Volume 40,Issue 4,2011 Table of Contents
2011, 40(4):565-570.
Abstract:
The word “blisk” means that all the blades are integrated with a disk. The application of the blisk is a key technology for improving performance of aero-engines. High quality of the blisk conduces to expand its application. Because of a strong influence of microstructure homogeneity on the quality of blisk, the author gives attention to it. In this paper, a loss function (LF) referring to the concept of Taguchi method was proposed. In the proposed LF, the distribution homogeneity of thermomechanical parameters was employed to evaluate the microstructure homogeneity of TC11 blisk forging. Then, the forging process of the TC11 alloy blisk was analyzed using FEM technique. Based on the FEM simulation results, the microstructure homogeneity of TC11 blisk forging was evaluated. Experiment was performed to verify the proposed method.
The word “blisk” means that all the blades are integrated with a disk. The application of the blisk is a key technology for improving performance of aero-engines. High quality of the blisk conduces to expand its application. Because of a strong influence of microstructure homogeneity on the quality of blisk, the author gives attention to it. In this paper, a loss function (LF) referring to the concept of Taguchi method was proposed. In the proposed LF, the distribution homogeneity of thermomechanical parameters was employed to evaluate the microstructure homogeneity of TC11 blisk forging. Then, the forging process of the TC11 alloy blisk was analyzed using FEM technique. Based on the FEM simulation results, the microstructure homogeneity of TC11 blisk forging was evaluated. Experiment was performed to verify the proposed method.
2011, 40(4):571-574.
Abstract:
The fine-grained and coarse-grained CuW70 alloys were prepared by sintering and infiltrating. The motion of cathode spots was observed by a digital high speed video camera and a scanning electron microscope (SEM). The results show that the fine-grained CuW70 alloy has larger breakdown strength, longer average arc life and lower chopping current. For coarse-grained CuW70 alloy, the cathode spots ignite and extinguish alternately beneath the anode, the breakdown is mainly located on copper phase, and the erosion pits are much deeper. However, the cathode spots of fine-grained CuW70 alloys have the characteristics of division and deviation, with the uniform distribution of the erosion pits on the entire cathode surface.
The fine-grained and coarse-grained CuW70 alloys were prepared by sintering and infiltrating. The motion of cathode spots was observed by a digital high speed video camera and a scanning electron microscope (SEM). The results show that the fine-grained CuW70 alloy has larger breakdown strength, longer average arc life and lower chopping current. For coarse-grained CuW70 alloy, the cathode spots ignite and extinguish alternately beneath the anode, the breakdown is mainly located on copper phase, and the erosion pits are much deeper. However, the cathode spots of fine-grained CuW70 alloys have the characteristics of division and deviation, with the uniform distribution of the erosion pits on the entire cathode surface.
2011, 40(4):575-579.
Abstract:
The transverse tensile properties of SiC/Ti-6Al-4V composites, subjected to both residual stress and applied transverse stress, have been investigated with emphasis on effects of fiber volume fractions by finite element analysis. Coincident nodes at fiber/matrix interfaces were connected by springs to simulate interfacial debonding. The results indicate that the applied stresses required to cause interfacial debonding (corresponding to strain jumps in stress-strain curves) are mainly affected by interfacial residual radial stresses at θ=0° under fixed interfacial bonding strength. The collapse stresses (corresponding to horizontal parts in stress-strain curves) of the composites, however, are a function of fiber volume fractions. Furthermore, the lower the fiber volume fractions are, the higher the collapse stresses are.
The transverse tensile properties of SiC/Ti-6Al-4V composites, subjected to both residual stress and applied transverse stress, have been investigated with emphasis on effects of fiber volume fractions by finite element analysis. Coincident nodes at fiber/matrix interfaces were connected by springs to simulate interfacial debonding. The results indicate that the applied stresses required to cause interfacial debonding (corresponding to strain jumps in stress-strain curves) are mainly affected by interfacial residual radial stresses at θ=0° under fixed interfacial bonding strength. The collapse stresses (corresponding to horizontal parts in stress-strain curves) of the composites, however, are a function of fiber volume fractions. Furthermore, the lower the fiber volume fractions are, the higher the collapse stresses are.
2011, 40(4):580-584.
Abstract:
TiN coating was deposited by arc evaporation PVD (physical vapor deposition) onto tool steel. A netted screen made of the stainless steel was placed between substrate and vaporizer in order to get discontinuous TiN coatings. Three kinds of surface condition (uncoated, continuous and discontinuous TiN coatings) were prepared and examined for their performance. Tribological behavior was investigated by means of dry and lubricated sliding tests at room temperature and 200 °C, on a disk-on-block and sphere-on-flat tribometer. The results show that the discontinuous TiN coating significantly decreases both the wear and the wearing speed of tool steel under sliding tests, and reduces friction under conditions of bidirectional sliding. In the three kinds of surface condition, the discontinuously coating has superiority for high speed cutting owing to its lifetime increasing compared with uncoated and continuously coated.
TiN coating was deposited by arc evaporation PVD (physical vapor deposition) onto tool steel. A netted screen made of the stainless steel was placed between substrate and vaporizer in order to get discontinuous TiN coatings. Three kinds of surface condition (uncoated, continuous and discontinuous TiN coatings) were prepared and examined for their performance. Tribological behavior was investigated by means of dry and lubricated sliding tests at room temperature and 200 °C, on a disk-on-block and sphere-on-flat tribometer. The results show that the discontinuous TiN coating significantly decreases both the wear and the wearing speed of tool steel under sliding tests, and reduces friction under conditions of bidirectional sliding. In the three kinds of surface condition, the discontinuously coating has superiority for high speed cutting owing to its lifetime increasing compared with uncoated and continuously coated.
2011, 40(4):585-589.
Abstract:
An internal oxidation method was applied to investigate the dispersion-strengthening of Pt-Ir-Zr alloy, and the thermodynamic condition was explored for this alloy. Scanning electron microscopy (SEM) was employed to analyze the internal oxidation morphologies. Combining with tensile strength, the optimal internal oxidation time was determined. The results show that oxidation of Ir and Zr will occur under the experimental condition, and the oxygen pressure of Zr is lower than that of Ir. The grain size of the alloy increases with the prolonging of time and remains stable when the oxidation time is up to 40 h. The tensile strength decreases exponentially with the increase of oxidation time. The time for optimal internal oxidation is 40 h at 1100 °C.
An internal oxidation method was applied to investigate the dispersion-strengthening of Pt-Ir-Zr alloy, and the thermodynamic condition was explored for this alloy. Scanning electron microscopy (SEM) was employed to analyze the internal oxidation morphologies. Combining with tensile strength, the optimal internal oxidation time was determined. The results show that oxidation of Ir and Zr will occur under the experimental condition, and the oxygen pressure of Zr is lower than that of Ir. The grain size of the alloy increases with the prolonging of time and remains stable when the oxidation time is up to 40 h. The tensile strength decreases exponentially with the increase of oxidation time. The time for optimal internal oxidation is 40 h at 1100 °C.
2011, 40(4):590-594.
Abstract:
Using the first-principle pseudopotential plane wave (PPW) method based on the density functional theory, structural optimization was conducted on various intermetallic compounds of the binary Mg-Nd alloy. With their ground-state energies obtained, the structural stabilities of these intermetallic compounds were studied in terms of formation heat and binding energy of the alloy. The results show that the absolute values of the binding energies of various intermetallic compounds increase with the increase of Nd content, among which the absolute value of the binding energy of MgNd is the greatest while that of Mg12Nd is the smallest. It is indicated that among all the intermetallic compounds formed in Mg-Nd, the structure of MgNd is the most stable while that of Mg12Nd is the most unstable. This result is consistent with the experiment data. The Mg12Nd phase does not exist in the phase diagram of Mg-Nd alloy. In addition, the densities of electronic state of these structures were calculated and an explanation was given in terms of the electronic structure.
Using the first-principle pseudopotential plane wave (PPW) method based on the density functional theory, structural optimization was conducted on various intermetallic compounds of the binary Mg-Nd alloy. With their ground-state energies obtained, the structural stabilities of these intermetallic compounds were studied in terms of formation heat and binding energy of the alloy. The results show that the absolute values of the binding energies of various intermetallic compounds increase with the increase of Nd content, among which the absolute value of the binding energy of MgNd is the greatest while that of Mg12Nd is the smallest. It is indicated that among all the intermetallic compounds formed in Mg-Nd, the structure of MgNd is the most stable while that of Mg12Nd is the most unstable. This result is consistent with the experiment data. The Mg12Nd phase does not exist in the phase diagram of Mg-Nd alloy. In addition, the densities of electronic state of these structures were calculated and an explanation was given in terms of the electronic structure.
2011, 40(4):595-599.
Abstract:
According to the empirical electron theory (EET) of solid and molecule, the valence electron structure and theoretical bond energy of C11b-MoSi2 were calculated by the bond length difference (BLD) method. The effects of partial substitution of Al for Si of MoSi2 lattices were considered. According to the average atom model in substitutional solid solutions of EET, the valence electron structure and theoretical bond energy of C11b Mo(Si0.95,Al0.05)2 were analyzed and calculated. The results show that the hybridization state of Mo and Si atoms is altered with Al addition in MoSi2, and then the parameters of valence electron structure change. Compared with MoSi2, the proportion of covalent electrons in total valence electrons decreases from 65.87% to 64.28% and therefore it is concluded that the strength of MoSi2 can be reduced by microalloying with aluminum. However, the lattice electrons increase from 4.7141 to 4.9202, so the plasticity of MoSi2 can be improved by microalloying with aluminum.
According to the empirical electron theory (EET) of solid and molecule, the valence electron structure and theoretical bond energy of C11b-MoSi2 were calculated by the bond length difference (BLD) method. The effects of partial substitution of Al for Si of MoSi2 lattices were considered. According to the average atom model in substitutional solid solutions of EET, the valence electron structure and theoretical bond energy of C11b Mo(Si0.95,Al0.05)2 were analyzed and calculated. The results show that the hybridization state of Mo and Si atoms is altered with Al addition in MoSi2, and then the parameters of valence electron structure change. Compared with MoSi2, the proportion of covalent electrons in total valence electrons decreases from 65.87% to 64.28% and therefore it is concluded that the strength of MoSi2 can be reduced by microalloying with aluminum. However, the lattice electrons increase from 4.7141 to 4.9202, so the plasticity of MoSi2 can be improved by microalloying with aluminum.
2011, 40(4):600-604.
Abstract:
Isotropic magnets were prepared by hot-pressing/die-upset process with Nd9Fe85.5-xCoxB5.5(x=0, 1, 3, 5) melt-spun ribbons as starting material at the wheel surface speed V=35 m/s. The microstructure analysis indicates that Co-doped alloy melt-spun ribbons consists of a large amount of amorphous phase and a little amount of α-(Fe, Co) and Nd2(Fe,Co)14B, and Nd3(Fe,Co)62B14 metastable phase exists in the melt-spun ribbons with x=5. The metastable phase will decomposes into α-(Fe,Co) and Nd2(Fe,Co)14B mixture during the following hot-pressing/die-upset process. The average grain sizes of both soft and hard magnetic phases decrease respectively from 61 and 168 nm to 24 and 50 nm, with the Co content increasing from 0 at% to 1at%. The magnetic property research show that corresponding to the change of grain sizes, magnetostatic coupling interaction is dominant for Co-free alloy, while exchange coupling interaction is dominant for Co-doped alloys. The effect of exchange-coupling becomes weaker with more Co-doping, resulting in the monotonous increasing of the intrinsic coercivity from 151 kA/m for Co-free magnet to 218 kA/m for 5 at% Co magnet.
Isotropic magnets were prepared by hot-pressing/die-upset process with Nd9Fe85.5-xCoxB5.5(x=0, 1, 3, 5) melt-spun ribbons as starting material at the wheel surface speed V=35 m/s. The microstructure analysis indicates that Co-doped alloy melt-spun ribbons consists of a large amount of amorphous phase and a little amount of α-(Fe, Co) and Nd2(Fe,Co)14B, and Nd3(Fe,Co)62B14 metastable phase exists in the melt-spun ribbons with x=5. The metastable phase will decomposes into α-(Fe,Co) and Nd2(Fe,Co)14B mixture during the following hot-pressing/die-upset process. The average grain sizes of both soft and hard magnetic phases decrease respectively from 61 and 168 nm to 24 and 50 nm, with the Co content increasing from 0 at% to 1at%. The magnetic property research show that corresponding to the change of grain sizes, magnetostatic coupling interaction is dominant for Co-free alloy, while exchange coupling interaction is dominant for Co-doped alloys. The effect of exchange-coupling becomes weaker with more Co-doping, resulting in the monotonous increasing of the intrinsic coercivity from 151 kA/m for Co-free magnet to 218 kA/m for 5 at% Co magnet.
2011, 40(4):605-609.
Abstract:
The hot deformation behavior and the subsequent microstructure characteristics of Hastelloy G-3 alloy were studied by isothermal compression tests at the strain rates of 0.1-10 s-1 and the temperatures of 1050-1200 oC. The flow-stress at high strain rates were corrected considering the effect of deformation heating, and a new constitutive relationship between peak stress and deformation temperature as well as strain rate for G-3 alloy at high temperature was established. The results show that the built material model has good fitting accuracy to satisfy the engineering need. The softening mechanism of G-3 alloy is dynamic recrystalization during hot working process. According to the microstructures after deformation, for G-3 alloy the proper deformation temperature is 1180-1200 oC and the proper strain rate is 5-10 s-1.
The hot deformation behavior and the subsequent microstructure characteristics of Hastelloy G-3 alloy were studied by isothermal compression tests at the strain rates of 0.1-10 s-1 and the temperatures of 1050-1200 oC. The flow-stress at high strain rates were corrected considering the effect of deformation heating, and a new constitutive relationship between peak stress and deformation temperature as well as strain rate for G-3 alloy at high temperature was established. The results show that the built material model has good fitting accuracy to satisfy the engineering need. The softening mechanism of G-3 alloy is dynamic recrystalization during hot working process. According to the microstructures after deformation, for G-3 alloy the proper deformation temperature is 1180-1200 oC and the proper strain rate is 5-10 s-1.
2011, 40(4):610-614.
Abstract:
The interdiffusion behavior of Ti-Zr binary alloy in the β phase (950 to 1150 oC) was studied through the diffusion couples by EPMA. The interdiffusion coefficients of the Ti-Zr binary alloy were calculated by the Den Broeder method and modified by the Hall method in the concentration limits between 10-14 and 10-12 m2/s. The diffusion activation energy Q and frequency factor D0 were calculated. The results show that Q and D0 increase at first and then decrease with the increase of Zr concentration and a summit can be got at about 50at% Zr concentration. The impurity diffusion coefficients in concentration limits were calculated by Vignes-Birchenall method and they were compared with the interdiffusion coefficients determined by Hall modification method. It is found that their results are similar.
The interdiffusion behavior of Ti-Zr binary alloy in the β phase (950 to 1150 oC) was studied through the diffusion couples by EPMA. The interdiffusion coefficients of the Ti-Zr binary alloy were calculated by the Den Broeder method and modified by the Hall method in the concentration limits between 10-14 and 10-12 m2/s. The diffusion activation energy Q and frequency factor D0 were calculated. The results show that Q and D0 increase at first and then decrease with the increase of Zr concentration and a summit can be got at about 50at% Zr concentration. The impurity diffusion coefficients in concentration limits were calculated by Vignes-Birchenall method and they were compared with the interdiffusion coefficients determined by Hall modification method. It is found that their results are similar.
2011, 40(4):615-619.
Abstract:
The Bauschinger effect (BE) of AZ31 magnesium alloy was tested by the experiment of cyclical tension and compression, and the mechanisms of BE were investigated. The test results show that the BE is apparent during tension after compression pre-strain, but in compression after tension pre-strain the reverse Bauschinger effect (RBE) is displayed. Furthermore, the BE is much stronger than the RBE. The microstructure and grain orientation evolvement during cyclical tension and compression show that the cause of the BE is the combination of the re-orientation in pre-compression and the effect of de-twinning during subsequent tension, which make the tension yield limit decrease. Though the grain orientation is not changed, the decrease of c/a ratio after pre-tension makes the twinning more difficult in re-compression, resulting in the RBE.
The Bauschinger effect (BE) of AZ31 magnesium alloy was tested by the experiment of cyclical tension and compression, and the mechanisms of BE were investigated. The test results show that the BE is apparent during tension after compression pre-strain, but in compression after tension pre-strain the reverse Bauschinger effect (RBE) is displayed. Furthermore, the BE is much stronger than the RBE. The microstructure and grain orientation evolvement during cyclical tension and compression show that the cause of the BE is the combination of the re-orientation in pre-compression and the effect of de-twinning during subsequent tension, which make the tension yield limit decrease. Though the grain orientation is not changed, the decrease of c/a ratio after pre-tension makes the twinning more difficult in re-compression, resulting in the RBE.
2011, 40(4):620-624.
Abstract:
(TiC)PNi/TiAl/Ti functional gradient materials (FGMs) were prepared by field-activated pressure-assisted synthesis ( FAPAS) and in-situ synthesis processes. The roles of the electric field in material synthesis and diffusion bonding of layers were investigated. The microstructure and phase composition of each layer as well as component distribution of elements across the interfaces of the layers were analyzed by means of OM, SEM, EDS and XRD. The results show that the imposition of the electric field and the combustion reaction of TiAl is the key for the successful synthesis of FGMs; the TiC particles formed by in-situ synthesis process are fine and distributed uniformly; moreover, concentration profiles of elements across the interfaces of the layers show significant inter-diffusion and good metallurgical bonding. The sample has an excellent thermal shock resistance ability and gradient distribution of micro-hardness across the titanium substrate to the surface layer.
(TiC)PNi/TiAl/Ti functional gradient materials (FGMs) were prepared by field-activated pressure-assisted synthesis ( FAPAS) and in-situ synthesis processes. The roles of the electric field in material synthesis and diffusion bonding of layers were investigated. The microstructure and phase composition of each layer as well as component distribution of elements across the interfaces of the layers were analyzed by means of OM, SEM, EDS and XRD. The results show that the imposition of the electric field and the combustion reaction of TiAl is the key for the successful synthesis of FGMs; the TiC particles formed by in-situ synthesis process are fine and distributed uniformly; moreover, concentration profiles of elements across the interfaces of the layers show significant inter-diffusion and good metallurgical bonding. The sample has an excellent thermal shock resistance ability and gradient distribution of micro-hardness across the titanium substrate to the surface layer.
13 Research on Evaporation Mechanism of Elements in TC4 Alloys during Electron Beam Cold Hearth Melting
Luo Lei
,
Yu Lanlan
,
Lei Wenguang
,
Mao Xiaonan
,
Yang Guanjun
,
Niu Rongrong
,
Zhang Yingming
,
Wang Chen
2011, 40(4):625-629.
Abstract:
A mathematical model was set up to calculate the saturated vapor pressure of components in TC4 alloys during electron beam cold hearth melting (EBCHM). The saturated vapor pressure and evaporation rate of components in TC4 alloy were calculated by this model, whose results basically agree with the experiment results. The calculation result shows that at the same temperature the saturated vapor pressure of Al is the biggest, about hundreds of times as large as others, and the evaporation loss is also the most serious. With the increase of the melt temperature, the evaporation trend increases. The evaporation loss of V is very little, which can be neglected. Moreover, electron beam cold hearth melting has the prominent effect in removing inclusions, and it can produce the slabs achieving the national standard.
A mathematical model was set up to calculate the saturated vapor pressure of components in TC4 alloys during electron beam cold hearth melting (EBCHM). The saturated vapor pressure and evaporation rate of components in TC4 alloy were calculated by this model, whose results basically agree with the experiment results. The calculation result shows that at the same temperature the saturated vapor pressure of Al is the biggest, about hundreds of times as large as others, and the evaporation loss is also the most serious. With the increase of the melt temperature, the evaporation trend increases. The evaporation loss of V is very little, which can be neglected. Moreover, electron beam cold hearth melting has the prominent effect in removing inclusions, and it can produce the slabs achieving the national standard.
2011, 40(4):630-634.
Abstract:
The crack propagation behavior of GH864 alloy was studied at 650 oC under fatigue/creep interaction with different dwell time; the effects of creep and oxidation and the meaning of transition point were analyzed in da-dN and a-N curves. The results indicate that the crack growth rate under dwell 90 s is higher than that under dwell 5 s. The alloy is mainly trans-granular fracture under dwell 5 s and the fatigue effect is principle. The alloy is mainly inter-granular fracture under dwell 90 s and the creep effect is dominant. The crack propagation rate curves of fatigue/creep interaction at 650 oC could well be described by Saxena model under the condition of this test. The descriptions could estimate the crack growth rates at lower and higher stress intensity factors. In addition, the expressions of different alloys from Saxena could contrast the effects of fatigue and creep as well as their proportion. At last, the transition points of a-Ni/Nf, da/dN-a and da/dN-N curves were obtained and the meaning of these points was analyzed with fracture analysis. The curve analysis method can also be used for the crack propagation rate curves of superalloys and other materials.
The crack propagation behavior of GH864 alloy was studied at 650 oC under fatigue/creep interaction with different dwell time; the effects of creep and oxidation and the meaning of transition point were analyzed in da-dN and a-N curves. The results indicate that the crack growth rate under dwell 90 s is higher than that under dwell 5 s. The alloy is mainly trans-granular fracture under dwell 5 s and the fatigue effect is principle. The alloy is mainly inter-granular fracture under dwell 90 s and the creep effect is dominant. The crack propagation rate curves of fatigue/creep interaction at 650 oC could well be described by Saxena model under the condition of this test. The descriptions could estimate the crack growth rates at lower and higher stress intensity factors. In addition, the expressions of different alloys from Saxena could contrast the effects of fatigue and creep as well as their proportion. At last, the transition points of a-Ni/Nf, da/dN-a and da/dN-N curves were obtained and the meaning of these points was analyzed with fracture analysis. The curve analysis method can also be used for the crack propagation rate curves of superalloys and other materials.
2011, 40(4):635-639.
Abstract:
The microstructures and properties of GWN751K magnesium alloy in different states were investigated by OM, SEM, TEM and XRD. The results show that the microstructure of the as-cast alloy is composed of α-Mg and net-like eutectic phase and σb=215 MPa, σ0.2=187 MPa and δ=3.5% with a low temperature endothermic peak in DSC curve. After 535 oC, 16 h heat treatment, the eutectic structure decomposes and the Mg-Y rich phases remain in the boundary with grains growing up obviously. Mechanical properties become better with σb=240 MPa, σ0.2=189 MPa and δ=10%, and the low temperature endothermic peak disappears. After extrusion, the dynamic recrystallization occurs and as a result the mechanical properties are increased obviously with σb=320 MPa, σ0.2=260 MPa and δ=18%; the main reason is that the high-density dislocation and fine grains can greatly increase the strength and elongation. After aging at 220 oC for 6 h, the average ultimate tensile strength is over 400 MPa but the elongation is decreased sharply. In the as-cast alloy, the secondary cracks were observed along the grain boundaries, mainly at the inside of eutectics. After 535 oC, 16 h heat treatment and extrusion, the secondary cracks mainly locate at the grain interior.
The microstructures and properties of GWN751K magnesium alloy in different states were investigated by OM, SEM, TEM and XRD. The results show that the microstructure of the as-cast alloy is composed of α-Mg and net-like eutectic phase and σb=215 MPa, σ0.2=187 MPa and δ=3.5% with a low temperature endothermic peak in DSC curve. After 535 oC, 16 h heat treatment, the eutectic structure decomposes and the Mg-Y rich phases remain in the boundary with grains growing up obviously. Mechanical properties become better with σb=240 MPa, σ0.2=189 MPa and δ=10%, and the low temperature endothermic peak disappears. After extrusion, the dynamic recrystallization occurs and as a result the mechanical properties are increased obviously with σb=320 MPa, σ0.2=260 MPa and δ=18%; the main reason is that the high-density dislocation and fine grains can greatly increase the strength and elongation. After aging at 220 oC for 6 h, the average ultimate tensile strength is over 400 MPa but the elongation is decreased sharply. In the as-cast alloy, the secondary cracks were observed along the grain boundaries, mainly at the inside of eutectics. After 535 oC, 16 h heat treatment and extrusion, the secondary cracks mainly locate at the grain interior.
2011, 40(4):640-644.
Abstract:
The mechanical and thermodynamic properties of intermetallic compound in Mg-Al-Ca alloy have been investigated by Castep and Dmol program based on the density functional theory. The results show that DI3-Al4Ca is a ductility phase, on the contrary C15-Al2Ca and C14-Mg2Ca are of very good brittleness in Mg-Al-Ca alloy, and among the three phases, C15-Al2Ca is a phase with the worst plasticity. The melting point of intermetallic compound are estimated based on the calculated elastic constants; it is found that the estimated values of Al2Ca are in well agreement with the corresponding experimental values and the error relative to the experiment result is about 4.06%. By calculating the thermodynamic properties of intermetallic compound in Mg-Al-Ca alloy at different temperatures, it is found that Gibbs free energy of Al2Ca is the smallest as well as has the highest structural stability within the temperature range of 298.15-425 K, the next is Al4Ca, and the last one is Mg2Ca. In addition, with the elevated temperature, Gibbs free energy of Mg2Ca is decreased at the most rapid speed, meaning that its structural stability may be improved more rapidly as well. When the temperature is above 525 K, the case is changed; it is found that Mg2Ca has the highest structural stability, the next is Al2Ca, and the last one is Al4Ca.
The mechanical and thermodynamic properties of intermetallic compound in Mg-Al-Ca alloy have been investigated by Castep and Dmol program based on the density functional theory. The results show that DI3-Al4Ca is a ductility phase, on the contrary C15-Al2Ca and C14-Mg2Ca are of very good brittleness in Mg-Al-Ca alloy, and among the three phases, C15-Al2Ca is a phase with the worst plasticity. The melting point of intermetallic compound are estimated based on the calculated elastic constants; it is found that the estimated values of Al2Ca are in well agreement with the corresponding experimental values and the error relative to the experiment result is about 4.06%. By calculating the thermodynamic properties of intermetallic compound in Mg-Al-Ca alloy at different temperatures, it is found that Gibbs free energy of Al2Ca is the smallest as well as has the highest structural stability within the temperature range of 298.15-425 K, the next is Al4Ca, and the last one is Mg2Ca. In addition, with the elevated temperature, Gibbs free energy of Mg2Ca is decreased at the most rapid speed, meaning that its structural stability may be improved more rapidly as well. When the temperature is above 525 K, the case is changed; it is found that Mg2Ca has the highest structural stability, the next is Al2Ca, and the last one is Al4Ca.
2011, 40(4):645-649.
Abstract:
Uniaxial hot compression deformation experiments for a new type nickel-based powder metallurgy (P/M) superalloy FGH98 I have been performed on Gleeble-1500 thermal simulator, and the hot deformation behavior has been investigated under the conditions of deformation temperatures of 950-1150 oC and strain rates of 0.0003-1 s-1. The strain rate sensitivity m maps and the power dissipation efficiency η maps have been established and compared at different strains. The microstructural validation of processing maps also has been done. The results show that the flow stress decreases with the deformation temperature increasing and strain rate decreasing. The maps of m and η are similar at different strains, and the values of m and η in the peak zones gradually increase with the strain increasing. When the true strain is 0.5, the alloy has peak η of 40% and peak m of 25% at 1050 oC and 0.0003 s-1, which corresponds to dynamic recrystallization and grain refinement without inner cracks. The above results can be used as a theoretical reference for the optimization of actual hot working processing of FGH98 I alloy.
Uniaxial hot compression deformation experiments for a new type nickel-based powder metallurgy (P/M) superalloy FGH98 I have been performed on Gleeble-1500 thermal simulator, and the hot deformation behavior has been investigated under the conditions of deformation temperatures of 950-1150 oC and strain rates of 0.0003-1 s-1. The strain rate sensitivity m maps and the power dissipation efficiency η maps have been established and compared at different strains. The microstructural validation of processing maps also has been done. The results show that the flow stress decreases with the deformation temperature increasing and strain rate decreasing. The maps of m and η are similar at different strains, and the values of m and η in the peak zones gradually increase with the strain increasing. When the true strain is 0.5, the alloy has peak η of 40% and peak m of 25% at 1050 oC and 0.0003 s-1, which corresponds to dynamic recrystallization and grain refinement without inner cracks. The above results can be used as a theoretical reference for the optimization of actual hot working processing of FGH98 I alloy.
2011, 40(4):650-654.
Abstract:
The valence electron structures of Al3Er and Al3(ZrxEr1-x) phases resulted from minor elements Er and Zr addition to Al alloys were calculated according to the empirical electron theory in solid and molecule (EET). Effects of Zr contents on the valence electron structure parameters of Al3(ZrxEr1-x) phases were discussed. The calculation results show that with the increase of Zr atom content, both the covalent electron pairs nα on the strongest bond for strength properties characterization and the phase structure forming factor S decrease, which indicates Al3Er phases firstly precipitate during the solidification process and Al3Zr and Al3(ZrxEr1-x) also precipitate during the subsequent heat treatment; whereas, Zr addition has few influence on the strength of the alloys. The density of crystal lattice electron ρ for plastic properties characterization increases first and then decreases, revealing that Zr addition can obviously improve the plastic properties of the alloys.
The valence electron structures of Al3Er and Al3(ZrxEr1-x) phases resulted from minor elements Er and Zr addition to Al alloys were calculated according to the empirical electron theory in solid and molecule (EET). Effects of Zr contents on the valence electron structure parameters of Al3(ZrxEr1-x) phases were discussed. The calculation results show that with the increase of Zr atom content, both the covalent electron pairs nα on the strongest bond for strength properties characterization and the phase structure forming factor S decrease, which indicates Al3Er phases firstly precipitate during the solidification process and Al3Zr and Al3(ZrxEr1-x) also precipitate during the subsequent heat treatment; whereas, Zr addition has few influence on the strength of the alloys. The density of crystal lattice electron ρ for plastic properties characterization increases first and then decreases, revealing that Zr addition can obviously improve the plastic properties of the alloys.
2011, 40(4):655-660.
Abstract:
The effects of the substitution of Co and Cu for Ni and magnetic-heat treatment on the thermodynamics and kinetics properties of hydriding/dehydriding reaction for La0.67Mg0.33Ni3-xMx (M=Co,Cu)(x=0,0.5) hydrogen storage alloys were studied. Results show that after the partial substitution of Co and Cu for Ni, the hydrogen absorption/desorption capacity of the alloys is increased, and the temperature of endothermic peak, characteristic time (tc) of hydriding/dehydriding reaction and the activation energy are decreased. The magnetic-heat treatment improves performances of La-Mg-Ni type alloys, including hydrogen absorption capacity, the hydriding/dehydriding platform width and the hydriding/dehydriding kinetics. The thermodynamic and kinetic property of magnetic-heated La0.67Mg0.33Ni2.5Co0.5 alloy is excellent. It can absorb 1.40 wt% H and desorb 1.32wt% H. Its DSC measurement shows endothermic peak of 77.8 oC. The characteristic time (tc) of hydriding/dehydriding reaction is 91.4 and 379.3 s. The hydriding/dehydriding activation energy is calculated to be 16.3 and 23.3 kJ/mol by the Chou model.
The effects of the substitution of Co and Cu for Ni and magnetic-heat treatment on the thermodynamics and kinetics properties of hydriding/dehydriding reaction for La0.67Mg0.33Ni3-xMx (M=Co,Cu)(x=0,0.5) hydrogen storage alloys were studied. Results show that after the partial substitution of Co and Cu for Ni, the hydrogen absorption/desorption capacity of the alloys is increased, and the temperature of endothermic peak, characteristic time (tc) of hydriding/dehydriding reaction and the activation energy are decreased. The magnetic-heat treatment improves performances of La-Mg-Ni type alloys, including hydrogen absorption capacity, the hydriding/dehydriding platform width and the hydriding/dehydriding kinetics. The thermodynamic and kinetic property of magnetic-heated La0.67Mg0.33Ni2.5Co0.5 alloy is excellent. It can absorb 1.40 wt% H and desorb 1.32wt% H. Its DSC measurement shows endothermic peak of 77.8 oC. The characteristic time (tc) of hydriding/dehydriding reaction is 91.4 and 379.3 s. The hydriding/dehydriding activation energy is calculated to be 16.3 and 23.3 kJ/mol by the Chou model.
2011, 40(4):661-664.
Abstract:
Al coating, which has similar properties to droplet metal and metallurgical bonding with the substrate, was prepared on AZ91 alloy surface by droplet coating treatment. The microstructure, phase structure and composition of the area near the coating interface were analyzed. The microhardness and corrosion resistance of the coating were also tested. The results show that the element diffusion takes place between Mg and Al during the droplet coating process, but the process of mixing Mg-rich and Al-rich liquids is limited within a thin layer. The composition, microhardness and corrosion resistance of the prepared coating are similar to those of droplet metal Al. The results demonstrate that droplet coating which can prepare the composition-controllable coating is a promising way for magnesium surface protection by the available corrosion resistant materials.
Al coating, which has similar properties to droplet metal and metallurgical bonding with the substrate, was prepared on AZ91 alloy surface by droplet coating treatment. The microstructure, phase structure and composition of the area near the coating interface were analyzed. The microhardness and corrosion resistance of the coating were also tested. The results show that the element diffusion takes place between Mg and Al during the droplet coating process, but the process of mixing Mg-rich and Al-rich liquids is limited within a thin layer. The composition, microhardness and corrosion resistance of the prepared coating are similar to those of droplet metal Al. The results demonstrate that droplet coating which can prepare the composition-controllable coating is a promising way for magnesium surface protection by the available corrosion resistant materials.
2011, 40(4):665-668.
Abstract:
The microstructural evolution of coarse-grained Ni-48Al alloy during superplastic deformation at 1075 oC with initial strain rate of 1.5×10-3 s-1 was studied using EBSD (electron back-scattered diffraction) technique. The results show that before deformation, high angle grain boundaries dominate in the coarse-grained Ni-48Al alloy with few low angle grain boundaries. During the superplastic deformation, low angle grain boundaries with misorientations less than 5° occur successively. With the increase of the deformation, the misorientations of the newly-formed low angle grain boundaries increase, low angle grain boundaries with misorientations between 6o-15° are formed, and finally high angle grain boundaries with misorientations larger than 15° are formed. There exists a sort of dynamic equilibrium between the formation rate of low-angle grain boundaries and the rate of changing into higher-angle grain boundaries. The transformation from low angle grain boundaries to high angle grain boundaries makes the number of high-angle grain boundaries increase continuously and finally the grains are refined markedly.
The microstructural evolution of coarse-grained Ni-48Al alloy during superplastic deformation at 1075 oC with initial strain rate of 1.5×10-3 s-1 was studied using EBSD (electron back-scattered diffraction) technique. The results show that before deformation, high angle grain boundaries dominate in the coarse-grained Ni-48Al alloy with few low angle grain boundaries. During the superplastic deformation, low angle grain boundaries with misorientations less than 5° occur successively. With the increase of the deformation, the misorientations of the newly-formed low angle grain boundaries increase, low angle grain boundaries with misorientations between 6o-15° are formed, and finally high angle grain boundaries with misorientations larger than 15° are formed. There exists a sort of dynamic equilibrium between the formation rate of low-angle grain boundaries and the rate of changing into higher-angle grain boundaries. The transformation from low angle grain boundaries to high angle grain boundaries makes the number of high-angle grain boundaries increase continuously and finally the grains are refined markedly.
2011, 40(4):669-672.
Abstract:
Hot workability of powder metallurgy molybdenum in the temperature range of 900-1450 oC and strain rate range of 0.01-10 s-1 was investigated by hot compression tests on a Gleeble-1500 thermal mechanical simulator. According to experimental results, the dynamic recrystallization (DRX) behavior of powder metallurgy molybdenum was studied and its θ-σ and ?θ/?σ-σ curves were established. Based on working hardening rate-stress (θ-σ) and working hardening rate-strain (θ-ε) curves, the critical strain εc of DRX was determined. The average grain size (D) and Zener-Hollmon parameter (Z) during DRX process obey the following equation: lnD=3.65597–0.05409lnZ; these researches provide fundamental data for cogging and hot working technology of powder metallurgy molybdenum.
Hot workability of powder metallurgy molybdenum in the temperature range of 900-1450 oC and strain rate range of 0.01-10 s-1 was investigated by hot compression tests on a Gleeble-1500 thermal mechanical simulator. According to experimental results, the dynamic recrystallization (DRX) behavior of powder metallurgy molybdenum was studied and its θ-σ and ?θ/?σ-σ curves were established. Based on working hardening rate-stress (θ-σ) and working hardening rate-strain (θ-ε) curves, the critical strain εc of DRX was determined. The average grain size (D) and Zener-Hollmon parameter (Z) during DRX process obey the following equation: lnD=3.65597–0.05409lnZ; these researches provide fundamental data for cogging and hot working technology of powder metallurgy molybdenum.
2011, 40(4):673-676.
Abstract:
The stress rupture test was conducted to a nickel-base single crystal superalloy DD499 along [001], [011] and [111] orientations. The results indicate that anisotropic behaviors of singe crystal superalloy are significantly affected by temperature and stress level. At 760 oC, 790 MPa, the stress rupture property of [001] orientation is outstandingly superior to that of [011] and [111] orientations; while at 1040 oC, 165 MPa, the order of stress rupture is [111]>[001]>[011], but the anisotropic properties of different orientations are weakened. Fracture surface and deformation microstructure were examined by SEM. The results show that at 760 oC, 790 MPa, the fracture mode of [001] orientation is the combination of cleavage and quasi-cleavage; while the fracture mode of [011] orientation is pure shear due to single slip system and [111] orientation is pure shear caused by multiple slip systems. At 1040 oC, 165 MPa, the fracture mode of the three orientations all turns to be microvoid coalescence fracture.
The stress rupture test was conducted to a nickel-base single crystal superalloy DD499 along [001], [011] and [111] orientations. The results indicate that anisotropic behaviors of singe crystal superalloy are significantly affected by temperature and stress level. At 760 oC, 790 MPa, the stress rupture property of [001] orientation is outstandingly superior to that of [011] and [111] orientations; while at 1040 oC, 165 MPa, the order of stress rupture is [111]>[001]>[011], but the anisotropic properties of different orientations are weakened. Fracture surface and deformation microstructure were examined by SEM. The results show that at 760 oC, 790 MPa, the fracture mode of [001] orientation is the combination of cleavage and quasi-cleavage; while the fracture mode of [011] orientation is pure shear due to single slip system and [111] orientation is pure shear caused by multiple slip systems. At 1040 oC, 165 MPa, the fracture mode of the three orientations all turns to be microvoid coalescence fracture.
2011, 40(4):677-680.
Abstract:
Considering the brittleness of tungsten alloys as pre-fabricated fragment ammunition after armour-piercing, tungsten alloy spheres embedded in cylinders were employed; the microstructure and fracture mechanism of 97.5W-Ni-Fe alloy were investigated under explosive loading before and after armour-piercing. The results show that high strain rate explosive loading induces a large amount of deformation twins in tungsten particles. The twining deformation after armour-piercing induces lots of micro-cracks and these micro-cracks extend to connect with the W-W interface fracture, becoming macro-cracks due to the tensile stress. As a result, the tungsten alloy spheres are fractured to efficient fragments and the second damage ability is enhanced.
Considering the brittleness of tungsten alloys as pre-fabricated fragment ammunition after armour-piercing, tungsten alloy spheres embedded in cylinders were employed; the microstructure and fracture mechanism of 97.5W-Ni-Fe alloy were investigated under explosive loading before and after armour-piercing. The results show that high strain rate explosive loading induces a large amount of deformation twins in tungsten particles. The twining deformation after armour-piercing induces lots of micro-cracks and these micro-cracks extend to connect with the W-W interface fracture, becoming macro-cracks due to the tensile stress. As a result, the tungsten alloy spheres are fractured to efficient fragments and the second damage ability is enhanced.
2011, 40(4):681-684.
Abstract:
In order to research the tritium aging effect in hydrogen deuterium exchange at a constant flow rate between gaseous hydrogen and palladium hydride powder, the reasons that affect exchange performance were analyzed by speed theory of chromatography separation, and the breakthrough curves of the exchange reaction were simulated by plate theory. And, hydrogen deuterium exchange experiments over 0 year and 1.6 years aged palladium were compared. The theoretical simulation results indicate that in aged palladium, the plate number of exchange reaction is decreased, the plate height is increased, the equilibration time of exchange reaction is prolonged, the breakthrough curves become smooth, and the exchange performance declines. The plate height increasing is due to decay product 3He, which accumulate and cumber hydrogen isotope diffusion in aged palladium; further more, because of the existence of 3He, the hydrogen isotope separation factor of aged palladium changes. The comparison results indicate that the hydrogen deuterium exchange breakthrough curve of 1.6 years aged palladium go smooth, and the hydrogen deuterium exchange performance declines at a constant hydrogen flow rate. The theoretical simulation results accord with the experiment results.
In order to research the tritium aging effect in hydrogen deuterium exchange at a constant flow rate between gaseous hydrogen and palladium hydride powder, the reasons that affect exchange performance were analyzed by speed theory of chromatography separation, and the breakthrough curves of the exchange reaction were simulated by plate theory. And, hydrogen deuterium exchange experiments over 0 year and 1.6 years aged palladium were compared. The theoretical simulation results indicate that in aged palladium, the plate number of exchange reaction is decreased, the plate height is increased, the equilibration time of exchange reaction is prolonged, the breakthrough curves become smooth, and the exchange performance declines. The plate height increasing is due to decay product 3He, which accumulate and cumber hydrogen isotope diffusion in aged palladium; further more, because of the existence of 3He, the hydrogen isotope separation factor of aged palladium changes. The comparison results indicate that the hydrogen deuterium exchange breakthrough curve of 1.6 years aged palladium go smooth, and the hydrogen deuterium exchange performance declines at a constant hydrogen flow rate. The theoretical simulation results accord with the experiment results.
2011, 40(4):685-688.
Abstract:
Conductive La0.4Sr0.6CoO3 (LaSrCoO) buffer layers with cubic-perovskite structure were prepared on LaAlO3(100) single crystal substrates by the metal organic deposition (MOD) process. The heat-treatment process was designed according to the differential thermal analysis and thermogravimetric analysis, in which the thermolysis temperature of the precursor layer is 620-800 oC and the crystallization temperature of the buffer layer is 825 oC. According to X-ray diffraction (XRD) analysis, the main phase is LaSrCoO with <100> preferred orientation after heat treatment; in addition, impurity phases are La2CO5 and LaCoO3. The LaSrCoO buffer layers have the strong biaxial texture by φ-scan and (100) polar figure. The resistivity of the buffer layers was measured by standard four-probe DC method from room-temperature to liquid-N2 temperature, and the result show that its resistivity is 1.04×10-4 Ω·m at 77 K, achieving the purpose of conductive buffer layer deposition.
Conductive La0.4Sr0.6CoO3 (LaSrCoO) buffer layers with cubic-perovskite structure were prepared on LaAlO3(100) single crystal substrates by the metal organic deposition (MOD) process. The heat-treatment process was designed according to the differential thermal analysis and thermogravimetric analysis, in which the thermolysis temperature of the precursor layer is 620-800 oC and the crystallization temperature of the buffer layer is 825 oC. According to X-ray diffraction (XRD) analysis, the main phase is LaSrCoO with <100> preferred orientation after heat treatment; in addition, impurity phases are La2CO5 and LaCoO3. The LaSrCoO buffer layers have the strong biaxial texture by φ-scan and (100) polar figure. The resistivity of the buffer layers was measured by standard four-probe DC method from room-temperature to liquid-N2 temperature, and the result show that its resistivity is 1.04×10-4 Ω·m at 77 K, achieving the purpose of conductive buffer layer deposition.
2011, 40(4):689-692.
Abstract:
The microstructure and mechanical properties of a spray-deposited Mg-12.55Al-3.33Zn-0.58Ca-1.0Nd alloy under the hot extrusion condition were studied by XRD, OM, SEM, TEM and tensile tester. The results show that the spray-deposited as-extruded Mg alloy mainly consists of α-Mg matrix and Al2Ca phases. The matrix structure is equiaxed grain and the average grain size is about 3 μm. The Al2Ca phases with the grain size of about 1.0 μm, mainly distribute along the boundaries of the Mg matrix; furthermore, the twin structures exist in the Al2Ca phase. The σb, σ0.2 and δ of the Mg alloy reach 450, 325 MPa and 5%, respectively. Fracture morphologies show the massive stone-like Al2Ca phases, and it is the characteristic of intergranular fracture mode. Compared with conventional cast AZ91 alloy after hot extrusion, the spray deposited Mg-12.55Al-3.33Zn-0.58Ca-1.0Nd alloy possesses higher strength, but with poor ductility. High strength of the spray deposited Mg alloy is attributed to fine crystal strengthening and solution strengthening of Al and Zn atoms in the Mg matrix, while massive Al2Ca phases distributing along grain boundaries of the Mg matrix are responsible for the poor ductility in the Mg alloy.
The microstructure and mechanical properties of a spray-deposited Mg-12.55Al-3.33Zn-0.58Ca-1.0Nd alloy under the hot extrusion condition were studied by XRD, OM, SEM, TEM and tensile tester. The results show that the spray-deposited as-extruded Mg alloy mainly consists of α-Mg matrix and Al2Ca phases. The matrix structure is equiaxed grain and the average grain size is about 3 μm. The Al2Ca phases with the grain size of about 1.0 μm, mainly distribute along the boundaries of the Mg matrix; furthermore, the twin structures exist in the Al2Ca phase. The σb, σ0.2 and δ of the Mg alloy reach 450, 325 MPa and 5%, respectively. Fracture morphologies show the massive stone-like Al2Ca phases, and it is the characteristic of intergranular fracture mode. Compared with conventional cast AZ91 alloy after hot extrusion, the spray deposited Mg-12.55Al-3.33Zn-0.58Ca-1.0Nd alloy possesses higher strength, but with poor ductility. High strength of the spray deposited Mg alloy is attributed to fine crystal strengthening and solution strengthening of Al and Zn atoms in the Mg matrix, while massive Al2Ca phases distributing along grain boundaries of the Mg matrix are responsible for the poor ductility in the Mg alloy.
2011, 40(4):693-696.
Abstract:
AgNi10/Cu/Fe layered composites were prepared by cold roll bonding with equal-roller-diameter and equal-rolling-speed. The interface bonding mechanism was investigated. The raw tapes of the AgNi10, Cu and Fe were singly annealed before bonding so as to obtain homogeneous recrystallized microstructures and similar hardness. The surfaces to be bonded were cleaned by a scratch brush just before entering the roll gap. After bonding, the peeled interfaces of the composites were analyzed by SEM and EDS. Results show that the bonding mechanism of the as-rolled interfaces is primarily cracking. During roll bonding, the work-hardened surface layers are fractured. Virgin metals of the softer layers (AgNi10 and Cu for AgNi10/Cu and Cu/Fe respectively) are extruded from the cracks and bonded with the harder ones (Cu and Fe). The bonding strength is greater than the fracture strength of AgNi10 and Cu in AgNi10/Cu and Cu/Fe.
AgNi10/Cu/Fe layered composites were prepared by cold roll bonding with equal-roller-diameter and equal-rolling-speed. The interface bonding mechanism was investigated. The raw tapes of the AgNi10, Cu and Fe were singly annealed before bonding so as to obtain homogeneous recrystallized microstructures and similar hardness. The surfaces to be bonded were cleaned by a scratch brush just before entering the roll gap. After bonding, the peeled interfaces of the composites were analyzed by SEM and EDS. Results show that the bonding mechanism of the as-rolled interfaces is primarily cracking. During roll bonding, the work-hardened surface layers are fractured. Virgin metals of the softer layers (AgNi10 and Cu for AgNi10/Cu and Cu/Fe respectively) are extruded from the cracks and bonded with the harder ones (Cu and Fe). The bonding strength is greater than the fracture strength of AgNi10 and Cu in AgNi10/Cu and Cu/Fe.
2011, 40(4):697-700.
Abstract:
The oxidation of palladium membrane at different temperatures and the hydrogenization of the oxidized membrane at room temperature were carried out in a silica tubular furnace. The variation of surface phase was observed and analyzed by XPS, SEM and XRD. The effects of O2 poison and hydrogenization on the surface morphology and composition of the Pd membrane were investigated. The results show that when the oxidation temperature is below 240 oC, the adsorptive capacity of O on the Pd surface is increased with the temperature rising but there is no obvious PdO. However, PdO together with micropores could be detected apparently at the oxidation temperature above 240 oC, and the mass ratio of PdO and the amount and dimension of the micropores are increased by further increasing the temperature. The Pd surface turns into PdO completely for the Pd membrane oxidized at 390 oC for 1 h. After hydrogenization, all of the PdO and free O on the Pd surface vanish; the surface phases of Pd membrane are reduced fully to the state before reaction, but the multiaperture surface is reserved. At 240 oC and the higher temperature, the oxidized Pd membrane can react with hydrogen, resulting in obvious plastic deformation.
The oxidation of palladium membrane at different temperatures and the hydrogenization of the oxidized membrane at room temperature were carried out in a silica tubular furnace. The variation of surface phase was observed and analyzed by XPS, SEM and XRD. The effects of O2 poison and hydrogenization on the surface morphology and composition of the Pd membrane were investigated. The results show that when the oxidation temperature is below 240 oC, the adsorptive capacity of O on the Pd surface is increased with the temperature rising but there is no obvious PdO. However, PdO together with micropores could be detected apparently at the oxidation temperature above 240 oC, and the mass ratio of PdO and the amount and dimension of the micropores are increased by further increasing the temperature. The Pd surface turns into PdO completely for the Pd membrane oxidized at 390 oC for 1 h. After hydrogenization, all of the PdO and free O on the Pd surface vanish; the surface phases of Pd membrane are reduced fully to the state before reaction, but the multiaperture surface is reserved. At 240 oC and the higher temperature, the oxidized Pd membrane can react with hydrogen, resulting in obvious plastic deformation.
2011, 40(4):701-704.
Abstract:
Co-Al-W合金; 高温氧化; 激活能; 合金元素
Co-Al-W合金; 高温氧化; 激活能; 合金元素
2011, 40(4):705-707.
Abstract:
(1–X)BiScO3-XPbTiO3(X=0.60, 0.62, 0.64, 0.66, 0.68) piezoelectric ceramics were synthesized by a conventional solid-reaction method, and their microstructure and piezoelectric/dielectric properties were investigated. XRD results show that there is morphotropic phase boundary (MPB) when X=0.64, the samples are rombohedral phases when X<0.64, and tetragonal phases when X>0.64. The maximum piezoelectric constant of 430 pC/N is obtained with the MPB composition. The dielectric-temperature test results indicate that BiScO3-PbTiO3 system is relaxor ferroelectric and has a very high Curie temperature of 450 oC.
(1–X)BiScO3-XPbTiO3(X=0.60, 0.62, 0.64, 0.66, 0.68) piezoelectric ceramics were synthesized by a conventional solid-reaction method, and their microstructure and piezoelectric/dielectric properties were investigated. XRD results show that there is morphotropic phase boundary (MPB) when X=0.64, the samples are rombohedral phases when X<0.64, and tetragonal phases when X>0.64. The maximum piezoelectric constant of 430 pC/N is obtained with the MPB composition. The dielectric-temperature test results indicate that BiScO3-PbTiO3 system is relaxor ferroelectric and has a very high Curie temperature of 450 oC.
2011, 40(4):708-713.
Abstract:
The influence of simplex aging and duplex aging on the microstructures and mechanical properties of Ti-10V-2Fe-3Al (Ti1023) alloys were investigated. Results show that for the same aging time, yield strength of duplex aged samples is slightly lower than that of simplex aged samples. However, elongation of duplex aged samples is significantly higher than that of simplex aged ones. Compared with the simplex aged samples, the better combination of strength and ductility occurs in duplex aged ones. SEM fractography of simplex aged samples shows intergranular fracture mode at lower magnification but grain boundary ductile fracture at higher magnification. However, for duplex aged samples, transgranular dimple fracture is dominant. Microstructure observations show that the good combination of strength and ductility of duplex aged samples is attributed to the microstructure of alternately arranged α/β plates, the suppression of continuous grain boundary α film and the decreased strength difference between the β aged matrix and the β grain boundary precipitate zone.
The influence of simplex aging and duplex aging on the microstructures and mechanical properties of Ti-10V-2Fe-3Al (Ti1023) alloys were investigated. Results show that for the same aging time, yield strength of duplex aged samples is slightly lower than that of simplex aged samples. However, elongation of duplex aged samples is significantly higher than that of simplex aged ones. Compared with the simplex aged samples, the better combination of strength and ductility occurs in duplex aged ones. SEM fractography of simplex aged samples shows intergranular fracture mode at lower magnification but grain boundary ductile fracture at higher magnification. However, for duplex aged samples, transgranular dimple fracture is dominant. Microstructure observations show that the good combination of strength and ductility of duplex aged samples is attributed to the microstructure of alternately arranged α/β plates, the suppression of continuous grain boundary α film and the decreased strength difference between the β aged matrix and the β grain boundary precipitate zone.
2011, 40(4):714-717.
Abstract:
Hydroxyapatite (Ca10(PO4)6(OH)2, HA) coatings were prepared on pure Ti substrates by laser cladding (LC) in situ synthesis using mixed powders of CaCO3 and CaHPO4. In order to increase the amount of HA in the coatings, the effects of processing parameters including laser power and scanning velocity and heat treatment on the phase structure of the coatings were investigated. The results show that the coatings consist of large amount of tetracalcium phosphate (Ca4(PO4)2O, TTCP) as well as a little HA, α-tricalcium phosphate (α-Ca3(PO4)2, α-TCP), calcium oxide(CaO) and CaTiO3 when the laser power is low. As the laser power increases, the amount of TTCP, HA and CaO in the coatings decreases gradually, and finally only α-TCP and CaTiO3 remain. Compared with the laser power, the effect of scanning velocity on the phase structure of the coatings is much weaker. At the laser power of 400 W, there is no obvious difference for the phase structures at different scanning velocities and the main phase is always TTCP. It is found that the amount of HA can be increased greatly by heat treatment at 800 oC for 5 h followed by furnace cooling, due to the total transformation from TTCP and α-TCP to HA.
Hydroxyapatite (Ca10(PO4)6(OH)2, HA) coatings were prepared on pure Ti substrates by laser cladding (LC) in situ synthesis using mixed powders of CaCO3 and CaHPO4. In order to increase the amount of HA in the coatings, the effects of processing parameters including laser power and scanning velocity and heat treatment on the phase structure of the coatings were investigated. The results show that the coatings consist of large amount of tetracalcium phosphate (Ca4(PO4)2O, TTCP) as well as a little HA, α-tricalcium phosphate (α-Ca3(PO4)2, α-TCP), calcium oxide(CaO) and CaTiO3 when the laser power is low. As the laser power increases, the amount of TTCP, HA and CaO in the coatings decreases gradually, and finally only α-TCP and CaTiO3 remain. Compared with the laser power, the effect of scanning velocity on the phase structure of the coatings is much weaker. At the laser power of 400 W, there is no obvious difference for the phase structures at different scanning velocities and the main phase is always TTCP. It is found that the amount of HA can be increased greatly by heat treatment at 800 oC for 5 h followed by furnace cooling, due to the total transformation from TTCP and α-TCP to HA.
2011, 40(4):718-722.
Abstract:
A new type of continuous production technology of low pressure casting for magnesium alloy was developed. Using the duplex station design, the technology achieves the switch between two pieces of low pressure casting equipment of magnesium alloy at different stations through the furnace transportation vehicle’s movements, ensuring the continuous production of magnesium alloy casting. A level suspension technology has been used in the pressure control system, which realizes the precise suspension control of metal level in riser tube orifice, reduces the oxide inclusion defects and improves the production efficiency. The developed fuzzy-PID hybrid control technology possesses high precision during the course of low pressure casting process for magnesium alloy. The pressure control error is less than 0.5 kPa.
A new type of continuous production technology of low pressure casting for magnesium alloy was developed. Using the duplex station design, the technology achieves the switch between two pieces of low pressure casting equipment of magnesium alloy at different stations through the furnace transportation vehicle’s movements, ensuring the continuous production of magnesium alloy casting. A level suspension technology has been used in the pressure control system, which realizes the precise suspension control of metal level in riser tube orifice, reduces the oxide inclusion defects and improves the production efficiency. The developed fuzzy-PID hybrid control technology possesses high precision during the course of low pressure casting process for magnesium alloy. The pressure control error is less than 0.5 kPa.
2011, 40(4):723-727.
Abstract:
TiO2 nanotube arrays were prepared by anodic oxidation, and then an electrochemical process was conducted using the as-prepared TiO2 nanotube arrays as cathode and Pt as anode; the electrolyte was Zr(NO3)4, NH4Cl and mixture of Zr(NO3)4 and NH4Cl, respectively. Zr-doped, N-doped and Zr, N-codoped titania nanotube arrays were prepared. The nanotube arrays were characterized by FESEM, UV-vis DRS, XRD and XPS. FESEM show that the nanotube arrays are about 70 nm in diameter and 400 nm in length. UV-vis DRS reveal that the absorption band of co-doped nanotube arrays moves towards long wavelength. XPS indicate that the concentrations of Zr in Zr/TiO2, N in N/TiO2 and Zr, N in Zr, N/TiO2 nanotube arrays are 0.51%, 1.92%, 0.77% and 1.29%, respectively (atom fraction). N1s exhibits a single peak in N/TiO2 and double peaks in Zr, N/TiO2 nanotube arrays, which indicates that N forms are different in N/TiO2 and Zr, N/TiO2 nanotube arrays. The photocatalytic activities were tested by degradation of Rhodamine B aqueous solution. The results show that Zr-doping improves TiO2 photocatalytic activity in UV region, N-doping improves TiO2 photocatalytic activity in visible light region, and Zr, N-codoping evokes synergetic reaction and enhances TiO2 photocatalytic activity greatly both in UV and Vis regions.
TiO2 nanotube arrays were prepared by anodic oxidation, and then an electrochemical process was conducted using the as-prepared TiO2 nanotube arrays as cathode and Pt as anode; the electrolyte was Zr(NO3)4, NH4Cl and mixture of Zr(NO3)4 and NH4Cl, respectively. Zr-doped, N-doped and Zr, N-codoped titania nanotube arrays were prepared. The nanotube arrays were characterized by FESEM, UV-vis DRS, XRD and XPS. FESEM show that the nanotube arrays are about 70 nm in diameter and 400 nm in length. UV-vis DRS reveal that the absorption band of co-doped nanotube arrays moves towards long wavelength. XPS indicate that the concentrations of Zr in Zr/TiO2, N in N/TiO2 and Zr, N in Zr, N/TiO2 nanotube arrays are 0.51%, 1.92%, 0.77% and 1.29%, respectively (atom fraction). N1s exhibits a single peak in N/TiO2 and double peaks in Zr, N/TiO2 nanotube arrays, which indicates that N forms are different in N/TiO2 and Zr, N/TiO2 nanotube arrays. The photocatalytic activities were tested by degradation of Rhodamine B aqueous solution. The results show that Zr-doping improves TiO2 photocatalytic activity in UV region, N-doping improves TiO2 photocatalytic activity in visible light region, and Zr, N-codoping evokes synergetic reaction and enhances TiO2 photocatalytic activity greatly both in UV and Vis regions.
36 Synthesis of Silver Nanoparticles via Indirect Electrochemical Reduction and Antibacterial Property
2011, 40(4):728-732.
Abstract:
Silver nanoparticles were synthesized by the reduction of silver ions through indirect electrochemical-reduction method using 12-phosphotungstic with Keggin structure as reductant. The effects of the molar ratio of phosphotungstic acid to silver ions on the silver nanoparticle sizes were investigated. The morphology, composition, particle size and phase structure of the silver nanoparticles were characterized by transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-vis), X-ray photoelectron spectra (XPS), and X-ray diffraction analysis (XRD). The antibacterial efficiency of silver nanoparticles was tested against E. coli and B. subtilis. The results show that the average size of silver nanoparticles increases with the decrease of the molar ratio of phosphotungstic acid to silver ions. The silver nanoparticles have good and steady antimicrobial property against E. coli and B. subtilis.
Silver nanoparticles were synthesized by the reduction of silver ions through indirect electrochemical-reduction method using 12-phosphotungstic with Keggin structure as reductant. The effects of the molar ratio of phosphotungstic acid to silver ions on the silver nanoparticle sizes were investigated. The morphology, composition, particle size and phase structure of the silver nanoparticles were characterized by transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-vis), X-ray photoelectron spectra (XPS), and X-ray diffraction analysis (XRD). The antibacterial efficiency of silver nanoparticles was tested against E. coli and B. subtilis. The results show that the average size of silver nanoparticles increases with the decrease of the molar ratio of phosphotungstic acid to silver ions. The silver nanoparticles have good and steady antimicrobial property against E. coli and B. subtilis.
2011, 40(4):733-736.
Abstract:
Ti-Nb-Ni alloy films were prepared on uranium substrate by unbalanced twin target magnetron sputtering at different bias voltages and deposition rates. The microstructure and corrosion resistance of the films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical polarization experiments. The results show that the Ti-Nb-Ni films are crystal when the deposition rate ratio of Ti:Nb:Ni is 3:1.5:1.5 at 0 V bias voltage. But the Ti-Nb-Ni films are amorphous when the control current of Ti deposition rates is from 5 A to 7 A with unchanged deposition rates of Nb and Ni. The microstructure evolution of the alloy films is as following: amorphous→dispersed small grains→dense small grains→large grains with the bias voltage increasing from 0 to –2000 V. The electrochemical polarization experiments indicate that the films prepared by the compounding techniques of non-crystallization and crystallization have excellent corrosion resistance.
Ti-Nb-Ni alloy films were prepared on uranium substrate by unbalanced twin target magnetron sputtering at different bias voltages and deposition rates. The microstructure and corrosion resistance of the films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical polarization experiments. The results show that the Ti-Nb-Ni films are crystal when the deposition rate ratio of Ti:Nb:Ni is 3:1.5:1.5 at 0 V bias voltage. But the Ti-Nb-Ni films are amorphous when the control current of Ti deposition rates is from 5 A to 7 A with unchanged deposition rates of Nb and Ni. The microstructure evolution of the alloy films is as following: amorphous→dispersed small grains→dense small grains→large grains with the bias voltage increasing from 0 to –2000 V. The electrochemical polarization experiments indicate that the films prepared by the compounding techniques of non-crystallization and crystallization have excellent corrosion resistance.
2011, 40(4):737-740.
Abstract:
The influence of cooling rates on the microstructure and transport properties of (Bi,Pb)-2223/Ag tapes after the first heat treatment was investigated. The samples were characterized by XRD and SEM. Results show that the 2201 phases decrease until disappear while Ca2PbO4 increases continuously as the cooling rate decreases; at the same time the size of non-superconducting secondary phase particles become larger. The transport current tests show that the critical current density increases linearly with the cooling rate decreasing logarithmically; meanwhile, the transport current properties of the tapes in the magnetic field increases. This behavior is attributed to improvement of the grain connectivity and flux pinning properties of the tapes as the cooling rate is decreased.
The influence of cooling rates on the microstructure and transport properties of (Bi,Pb)-2223/Ag tapes after the first heat treatment was investigated. The samples were characterized by XRD and SEM. Results show that the 2201 phases decrease until disappear while Ca2PbO4 increases continuously as the cooling rate decreases; at the same time the size of non-superconducting secondary phase particles become larger. The transport current tests show that the critical current density increases linearly with the cooling rate decreasing logarithmically; meanwhile, the transport current properties of the tapes in the magnetic field increases. This behavior is attributed to improvement of the grain connectivity and flux pinning properties of the tapes as the cooling rate is decreased.
2011, 40(4):741-744.
Abstract:
Using ascorbic acid as reducing agent and gelatin as dispersant, the spherical ultra-fine silver powder was synthesized by the chemical reduction method. The influence of AgNO3 solution concentration, pH value, gelatin dosage and reagents adding orders on the diameter of silver particles and particle distribution were studied. The spherical ultra-fine silver powder with the diameter of about 1.5 μm and homogeneous particle size distribution is prepared under the conditions as following: adding 0.5 mol/L AgNO3 solution into 0.25 mol/L ascorbic acid solution, gelatin dosage 1.5% of AgNO3 mass, adding gelatin drop by drop after the precipitate appearing, and pH=7.
Using ascorbic acid as reducing agent and gelatin as dispersant, the spherical ultra-fine silver powder was synthesized by the chemical reduction method. The influence of AgNO3 solution concentration, pH value, gelatin dosage and reagents adding orders on the diameter of silver particles and particle distribution were studied. The spherical ultra-fine silver powder with the diameter of about 1.5 μm and homogeneous particle size distribution is prepared under the conditions as following: adding 0.5 mol/L AgNO3 solution into 0.25 mol/L ascorbic acid solution, gelatin dosage 1.5% of AgNO3 mass, adding gelatin drop by drop after the precipitate appearing, and pH=7.
2011, 40(4):745-748.
Abstract:
Polyester cloth and viscose fiber cloth used as precursors were treated by solution dipping process. After drying they were reduced and sintered in hydrogen atmosphere and finally nickel metal cloth was obtained. The effects of sintering systems on the microstructure and phases of the nickel metal cloth were studied by SEM and XRD. The reaction mechanism of the reduction sintering was investigated by TG-DTA analysis. The results show that the complete, continuous and flexible nickel metal cloth can be prepared when the viscose fiber cloth used as precursor is dipped in the NiCl2 solution and then sintered at 900 oC in hydrogen atmosphere.
Polyester cloth and viscose fiber cloth used as precursors were treated by solution dipping process. After drying they were reduced and sintered in hydrogen atmosphere and finally nickel metal cloth was obtained. The effects of sintering systems on the microstructure and phases of the nickel metal cloth were studied by SEM and XRD. The reaction mechanism of the reduction sintering was investigated by TG-DTA analysis. The results show that the complete, continuous and flexible nickel metal cloth can be prepared when the viscose fiber cloth used as precursor is dipped in the NiCl2 solution and then sintered at 900 oC in hydrogen atmosphere.
2011, 40(4):749-752.
Abstract:
The nanocomposites of TiO2 doped with different Ag contents were prepared by hydrothermal process, and PANI/Ag-TiO2 fibrous nanocomposites were synthesized via in-situ polymerization. The structures of products were characterized by the detection techniques including XRD, SEM and FT-IR. The effects of light source, Ag doping content and types of bacterias on the antibacterial activity of PANI/Ag-TiO2 fibrous nanocomposites were investigated. The results show that the PANI/Ag-TiO2 fibrous nanocomposites have excellent antibacterial activity under the dark light, which is further improved under long-wave UV condition. With the concentration of 1 mg/mL, the sterilization rate to 4 kinds of bacterias of the PANI/Ag-TiO2 nanocomposites can reach 99.99% averagely under the dark light.
The nanocomposites of TiO2 doped with different Ag contents were prepared by hydrothermal process, and PANI/Ag-TiO2 fibrous nanocomposites were synthesized via in-situ polymerization. The structures of products were characterized by the detection techniques including XRD, SEM and FT-IR. The effects of light source, Ag doping content and types of bacterias on the antibacterial activity of PANI/Ag-TiO2 fibrous nanocomposites were investigated. The results show that the PANI/Ag-TiO2 fibrous nanocomposites have excellent antibacterial activity under the dark light, which is further improved under long-wave UV condition. With the concentration of 1 mg/mL, the sterilization rate to 4 kinds of bacterias of the PANI/Ag-TiO2 nanocomposites can reach 99.99% averagely under the dark light.
