012 Table of Contents
2012, 41(7):1129-1134.
Abstract:
The surface of nickel hydroxide [Ni(OH)2] coated with ytterbium hydroxide [Yb(OH)3] and cobalt hydroxide [Co(OH)2] were studied and characterized by XRD, XPS, SEM and constant current recharge technology. The results show that the structure of β-Ni(OH)2 is hexagonal, Co exists mainly in the form of Co2+ with a small amount of Co3+, and the atomic ratio of Co and Ni on the sample surface is more than 8:1. The samples coated of 2 wt% Yb(OH)3 show the maximum discharge capacity and active material utilization rate at 65 °C (0.2, 1, 3 C). After 30 charge/discharge cycles, the discharge cycling stability and the discharge capacity of Ni(OH)2 coated with different contents of Yb (OH)3 are enhanced with increasing of content of Yb(OH)3 under different charge/discharge rates at 65 °C.
The surface of nickel hydroxide [Ni(OH)2] coated with ytterbium hydroxide [Yb(OH)3] and cobalt hydroxide [Co(OH)2] were studied and characterized by XRD, XPS, SEM and constant current recharge technology. The results show that the structure of β-Ni(OH)2 is hexagonal, Co exists mainly in the form of Co2+ with a small amount of Co3+, and the atomic ratio of Co and Ni on the sample surface is more than 8:1. The samples coated of 2 wt% Yb(OH)3 show the maximum discharge capacity and active material utilization rate at 65 °C (0.2, 1, 3 C). After 30 charge/discharge cycles, the discharge cycling stability and the discharge capacity of Ni(OH)2 coated with different contents of Yb (OH)3 are enhanced with increasing of content of Yb(OH)3 under different charge/discharge rates at 65 °C.
Shan Di
,
Yan Guo
,
Zhou Lian
,
Li Chengshan
,
Wang Qingyang
,
Zhang Shengnan
,
Xiong Xiaomei
,
Liu Guoqing
2012, 41(7):1135-1138.
Abstract:
The effects of Ti3SiC2 doping on lattice parameter (a), microstructure, critical temperature (Tc) and critical current density (Jc) of MgB2 superconductors were studied. Carbon substitution for boron could be confirmed by the shrinkage of the lattice parameter a with increasing of Ti3SiC2 doping level. A reduction of Tc from 37.15 K to 36.55 K with increasing of Ti3SiC2 doping was observed. The Jc values were determined by M-H hysteresis loops. Results show that in low magnetic field region, the Jc value for the undoped sample is higher than those for the doped samples. However, with the increase of the magnetic field, the Jc for the properly doped samples will be enhanced.
The effects of Ti3SiC2 doping on lattice parameter (a), microstructure, critical temperature (Tc) and critical current density (Jc) of MgB2 superconductors were studied. Carbon substitution for boron could be confirmed by the shrinkage of the lattice parameter a with increasing of Ti3SiC2 doping level. A reduction of Tc from 37.15 K to 36.55 K with increasing of Ti3SiC2 doping was observed. The Jc values were determined by M-H hysteresis loops. Results show that in low magnetic field region, the Jc value for the undoped sample is higher than those for the doped samples. However, with the increase of the magnetic field, the Jc for the properly doped samples will be enhanced.
2012, 41(7):1139-1143.
Abstract:
Iridium layer was prepared on platinum substrate under constant current in aqueous system using anhydrous iridium chloride as precursors. The surface morphology and the composition of the iridium layer were characterized by SEM, EDS and XPS. The optimized condition was derived. The results show that the concentration of iridium chloride has great influence on the surface morphology of the iridium layer. When the concentration is low, too thin iridium layer is formed, resulting in peeling or cracking. Therefore, an appropriate increase in the concentration of the precursors will help to improve the quality of the Ir layer. In a certain range of pH values, the surface morphologies of the iridium layers prepared on different conditions are nearly the same. The surface is smooth and iridium particles are uniform and dense. Current density has great influence on the surface morphology of the iridium layer, especially on the size and the density of crystalline particle. The iridium layer cannot be deposited at low solution temperature. Whereas the iridium layer is rough and its surface morphology is uneven at too high temperature.
Iridium layer was prepared on platinum substrate under constant current in aqueous system using anhydrous iridium chloride as precursors. The surface morphology and the composition of the iridium layer were characterized by SEM, EDS and XPS. The optimized condition was derived. The results show that the concentration of iridium chloride has great influence on the surface morphology of the iridium layer. When the concentration is low, too thin iridium layer is formed, resulting in peeling or cracking. Therefore, an appropriate increase in the concentration of the precursors will help to improve the quality of the Ir layer. In a certain range of pH values, the surface morphologies of the iridium layers prepared on different conditions are nearly the same. The surface is smooth and iridium particles are uniform and dense. Current density has great influence on the surface morphology of the iridium layer, especially on the size and the density of crystalline particle. The iridium layer cannot be deposited at low solution temperature. Whereas the iridium layer is rough and its surface morphology is uneven at too high temperature.
Liu Zhiyong
,
Suo Hongli
,
Ma Lin
,
Zhao Junjing
,
Ni Baorong
,
Guo Zhichao
,
Yan Binjie
,
Liu Min
,
Wu Ziping
,
Zhou Meiling
2012, 41(7):1144-1148.
Abstract:
We report the effect of fluorine doping on the fabrication and superconductivity of the iron-based arsenic oxide SmO1-xFδFeAs (δ≥x) compound. The fluorine over-doping can greatly reduce the heat treatment temperature and the heat treatment time, meanwhile the superconductivity of the SmO1-xFδFeAs samples does not reduce. The critical transition temperature (Tc) is as high as 56.5 K for the SmO0.7F0.3FeAs sample prepared by the two-step solid state reaction method at 1120 °C for 40 h, the Jc of the sample is 2.4×105 A/cm2 (10 K, 0 T). Tc of the fluorine over-doped SmO0.7F0.35FeAs and SmO0.7F0.4FeAs samples prepared by the two-step solid state reaction method at 1100 °C for 20 h are 56 and 55 K, respectively. Jc of the both samples are 1.9×105 and 1.7×105 A/cm2 (10 K, 0 T), respectively.
We report the effect of fluorine doping on the fabrication and superconductivity of the iron-based arsenic oxide SmO1-xFδFeAs (δ≥x) compound. The fluorine over-doping can greatly reduce the heat treatment temperature and the heat treatment time, meanwhile the superconductivity of the SmO1-xFδFeAs samples does not reduce. The critical transition temperature (Tc) is as high as 56.5 K for the SmO0.7F0.3FeAs sample prepared by the two-step solid state reaction method at 1120 °C for 40 h, the Jc of the sample is 2.4×105 A/cm2 (10 K, 0 T). Tc of the fluorine over-doped SmO0.7F0.35FeAs and SmO0.7F0.4FeAs samples prepared by the two-step solid state reaction method at 1100 °C for 20 h are 56 and 55 K, respectively. Jc of the both samples are 1.9×105 and 1.7×105 A/cm2 (10 K, 0 T), respectively.
2012, 41(7):1149-1152.
Abstract:
Solid state reactions between Ir and SiC and between Ir and Y2O3 were studied. The thermodynamics and mechanism of solid state reaction were discussed. The results indicate that Ir reacts with SiC at 1000 °C to yield Ir3Si and graphitized carbon. The products of Ir silicide changes from Ir3Si and IrSi at 1200 °C to IrSi at 1400 °C. The solid state reaction between Ir and Y2O3 is thermodynamically favorable above 1800 °C in a reductive carbon atmosphere. The reaction mechanism between Ir and Y2O3 was analyzed based on the Engel correlation between electronic configuration and structures of metals and alloy crystal structure.
Solid state reactions between Ir and SiC and between Ir and Y2O3 were studied. The thermodynamics and mechanism of solid state reaction were discussed. The results indicate that Ir reacts with SiC at 1000 °C to yield Ir3Si and graphitized carbon. The products of Ir silicide changes from Ir3Si and IrSi at 1200 °C to IrSi at 1400 °C. The solid state reaction between Ir and Y2O3 is thermodynamically favorable above 1800 °C in a reductive carbon atmosphere. The reaction mechanism between Ir and Y2O3 was analyzed based on the Engel correlation between electronic configuration and structures of metals and alloy crystal structure.
6 One-Step Synthesis, Characterization and Optical Property of Graphene-Silver Selenide Nanocomposites
2012, 41(7):1153-1155.
Abstract:
We report a facile and efficient strategy for the preparation of graphene-Ag2Se nanocomposites. The reduction of graphene oxide (GO) to graphene was accompanied by the formation of Ag2Se particles on the surface of graphene nanosheets. The results of X-ray diffraction (XRD) and Fourier transform infrared (FTIR) confirmed the efficient reduction of GO. Transmission electron microscopy (TEM) images of the sample revealed the morphology of the architecture of graphene-Ag2Se hybrid. Photoluminescence (PL) measurement was further employed to study the optical properties of the nanocomposites. The results show that the graphene-Ag2Se nanocomposites can be prepared by a simple hydrothermal method, and Ag2Se particles are well distributed on the graphene nanosheets.
We report a facile and efficient strategy for the preparation of graphene-Ag2Se nanocomposites. The reduction of graphene oxide (GO) to graphene was accompanied by the formation of Ag2Se particles on the surface of graphene nanosheets. The results of X-ray diffraction (XRD) and Fourier transform infrared (FTIR) confirmed the efficient reduction of GO. Transmission electron microscopy (TEM) images of the sample revealed the morphology of the architecture of graphene-Ag2Se hybrid. Photoluminescence (PL) measurement was further employed to study the optical properties of the nanocomposites. The results show that the graphene-Ag2Se nanocomposites can be prepared by a simple hydrothermal method, and Ag2Se particles are well distributed on the graphene nanosheets.
2012, 41(7):1156-1160.
Abstract:
The size, the distribution and the shape of secondary γ′ in powder metallurgy superalloy FGH95 were researched by field emission scanning electron microscopy, the alloy was long-term aged at 750 °C for 5000 h, in order to provide a theoretical basis for its application in newly aero-engines. The results show that with prolonging of the aging time, the morphological character of secondary γ' is unstable, and its size does not follow the law of LSW theory. During 0~500 h the splitting of reverse coarsening occurs in the second γ', resulting in splitting of a single butterfly precipitate into a group of eight cuboids. In 500~1000 h, the split γ′ coarsens to a certain extent and then start to split again after 1000 h. With prolonging of the aging time, they gradually grow after 2000 h, ellipsoidal secondary γ' phase become more and more. It is proved that the shape evolution strongly depends on the elastic interaction between γ' precipitates. Shape changes in order to minimize the sum of interfacial and elastic interaction energies.
The size, the distribution and the shape of secondary γ′ in powder metallurgy superalloy FGH95 were researched by field emission scanning electron microscopy, the alloy was long-term aged at 750 °C for 5000 h, in order to provide a theoretical basis for its application in newly aero-engines. The results show that with prolonging of the aging time, the morphological character of secondary γ' is unstable, and its size does not follow the law of LSW theory. During 0~500 h the splitting of reverse coarsening occurs in the second γ', resulting in splitting of a single butterfly precipitate into a group of eight cuboids. In 500~1000 h, the split γ′ coarsens to a certain extent and then start to split again after 1000 h. With prolonging of the aging time, they gradually grow after 2000 h, ellipsoidal secondary γ' phase become more and more. It is proved that the shape evolution strongly depends on the elastic interaction between γ' precipitates. Shape changes in order to minimize the sum of interfacial and elastic interaction energies.
2012, 41(7):1161-1165.
Abstract:
The porous ceramic layer was prepared on the surface of Ti6Al4V (TC4) alloy by a micro-arc oxidation (MAO) method. The electrochemical corrosion behaviors were investigated in the condition of Hank's simulated body fluid. The surface morphologies and phases were analyzed by SEM and XRD. The experimental results show that the free corrosion potential of MAO TC4 alloy increases by about 0.3 V, resulting in improving the chemical stability of TC4 alloy in the biological fluid environments. In the potential range of the titanium alloy implants, the MAO treatment can increase the polarization resistance and reduce the corrosion current by one to two orders-of-magnitude. With the increasing of the corrosion time, the passive film on the surface of TC4 alloy is gradually corroded in Hank's simulated body fluid. The nucleation and growth of HA is the most active part of the electrode reactions for MAO layer at the early immersion. After two weeks, the uniform HA film will form on the surface of MAO TC4 alloy, which shows the good electrochemical corrosion resistance.
The porous ceramic layer was prepared on the surface of Ti6Al4V (TC4) alloy by a micro-arc oxidation (MAO) method. The electrochemical corrosion behaviors were investigated in the condition of Hank's simulated body fluid. The surface morphologies and phases were analyzed by SEM and XRD. The experimental results show that the free corrosion potential of MAO TC4 alloy increases by about 0.3 V, resulting in improving the chemical stability of TC4 alloy in the biological fluid environments. In the potential range of the titanium alloy implants, the MAO treatment can increase the polarization resistance and reduce the corrosion current by one to two orders-of-magnitude. With the increasing of the corrosion time, the passive film on the surface of TC4 alloy is gradually corroded in Hank's simulated body fluid. The nucleation and growth of HA is the most active part of the electrode reactions for MAO layer at the early immersion. After two weeks, the uniform HA film will form on the surface of MAO TC4 alloy, which shows the good electrochemical corrosion resistance.
2012, 41(7):1166-1170.
Abstract:
Hot deformation behavior and constitutive model play fundamental roles in processing and simulation of materials. The analysis of the hot deformation behavior of titanium alloy TB6 shows that the strain rate influences the flow stress significantly and the effect of deformation temperature on flow stress is correlated with the strain rate. In this paper, the constitutive model was established based Arrhenius-type hyperbolic sine equation. The investigation on the influence of deformation condition on flow stress was carried out. The results show that the flow stress and force can be controlled by changing the strain rate and activation energy. This study provides a guideline for the control and simulation of plastic deformation of titanium alloy TB6.
Hot deformation behavior and constitutive model play fundamental roles in processing and simulation of materials. The analysis of the hot deformation behavior of titanium alloy TB6 shows that the strain rate influences the flow stress significantly and the effect of deformation temperature on flow stress is correlated with the strain rate. In this paper, the constitutive model was established based Arrhenius-type hyperbolic sine equation. The investigation on the influence of deformation condition on flow stress was carried out. The results show that the flow stress and force can be controlled by changing the strain rate and activation energy. This study provides a guideline for the control and simulation of plastic deformation of titanium alloy TB6.
2012, 41(7):1171-1175.
Abstract:
The yttria mould with diacetatozirconic acid as binder was introduced for directional solidification of TiAl alloy. The infiltration of Ti-47Al-2Cr-2Nb (at%) molten metal on the mould was evaluated and the mould contamination on the metal-alloy rods was investigated. The results indicate that the infiltration of alloy occurs on the inner layer of the mould only and no structural damage or exudate is observed after holding 30 min at 1550, 1600, 1650 °C, respectively. Two types of inclusions are explored in the alloy, they are Al2O3 and admixture inclusion composed of by Al2O3 and Y-Al-O and the scale and volume fraction of the inclusions significantly increase by rising of holding temperature. At 1650 °C for 30 min holding time, the foreign inclusions are distributed on the entire cross-section of the as-cast rod. The amount of the inclusions trend to decrease from the edge to the center of the rods at 1550, 1600 °C for 30 min. Moreover, on the region around 2500 μm to the surface of the as-cast rod at 1550 °C for 30 min, no obvious ceramic inclusion is discovered. The forming mechanism of inclusions in the alloy was analyzed.
The yttria mould with diacetatozirconic acid as binder was introduced for directional solidification of TiAl alloy. The infiltration of Ti-47Al-2Cr-2Nb (at%) molten metal on the mould was evaluated and the mould contamination on the metal-alloy rods was investigated. The results indicate that the infiltration of alloy occurs on the inner layer of the mould only and no structural damage or exudate is observed after holding 30 min at 1550, 1600, 1650 °C, respectively. Two types of inclusions are explored in the alloy, they are Al2O3 and admixture inclusion composed of by Al2O3 and Y-Al-O and the scale and volume fraction of the inclusions significantly increase by rising of holding temperature. At 1650 °C for 30 min holding time, the foreign inclusions are distributed on the entire cross-section of the as-cast rod. The amount of the inclusions trend to decrease from the edge to the center of the rods at 1550, 1600 °C for 30 min. Moreover, on the region around 2500 μm to the surface of the as-cast rod at 1550 °C for 30 min, no obvious ceramic inclusion is discovered. The forming mechanism of inclusions in the alloy was analyzed.
2012, 41(7):1176-1180.
Abstract:
The microstructure evolution and morphologies of Ti-6Al-4V alloy fracture after superplastic tensile testing were investigated by the optical microscope and the scanning electron microscope. The results show that, the ultrafine-grained Ti-6Al-4V alloy displays quasi ductile fracture in room temperature testing, while the ductile dimples-voids gathered type fracture in the superplastic tensile testing. In the same initial strain-rate, the grains dimension and β phase contents increase, and the voids decrease with increasing of the tensile temperature. From 840 °C to 930 °C, the grains still retain in equiaxed state. At the higher temperature (960 °C), the grains are coarsed and exhibit lamellar crystal at some sections. At the same tensile temperature, the grains dimension and β phase contents increase and the voids decrease with decreasing of the initial strain-rate. At elevated temperature (above 960 °C), β phases have good plasticity and low hardness. More β phase contents are favorable to the grain boundary sliding and the voids are difficult to generate.
The microstructure evolution and morphologies of Ti-6Al-4V alloy fracture after superplastic tensile testing were investigated by the optical microscope and the scanning electron microscope. The results show that, the ultrafine-grained Ti-6Al-4V alloy displays quasi ductile fracture in room temperature testing, while the ductile dimples-voids gathered type fracture in the superplastic tensile testing. In the same initial strain-rate, the grains dimension and β phase contents increase, and the voids decrease with increasing of the tensile temperature. From 840 °C to 930 °C, the grains still retain in equiaxed state. At the higher temperature (960 °C), the grains are coarsed and exhibit lamellar crystal at some sections. At the same tensile temperature, the grains dimension and β phase contents increase and the voids decrease with decreasing of the initial strain-rate. At elevated temperature (above 960 °C), β phases have good plasticity and low hardness. More β phase contents are favorable to the grain boundary sliding and the voids are difficult to generate.
2012, 41(7):1181-1185.
Abstract:
Anodized films were prepared on AZ31 magnesium alloy. The forming process of the anodized films was studied by electrochemical impedance spectroscopy (EIS) measurements. The results show that a significant regularity appears among electrochemical impedance spectra for oxide films obtained from various oxide time; their forming can be divided into four stages. There are significant differences among stages. The equivalent electrical circuit R(C(R (QR))) (CR) was used to analyze the EIS data. The fitting results show that the number of pores and roughness of the film increase with increasing of the oxide time. The growth of barrier layer and porous layer is not synchronized while their growth is in the dynamic change.
Anodized films were prepared on AZ31 magnesium alloy. The forming process of the anodized films was studied by electrochemical impedance spectroscopy (EIS) measurements. The results show that a significant regularity appears among electrochemical impedance spectra for oxide films obtained from various oxide time; their forming can be divided into four stages. There are significant differences among stages. The equivalent electrical circuit R(C(R (QR))) (CR) was used to analyze the EIS data. The fitting results show that the number of pores and roughness of the film increase with increasing of the oxide time. The growth of barrier layer and porous layer is not synchronized while their growth is in the dynamic change.
2012, 41(7):1186-1190.
Abstract:
TiNi/Ti2Ni alloyed layer was prepared on surface of Ti6Al4V alloy by plasma surface alloying process. Surface morphology, composition distribution, cross-section morphology and phase structure of Ni modified layer were analyzed. Sliding dry friction performance of TiNi/Ti2Ni alloyed layer was observed and analyzed under different loads by Pin-on-disc test, and compared with the TC4 substrate. The results indicate that the wear mechanism of both TiNi/Ti2Ni alloyed layer and the TC4 substrate shows abrasion wear. Under the same wear condition, the friction coefficient of TiNi/Ti2Ni alloyed layer is slightly lower than that of the TC4 substrate, the wear resistance of TiNi/Ti2Ni alloyed layer is better than that of TC4 substrate. Friction coefficients under different loads fluctuate between 0.29~0.33 and wear rate increases with increasing of load.
TiNi/Ti2Ni alloyed layer was prepared on surface of Ti6Al4V alloy by plasma surface alloying process. Surface morphology, composition distribution, cross-section morphology and phase structure of Ni modified layer were analyzed. Sliding dry friction performance of TiNi/Ti2Ni alloyed layer was observed and analyzed under different loads by Pin-on-disc test, and compared with the TC4 substrate. The results indicate that the wear mechanism of both TiNi/Ti2Ni alloyed layer and the TC4 substrate shows abrasion wear. Under the same wear condition, the friction coefficient of TiNi/Ti2Ni alloyed layer is slightly lower than that of the TC4 substrate, the wear resistance of TiNi/Ti2Ni alloyed layer is better than that of TC4 substrate. Friction coefficients under different loads fluctuate between 0.29~0.33 and wear rate increases with increasing of load.
2012, 41(7):1191-1195.
Abstract:
Effects of solution annealing and aging on tensile property and microstructure of Ti-50.8Ni-0.3Cr shape memory alloy were investigated by tensile test and transmission electron microcopy. The plasticity of 800 °C solution annealed alloy is better than that of aged alloy. With increasing of the aging time tag, the tensile strengths Rm300 and Rm400 of 300 and 400 °C aged alloys increase sharply firstly and then tend to stabilizing, and Rm300 < Rm400; the elongation A300 and A400 decrease sharply firstly and then tend to stabilizing. After aging at 500 °C, the Rm500 decreases sharply firstly and then tend to stabilizing, the A500 increases sharply firstly and then tend to stabilizing. With increasing of tag, the critical stresses of inducing Martensitic transformation RM300 and RM400 for 300 and 400 °C aged alloys decrease gradually, while RM500 firstly decreases, then sharply increases, at last decrease gradually again, and the maximum of RM500 is reached at tag=5~10 h. Furthermore, with increasing of tag, the morphology of Ti3Ni4 precipitates of 300 °C aged alloy displays fine particle dispersed microstructure; the morphology of Ti3Ni4 precipitates of 400 °C aged alloy evolves from particle shape to the lenticular; the morphology of Ti3Ni4 precipitates of 500 °C aged alloy evolves from lenticular shape to needle to plate shape. The influence of the aging temperature on the morphology of Ti3Ni4 precipitates is more significant than that of the aging time.
Effects of solution annealing and aging on tensile property and microstructure of Ti-50.8Ni-0.3Cr shape memory alloy were investigated by tensile test and transmission electron microcopy. The plasticity of 800 °C solution annealed alloy is better than that of aged alloy. With increasing of the aging time tag, the tensile strengths Rm300 and Rm400 of 300 and 400 °C aged alloys increase sharply firstly and then tend to stabilizing, and Rm300 < Rm400; the elongation A300 and A400 decrease sharply firstly and then tend to stabilizing. After aging at 500 °C, the Rm500 decreases sharply firstly and then tend to stabilizing, the A500 increases sharply firstly and then tend to stabilizing. With increasing of tag, the critical stresses of inducing Martensitic transformation RM300 and RM400 for 300 and 400 °C aged alloys decrease gradually, while RM500 firstly decreases, then sharply increases, at last decrease gradually again, and the maximum of RM500 is reached at tag=5~10 h. Furthermore, with increasing of tag, the morphology of Ti3Ni4 precipitates of 300 °C aged alloy displays fine particle dispersed microstructure; the morphology of Ti3Ni4 precipitates of 400 °C aged alloy evolves from particle shape to the lenticular; the morphology of Ti3Ni4 precipitates of 500 °C aged alloy evolves from lenticular shape to needle to plate shape. The influence of the aging temperature on the morphology of Ti3Ni4 precipitates is more significant than that of the aging time.
2012, 41(7):1196-1022.
Abstract:
The Zr64.2Ni16.2Cu14.6Al5 and Zr63.4Ni16.2Cu15.4Al5 bulk amorphous alloys with heterogeneous structures were prepared through copper mould casting. The microstructures and thermal stabilities of two Zr-based bulk amorphous alloys were investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Compared with homogenous structure Zr65A10lNi10Cu15 bulk amorphous alloys, heterogeneous structure decreases alloy thermal stability. The two Zr-based bulk amorphous alloys exhibit large plastic strain (>25%) and high yield strength (>1.6 GPa) under uniaxial compression tests. The low potential-energy barrier of shear transition zones (STZs) and the high resistance of the shear bands propagation are regarded as the main reason of increasing of plasticity in the bulk amorphous alloy with heterostructure.
The Zr64.2Ni16.2Cu14.6Al5 and Zr63.4Ni16.2Cu15.4Al5 bulk amorphous alloys with heterogeneous structures were prepared through copper mould casting. The microstructures and thermal stabilities of two Zr-based bulk amorphous alloys were investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Compared with homogenous structure Zr65A10lNi10Cu15 bulk amorphous alloys, heterogeneous structure decreases alloy thermal stability. The two Zr-based bulk amorphous alloys exhibit large plastic strain (>25%) and high yield strength (>1.6 GPa) under uniaxial compression tests. The low potential-energy barrier of shear transition zones (STZs) and the high resistance of the shear bands propagation are regarded as the main reason of increasing of plasticity in the bulk amorphous alloy with heterostructure.
2012, 41(7):1201-1205.
Abstract:
The high cycle fatigue of 6156 aluminum alloy was investigated under the conditions of different orientations and stress concentration factor. In addition, the microstructures and the fatigue fracture surfaces of the alloy were examined by optical, transmission and scanning electron microscopy. The results show that the effect of different orientations on the fatigue life of 6156 aluminum alloy is rather little and the fatigue life of Kt=1 is longer than that of Kt = 3, exhibiting notch sensitivity. The second phase particles play a key role during fatigue crack initiation, and most part of the cracks originate from the coarse particles on the surface or from the interface between the second phase particles and matrix.
The high cycle fatigue of 6156 aluminum alloy was investigated under the conditions of different orientations and stress concentration factor. In addition, the microstructures and the fatigue fracture surfaces of the alloy were examined by optical, transmission and scanning electron microscopy. The results show that the effect of different orientations on the fatigue life of 6156 aluminum alloy is rather little and the fatigue life of Kt=1 is longer than that of Kt = 3, exhibiting notch sensitivity. The second phase particles play a key role during fatigue crack initiation, and most part of the cracks originate from the coarse particles on the surface or from the interface between the second phase particles and matrix.
2012, 41(7):1206-1210.
Abstract:
The effects of different strain ways (tension, bend and compression) on the formation and propagation of micro-cracks and critical current of Bi-2223/Ag superconducting tapes were studied. The results show an obviously differences on the critical strain values of the tapes under various strain ways are presented. Moreover, the propagation ways of the micro-cracks in the superconductor filaments are quite different: the micro-cracks form at the surface and then spread to the center in the bending samples, while the formation of the cracks are at random in the tensile samples. The formation mechanism of micro-cracks in the filaments was mainly discussed. It is found that multitudes of transversal and rolling direction micro-cracks form under tensile deformation. However, predominantly rolling direction micro-cracks and little transversal micro-cracks are found under compressive deformation. It is the interaction of the above mentioned two types of the micro-cracks that leads the degradation of Ic of the tapes.
The effects of different strain ways (tension, bend and compression) on the formation and propagation of micro-cracks and critical current of Bi-2223/Ag superconducting tapes were studied. The results show an obviously differences on the critical strain values of the tapes under various strain ways are presented. Moreover, the propagation ways of the micro-cracks in the superconductor filaments are quite different: the micro-cracks form at the surface and then spread to the center in the bending samples, while the formation of the cracks are at random in the tensile samples. The formation mechanism of micro-cracks in the filaments was mainly discussed. It is found that multitudes of transversal and rolling direction micro-cracks form under tensile deformation. However, predominantly rolling direction micro-cracks and little transversal micro-cracks are found under compressive deformation. It is the interaction of the above mentioned two types of the micro-cracks that leads the degradation of Ic of the tapes.
2012, 41(7):1211-1215.
Abstract:
A Ta-W alloy coating was deposited on pure Ta plate by coaxial laser cladding, using tungsten powder as cladding material. The microstructure of the coating was analyzed by scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS). The microhardness was examined by hardness tester. The high temperature hypersonic flow ablation property was tested in the wind tunnel system. It is found that the coating is metallurgically bonded with the substrate. The clad layer has a microstructure consisting of dendrite Ta-W solid solution uniformly dispersed in the Ta matrix. The average microhardness of the clad layer is approximately 8 GPa and it is 5 times greater than that of the Ta substrate. The ablative property is also obviously improved.
A Ta-W alloy coating was deposited on pure Ta plate by coaxial laser cladding, using tungsten powder as cladding material. The microstructure of the coating was analyzed by scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS). The microhardness was examined by hardness tester. The high temperature hypersonic flow ablation property was tested in the wind tunnel system. It is found that the coating is metallurgically bonded with the substrate. The clad layer has a microstructure consisting of dendrite Ta-W solid solution uniformly dispersed in the Ta matrix. The average microhardness of the clad layer is approximately 8 GPa and it is 5 times greater than that of the Ta substrate. The ablative property is also obviously improved.
19 Study on the Effect of Elastic Strain Energy on the Ordering Process of Ni-Al Alloy by Phase-Field
2012, 41(7):1216-1220.
Abstract:
Using the phase-field microelasticity model, we studied the effect of elastic strain energy (ESE) resulted from the precipitation misfit on the ordering process of γ′ (Ni3Al) phase. The simulation results show that ESE always presents impediment effect for different precipitation mechanisms, such as non-classical nucleation, the mixed style of non-classical nucleation and spinodal decomposition, spinodal ordering; and slows down the occupation probability (OP) of Al atom at β site, and impedes the ordering process. At the same time step, the height and the width of the concentration and long-range order parameter (LROP) are small in the system involving ESE.ESE changes the spatial arrangement and microstructure, and leads to the preferred orientation microstructure.
Using the phase-field microelasticity model, we studied the effect of elastic strain energy (ESE) resulted from the precipitation misfit on the ordering process of γ′ (Ni3Al) phase. The simulation results show that ESE always presents impediment effect for different precipitation mechanisms, such as non-classical nucleation, the mixed style of non-classical nucleation and spinodal decomposition, spinodal ordering; and slows down the occupation probability (OP) of Al atom at β site, and impedes the ordering process. At the same time step, the height and the width of the concentration and long-range order parameter (LROP) are small in the system involving ESE.ESE changes the spatial arrangement and microstructure, and leads to the preferred orientation microstructure.
2012, 41(7):1221-1225.
Abstract:
The influence of the springback in high strength TA18 tubes on the wall thinning and section distortion under different process parameters was investigated using ABAQUS Explicit/Standard finite element models. The results show that the wall thinning ratios after unloading-springback are less than 10% under different process parameters for high strength TA18 tubes, while the section distortion ratios after springback are more than 35%, even 60% except a few measured points. The "platform" of section distortion ratio at stable forming zone disappears after springback.
The influence of the springback in high strength TA18 tubes on the wall thinning and section distortion under different process parameters was investigated using ABAQUS Explicit/Standard finite element models. The results show that the wall thinning ratios after unloading-springback are less than 10% under different process parameters for high strength TA18 tubes, while the section distortion ratios after springback are more than 35%, even 60% except a few measured points. The "platform" of section distortion ratio at stable forming zone disappears after springback.
2012, 41(7):1226-1230.
Abstract:
The oxidation behavior of Ti600 alloy at high temperature was investigated. Thermodynamic and dynamic laws were studied by means of calculating the oxidation mass gain, oxidation rate constants and activities. The phase structure and morphology of oxidation scales on surface were examined with XRD and SEM. The element distribution profile along cross-section of the oxidation layer was studied by EDS to understand the diffusion behavior. The results indicate that Ti600 alloy exhibits the parabolic rule of oxidation rate at 600~700 ℃, but obeys the parabolic-linear rule at 750 ℃. The oxidation scales are composed of TiO2 and Al2O3.
The oxidation behavior of Ti600 alloy at high temperature was investigated. Thermodynamic and dynamic laws were studied by means of calculating the oxidation mass gain, oxidation rate constants and activities. The phase structure and morphology of oxidation scales on surface were examined with XRD and SEM. The element distribution profile along cross-section of the oxidation layer was studied by EDS to understand the diffusion behavior. The results indicate that Ti600 alloy exhibits the parabolic rule of oxidation rate at 600~700 ℃, but obeys the parabolic-linear rule at 750 ℃. The oxidation scales are composed of TiO2 and Al2O3.
2012, 41(7):1231-1234.
Abstract:
To further improve the performance of TC4 alloy, especially corrosion resistance to the seawater, 1wt%, 2wt% Cu and 1wt% Ag were added into TC4 alloy to fabricate three kinds of alloys of TC4-Cu and TC4-Ag with VAR. The corrosion behavior and characteristics of different kinds of alloys in artificial seawater were researched by electrochemical methods. The result shows that the corrosion potentials of TC4 with addition of Cu and Ag are raised and their corrosion currents are decreased, so the corrosion resistance of TC4 alloy can be improved effectively.
To further improve the performance of TC4 alloy, especially corrosion resistance to the seawater, 1wt%, 2wt% Cu and 1wt% Ag were added into TC4 alloy to fabricate three kinds of alloys of TC4-Cu and TC4-Ag with VAR. The corrosion behavior and characteristics of different kinds of alloys in artificial seawater were researched by electrochemical methods. The result shows that the corrosion potentials of TC4 with addition of Cu and Ag are raised and their corrosion currents are decreased, so the corrosion resistance of TC4 alloy can be improved effectively.
2012, 41(7):1235-1238.
Abstract:
Ti interlayer was selected for the bonding of tungsten to CuCrZr alloy. The effects of bonding temperature on the microstructures and shear strength of the joints were investigated. The results show that the brittle intermetallic compound of diffusion layers significantly effect the strength of the joint. The molten is formed due to eutectic reaction between Ti and Cu at 1030 °C, most part of the molten is extruded out from the bonding zone, where a little amount of intermetallic compound is remained in the interfacial layer, resulting in increasing of joint strength. The shearing strength of the joint is even higher than that of W substrate.
Ti interlayer was selected for the bonding of tungsten to CuCrZr alloy. The effects of bonding temperature on the microstructures and shear strength of the joints were investigated. The results show that the brittle intermetallic compound of diffusion layers significantly effect the strength of the joint. The molten is formed due to eutectic reaction between Ti and Cu at 1030 °C, most part of the molten is extruded out from the bonding zone, where a little amount of intermetallic compound is remained in the interfacial layer, resulting in increasing of joint strength. The shearing strength of the joint is even higher than that of W substrate.
2012, 41(7):1239-1242.
Abstract:
The performance evaluation and the control methods of high strength TA18 alloy tubes were investigated. The pole-figures, inverse pole-figures and orientation distribution function were measured and calculated by X-ray diffraction technique and used to characterize the textures in tubes. The textures and properties of domestic and abroad tubes were evaluated. It is found that the {0001}<100> texture is commonly dominant in high performance tubes. The test methods of contractile strain ratio (CSR) were presented. The relationship between CSR and other properties was discussed. The performance control method by controlling ratio of wall reduction to diameter decrease (Q) was put forward for Ti alloy tubes. Results show that increasing of the Q can increase the radial texture in Ti alloy tubes and enhance the value of CSR, resulting in improving the performance of the tubes.
The performance evaluation and the control methods of high strength TA18 alloy tubes were investigated. The pole-figures, inverse pole-figures and orientation distribution function were measured and calculated by X-ray diffraction technique and used to characterize the textures in tubes. The textures and properties of domestic and abroad tubes were evaluated. It is found that the {0001}<100> texture is commonly dominant in high performance tubes. The test methods of contractile strain ratio (CSR) were presented. The relationship between CSR and other properties was discussed. The performance control method by controlling ratio of wall reduction to diameter decrease (Q) was put forward for Ti alloy tubes. Results show that increasing of the Q can increase the radial texture in Ti alloy tubes and enhance the value of CSR, resulting in improving the performance of the tubes.
2012, 41(7):1243-1246.
Abstract:
The textures of homemade cold rolled Ti-3Al-2.5V alloy tubes with the diameter of 6 mm were investigated. The textures were measured by means of pole figure technique of X-ray diffraction. Meanwhile, the components and intensity of textures of the imported commercially aviational tubes with the same diameter were measured and compared to those of the homemade tubes. The difficulty of the inable revision of the shape effect on X-ray diffraction intensity was solved by the method of thinning and flattening, resulting in realizing of the accurate measurement of the tube texture. The experimental results show that the textures type of domestic and imported tubes are the similar. Main type of texture is that the included angle between the crystal orientation [0002] and radial direction of tube is 24°, meanwhile the crystal orientation [100] is parallel to the axial direction of tubes. However, the texture intensity difference between domestic and imported tubes is remarkable. The quantitative value of the latter is twice as much as that of the former. Thus inceasing of the texture intensity and reducing of dispersion degree are an important factor of improving the properties of domestic tubes.
The textures of homemade cold rolled Ti-3Al-2.5V alloy tubes with the diameter of 6 mm were investigated. The textures were measured by means of pole figure technique of X-ray diffraction. Meanwhile, the components and intensity of textures of the imported commercially aviational tubes with the same diameter were measured and compared to those of the homemade tubes. The difficulty of the inable revision of the shape effect on X-ray diffraction intensity was solved by the method of thinning and flattening, resulting in realizing of the accurate measurement of the tube texture. The experimental results show that the textures type of domestic and imported tubes are the similar. Main type of texture is that the included angle between the crystal orientation [0002] and radial direction of tube is 24°, meanwhile the crystal orientation [100] is parallel to the axial direction of tubes. However, the texture intensity difference between domestic and imported tubes is remarkable. The quantitative value of the latter is twice as much as that of the former. Thus inceasing of the texture intensity and reducing of dispersion degree are an important factor of improving the properties of domestic tubes.
2012, 41(7):1247-1250.
Abstract:
The TiAl alloy was brazed to Si3N4f/Si3N4 composite using AgCuTi filler metal. The typical interfacial microstructure of the joint is TiAl/AlCuTi reaction layer/Ag based solid solution/TiN reaction layer/Si3N4f/Si3N4. During the brazing process, liquid solder wets the surfaces of Si3N4f/Si3N4 composite well, and the active element Ti reacts with Si3N4 matrix and fibers to form continuous TiN compounds layer. The amount of brittle AlCuTi intermetallics increases when the brazing temperature is much higher or the brazing time is much longer. Some microcracks form in AlCuTi intermetallics due to the residual stress in the joint, which seriously degrade the joining properties. A maximum of 9.4 MPa of the shear strength can be obtained when the brazing temperature T=860 °C and holding time t=5 min, which exceeds 60% of the strength of composite materials. Fracture analysis shows that fracture occurs in the side of Si3N4f/Si3N4 composite.
The TiAl alloy was brazed to Si3N4f/Si3N4 composite using AgCuTi filler metal. The typical interfacial microstructure of the joint is TiAl/AlCuTi reaction layer/Ag based solid solution/TiN reaction layer/Si3N4f/Si3N4. During the brazing process, liquid solder wets the surfaces of Si3N4f/Si3N4 composite well, and the active element Ti reacts with Si3N4 matrix and fibers to form continuous TiN compounds layer. The amount of brittle AlCuTi intermetallics increases when the brazing temperature is much higher or the brazing time is much longer. Some microcracks form in AlCuTi intermetallics due to the residual stress in the joint, which seriously degrade the joining properties. A maximum of 9.4 MPa of the shear strength can be obtained when the brazing temperature T=860 °C and holding time t=5 min, which exceeds 60% of the strength of composite materials. Fracture analysis shows that fracture occurs in the side of Si3N4f/Si3N4 composite.
2012, 41(7):1251-1254.
Abstract:
The magnetic viscosity of the bulk amorphous Nd60-xPrxFe30Al10 (x=0, 9, 15) alloys were investigated, and the coercivity mechanism was discussed. The results show that the bulk amorphous Nd60-xPrxFe30Al10 (x=0, 9, 15) alloys present hard magnetic behavior at room temperature. The intrinsic coercivity of the bulk amorphous decreases with increasing of the Pr addition from 0at% to 15at%. A single sharp and narrow peak close to the coercivity appears in the irreversible susceptibility (χirr) curve for each alloy. The addition of Pr has little influence on the magnetic viscosity of the alloys. With the substitution of Pr for Nd, the fluctuation field Hf decreases from 11.1 mT to 9.9 mT, and the activation volume Va increases from 2.6×10-18 cm3 to 2.9×10-18 cm3, which leads to an increase of the activation diameter Da from 17.1 nm to 17.7 nm. The value of Da deduced from the magnetic viscosity measurements is similar to the size of clusters of Nd-based bulk amorphous alloys, which may be responsible for the hard magnetic property exhibited at room temperature.
The magnetic viscosity of the bulk amorphous Nd60-xPrxFe30Al10 (x=0, 9, 15) alloys were investigated, and the coercivity mechanism was discussed. The results show that the bulk amorphous Nd60-xPrxFe30Al10 (x=0, 9, 15) alloys present hard magnetic behavior at room temperature. The intrinsic coercivity of the bulk amorphous decreases with increasing of the Pr addition from 0at% to 15at%. A single sharp and narrow peak close to the coercivity appears in the irreversible susceptibility (χirr) curve for each alloy. The addition of Pr has little influence on the magnetic viscosity of the alloys. With the substitution of Pr for Nd, the fluctuation field Hf decreases from 11.1 mT to 9.9 mT, and the activation volume Va increases from 2.6×10-18 cm3 to 2.9×10-18 cm3, which leads to an increase of the activation diameter Da from 17.1 nm to 17.7 nm. The value of Da deduced from the magnetic viscosity measurements is similar to the size of clusters of Nd-based bulk amorphous alloys, which may be responsible for the hard magnetic property exhibited at room temperature.
2012, 41(7):1255-1258.
Abstract:
Nanocrystalline Ti powder was prepared using cryogenic mechanical milling. The evolution of morphologies and structures for Ti powder during cryomilling were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The experimental results show that the particle sizes decrease from original 45 mm to 5 mm after 8 h cryomilling. Embrittlement cracking is the dominating way of the refinement for Ti particles. The time required for preparing nanocrystalline Ti powder by cryomilling technique is only 8 h.
Nanocrystalline Ti powder was prepared using cryogenic mechanical milling. The evolution of morphologies and structures for Ti powder during cryomilling were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The experimental results show that the particle sizes decrease from original 45 mm to 5 mm after 8 h cryomilling. Embrittlement cracking is the dominating way of the refinement for Ti particles. The time required for preparing nanocrystalline Ti powder by cryomilling technique is only 8 h.
29 Microstructure and Wear Resistance of TiCp/Ti Composite Coating on TC4 Alloy by Argon Arc Cladding
2012, 41(7):1259-1262.
Abstract:
Ti-based composite coating reinforced by TiC particles was prepared on the surface of TC4 alloy by means of argon arc cladding technique using the pre-alloyed powder of TiC and Ti. The microstructure of the coating was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectrum (EDS). Microhardness and wear resistance at room temperature of the composite coating were examined by means of microhardness tester and wear tester, respectively. The results indicate that the coating microstructure is uniform and dense, and excellent bonding exists between the coating and the TC4 alloy substrate. The coating has a great quantity of dendrite TiC and lump shaped TiC particles. The composite coating reinforced by TiC particle apparently improves surface hardness of TC4 alloy, the average microhardness can reach 9 GPa. The wear mechanism of coatings results from abrasive wear and slight adhesive wear.
Ti-based composite coating reinforced by TiC particles was prepared on the surface of TC4 alloy by means of argon arc cladding technique using the pre-alloyed powder of TiC and Ti. The microstructure of the coating was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectrum (EDS). Microhardness and wear resistance at room temperature of the composite coating were examined by means of microhardness tester and wear tester, respectively. The results indicate that the coating microstructure is uniform and dense, and excellent bonding exists between the coating and the TC4 alloy substrate. The coating has a great quantity of dendrite TiC and lump shaped TiC particles. The composite coating reinforced by TiC particle apparently improves surface hardness of TC4 alloy, the average microhardness can reach 9 GPa. The wear mechanism of coatings results from abrasive wear and slight adhesive wear.
2012, 41(7):1263-1266.
Abstract:
LiFePO4/C cathode materials were synthesized by carbothermal reduction method, using Fe2O3, LiH2PO4 as starting materials, glueose as carbon source. The effect of the amount of lithium in reactant on the electrochemical properties of LiFePO4/C cathode materials was investigated. The structure, morphology and electrochemical properties of LiFePO4/C were analyzed by XRD, SEM and galvanostatic charge-discharge method and cyclic voltammetry (CV), respectively. The results indicate that when excess additional amount of lithium element is 10% of theoretical value, the sample has optimal electrochemical properties and exhibits a initial discharge capacity of 156.3 and 137.5 mAh/g at 0.2 and 1 C (1 C=170 mA/g) rates, respectively, there is no significant capacity fade after 20 cycles.
LiFePO4/C cathode materials were synthesized by carbothermal reduction method, using Fe2O3, LiH2PO4 as starting materials, glueose as carbon source. The effect of the amount of lithium in reactant on the electrochemical properties of LiFePO4/C cathode materials was investigated. The structure, morphology and electrochemical properties of LiFePO4/C were analyzed by XRD, SEM and galvanostatic charge-discharge method and cyclic voltammetry (CV), respectively. The results indicate that when excess additional amount of lithium element is 10% of theoretical value, the sample has optimal electrochemical properties and exhibits a initial discharge capacity of 156.3 and 137.5 mAh/g at 0.2 and 1 C (1 C=170 mA/g) rates, respectively, there is no significant capacity fade after 20 cycles.
2012, 41(7):1267-1272.
Abstract:
The effects of solution cooling rate on γ′ precipitation and microhardness of a novel nickel-based powder metallurgy (P/M) superalloy FGH98Ⅰin superslovus and superslovus plus subslovus post treatment condition were studied by means of field emission scanning electron microscope (FESEM) and microhardness tester. The results show that the average sizes of secondary and tertiary γ' precipitates decrease with increasing of the cooling rate. Meanwhile, the shape of secondary γ' precipitates changes from the butterfly-like to the spherical, the shape factor and particle density increase, while the area fraction and the apparent width of the grain boundary decrease. It is also found that γ′ phases nucleate and precipitate in two stages if the cooling rate is not faster than 1.4 °C/s. The faster the cooling rate is, the higher the hardness is, and the more the hardness increases are after aging. Subslovus post-heat treatment makes the cooling γ' phases coarser and more cubic, decreases the shape factor, eliminates the γ′ precipitates-riched grain boundary and lowers the microhardness. In addition, the average sizes of γ′ phases and the hardness as a function of cooling rate are established. The above results can be used as a theoretical reference for the selection of actual superslovus processing of FGH98Ⅰdual-property disk.
The effects of solution cooling rate on γ′ precipitation and microhardness of a novel nickel-based powder metallurgy (P/M) superalloy FGH98Ⅰin superslovus and superslovus plus subslovus post treatment condition were studied by means of field emission scanning electron microscope (FESEM) and microhardness tester. The results show that the average sizes of secondary and tertiary γ' precipitates decrease with increasing of the cooling rate. Meanwhile, the shape of secondary γ' precipitates changes from the butterfly-like to the spherical, the shape factor and particle density increase, while the area fraction and the apparent width of the grain boundary decrease. It is also found that γ′ phases nucleate and precipitate in two stages if the cooling rate is not faster than 1.4 °C/s. The faster the cooling rate is, the higher the hardness is, and the more the hardness increases are after aging. Subslovus post-heat treatment makes the cooling γ' phases coarser and more cubic, decreases the shape factor, eliminates the γ′ precipitates-riched grain boundary and lowers the microhardness. In addition, the average sizes of γ′ phases and the hardness as a function of cooling rate are established. The above results can be used as a theoretical reference for the selection of actual superslovus processing of FGH98Ⅰdual-property disk.
2012, 41(7):1273-1278.
Abstract:
The superfine pure tungsten powder with a BET particle size of 0.21 μm was prepared by sol spray drying-calcination-hydrogen reduction process, and then it was treated by ball-milling activation. The changes of the morphology as well as other performance characteristics of the superfine pure tungsten powder with the increasing of ball-milling time were investigated, the sintering densification technologies of the as-received powder, the powders ball-milled for 5 h and 10 h, respectively, were explored. Additionally, the rules of properties changes such as the microstructure morphology, the grain size and the microhardness of the pure tungsten sintered body with sintering temperature and ball-milling time were studied in detail. Results show that the ball-milling treatment plays a great activation role in sintering of the superfine pure tungsten powder. When the green compact prepared by the powder milled for 10 h is sintered at 1900 °C for 2 h, the relative density of the sintered compact can reach 97.3%, the sinter temperature reduces by more 600 °C compared to that required for sintering the traditional micro scale powder compact. At the same time, ball-milling treatment can reduce the onset sintering temperature as well as recrystallization temperature substantially, so the sintered tungsten compact with much uniformer and finer microstructure and much better mechanical properties (hardness) can be obtained.
The superfine pure tungsten powder with a BET particle size of 0.21 μm was prepared by sol spray drying-calcination-hydrogen reduction process, and then it was treated by ball-milling activation. The changes of the morphology as well as other performance characteristics of the superfine pure tungsten powder with the increasing of ball-milling time were investigated, the sintering densification technologies of the as-received powder, the powders ball-milled for 5 h and 10 h, respectively, were explored. Additionally, the rules of properties changes such as the microstructure morphology, the grain size and the microhardness of the pure tungsten sintered body with sintering temperature and ball-milling time were studied in detail. Results show that the ball-milling treatment plays a great activation role in sintering of the superfine pure tungsten powder. When the green compact prepared by the powder milled for 10 h is sintered at 1900 °C for 2 h, the relative density of the sintered compact can reach 97.3%, the sinter temperature reduces by more 600 °C compared to that required for sintering the traditional micro scale powder compact. At the same time, ball-milling treatment can reduce the onset sintering temperature as well as recrystallization temperature substantially, so the sintered tungsten compact with much uniformer and finer microstructure and much better mechanical properties (hardness) can be obtained.
2012, 41(7):1279-1283.
Abstract:
The experiment of nickel electroforming with non-ionic surfactant was carried out under supercritical CO2 fluid. The effects of current density on microstructure, Vickers hardness, current efficiency, depositing rate and thickness were discussed. The results indicate that the microhardness, the depositing rate, the thickness of the nickel films gradually increase while the current efficiency decreases with the current density growing from 3 A/dm2 to 9 A/dm2. In the cases of 10 MPa, 323 K and 5 A/dm2, the microhardness, the current efficiency, the depositing rate and the thickness of nickel films are 7.01 GPa, 94.51%, 51.85 mg/cm2·h and 30.5 μm, respectively. Compared to the conventional electroforming method, the nickel film by SCF-CO2 electroforming has more flat surface and more dense microstructure.
The experiment of nickel electroforming with non-ionic surfactant was carried out under supercritical CO2 fluid. The effects of current density on microstructure, Vickers hardness, current efficiency, depositing rate and thickness were discussed. The results indicate that the microhardness, the depositing rate, the thickness of the nickel films gradually increase while the current efficiency decreases with the current density growing from 3 A/dm2 to 9 A/dm2. In the cases of 10 MPa, 323 K and 5 A/dm2, the microhardness, the current efficiency, the depositing rate and the thickness of nickel films are 7.01 GPa, 94.51%, 51.85 mg/cm2·h and 30.5 μm, respectively. Compared to the conventional electroforming method, the nickel film by SCF-CO2 electroforming has more flat surface and more dense microstructure.
2012, 41(7):1284-1288.
Abstract:
The effects of temperature and time of microwave sintering on the microstructure and properties of powder extruded rods of W-based alloy were studied. Fracture morphologies and microstructures were examined by SEM and optical microscope, respectively. The relative density, the tensile strength, the elongation and the hardness of samples were measured and analyzed. The results show that when microwave sintering time is 30 min, the properties of samples change as a peak shape with the increase of sintering temperature. Upon sintered at 1550 °C, relative density, the tensile strength, the elongation and the hardness of the samples reach the maximum values of 98.3%, 920 MPa, 9.7% and 30.5, respectively. When the microwave sintering temperature is 1550 °C, the mechanical properties of samples increase firstly and then decrease with the increase of sintering time. The size of tungsten grains increases gradually with increasing of microwave sintering temperature and prolonging of microwave sintering time.
The effects of temperature and time of microwave sintering on the microstructure and properties of powder extruded rods of W-based alloy were studied. Fracture morphologies and microstructures were examined by SEM and optical microscope, respectively. The relative density, the tensile strength, the elongation and the hardness of samples were measured and analyzed. The results show that when microwave sintering time is 30 min, the properties of samples change as a peak shape with the increase of sintering temperature. Upon sintered at 1550 °C, relative density, the tensile strength, the elongation and the hardness of the samples reach the maximum values of 98.3%, 920 MPa, 9.7% and 30.5, respectively. When the microwave sintering temperature is 1550 °C, the mechanical properties of samples increase firstly and then decrease with the increase of sintering time. The size of tungsten grains increases gradually with increasing of microwave sintering temperature and prolonging of microwave sintering time.
2012, 41(7):1289-1292.
Abstract:
Ni nanoparticles filled carbon nanotubes were prepared by anodic arc discharging plasma. The composition, the morphology and the phase structure of the products by this process were investigated via the high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and X-ray energy dispersive spectrometry (XEDS). The present experiment technology can obtain great amount of the carbon nanotubes filled with metallic nanoparticles, it means that inside there are Ni nanoparticles with fcc structure, outside thin layers are well-graphitized nanotubes. The diameter of carbon nanotubes ranges from 30 to 40 nm, the wall thickness is approximately 5~8 nm, and the particles encapsulated in carbon nanotubes are scattered homogeneously in spherical or ellipsoidal shapes.
Ni nanoparticles filled carbon nanotubes were prepared by anodic arc discharging plasma. The composition, the morphology and the phase structure of the products by this process were investigated via the high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and X-ray energy dispersive spectrometry (XEDS). The present experiment technology can obtain great amount of the carbon nanotubes filled with metallic nanoparticles, it means that inside there are Ni nanoparticles with fcc structure, outside thin layers are well-graphitized nanotubes. The diameter of carbon nanotubes ranges from 30 to 40 nm, the wall thickness is approximately 5~8 nm, and the particles encapsulated in carbon nanotubes are scattered homogeneously in spherical or ellipsoidal shapes.
2012, 41(7):1293-1297.
Abstract:
The solidification characteristics of centrifugal casting Ti47Al2Nb1Cr1W0.2Si alloy was studied by means of the isothermal quenching technology and optical microscope (OM) observation. The solidus and liquidus of the alloy were determined to be 1465 °C and 1520 °C, respectively. The Ti47Al2Nb1Cr1W0.2Si alloy car valves were cast with different superheats by the single step centrifugal casting process. The influence of the superheat on the fraction of fully filled mould and oxygen content of valve was studied. The results show that the best superheat for casting car valves is 160 °C.
The solidification characteristics of centrifugal casting Ti47Al2Nb1Cr1W0.2Si alloy was studied by means of the isothermal quenching technology and optical microscope (OM) observation. The solidus and liquidus of the alloy were determined to be 1465 °C and 1520 °C, respectively. The Ti47Al2Nb1Cr1W0.2Si alloy car valves were cast with different superheats by the single step centrifugal casting process. The influence of the superheat on the fraction of fully filled mould and oxygen content of valve was studied. The results show that the best superheat for casting car valves is 160 °C.
2012, 41(7):1298-1301.
Abstract:
In order to reduce defects and improve the mechanical and electrical properties of W-Cu thin sheet under pressure process, a new Cu/WCu/Cu ultra-thin sheet with three-layer sandwich structure was designed, and then the changes of microstructures and properties of two structure specimens in cold-rolling process were compared and analyzed. The results show that compared with conventional structure specimens, the surface Cu-coated layer of the sandwich structure specimen can clad the tungsten particles and fill the pores on the surface of the substrate, thus achieve surface modification; in rolling process, sandwich structure specimens have relatively fewer defects, and working hardening is not obvious, the tensile strength and electrical conductivity are better than that of conventional structure specimens.
In order to reduce defects and improve the mechanical and electrical properties of W-Cu thin sheet under pressure process, a new Cu/WCu/Cu ultra-thin sheet with three-layer sandwich structure was designed, and then the changes of microstructures and properties of two structure specimens in cold-rolling process were compared and analyzed. The results show that compared with conventional structure specimens, the surface Cu-coated layer of the sandwich structure specimen can clad the tungsten particles and fill the pores on the surface of the substrate, thus achieve surface modification; in rolling process, sandwich structure specimens have relatively fewer defects, and working hardening is not obvious, the tensile strength and electrical conductivity are better than that of conventional structure specimens.
2012, 41(7):1302-1305.
Abstract:
In order to overcome the limitations of traditional methods for measuring elastic modulus of the metal fiber, a novel method is proposed for measuring the elastic modulus of the metal fiber by vibration method．The measurement principle, apparatus, manipulation and error analysis were introduced. In this method, the measured metal fiber was generated in the form of a micro cantilever, and the cantilever can be vibrated for a short time when transient excitation is applied. The natural frequency of the cantilever can be used to calculate the elastic modulus of the material. Two kinds of materials, i.e. molybdenum wire and platinoiridium 25 fiber were tested in this work. The results prove that the measured values are consistent with that given in static tension method. The effect of beam length on determination of elastic modulus of materials was analyzed. The result shows that the influence of the ratio of L/d can be neglected only if the beam length is equal to or more than 8 times of the beam height (or diameter).
In order to overcome the limitations of traditional methods for measuring elastic modulus of the metal fiber, a novel method is proposed for measuring the elastic modulus of the metal fiber by vibration method．The measurement principle, apparatus, manipulation and error analysis were introduced. In this method, the measured metal fiber was generated in the form of a micro cantilever, and the cantilever can be vibrated for a short time when transient excitation is applied. The natural frequency of the cantilever can be used to calculate the elastic modulus of the material. Two kinds of materials, i.e. molybdenum wire and platinoiridium 25 fiber were tested in this work. The results prove that the measured values are consistent with that given in static tension method. The effect of beam length on determination of elastic modulus of materials was analyzed. The result shows that the influence of the ratio of L/d can be neglected only if the beam length is equal to or more than 8 times of the beam height (or diameter).
2012, 41(7):1306-1312.
Abstract:
Based on the influence of B-side or A-side elements substitution, non-stoichiometric ratio and preparation methods, the development of low-cost RE-Ni-base AB5-type hydrogen storage alloys was reviewed. Considering the raw materials cost, the chemical composition, and the performance of the low-cost AB5-type alloys, they can be classified as the low-cost-type, the super-low-cost-type and the high-cost-effective-type. It is important and eternal to develop low-cost AB5-type alloys, the sales volume of which takes up more than 50% of the total volume of hydrogen storage alloys in China.
Based on the influence of B-side or A-side elements substitution, non-stoichiometric ratio and preparation methods, the development of low-cost RE-Ni-base AB5-type hydrogen storage alloys was reviewed. Considering the raw materials cost, the chemical composition, and the performance of the low-cost AB5-type alloys, they can be classified as the low-cost-type, the super-low-cost-type and the high-cost-effective-type. It is important and eternal to develop low-cost AB5-type alloys, the sales volume of which takes up more than 50% of the total volume of hydrogen storage alloys in China.
2012, 41(7):1313-1316.
Abstract:
The microstructure has an important effect on the strength and fracture toughness in α+β titanium alloys. The qualitative and quantitative relationships between microstructure parameters and mechanical performances were mainly reviewed in alloys, for example, Ti-6AL-4V, Ti-62222s, Ti-6Al-2Sn-4Zr-6Mo, etc.. Meanwhile, the comprehensive utilization of quantitative microstructure parameters, finite element and neural network can predict quantitative relationship between microstructure and performances.
The microstructure has an important effect on the strength and fracture toughness in α+β titanium alloys. The qualitative and quantitative relationships between microstructure parameters and mechanical performances were mainly reviewed in alloys, for example, Ti-6AL-4V, Ti-62222s, Ti-6Al-2Sn-4Zr-6Mo, etc.. Meanwhile, the comprehensive utilization of quantitative microstructure parameters, finite element and neural network can predict quantitative relationship between microstructure and performances.
