Volume 42,Issue 4,2013 Table of Contents
2013, 42(4):661-666.
Abstract:
In order to investigate the effect of Nd on the microstructure and corrosion resistance of Mg-Zn-Mn-Ca alloy, 0.4 wt% Nd was added into Mg-6Zn-1Mn-0.5Ca alloy. OM, SEM equipped with EDS and XRD were used to characterize the microstructures, and crystal structures. The bio-corrosion resistance were studied by immersion corrosion, hydrogen evolution and electrochemical measurement in simulated body fluid (SBF). Results show that the grain size decreases with the addition of Nd. A mixture of secondary phases Ca2Mg6Zn3+Mg41Nd5 is found in Mg-6Zn-1Mn-0.5Ca-0.4Nd alloy. After immersion in SBF for 7 d, more such mixture still remains on the Nd-containing alloy surface, whereas few Ca2Mg6Zn3 particles remain on the alloy without Nd. Thus, the bio-corrosion resistance increases due to presence of Nd.
In order to investigate the effect of Nd on the microstructure and corrosion resistance of Mg-Zn-Mn-Ca alloy, 0.4 wt% Nd was added into Mg-6Zn-1Mn-0.5Ca alloy. OM, SEM equipped with EDS and XRD were used to characterize the microstructures, and crystal structures. The bio-corrosion resistance were studied by immersion corrosion, hydrogen evolution and electrochemical measurement in simulated body fluid (SBF). Results show that the grain size decreases with the addition of Nd. A mixture of secondary phases Ca2Mg6Zn3+Mg41Nd5 is found in Mg-6Zn-1Mn-0.5Ca-0.4Nd alloy. After immersion in SBF for 7 d, more such mixture still remains on the Nd-containing alloy surface, whereas few Ca2Mg6Zn3 particles remain on the alloy without Nd. Thus, the bio-corrosion resistance increases due to presence of Nd.
2013, 42(4):667-672.
Abstract:
The effect of manufacturing conditions such as rolling reductions and steps on the texture and microstructure was investigated for an hot-rolled Zr-1.0Nb sheet. The crystallographic texture of the cold-rolled and annealed sheet was examined by X-ray diffraction (XRD) for the rolling plane, and the microstructure was characterized by transmission electron microscopy (TEM) and electron back-scattering diffraction (SEM-EBSD). The results show that the grain size ranges from bimodal distribution to homogeneous distribution with the increase of cold rolling reductions from 30% to 70%. Textural developments are generalized in terms of (0001) and <100> fibers and enhanced by the progressive cold rolling and annealing. The correlation between texture and microstructure developments has been discussed extensively based on the obtained results.
The effect of manufacturing conditions such as rolling reductions and steps on the texture and microstructure was investigated for an hot-rolled Zr-1.0Nb sheet. The crystallographic texture of the cold-rolled and annealed sheet was examined by X-ray diffraction (XRD) for the rolling plane, and the microstructure was characterized by transmission electron microscopy (TEM) and electron back-scattering diffraction (SEM-EBSD). The results show that the grain size ranges from bimodal distribution to homogeneous distribution with the increase of cold rolling reductions from 30% to 70%. Textural developments are generalized in terms of (0001) and <100> fibers and enhanced by the progressive cold rolling and annealing. The correlation between texture and microstructure developments has been discussed extensively based on the obtained results.
2013, 42(4):673-678.
Abstract:
The microstructure and texture evolution in the hot-deformed Mg-8Li-5Zn-2Re alloy were investigated by optical micrography, SEM and X-ray diffraction. In the hot-extruded Mg-8Li-5Zn-2Re alloy, α phase is elongated approximately parallel to the extruding direction and exhibits a deformed structure. During hot compression, α phase is transformed to β phase with increasing of temperature. At the stage of hot extrusion, {001} <110> and {110} <110> textures of β phase are exhibited, while {0001} <100> texture in α phase is detected due to basal slip. As a result of the frequent changes of compression condition, grain orientation distribution changes obviously. The evolution of deformation texture was analyzed using the XRD analysis in the hot compression test under different deformation temperatures and strain rates.
The microstructure and texture evolution in the hot-deformed Mg-8Li-5Zn-2Re alloy were investigated by optical micrography, SEM and X-ray diffraction. In the hot-extruded Mg-8Li-5Zn-2Re alloy, α phase is elongated approximately parallel to the extruding direction and exhibits a deformed structure. During hot compression, α phase is transformed to β phase with increasing of temperature. At the stage of hot extrusion, {001} <110> and {110} <110> textures of β phase are exhibited, while {0001} <100> texture in α phase is detected due to basal slip. As a result of the frequent changes of compression condition, grain orientation distribution changes obviously. The evolution of deformation texture was analyzed using the XRD analysis in the hot compression test under different deformation temperatures and strain rates.
2013, 42(4):679-683.
Abstract:
The simplified slice-plain-strain method and the incorporating incremental superposition theory were adopted for the cumulative effective strain (CES) of elliptical cross-section spiral equal-channel extrusion (ECSEE) process. The ECSEE deformation was divided into two basic deformation modes: round-ellipse/ellipse-round cross-section transitional channel deformation and elliptical cross-section torsion transitional channel deformation, through tracking a particle of the cross section. The change laws for the combined CES of the particle with the channel length and the combined effective strain (ES) distribution were obtained by MATLAB software programming, and the results were compared with these via Deform-3D finite element method (FEM). The results show that the ECSEE accumulation torsion strain is greater than that of other forms, and the shear deformation is dominant. The blank cross-section ES presents the gradient decreasing trend from the periphery to the center. The FEM results also verify the accuracy of analytical solution.
The simplified slice-plain-strain method and the incorporating incremental superposition theory were adopted for the cumulative effective strain (CES) of elliptical cross-section spiral equal-channel extrusion (ECSEE) process. The ECSEE deformation was divided into two basic deformation modes: round-ellipse/ellipse-round cross-section transitional channel deformation and elliptical cross-section torsion transitional channel deformation, through tracking a particle of the cross section. The change laws for the combined CES of the particle with the channel length and the combined effective strain (ES) distribution were obtained by MATLAB software programming, and the results were compared with these via Deform-3D finite element method (FEM). The results show that the ECSEE accumulation torsion strain is greater than that of other forms, and the shear deformation is dominant. The blank cross-section ES presents the gradient decreasing trend from the periphery to the center. The FEM results also verify the accuracy of analytical solution.
2013, 42(4):684-687.
Abstract:
The electrochemical performance of high-voltage LiCoPO4 electrode synthesized by high-temperature solid-state reaction was investigated. It is found that the existence of the carbon and Co2P decreases the discharge capacity; the LiCoPO4 with pure olivine phase has a maximum discharge capacity and it can reach 135 mAh/g. The cyclic voltammetric measurements have shown that the impurity of carbon and Co2P can change the Li-deintercalation reaction mechanism. There are two oxidation peaks when the impurity content is relatively low; however, there is only on oxidation peak with the larger amount of impurities in the cyclic voltammetry. The interface capacitance between the LiCoPO4 electrode and the electrolyte is about 16.9 mF/cm2 and the apparent diffusion coefficient of the lithium ion in the solid phase is (2.0~3.4)′10-9 m2/s, based on the impedance measurements.
The electrochemical performance of high-voltage LiCoPO4 electrode synthesized by high-temperature solid-state reaction was investigated. It is found that the existence of the carbon and Co2P decreases the discharge capacity; the LiCoPO4 with pure olivine phase has a maximum discharge capacity and it can reach 135 mAh/g. The cyclic voltammetric measurements have shown that the impurity of carbon and Co2P can change the Li-deintercalation reaction mechanism. There are two oxidation peaks when the impurity content is relatively low; however, there is only on oxidation peak with the larger amount of impurities in the cyclic voltammetry. The interface capacitance between the LiCoPO4 electrode and the electrolyte is about 16.9 mF/cm2 and the apparent diffusion coefficient of the lithium ion in the solid phase is (2.0~3.4)′10-9 m2/s, based on the impedance measurements.
2013, 42(4):688-691.
Abstract:
The formation, wetting and spreading process of the liquid amorphous filler metal were investigated. The results indicate that the eutectic phase of the amorphous filler metal is damaged and plenty of high melting-point copper solid solution and copper-nickel compound are generated due to the full solid-phase diffusion before melting. Therefore, relatively less liquid phase is produced by amorphous filler metal than crystalline filler metal and the liquid phase spreading and flow is weak. However, the crystalline filler metal generates a large amount of liquid phase. Spreading and flowing of the liquid phase is the main process of crystalline filler metal brazing. As the amorphous filler metal is very thin, the atomic diffusion distance is very short in the filler metal, which is quite favorable for the rapid dissolution into the base metals. The ordinary filler metal is relatively thick, and it tends to take longer time to dissolve than the amorphous filler metal. The thickness of the residual filler metal decreases with the increase of brazing temperature and dwell time. The thickness of the residual layer of amorphous filler metal is smaller than that of the crystalline filler metal under the same brazing temperature and dwell time.
The formation, wetting and spreading process of the liquid amorphous filler metal were investigated. The results indicate that the eutectic phase of the amorphous filler metal is damaged and plenty of high melting-point copper solid solution and copper-nickel compound are generated due to the full solid-phase diffusion before melting. Therefore, relatively less liquid phase is produced by amorphous filler metal than crystalline filler metal and the liquid phase spreading and flow is weak. However, the crystalline filler metal generates a large amount of liquid phase. Spreading and flowing of the liquid phase is the main process of crystalline filler metal brazing. As the amorphous filler metal is very thin, the atomic diffusion distance is very short in the filler metal, which is quite favorable for the rapid dissolution into the base metals. The ordinary filler metal is relatively thick, and it tends to take longer time to dissolve than the amorphous filler metal. The thickness of the residual filler metal decreases with the increase of brazing temperature and dwell time. The thickness of the residual layer of amorphous filler metal is smaller than that of the crystalline filler metal under the same brazing temperature and dwell time.
7 Preparation of Nano-SnO2 Abrasives and Their Application in Chemical Mechanical Polish of Ruthenium
2013, 42(4):692-695.
Abstract:
SnO2 abrasives were prepared by solid-state reaction and the effect of the preparation conditions on the average particle size of SnO2 suspension was investigated. The result manifests that the suspension prepared from SnO2 powder obtained by calcining at 500 °C for 4 h has good dispersion and good stability. CMP (chemical mechanical polish) experiments were performed on high purity Ru by home-made slurry. The MRR (material removed rate) and the roughness of the surface decrease compared with SiO2 slurry. The results reveal that MRR can reach 6.8 nm/min under the following conditions: the main constituents in slurry are 1 wt% SnO2, 1 wt% (NH4)2S2O8, 1 wt% tartaric acid and 3 mmol/L imidazole, the pH value is 8.0, the down force is 17.24 kPa; the roughness Ra is 4.8 nm under these conditions.
SnO2 abrasives were prepared by solid-state reaction and the effect of the preparation conditions on the average particle size of SnO2 suspension was investigated. The result manifests that the suspension prepared from SnO2 powder obtained by calcining at 500 °C for 4 h has good dispersion and good stability. CMP (chemical mechanical polish) experiments were performed on high purity Ru by home-made slurry. The MRR (material removed rate) and the roughness of the surface decrease compared with SiO2 slurry. The results reveal that MRR can reach 6.8 nm/min under the following conditions: the main constituents in slurry are 1 wt% SnO2, 1 wt% (NH4)2S2O8, 1 wt% tartaric acid and 3 mmol/L imidazole, the pH value is 8.0, the down force is 17.24 kPa; the roughness Ra is 4.8 nm under these conditions.
2013, 42(4):696-699.
Abstract:
Aiming to improve vanadium leaching rate and provide theoretical basis for vanadium leaching from low-vanadium steel slag through wet leaching, the whole leaching process was studied in dynamics and effects of temperature, liquid-solid ratio, leaching time and stirring velocity were observed. Results show that vanadium leaching rate from low-vanadium steel slag could reach to 98.8% at 90 °C when leaching in the solution with liquid-solid ratio of 10:1 and containing 4.0 mol/L hydrochloric acid and 8.0 mL hydrogen peroxide for 90 min. An empirical equation describing the leaching process was obtained from orthogonal experiment and dynamics derivation. The dynamical model of wet leaching vanadium from low-vanadium steel slag is the unreacted shrinking core model while the apparent activation energy of the leaching process is 7.21 kJ/mol. The model shows that control steps of the leaching process depend on the diffusion speed of the boundary layers. Vanadium leaching velocity could be sped up and the yield could be improved by enhancing temperature, liquid-solid ratio and leaching time.
Aiming to improve vanadium leaching rate and provide theoretical basis for vanadium leaching from low-vanadium steel slag through wet leaching, the whole leaching process was studied in dynamics and effects of temperature, liquid-solid ratio, leaching time and stirring velocity were observed. Results show that vanadium leaching rate from low-vanadium steel slag could reach to 98.8% at 90 °C when leaching in the solution with liquid-solid ratio of 10:1 and containing 4.0 mol/L hydrochloric acid and 8.0 mL hydrogen peroxide for 90 min. An empirical equation describing the leaching process was obtained from orthogonal experiment and dynamics derivation. The dynamical model of wet leaching vanadium from low-vanadium steel slag is the unreacted shrinking core model while the apparent activation energy of the leaching process is 7.21 kJ/mol. The model shows that control steps of the leaching process depend on the diffusion speed of the boundary layers. Vanadium leaching velocity could be sped up and the yield could be improved by enhancing temperature, liquid-solid ratio and leaching time.
2013, 42(4):700-705.
Abstract:
In order to simulate three-dimensional dendritic evolution of binary alloys under melt convection, a modified cellular automaton (MCA) model was developed. With considering the influence of surface energy anisotropy and solute diffusion on the evolution of solid/liquid interface, and solving the mass transport equation coupled with Navier-Stokes equations on the same grid, the MCA model could simulate the interaction between solute diffusion and melt convection. In this study, 3-D dendritic growth of Al-7wt%Si alloy was simulated with forced convection at constant undercooling by the MCA model. It is found that the upstream tip of the dendrite grows faster than that of the downstream tip under forced convection, due to lower solute concentration and larger solute gradient in the front of the upstream interface caused by forced convection. Meanwhile, the simulated dimensionless solute supersaturation agrees well with Oseen-Ivantsov solution at higher forced convection. The effect of forced convection on dendrite morphology was also studied under 3-D and 2-D simulation. The solute enriched at the upstream frontier of solid/liquid interface is washed away bypassing the primary dendrite arms from the upstream to downstream direction by 3-D forced convection. However, in 2-D convection, the solute could only go over the tips of the perpendicular dendrite arms from the upstream to downstream direction. Therefore, the 3-D MCA model is more accurate in simulating the influence of forced convection on dendritic growth than a 2-D model.
In order to simulate three-dimensional dendritic evolution of binary alloys under melt convection, a modified cellular automaton (MCA) model was developed. With considering the influence of surface energy anisotropy and solute diffusion on the evolution of solid/liquid interface, and solving the mass transport equation coupled with Navier-Stokes equations on the same grid, the MCA model could simulate the interaction between solute diffusion and melt convection. In this study, 3-D dendritic growth of Al-7wt%Si alloy was simulated with forced convection at constant undercooling by the MCA model. It is found that the upstream tip of the dendrite grows faster than that of the downstream tip under forced convection, due to lower solute concentration and larger solute gradient in the front of the upstream interface caused by forced convection. Meanwhile, the simulated dimensionless solute supersaturation agrees well with Oseen-Ivantsov solution at higher forced convection. The effect of forced convection on dendrite morphology was also studied under 3-D and 2-D simulation. The solute enriched at the upstream frontier of solid/liquid interface is washed away bypassing the primary dendrite arms from the upstream to downstream direction by 3-D forced convection. However, in 2-D convection, the solute could only go over the tips of the perpendicular dendrite arms from the upstream to downstream direction. Therefore, the 3-D MCA model is more accurate in simulating the influence of forced convection on dendritic growth than a 2-D model.
10 Reflections of Superconductivity Unrelated to Valence Electron Density in Metal Doped Y123 Cuprates
2013, 42(4):706-711.
Abstract:
Through XRD, the superconductivity tests, the positron annihilation technology, oxygen content variation and theoretic calculations, the superconductivity of the high-Tc cuprates YBa2Cu3-x (Fe, Co, Al)xO7-δ (x=0.0~0.5) was investigated, and Zn doped cuprates were also mentioned for comparison. The results and theoretic calculations support congruously that the superconducting transition temperature Tc is unrelated to the density of valence electron, and the same conclusion is from Hall Effect experiments that the Tc is not related with the carrier concentration of oxygen hole. Thus it is concluded either hole pairing or electron pairing is only a precondition but is not a real decisive factor that superconducting state occurs. If still following “electric-phonon coupling” the microcosmic mechanism of high-Tc cuprates will go astray.
Through XRD, the superconductivity tests, the positron annihilation technology, oxygen content variation and theoretic calculations, the superconductivity of the high-Tc cuprates YBa2Cu3-x (Fe, Co, Al)xO7-δ (x=0.0~0.5) was investigated, and Zn doped cuprates were also mentioned for comparison. The results and theoretic calculations support congruously that the superconducting transition temperature Tc is unrelated to the density of valence electron, and the same conclusion is from Hall Effect experiments that the Tc is not related with the carrier concentration of oxygen hole. Thus it is concluded either hole pairing or electron pairing is only a precondition but is not a real decisive factor that superconducting state occurs. If still following “electric-phonon coupling” the microcosmic mechanism of high-Tc cuprates will go astray.
2013, 42(4):712-717.
Abstract:
The distribution of the von Mises stress and strain energy density in the regions near the interfaces of g/g ￠ phases were calculated by the elastic-plastic stress-strain finite element method (FEM), and the influences of the applied stress on the von Mises stress distribution and the coarsening regularity of g ￠ phase in a [011] oriented single crystal nickel-based superalloy were investigated. Results show that after heat treating for the [011] oriented single crystal nickel-base superalloy, the cubical g ￠ phase is embedded coherently in the g matrix, and arranges regularly along the <100> direction. When the compressive stress is applied along the [011] direction, the lattice contraction of (100)g ￠ plane along [001] and [010] directions occurs, whose extrusion action may reject the Al and Ti atoms with bigger radius, while the expansion strain on (010)g ￠ and (001) g ￠ planes takes place along the [100] orientation which may trap the Al and Ti atoms with bigger radius to promote the directional growing of g ￠ phase in the (100) plane along the [010] and [001] orientations, which is thought to be the main reason of the g ￠ phase grown directionally into the mesh-like rafted structure.
The distribution of the von Mises stress and strain energy density in the regions near the interfaces of g/g ￠ phases were calculated by the elastic-plastic stress-strain finite element method (FEM), and the influences of the applied stress on the von Mises stress distribution and the coarsening regularity of g ￠ phase in a [011] oriented single crystal nickel-based superalloy were investigated. Results show that after heat treating for the [011] oriented single crystal nickel-base superalloy, the cubical g ￠ phase is embedded coherently in the g matrix, and arranges regularly along the <100> direction. When the compressive stress is applied along the [011] direction, the lattice contraction of (100)g ￠ plane along [001] and [010] directions occurs, whose extrusion action may reject the Al and Ti atoms with bigger radius, while the expansion strain on (010)g ￠ and (001) g ￠ planes takes place along the [100] orientation which may trap the Al and Ti atoms with bigger radius to promote the directional growing of g ￠ phase in the (100) plane along the [010] and [001] orientations, which is thought to be the main reason of the g ￠ phase grown directionally into the mesh-like rafted structure.
2013, 42(4):718-723.
Abstract:
The electronic structure of LiFePO4, including the energy band, PDOS and popularity analysis was determined by the first-principles based on the density functional theory (DFT), via Nb substituting for Fe or Li with Nb in LiFePO4 supercell. Results show that after Nb doping, the structure is stable and the band gap decreases resulting in the increase of the electronic conductivity and the rate of discharge/recharge, and this can be attributed to the electrons in orbital d, which leads to the increasing of the band near the Fermi level. The bond length of Li-O increases, which benefits the diffusivity of lithium ion. The band gap decreases with more doping amount, and it can influence the diffusivity of lithium ion, especially at Li site. Therefore, it is concluded that the doping content should not be too much.
The electronic structure of LiFePO4, including the energy band, PDOS and popularity analysis was determined by the first-principles based on the density functional theory (DFT), via Nb substituting for Fe or Li with Nb in LiFePO4 supercell. Results show that after Nb doping, the structure is stable and the band gap decreases resulting in the increase of the electronic conductivity and the rate of discharge/recharge, and this can be attributed to the electrons in orbital d, which leads to the increasing of the band near the Fermi level. The bond length of Li-O increases, which benefits the diffusivity of lithium ion. The band gap decreases with more doping amount, and it can influence the diffusivity of lithium ion, especially at Li site. Therefore, it is concluded that the doping content should not be too much.
2013, 42(4):724-729.
Abstract:
Microstructure characteristics of the laser melting deposited TC17 titanium alloy components were analyzed by OM, SEM and XRD. The solid-state phase transformation and the microstructure evolution under the effect of laser short term cycle of heating and cooling were researched. Results show that the laser melting deposited TC17 titanium alloy consists of directionally solidified “knuckle” grains and a few equiaxed grains, which are arranged alternately. The microstructure of the laser melting deposited TC17 titanium alloy is fine duplex microstructure composed of irregular primary lamellar a and basketwave transformed β. Solid-phase transformation is shown in the last twelve depositing layers: the microstructure in the last four layers is Martensite; in the 5th to 7th layer is mainly acicular a and a little irregular coarse a; in the 8th to 12th layer is coarser and shorter a with underdeveloped serrated interface and the second a is fine basketwave microstructure.
Microstructure characteristics of the laser melting deposited TC17 titanium alloy components were analyzed by OM, SEM and XRD. The solid-state phase transformation and the microstructure evolution under the effect of laser short term cycle of heating and cooling were researched. Results show that the laser melting deposited TC17 titanium alloy consists of directionally solidified “knuckle” grains and a few equiaxed grains, which are arranged alternately. The microstructure of the laser melting deposited TC17 titanium alloy is fine duplex microstructure composed of irregular primary lamellar a and basketwave transformed β. Solid-phase transformation is shown in the last twelve depositing layers: the microstructure in the last four layers is Martensite; in the 5th to 7th layer is mainly acicular a and a little irregular coarse a; in the 8th to 12th layer is coarser and shorter a with underdeveloped serrated interface and the second a is fine basketwave microstructure.
2013, 42(4):730-735.
Abstract:
A micro-scale W skeleton porous model was built by random Voronoi segments, and the infiltration process of CuW alloy was then simulated using a finite volume method based on the Navier-Stokes momentum equation modified by Young-Laplace. The simulation results show that improving the wettability of Cu-W can accelerate the velocity in the center of copper flow and strengthen the adhesion of liquid copper to the wall of W skeleton, resulting in the mechanical combination at the interface of Cu-W. Moreover, the transition of reaming and shrinkage due to the ununiform pore size can produce whirlpools of copper liquid in the pores, resulting in pores in the CuW alloy, and thus the filling rate of copper liquid is decreased.
A micro-scale W skeleton porous model was built by random Voronoi segments, and the infiltration process of CuW alloy was then simulated using a finite volume method based on the Navier-Stokes momentum equation modified by Young-Laplace. The simulation results show that improving the wettability of Cu-W can accelerate the velocity in the center of copper flow and strengthen the adhesion of liquid copper to the wall of W skeleton, resulting in the mechanical combination at the interface of Cu-W. Moreover, the transition of reaming and shrinkage due to the ununiform pore size can produce whirlpools of copper liquid in the pores, resulting in pores in the CuW alloy, and thus the filling rate of copper liquid is decreased.
2013, 42(4):736-740.
Abstract:
The electronic structures, elastic constants and Mullikan population of Nb and Al codoped MoSi2 were calculated by the density functional theory. The results show that the co-doping of Nb, Al can improve greatly the toughness and conductivity of MoSi2. When the doping volume of Nb and Al reaches to x= 0.25, the elastic modulus of MoSi2 decreases from 408.86 GPa to 261.30 GPa. By analyzing the density of states and Mullikan population, after doping the total density of states has a blue-shift, the charge density on Fermi level increases, the conductivity of the system improves and Mo-Al and Nb-Si bond populations decreases with their bond lengths increase. In addition, the covalent between atoms weakens, while the covalent bonds between Al and Si enhances. As the distribution of bond length and bond energy along each crystal orientation tends to be symmetrical, the fracture toughness of doped MoSi2 would improve.
The electronic structures, elastic constants and Mullikan population of Nb and Al codoped MoSi2 were calculated by the density functional theory. The results show that the co-doping of Nb, Al can improve greatly the toughness and conductivity of MoSi2. When the doping volume of Nb and Al reaches to x= 0.25, the elastic modulus of MoSi2 decreases from 408.86 GPa to 261.30 GPa. By analyzing the density of states and Mullikan population, after doping the total density of states has a blue-shift, the charge density on Fermi level increases, the conductivity of the system improves and Mo-Al and Nb-Si bond populations decreases with their bond lengths increase. In addition, the covalent between atoms weakens, while the covalent bonds between Al and Si enhances. As the distribution of bond length and bond energy along each crystal orientation tends to be symmetrical, the fracture toughness of doped MoSi2 would improve.
2013, 42(4):741-745.
Abstract:
Using the established three-dimensional FE model of multi-strokes pilgering cold roll of TA18 titanium alloy tube, the plastic deformation behavior of TA18 titanium alloy tube F 25.4 mm×1.32 mm during the forming process was investigated. Results show that the average total rolling force of simulation is a little larger than that of theoretical calculation. Maximal equivalent plastic strain of the final tube symmetrically appears in the pass ridge of dies deviating from 63.80°, and the minimal equivalent plastic strain of the final tube appears in the above position deviating from 90°. Both radial and circumferential plastic true strains are compressive strains, and axial plastic true strain is tensile strain. Meanwhile radial plastic deformation is maximal, the second is axial plastic deformation, and circumferential plastic deformation is minimal. Anisotropic characteristics of the final tube in outer surface are the heaviest, and then are the neutropause and the inner surface in sequence. There are three stages in the distributions of plastic true strain vector of middle tube, and the change curve and Q-value are different. Strain ratio of plastic true strain vector of middle tube ranges from –30° (Q=0) to 0° (Q=1), and then to +30° (Q=￥). The radial texture of middle tube is changed into the circumferential texture during the forming process, and the final strain ratio keeps within 20° to 27° in order to satisfy the stable texture state of the hexagonal close-packed metals tube.
Using the established three-dimensional FE model of multi-strokes pilgering cold roll of TA18 titanium alloy tube, the plastic deformation behavior of TA18 titanium alloy tube F 25.4 mm×1.32 mm during the forming process was investigated. Results show that the average total rolling force of simulation is a little larger than that of theoretical calculation. Maximal equivalent plastic strain of the final tube symmetrically appears in the pass ridge of dies deviating from 63.80°, and the minimal equivalent plastic strain of the final tube appears in the above position deviating from 90°. Both radial and circumferential plastic true strains are compressive strains, and axial plastic true strain is tensile strain. Meanwhile radial plastic deformation is maximal, the second is axial plastic deformation, and circumferential plastic deformation is minimal. Anisotropic characteristics of the final tube in outer surface are the heaviest, and then are the neutropause and the inner surface in sequence. There are three stages in the distributions of plastic true strain vector of middle tube, and the change curve and Q-value are different. Strain ratio of plastic true strain vector of middle tube ranges from –30° (Q=0) to 0° (Q=1), and then to +30° (Q=￥). The radial texture of middle tube is changed into the circumferential texture during the forming process, and the final strain ratio keeps within 20° to 27° in order to satisfy the stable texture state of the hexagonal close-packed metals tube.
2013, 42(4):746-750.
Abstract:
Mg/C nanocomposites were compounded of C, Mg and Ni by reaction ball milling in hydrogen. The average size of nano-crystal in the composites is 16.8~33.6 nm. The absorption/desorption hydrogen performances show that the composites possess high reactivity and high hydrogen storage density. In the composite of 70Mg30C4Ni, 5.0 wt% hydrogen can be stored in 2 min at 160 °C and 2 MPa hydrogen pressure. The XRD analysis indicates that the synergistic action of Mg nano-crystal, nano carbon and the catalyst Ni is the main factor to the increase of hydrogen storage density and the improvement of dynamics performance. The chemical adsorption of carbon and pipeline of hydrogen in the Mg/C composite were studied by IR. Hydrogen is absorbed by C with priority and then analyzed to Mg, which is reversible.
Mg/C nanocomposites were compounded of C, Mg and Ni by reaction ball milling in hydrogen. The average size of nano-crystal in the composites is 16.8~33.6 nm. The absorption/desorption hydrogen performances show that the composites possess high reactivity and high hydrogen storage density. In the composite of 70Mg30C4Ni, 5.0 wt% hydrogen can be stored in 2 min at 160 °C and 2 MPa hydrogen pressure. The XRD analysis indicates that the synergistic action of Mg nano-crystal, nano carbon and the catalyst Ni is the main factor to the increase of hydrogen storage density and the improvement of dynamics performance. The chemical adsorption of carbon and pipeline of hydrogen in the Mg/C composite were studied by IR. Hydrogen is absorbed by C with priority and then analyzed to Mg, which is reversible.
Zhang Huafeng
,
Zheng Jianping
,
Yang Qifa
,
Zhang Zheng
,
Li Xin
,
Zhao Jun
,
Hu Zhongwu
,
Rao Liqiang
2013, 42(4):751-755.
Abstract:
The inner pressure creep resistance of two kinds of domestic Mo-Nb alloy single crystal was researched by applying biaxial load on the tube specimen through the inert gas medium. The niobium contents of them were 3wt% and 6wt%, respectively. Results show that the inner pressure creep resistance strengthens, while the steady-state creep rate and the sensitivity to hoop stress drop with the increasing solute niobium atoms. With the increase of niobium content, more multilateral structures of the dislocation form and the shape of the Nb-rich precipitate changes from particle to shaft. These factors induce that the molybdenum atom diffusion become more difficult, and the inner pressure creep resistance of Mo-Nb alloy single crystal becomes more superior.
The inner pressure creep resistance of two kinds of domestic Mo-Nb alloy single crystal was researched by applying biaxial load on the tube specimen through the inert gas medium. The niobium contents of them were 3wt% and 6wt%, respectively. Results show that the inner pressure creep resistance strengthens, while the steady-state creep rate and the sensitivity to hoop stress drop with the increasing solute niobium atoms. With the increase of niobium content, more multilateral structures of the dislocation form and the shape of the Nb-rich precipitate changes from particle to shaft. These factors induce that the molybdenum atom diffusion become more difficult, and the inner pressure creep resistance of Mo-Nb alloy single crystal becomes more superior.
19 Effect of Incubated Nucleation Treatment on Solidification Microstructure of Au-Sn Eutectic Alloy
2013, 42(4):756-760.
Abstract:
The effects of incubated nucleation treatment with adding trace Au or Sn on the solidification microstructure of Au-Sn eutectic alloy Au20Sn were investigated. The results indicate that compared with no incubated nucleation treatment, the solidification microstructures of Au-Sn eutectic alloy are modified greatly by incubated nucleation treatment with Au or Sn. The structure, the morphology and the size of the primary phase are also changed. The primary phase transforms into d-AuSn phase with the shape of rod or egg of uniform distribution and small size from conventional z ’-Au5Sn phase with coarse dendrite of non-uniform distribution. The primary d-AuSn phase in the solidification microstructure becomes more uniform by adding trace Sn than by adding trace Au. Meanwhile the eutectic structure is also refined by the incubated nucleation treatment.
The effects of incubated nucleation treatment with adding trace Au or Sn on the solidification microstructure of Au-Sn eutectic alloy Au20Sn were investigated. The results indicate that compared with no incubated nucleation treatment, the solidification microstructures of Au-Sn eutectic alloy are modified greatly by incubated nucleation treatment with Au or Sn. The structure, the morphology and the size of the primary phase are also changed. The primary phase transforms into d-AuSn phase with the shape of rod or egg of uniform distribution and small size from conventional z ’-Au5Sn phase with coarse dendrite of non-uniform distribution. The primary d-AuSn phase in the solidification microstructure becomes more uniform by adding trace Sn than by adding trace Au. Meanwhile the eutectic structure is also refined by the incubated nucleation treatment.
2013, 42(4):761-765.
Abstract:
Magnesium (AZ91D) matrix nanocomposite reinforced with nano-sized SiC particles (n-SiCp) was prepared by mechanical stirring and high intensity ultrasonic dispersion assisted casting. The tensile properties and fracture behavior of the magnesium alloy and its nanocomposites at elevated temperature were investigated. The results show that the addition of n-SiCp to AZ91D can improve the tensile strength of the nanocomposites, especially at high temperature. Furthermore the significant improvement of the elongation of the nanocomposites at high temperature is achieved, which results in the quite good ductility at elevated temperature. The fracture analysis on the nanocomposites shows that the fracture mechanism of the nanocomposites changes gradually from the brittle fracture at room temperature to the typical tough fracture at high temperature due to the addition of n-SiCp.
Magnesium (AZ91D) matrix nanocomposite reinforced with nano-sized SiC particles (n-SiCp) was prepared by mechanical stirring and high intensity ultrasonic dispersion assisted casting. The tensile properties and fracture behavior of the magnesium alloy and its nanocomposites at elevated temperature were investigated. The results show that the addition of n-SiCp to AZ91D can improve the tensile strength of the nanocomposites, especially at high temperature. Furthermore the significant improvement of the elongation of the nanocomposites at high temperature is achieved, which results in the quite good ductility at elevated temperature. The fracture analysis on the nanocomposites shows that the fracture mechanism of the nanocomposites changes gradually from the brittle fracture at room temperature to the typical tough fracture at high temperature due to the addition of n-SiCp.
2013, 42(4):766-770.
Abstract:
Grain boundary character distribution in cold-rolled Ni-Cr-W superalloys annealed for different time was investigated. Scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and orientation imaging microscopy (OIM) analyses were carried out. The results show that under the cold reduction of 70%, the samples’ recrystallization time is relatively short, and the ratio of special grain boundary increases firstly and then decreases with prolonging the annealing time; under the cold reduction of 10%, the recrystallization driving force is small, the recrystallization time is long, and the ratio of special grain boundary reaches the maximum after long-time annealing. In addition, boundaries have Σ3n misorientations inside the grains-cluster, while misorientations are random for those outside.
Grain boundary character distribution in cold-rolled Ni-Cr-W superalloys annealed for different time was investigated. Scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and orientation imaging microscopy (OIM) analyses were carried out. The results show that under the cold reduction of 70%, the samples’ recrystallization time is relatively short, and the ratio of special grain boundary increases firstly and then decreases with prolonging the annealing time; under the cold reduction of 10%, the recrystallization driving force is small, the recrystallization time is long, and the ratio of special grain boundary reaches the maximum after long-time annealing. In addition, boundaries have Σ3n misorientations inside the grains-cluster, while misorientations are random for those outside.
2013, 42(4):771-775.
Abstract:
The effects of Gd and Nd addition on microstructures and tensile properties of as-cast and extruded AZ80 magnesium alloy was investigated using OM, SEM, EPMA and mechanical property tests. The results show that the appropriate rare earth elements can improve the microstructures of as-cast AZ80 magnesium alloy with dendrite disappearing and more Mg17Al12 lamellar phase appearing along the grain boundaries. Grain size is reduced after homogenization. Dynamic recrystallization (DRX) occurs after extrusion and dynamically precipitated β phase distributes along the recrystallized grain boundaries in all the alloys. When adding 2% RE (Gd, Nd), the precipitated β phase hinders the grain growth and particle stimulated nucleation plays a common role in fine-grain strengthening. The highly rigid Al2Gd and Al2Nd phase can effectively impede dislocation movement and thus improve the yield strength. With the increase of RE (Gd, Nd) content, β phase precipitation decreases, RE phase particles become larger which weakens the effect of dynamic recrystallization and leads to stress concentration and strength decrease. The maximum tensile strength and best comprehensive performance can be achieved by adding 2% RE(Gd, Nd).
The effects of Gd and Nd addition on microstructures and tensile properties of as-cast and extruded AZ80 magnesium alloy was investigated using OM, SEM, EPMA and mechanical property tests. The results show that the appropriate rare earth elements can improve the microstructures of as-cast AZ80 magnesium alloy with dendrite disappearing and more Mg17Al12 lamellar phase appearing along the grain boundaries. Grain size is reduced after homogenization. Dynamic recrystallization (DRX) occurs after extrusion and dynamically precipitated β phase distributes along the recrystallized grain boundaries in all the alloys. When adding 2% RE (Gd, Nd), the precipitated β phase hinders the grain growth and particle stimulated nucleation plays a common role in fine-grain strengthening. The highly rigid Al2Gd and Al2Nd phase can effectively impede dislocation movement and thus improve the yield strength. With the increase of RE (Gd, Nd) content, β phase precipitation decreases, RE phase particles become larger which weakens the effect of dynamic recrystallization and leads to stress concentration and strength decrease. The maximum tensile strength and best comprehensive performance can be achieved by adding 2% RE(Gd, Nd).
2013, 42(4):776-780.
Abstract:
A novel electrochemical method was proposed to estimate the effective electroactive area, active volume and surface coverage of the porous three-dimensional film electrode. Nickel hexacyanoferrate (NiHCF) thin films were synthesized on the porous three-dimensional foam nickel substrate by cathodical deposition. Cyclic voltammograms of the foam nickel electrode and the NiHCF film electrode at various potential scan rates were obtained in alkali metal solution with and without K3Fe(CN)6, respectively. The effective electroactive area and the coverage of the porous three-dimensional film electrode were characterized by the reversible property of redox reaction of porous electrode in different solution systems. Combining with chronocoulometry, the active volume of the internal NiHCF film was obtained, and then the average thickness of the film was also calculated. The proposed method shows the characteristics of fast response, high sensitivity and excellent accuracy with easy operation and good reliability.
A novel electrochemical method was proposed to estimate the effective electroactive area, active volume and surface coverage of the porous three-dimensional film electrode. Nickel hexacyanoferrate (NiHCF) thin films were synthesized on the porous three-dimensional foam nickel substrate by cathodical deposition. Cyclic voltammograms of the foam nickel electrode and the NiHCF film electrode at various potential scan rates were obtained in alkali metal solution with and without K3Fe(CN)6, respectively. The effective electroactive area and the coverage of the porous three-dimensional film electrode were characterized by the reversible property of redox reaction of porous electrode in different solution systems. Combining with chronocoulometry, the active volume of the internal NiHCF film was obtained, and then the average thickness of the film was also calculated. The proposed method shows the characteristics of fast response, high sensitivity and excellent accuracy with easy operation and good reliability.
2013, 42(4):781-784.
Abstract:
The damage behavior of a sort of high strength titanium alloy target was studied by armor piercing test. The characteristics and the mechanism of damaging were analyzed according to damage appearance of the armor plate. Results show that at the opening stage, the bullet head enters more easily the target board, and metal accumulation is found on the target plate surface, but there is no overheated metal melting phenomenon. The adiabatic shear band is found at the stable stage. The large non-homogeneous deformation in adiabatic shear bands causes microcracks and micropores. The cracks initiate and propagate along adiabatic shear bands and these large cracks result in falling of fragments from the surface of penetrated hole. As a result, the armor plate is deteriorated.
The damage behavior of a sort of high strength titanium alloy target was studied by armor piercing test. The characteristics and the mechanism of damaging were analyzed according to damage appearance of the armor plate. Results show that at the opening stage, the bullet head enters more easily the target board, and metal accumulation is found on the target plate surface, but there is no overheated metal melting phenomenon. The adiabatic shear band is found at the stable stage. The large non-homogeneous deformation in adiabatic shear bands causes microcracks and micropores. The cracks initiate and propagate along adiabatic shear bands and these large cracks result in falling of fragments from the surface of penetrated hole. As a result, the armor plate is deteriorated.
2013, 42(4):785-788.
Abstract:
Ti2AlC/TiAl composite was prepared with self-propagating high-temperature synthesis (SHS) followed by vacuum arc melting using Ti, Al powers and short carbon fibers as raw materials. Precipitated phases and formed microstructures of Ti2AlC/TiAl composite were investigated by means of X-ray diffraction, scanning electron microscope and transmission electron microscopy, and the reaction process was also discussed. Results show the microstructure of as-cast Ti2AlC/TiAl composite is composed of Ti2AlC, TiAl and Ti3Al phases, the matrix are mainly of α2(Ti3Al)+γ(TiAl) phases with lamellar structure and γ(TiAl) phase with equiaxed structure, and the precipitated in-situ Ti2AlC short fibers or particles dispersively distribute in the matrix. Ti3Al phase is decomposed to TiAl and Ti2AlC particles after annealed at 1200 °C for 4 h, and the Ti2AlC short fibers are enlarged and secondary Ti2AlC is precipitated after the annealing treatment.
Ti2AlC/TiAl composite was prepared with self-propagating high-temperature synthesis (SHS) followed by vacuum arc melting using Ti, Al powers and short carbon fibers as raw materials. Precipitated phases and formed microstructures of Ti2AlC/TiAl composite were investigated by means of X-ray diffraction, scanning electron microscope and transmission electron microscopy, and the reaction process was also discussed. Results show the microstructure of as-cast Ti2AlC/TiAl composite is composed of Ti2AlC, TiAl and Ti3Al phases, the matrix are mainly of α2(Ti3Al)+γ(TiAl) phases with lamellar structure and γ(TiAl) phase with equiaxed structure, and the precipitated in-situ Ti2AlC short fibers or particles dispersively distribute in the matrix. Ti3Al phase is decomposed to TiAl and Ti2AlC particles after annealed at 1200 °C for 4 h, and the Ti2AlC short fibers are enlarged and secondary Ti2AlC is precipitated after the annealing treatment.
26 Photochemical Synthesis and Electro-catalytic Activity of Au Core/Pt Shell Composite Nanoparticles
2013, 42(4):789-792.
Abstract:
A series of Au@Pt composite nanoparticles was synthesized by photochemical coreduction in the PEG-acetone aqueous solutions containing Au(III) and Pt(IV) ions with different molar ratios. The resulting composites were supported on carbon black for preparing Au@Pt/C catalysts, respectively. By the characterization of UV-Vis spectrum, TEM and HR-TEM, a spherical Au core Pt shell composite nano-structure was confirmed. The chemical state and structure character of the composite nanoparticles and the catalytic property of Au@Pt/C catalysts were analyzed by XPS, EDS and electrochemical method, respectively. The results show that all of Au@Pt/C catalysts with different Au:Pt molar ratios have high catalytic activity and stability for methanol oxidation; among them, the catalytic activity of the Au@Pt/C catalyst formed at Au:Pt=1:1 is the highest and is about 4 times than that of commercial Pt/C catalyst. The primary cause of high catalytic activity of the core/shell structure was discussed.
A series of Au@Pt composite nanoparticles was synthesized by photochemical coreduction in the PEG-acetone aqueous solutions containing Au(III) and Pt(IV) ions with different molar ratios. The resulting composites were supported on carbon black for preparing Au@Pt/C catalysts, respectively. By the characterization of UV-Vis spectrum, TEM and HR-TEM, a spherical Au core Pt shell composite nano-structure was confirmed. The chemical state and structure character of the composite nanoparticles and the catalytic property of Au@Pt/C catalysts were analyzed by XPS, EDS and electrochemical method, respectively. The results show that all of Au@Pt/C catalysts with different Au:Pt molar ratios have high catalytic activity and stability for methanol oxidation; among them, the catalytic activity of the Au@Pt/C catalyst formed at Au:Pt=1:1 is the highest and is about 4 times than that of commercial Pt/C catalyst. The primary cause of high catalytic activity of the core/shell structure was discussed.
2013, 42(4):793-796.
Abstract:
The quasi-static tensile properties and dynamic tensile properties of as-sintered 90W-7Ni-3Fe (90W) alloy were studied. Quasi-static tensile tests were carried out by a CMT4105 tensile machine at the strain rate of 0.001 s-1, while dynamic tensile tests were carried out by Split Hopkinson Tensile Bar (SHTB) within a higher strain rate range of 1600~2000 s-1. The tensile properties and failure mechanism of 90W alloy at different strain rates were investigated. Results show that under the condition of tensile loading, 90W alloy exhibits an obvious strain rate effect. With the increasing of strain rate, the tensile strength increases obviously, while the critical true strain for fracture and the total energy absorbed by 90W alloy show a decreasing tendency. The failure mechanism of 90W alloy converts from the abruption of W-W boundaries to the cleavage of tungsten grains.
The quasi-static tensile properties and dynamic tensile properties of as-sintered 90W-7Ni-3Fe (90W) alloy were studied. Quasi-static tensile tests were carried out by a CMT4105 tensile machine at the strain rate of 0.001 s-1, while dynamic tensile tests were carried out by Split Hopkinson Tensile Bar (SHTB) within a higher strain rate range of 1600~2000 s-1. The tensile properties and failure mechanism of 90W alloy at different strain rates were investigated. Results show that under the condition of tensile loading, 90W alloy exhibits an obvious strain rate effect. With the increasing of strain rate, the tensile strength increases obviously, while the critical true strain for fracture and the total energy absorbed by 90W alloy show a decreasing tendency. The failure mechanism of 90W alloy converts from the abruption of W-W boundaries to the cleavage of tungsten grains.
2013, 42(4):797-800.
Abstract:
The poison of palladium membrane in H2O (gas) and the hydrogenization of the poisoned membrane were proceeded in a silica tubular furnace. The hydrogen isotope permeation capacity of palladium membrane was tested. The variation of palladium membrane phase was analyzed by XPS and SEM. The causes and the mechanism of the variation were discussed. The results show that the content of adsorptive C and O on the palladium surface can be decreased by the reaction between H2O (gas) and palladium surface without variation of chemical state. Some cracks can be observed on the palladium surface at a higher reaction temperature, which account for a physical change. At room temperature, there are no obvious changes on the palladium surface after the palladium membrane deoxidized again by H2. The deuterium permeability of Pd membrane which has reacted with H2O (gas) is higher than the original membrane. The improvement of deuterium permeability could be ascribed to the improving surface cleanness caused by the reaction between H2O (gas) and palladium surface.
The poison of palladium membrane in H2O (gas) and the hydrogenization of the poisoned membrane were proceeded in a silica tubular furnace. The hydrogen isotope permeation capacity of palladium membrane was tested. The variation of palladium membrane phase was analyzed by XPS and SEM. The causes and the mechanism of the variation were discussed. The results show that the content of adsorptive C and O on the palladium surface can be decreased by the reaction between H2O (gas) and palladium surface without variation of chemical state. Some cracks can be observed on the palladium surface at a higher reaction temperature, which account for a physical change. At room temperature, there are no obvious changes on the palladium surface after the palladium membrane deoxidized again by H2. The deuterium permeability of Pd membrane which has reacted with H2O (gas) is higher than the original membrane. The improvement of deuterium permeability could be ascribed to the improving surface cleanness caused by the reaction between H2O (gas) and palladium surface.
2013, 42(4):801-804.
Abstract:
The cylindrical pure Ti specimens were compressed by dynamic plastic deformation (DPD). The microstructure and microhardness of adiabatic shear bands (ASB) and transitional zones were investigated at high strains. The results show that ASBs are only found in DPD samples at high strains (ε≥0.6), but not found in low-strain or quasi-static compression samples. These suggest that the ASBs are affected by both strain rate and strain. The hardness of ASBs is slightly lower than that of the matrix; however, the hardness of transitional zones is obviously lower than that of the matrix. These results are researched by Zerilli-Armstrong constitutive model and heat diffuse equation. The computational widths of the heat-affected zone and the transitional zone are consistent with the experimental results. The formation of equiaxed grains is due to dynamic recrystallization of deformed grains. This process results in hardness reduction of the transitional zone.
The cylindrical pure Ti specimens were compressed by dynamic plastic deformation (DPD). The microstructure and microhardness of adiabatic shear bands (ASB) and transitional zones were investigated at high strains. The results show that ASBs are only found in DPD samples at high strains (ε≥0.6), but not found in low-strain or quasi-static compression samples. These suggest that the ASBs are affected by both strain rate and strain. The hardness of ASBs is slightly lower than that of the matrix; however, the hardness of transitional zones is obviously lower than that of the matrix. These results are researched by Zerilli-Armstrong constitutive model and heat diffuse equation. The computational widths of the heat-affected zone and the transitional zone are consistent with the experimental results. The formation of equiaxed grains is due to dynamic recrystallization of deformed grains. This process results in hardness reduction of the transitional zone.
2013, 42(4):805-808.
Abstract:
Mo specimens with different initial relative density were prepared by a vacuum sintering technique. The effects of the initial relative density on the flow stress of the sintered Mo powder were studied by room temperature quasi-static uniaxial compression tests at a MTS810 universal material testing machine. The mathematic model of the flow stress and the calculation model of the elasto-plastic parameters for the sintered Mo powder were established. Based on the yield criterion and plastic constitutive equation for compressible dense materials, the yield function and the elasto-plastic constitutive model of the sintered Mo powder during compression deformation was determined.
Mo specimens with different initial relative density were prepared by a vacuum sintering technique. The effects of the initial relative density on the flow stress of the sintered Mo powder were studied by room temperature quasi-static uniaxial compression tests at a MTS810 universal material testing machine. The mathematic model of the flow stress and the calculation model of the elasto-plastic parameters for the sintered Mo powder were established. Based on the yield criterion and plastic constitutive equation for compressible dense materials, the yield function and the elasto-plastic constitutive model of the sintered Mo powder during compression deformation was determined.
2013, 42(4):809-813.
Abstract:
Spheric silver nanoparticles were synthesized in the presence of polyvinyl pyrrolidone (PVP) as surfactant and sodium carbonate (Na2CO3) as controlled agent by the reduction of silver ions through a microwave-assisted polyol method. The effects of adding amount of Na2CO3 on the silver nanoparticle size were investigated. The morphology, composition, particle size and phase structure of the silver nanoparticles were characterized by SEM, TEM, XPS, XRD and UV-vis. The results show that the average size of silver nanoparticles decreases with the increase of the adding amount of Na2CO3.
Spheric silver nanoparticles were synthesized in the presence of polyvinyl pyrrolidone (PVP) as surfactant and sodium carbonate (Na2CO3) as controlled agent by the reduction of silver ions through a microwave-assisted polyol method. The effects of adding amount of Na2CO3 on the silver nanoparticle size were investigated. The morphology, composition, particle size and phase structure of the silver nanoparticles were characterized by SEM, TEM, XPS, XRD and UV-vis. The results show that the average size of silver nanoparticles decreases with the increase of the adding amount of Na2CO3.
2013, 42(4):814-818.
Abstract:
The novel gradient porous titanium, with the outer high porosity and inner low porosity, was prepared by a powder metallurgy method in order to solve the problem of high porosity and low strength of singer-layer porous titanium (SPT). The compressive strength (CS) and Young’s modulus (YM) of the gradient double-layer porous titanium (DPT) are 117.50~143.55 MPa and 1.95~3.08 GPa, respectively, when its inner porosity is about 30%, outer porosity more than 65% and the pore size range 100~255 μm. The inner/outer pore size and porosity are of gradient distribution. The mechanical properties of the DPT are further improved through adding rare earth lanthanum fluoride (LaF3) to the outer layer. The CS and YM of the DPT with 0.05wt% LaF3 in outer layer are up to 213.76 MPa and 3.38 GPa, respectively.
The novel gradient porous titanium, with the outer high porosity and inner low porosity, was prepared by a powder metallurgy method in order to solve the problem of high porosity and low strength of singer-layer porous titanium (SPT). The compressive strength (CS) and Young’s modulus (YM) of the gradient double-layer porous titanium (DPT) are 117.50~143.55 MPa and 1.95~3.08 GPa, respectively, when its inner porosity is about 30%, outer porosity more than 65% and the pore size range 100~255 μm. The inner/outer pore size and porosity are of gradient distribution. The mechanical properties of the DPT are further improved through adding rare earth lanthanum fluoride (LaF3) to the outer layer. The CS and YM of the DPT with 0.05wt% LaF3 in outer layer are up to 213.76 MPa and 3.38 GPa, respectively.
2013, 42(4):819-823.
Abstract:
Magnetostrictive composites were prepared by mixing Sm0.88Nd0.12Fe1.93 alloy particles with epoxy resin and curing under an external magnetic field. The microstructure, magnetostriction and electrical resistivity of bonded Sm0.88Nd0.12Fe1.93 composites prepared at different external magnetic fields were investigated. Results show that the maximum magnetostriction λ∥–λ⊥ at 1.3 T reaches –1088×10-6 for the bonded composites with 30% (volume fraction) Sm0.88Nd0.12Fe1.93 particles cured under 0.6 T, which is 86.6% of the magnetostriction for the as-cast alloy. Compared with the as-cast Sm0.88Nd0.12Fe1.93 alloy, electrical resistivity of the epoxy-bonded Sm0.88Nd0.12Fe1.93 composites prepared under 0.6 T is 6 orders of magnitude higher. Additionally, electrical resistivity for the composites cured under 0 field is higher than that cured under 0.6 T, which might be related to the alignment of SmNdFe powders.
Magnetostrictive composites were prepared by mixing Sm0.88Nd0.12Fe1.93 alloy particles with epoxy resin and curing under an external magnetic field. The microstructure, magnetostriction and electrical resistivity of bonded Sm0.88Nd0.12Fe1.93 composites prepared at different external magnetic fields were investigated. Results show that the maximum magnetostriction λ∥–λ⊥ at 1.3 T reaches –1088×10-6 for the bonded composites with 30% (volume fraction) Sm0.88Nd0.12Fe1.93 particles cured under 0.6 T, which is 86.6% of the magnetostriction for the as-cast alloy. Compared with the as-cast Sm0.88Nd0.12Fe1.93 alloy, electrical resistivity of the epoxy-bonded Sm0.88Nd0.12Fe1.93 composites prepared under 0.6 T is 6 orders of magnitude higher. Additionally, electrical resistivity for the composites cured under 0 field is higher than that cured under 0.6 T, which might be related to the alignment of SmNdFe powders.
2013, 42(4):824-828.
Abstract:
The influence of surface roughness and compression ratio on the lateral surface microcracks of the compressed specimens of Ti-3Al-5Mo-4.5V titanium alloy (BT16) has been investigated by cold upsetting experiments, scanning electron microscopy (SEM) and optical microscopy (OM). The results show that the rolled and annealed α+β BT16 alloy bars with the finest equiaxed grains have the good cold upsetting performance. With the increasing of compression ratio and surface roughness, the lateral surface microcracks gradually increase. The lateral surface of the cold upsetting specimens and bolts is without macrocracks when the compression ratio reaches 75%, but under high magnification lateral surface microcracks can be distinctly observed, which are entirely different from common macrocracks. Surface quality of cold upsetting fasteners was evaluated and the relation between lateral surface roughness, microcracks and compression ratio was determined in cold upsetting test.
The influence of surface roughness and compression ratio on the lateral surface microcracks of the compressed specimens of Ti-3Al-5Mo-4.5V titanium alloy (BT16) has been investigated by cold upsetting experiments, scanning electron microscopy (SEM) and optical microscopy (OM). The results show that the rolled and annealed α+β BT16 alloy bars with the finest equiaxed grains have the good cold upsetting performance. With the increasing of compression ratio and surface roughness, the lateral surface microcracks gradually increase. The lateral surface of the cold upsetting specimens and bolts is without macrocracks when the compression ratio reaches 75%, but under high magnification lateral surface microcracks can be distinctly observed, which are entirely different from common macrocracks. Surface quality of cold upsetting fasteners was evaluated and the relation between lateral surface roughness, microcracks and compression ratio was determined in cold upsetting test.
2013, 42(4):829-832.
Abstract:
The effects of three different heat treatments on microstructures and creep resistance of hot continuous rolled (HCR) GH4169 alloy were investigated. It is found that different heat treatments have an effect on grain size of HCR GH4169 alloy. The grain size of the sample after DA treatment is the smallest and that of the sample after HST treatment is the biggest. The content of d-phase increases with the increasing of the time of the solution heat treatment, and it mainly precipitates at the grain boundary. Under 650 °C/725 MPa experimental conditions, the HCR GH4169 after DA heat treatment has powerful creep resistance and long life time, while the HCR GH4169 after HST heat treatment has short life time. The fracture mode of creep specimens after heat treatments is intergranular fracture.
The effects of three different heat treatments on microstructures and creep resistance of hot continuous rolled (HCR) GH4169 alloy were investigated. It is found that different heat treatments have an effect on grain size of HCR GH4169 alloy. The grain size of the sample after DA treatment is the smallest and that of the sample after HST treatment is the biggest. The content of d-phase increases with the increasing of the time of the solution heat treatment, and it mainly precipitates at the grain boundary. Under 650 °C/725 MPa experimental conditions, the HCR GH4169 after DA heat treatment has powerful creep resistance and long life time, while the HCR GH4169 after HST heat treatment has short life time. The fracture mode of creep specimens after heat treatments is intergranular fracture.
2013, 42(4):833-836.
Abstract:
A mathematic model was established to analyze the effect of zone length and pass number on the uranium purification during zone melting process. The theoretically optimized condition was applied in the experiment and the elements of Al, Mo, W, Ni, Ca and C in uranium was chosen. The impurity concentration and inclusion distribution in uranium before and after purification were investigated by ICP-AES and OM. Results show that zone melting can remove the impurity elements in uranium. The total impurity concentration is reduced from 1189 μg/g to 402 μg/g. Zone melting has high removal efficiency to W, Ni, and C, but has low efficiency to Al and Mo. The inclusion decreases in size and enriches along the melting direction.
A mathematic model was established to analyze the effect of zone length and pass number on the uranium purification during zone melting process. The theoretically optimized condition was applied in the experiment and the elements of Al, Mo, W, Ni, Ca and C in uranium was chosen. The impurity concentration and inclusion distribution in uranium before and after purification were investigated by ICP-AES and OM. Results show that zone melting can remove the impurity elements in uranium. The total impurity concentration is reduced from 1189 μg/g to 402 μg/g. Zone melting has high removal efficiency to W, Ni, and C, but has low efficiency to Al and Mo. The inclusion decreases in size and enriches along the melting direction.
2013, 42(4):837-840.
Abstract:
Palladium nanoparticles were prepared by adding a small quantity of hexadecyl trimethyl ammonium bromide (CTAB) into the palladium (Ⅱ) chloride aqueous solution using ultrasonics. The samples were characterized by XRD, TEM, selected area electron diffraction (SAED), HRTEM and low temperature nitrogen adsorption-desorption. The effect of CTAB amount on the growth morphology of palladium nanoparticles was also investigated. The electrocatalytic properties of the nano-Pd modified glassy carbon (Pd/GC) electrode for formaldehyde oxidation were investigated by cyclic voltammetry. The results indicate that the size and the morphology of the nano-Pd particles can be controlled by adjusting the mole ratios of CTAB to PdCl2. The hexagonal nano-Pd particles with a narrowly distributed size of 8 nm are obtained when the mole ratio of CTAB to PdCl2 is 1:1 and the ultrasonic reaction time is 50 min. The nanoparticles obtained by CTAB addition possess larger BET surface area compared to that without surfactant by 10 m2/g, thus showing the excellent electrocatalytic activity for the formaldehyde oxidation.
Palladium nanoparticles were prepared by adding a small quantity of hexadecyl trimethyl ammonium bromide (CTAB) into the palladium (Ⅱ) chloride aqueous solution using ultrasonics. The samples were characterized by XRD, TEM, selected area electron diffraction (SAED), HRTEM and low temperature nitrogen adsorption-desorption. The effect of CTAB amount on the growth morphology of palladium nanoparticles was also investigated. The electrocatalytic properties of the nano-Pd modified glassy carbon (Pd/GC) electrode for formaldehyde oxidation were investigated by cyclic voltammetry. The results indicate that the size and the morphology of the nano-Pd particles can be controlled by adjusting the mole ratios of CTAB to PdCl2. The hexagonal nano-Pd particles with a narrowly distributed size of 8 nm are obtained when the mole ratio of CTAB to PdCl2 is 1:1 and the ultrasonic reaction time is 50 min. The nanoparticles obtained by CTAB addition possess larger BET surface area compared to that without surfactant by 10 m2/g, thus showing the excellent electrocatalytic activity for the formaldehyde oxidation.
2013, 42(4):841-844.
Abstract:
The effects of extruding temperatures on the microstructures and mechanical properties of the Mg-2.0Zn-0.3Zr-0.9Y magnesium alloy were investigated. The results show that the grain size of Mg-2.0Zn-0.3Zr-0.9Y alloy is significantly refined by decreasing the extruding temperature. Meanwhile the tensile strength and the yield strength are greatly enhanced, but the elongation is increased little. With the decrease of extruding temperature, the intensity of {102} texture is enhanced, while that of the {0002} basal ring type texture is decreased. The mechanical properties of the alloy are not only related with the average grain size, but also with the texture. Mg-2.0Zn-0.3Zr-0.9Y magnesium alloy extruded at 330 °C possesses a fine grain size of 1.76 μm on average and good mechanical properties including the elongation of 21.92%, the yield strength of 309 MPa and the tensile strength of 323 MPa.
The effects of extruding temperatures on the microstructures and mechanical properties of the Mg-2.0Zn-0.3Zr-0.9Y magnesium alloy were investigated. The results show that the grain size of Mg-2.0Zn-0.3Zr-0.9Y alloy is significantly refined by decreasing the extruding temperature. Meanwhile the tensile strength and the yield strength are greatly enhanced, but the elongation is increased little. With the decrease of extruding temperature, the intensity of {102} texture is enhanced, while that of the {0002} basal ring type texture is decreased. The mechanical properties of the alloy are not only related with the average grain size, but also with the texture. Mg-2.0Zn-0.3Zr-0.9Y magnesium alloy extruded at 330 °C possesses a fine grain size of 1.76 μm on average and good mechanical properties including the elongation of 21.92%, the yield strength of 309 MPa and the tensile strength of 323 MPa.
2013, 42(4):845-848.
Abstract:
The room temperature tensile properties of TC21 titanium alloy with three different microstructures were tested after solution treatment followed by different cooling. Optical microscope and scanning electron microscopy were used to observe the microstructures. Relationships between the microstructure and the tensile properties were analyzed. The result shows that the best match between the strength and the plasticity ( the yield strength>1000 MPa) can be achieved when the heat treatment processes and microstructures are as following: 920 °C /1 h, FC+550 °C/4 h equiaxed microstructure, 920 °C /1 h, FC+550 °C /4 h basket weave microstructure, and 960 °C/0.5 h, FC+550 °C/4 h lamellar microstructure. The better comprehensive properties could be obtained by controlling the α phase volume fraction and morphology, α phase colony size and α lamellae thickness in the colony.
The room temperature tensile properties of TC21 titanium alloy with three different microstructures were tested after solution treatment followed by different cooling. Optical microscope and scanning electron microscopy were used to observe the microstructures. Relationships between the microstructure and the tensile properties were analyzed. The result shows that the best match between the strength and the plasticity ( the yield strength>1000 MPa) can be achieved when the heat treatment processes and microstructures are as following: 920 °C /1 h, FC+550 °C/4 h equiaxed microstructure, 920 °C /1 h, FC+550 °C /4 h basket weave microstructure, and 960 °C/0.5 h, FC+550 °C/4 h lamellar microstructure. The better comprehensive properties could be obtained by controlling the α phase volume fraction and morphology, α phase colony size and α lamellae thickness in the colony.
2013, 42(4):849-852.
Abstract:
The rule of morphology evolution of products in producing tantalum by FFC was studied. Results show that overhead oxide changes into off-grade oxide of tantalum during electrolysis. The off-grade oxide of tantalum is not stable, so it combines metal ion to interphase of tantalite. When the content of oxygen in the interphase decreases to a certain level, the interphase will resolve to produce particles of 200~400 nm, which form cellular polymer by single stranded. The electrical property of tantalum powder with different electrolysis time was analyzed. The longer the time is, the bigger the capacity is.
The rule of morphology evolution of products in producing tantalum by FFC was studied. Results show that overhead oxide changes into off-grade oxide of tantalum during electrolysis. The off-grade oxide of tantalum is not stable, so it combines metal ion to interphase of tantalite. When the content of oxygen in the interphase decreases to a certain level, the interphase will resolve to produce particles of 200~400 nm, which form cellular polymer by single stranded. The electrical property of tantalum powder with different electrolysis time was analyzed. The longer the time is, the bigger the capacity is.
2013, 42(4):853-856.
Abstract:
Mo-Ti-Zr-TiC/ZrC alloys were prepared via a powder metallurgy method. The effects of trace TiC/ZrC additive on the mechanical properties and microstructure of TiC/ZrC reinforced TZM alloy at room and high temperature were studied. The results indicate that the relative density and the tensile strength of Mo-Ti-Zr-TiC/ZrC alloy at room temperature are effectively enhanced by adding trace TiC/ZrC (0.1wt%~0.5wt%). The tensile strength achieves the highest value when the content of TiC/ZrC is 0.4wt%. Meanwhile, Mo-Ti-Zr-TiC/ZrC alloy with 0.4wt% TiC/ZrC shows excellent mechanical properties at 800 °C. The dispersive distribution of trace carbide particles accelerates the formation of dimples in the tensile procedure at elevated temperature, which leads to the transformation of fracture mechanism from the compound of trans-granular cleavage fracture and dimple fracture to simplex dimple fracture pattern.
Mo-Ti-Zr-TiC/ZrC alloys were prepared via a powder metallurgy method. The effects of trace TiC/ZrC additive on the mechanical properties and microstructure of TiC/ZrC reinforced TZM alloy at room and high temperature were studied. The results indicate that the relative density and the tensile strength of Mo-Ti-Zr-TiC/ZrC alloy at room temperature are effectively enhanced by adding trace TiC/ZrC (0.1wt%~0.5wt%). The tensile strength achieves the highest value when the content of TiC/ZrC is 0.4wt%. Meanwhile, Mo-Ti-Zr-TiC/ZrC alloy with 0.4wt% TiC/ZrC shows excellent mechanical properties at 800 °C. The dispersive distribution of trace carbide particles accelerates the formation of dimples in the tensile procedure at elevated temperature, which leads to the transformation of fracture mechanism from the compound of trans-granular cleavage fracture and dimple fracture to simplex dimple fracture pattern.
2013, 42(4):857-860.
Abstract:
ITO powder precursors were prepared by chemical co-precipitation and then they were calcined at 600 °C for 4 h to obtain ITO powder with average particle size of 20~30 nm. 1%PVA was added to the ITO powder for granulation, and then the green compacts of ITO targets were prepared by a press forming method. Different heating rates were set, and then the ITO targets were produced by sintering at 1550 °C in oxygenated atmospheres. The effects of heating rate on relative density and microstructure of ITO target were studied during sintering process. The results show that when the heating rates are 3 °C /min (0~500 °C) and 8 °C /min (500~1550 °C), the heating system is better. The relative density of ITO target is 99.58%, the pores are hardly seen and the target is nearly fully densitified, in addition, no crack is observed from the macro perspective.
ITO powder precursors were prepared by chemical co-precipitation and then they were calcined at 600 °C for 4 h to obtain ITO powder with average particle size of 20~30 nm. 1%PVA was added to the ITO powder for granulation, and then the green compacts of ITO targets were prepared by a press forming method. Different heating rates were set, and then the ITO targets were produced by sintering at 1550 °C in oxygenated atmospheres. The effects of heating rate on relative density and microstructure of ITO target were studied during sintering process. The results show that when the heating rates are 3 °C /min (0~500 °C) and 8 °C /min (500~1550 °C), the heating system is better. The relative density of ITO target is 99.58%, the pores are hardly seen and the target is nearly fully densitified, in addition, no crack is observed from the macro perspective.
2013, 42(4):861-864.
Abstract:
Welding with impacting rotation compression was applied to control the TC4 thin plate buckling for the weld uneven heating. Influences of the welding on the weldment microstructure and joint properties were studied. Metallographic observation, Vickers hardness measurement and tensile tests of the joints were carried out. The result shows that based on the controlling of the buckling phenomena of TC4 thin plate weldment, the welding with impacting rotation compression decreases the hardness of the compressed part, the strain hardening does not occur, and the microstructures before and after impacting rotation compression are similar.
Welding with impacting rotation compression was applied to control the TC4 thin plate buckling for the weld uneven heating. Influences of the welding on the weldment microstructure and joint properties were studied. Metallographic observation, Vickers hardness measurement and tensile tests of the joints were carried out. The result shows that based on the controlling of the buckling phenomena of TC4 thin plate weldment, the welding with impacting rotation compression decreases the hardness of the compressed part, the strain hardening does not occur, and the microstructures before and after impacting rotation compression are similar.
2013, 42(4):865-867.
Abstract:
Sm2Co17 rare earth permanent magnets were prepared by a strip casting (SC) technique and general melting process, respectively. Metallographic microstructure and magnetic properties of the permanent magnets prepared by the two techniques were studied. In addition, the effect of aging treatment on the magnetic properties and the degree of orientation of the permanent magnets was studied. The results show that the columnar crystal structure as expected has been obtained from alloys prepared by the strip casting technique. But the magnetic properties of the permanent magnet are obviously lower, and the degree of orientation is 74% as prepared with general melting process. Aging treatment can greatly improve the magnetic properties of magnetic materials by strip casting, and the magnetic properties are similar to that of the permanent magnet prepared by general melting process.
Sm2Co17 rare earth permanent magnets were prepared by a strip casting (SC) technique and general melting process, respectively. Metallographic microstructure and magnetic properties of the permanent magnets prepared by the two techniques were studied. In addition, the effect of aging treatment on the magnetic properties and the degree of orientation of the permanent magnets was studied. The results show that the columnar crystal structure as expected has been obtained from alloys prepared by the strip casting technique. But the magnetic properties of the permanent magnet are obviously lower, and the degree of orientation is 74% as prepared with general melting process. Aging treatment can greatly improve the magnetic properties of magnetic materials by strip casting, and the magnetic properties are similar to that of the permanent magnet prepared by general melting process.
2013, 42(4):868-874.
Abstract:
Compared to pressure swing adsorption (PSA) and cryogenic separation methods, a membrane separation technique has superiority in simplicity and potentially less energy intensity for hydrogen separation and purification. To date, high purity of hydrogen is obtainable through dense metallic membranes, especially palladium and its alloys in industry. However, Pd-based alloy membranes are very expensive in large-scale industrial application. The application of non-palladium-based dense metallic separation membranes is currently receiving great attention. The mechanism of hydrogen separation, composition and current progress of non-palladium-based metallic membranes were reviewed, and the existing problems were identified.
Compared to pressure swing adsorption (PSA) and cryogenic separation methods, a membrane separation technique has superiority in simplicity and potentially less energy intensity for hydrogen separation and purification. To date, high purity of hydrogen is obtainable through dense metallic membranes, especially palladium and its alloys in industry. However, Pd-based alloy membranes are very expensive in large-scale industrial application. The application of non-palladium-based dense metallic separation membranes is currently receiving great attention. The mechanism of hydrogen separation, composition and current progress of non-palladium-based metallic membranes were reviewed, and the existing problems were identified.
2013, 42(4):875-880.
Abstract:
AgNi alloy is a kind of electrical contact materials, which has excellent comprehensive performances. In this work, the preparation technology and research developments of AgNi contact material were summarized, and three main preparation methods were focused on, i.e. mechanical mixing, chemical co-precipitation and mechanical alloying. One obstacle for the use of AgNi alloy is the lack of good melting welding-resistance, so the improvement of melting welding-resistance of AgNi contact material was discussed. At last, the development directions of AgNi contact material in the future were expected.
AgNi alloy is a kind of electrical contact materials, which has excellent comprehensive performances. In this work, the preparation technology and research developments of AgNi contact material were summarized, and three main preparation methods were focused on, i.e. mechanical mixing, chemical co-precipitation and mechanical alloying. One obstacle for the use of AgNi alloy is the lack of good melting welding-resistance, so the improvement of melting welding-resistance of AgNi contact material was discussed. At last, the development directions of AgNi contact material in the future were expected.
