Volume 39,Issue 12,2010 Table of Contents
2010, 39(12):2069-2074.
Abstract:
The hydroxyapatite (HA) coating, one of the most important biomaterials, was prepared on Ti6Al4V alloy by Mg sacrificial anode to improve the anticorrosion electrochemical characteristics. Energy dispersive X-ray analysis (EDX), electron probe microanalyzer (EPMA), Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) were used to analyze the HA coating. The results show that the HA coating is composed of needle-like hydroxyapatite crystals with the Ca/P ratio of 1.4063. After the immersion test of 30 d, the crystals become larger in Hank’s solution, from needle-like to sheet-like in Ringer’s solution and column-like in Tyrode’s solution. The tests of open circuit potential, polarizing curves and EIS method in Hank’s solution, Ringer’s solution, Tyrode’s solution and human blood show that the Ti6Al4V alloy with HA coating has better electrochemical characters than Ti6Al4V alloy
The hydroxyapatite (HA) coating, one of the most important biomaterials, was prepared on Ti6Al4V alloy by Mg sacrificial anode to improve the anticorrosion electrochemical characteristics. Energy dispersive X-ray analysis (EDX), electron probe microanalyzer (EPMA), Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) were used to analyze the HA coating. The results show that the HA coating is composed of needle-like hydroxyapatite crystals with the Ca/P ratio of 1.4063. After the immersion test of 30 d, the crystals become larger in Hank’s solution, from needle-like to sheet-like in Ringer’s solution and column-like in Tyrode’s solution. The tests of open circuit potential, polarizing curves and EIS method in Hank’s solution, Ringer’s solution, Tyrode’s solution and human blood show that the Ti6Al4V alloy with HA coating has better electrochemical characters than Ti6Al4V alloy
2010, 39(12):2075-2078.
Abstract:
The corrosion resistance of Ag ion implanted with dose of 1.5×1017 cm-2 for Mg-1.0 Ca-0.3 Zn magnesium alloy in the simulated body fluid was investigated. The surface hardness and elastic modulus of the alloy and the polarization curve in the SBF were obtained by Nano Snick and three electrode system, respectively. The results indicate that the hardness and the elastic modulus are improved obviously after the implantation of Ag ions, the surface hardness reaches the maximum at a depth of 250 nm below the alloy surface. Meanwhile, the polarization resistance is strengthened, and consequently the corrosion resistance of the alloy is improved. Moreover, the pH value of the SBF within 48 h increases gradually and the alkalization of the SBF is accelerated.
The corrosion resistance of Ag ion implanted with dose of 1.5×1017 cm-2 for Mg-1.0 Ca-0.3 Zn magnesium alloy in the simulated body fluid was investigated. The surface hardness and elastic modulus of the alloy and the polarization curve in the SBF were obtained by Nano Snick and three electrode system, respectively. The results indicate that the hardness and the elastic modulus are improved obviously after the implantation of Ag ions, the surface hardness reaches the maximum at a depth of 250 nm below the alloy surface. Meanwhile, the polarization resistance is strengthened, and consequently the corrosion resistance of the alloy is improved. Moreover, the pH value of the SBF within 48 h increases gradually and the alkalization of the SBF is accelerated.
2010, 39(12):2079-2083.
Abstract:
An ab initio method of the first-principles plane-wave pseudopotentials based on the density functional theory has been used to calculate the physical character and electrochemical performance of various alloy phases in Li-Si alloy. The results show that besides the growth of solid electrolyte interphase (SEI), the formation of Li12Si7 alloy phase also partly leads to the initial irreversible capacity loss. In addition, the pure silicon thin film electrode was prepared by the radio frequency (RF) magnetic sputtering on copper foil collector as anode materials. The structural and electrochemical characteristics of Li-Si alloy were examined using X-ray diffraction (XRD), cyclic voltammogram (CV) and repeatedly constant current charge/discharge (CC). The results show that the first irreversible capacity loss is very large and amorphous structure can accommodate the large volume expansions and improve cyclic performance
An ab initio method of the first-principles plane-wave pseudopotentials based on the density functional theory has been used to calculate the physical character and electrochemical performance of various alloy phases in Li-Si alloy. The results show that besides the growth of solid electrolyte interphase (SEI), the formation of Li12Si7 alloy phase also partly leads to the initial irreversible capacity loss. In addition, the pure silicon thin film electrode was prepared by the radio frequency (RF) magnetic sputtering on copper foil collector as anode materials. The structural and electrochemical characteristics of Li-Si alloy were examined using X-ray diffraction (XRD), cyclic voltammogram (CV) and repeatedly constant current charge/discharge (CC). The results show that the first irreversible capacity loss is very large and amorphous structure can accommodate the large volume expansions and improve cyclic performance
2010, 39(12):2084-2087.
Abstract:
The influence of extrusion deformation ratio on the dynamic mechanical behavior in a tungsten heavy alloy was investigated under uniaxial compression with loading direction perpendicular to the fiber orientation. With extrusion deformation ratio increasing from 0 to 40.8%, the sensitivity of adiabatic shear banding shows an obviously rising tendency. Microcracks could be seen near the centre of the shear band and initiate at the interface of tungsten-matrix as well as the interior of tungsten. Moreover, the observation by the transmission electron microscopy reveals the dislocation pile-ups at the interface of tungsten-matrix and the presence of a microcrack propagating along the boundary and inside of the subgrain in the interior of tungsten within the shear band
The influence of extrusion deformation ratio on the dynamic mechanical behavior in a tungsten heavy alloy was investigated under uniaxial compression with loading direction perpendicular to the fiber orientation. With extrusion deformation ratio increasing from 0 to 40.8%, the sensitivity of adiabatic shear banding shows an obviously rising tendency. Microcracks could be seen near the centre of the shear band and initiate at the interface of tungsten-matrix as well as the interior of tungsten. Moreover, the observation by the transmission electron microscopy reveals the dislocation pile-ups at the interface of tungsten-matrix and the presence of a microcrack propagating along the boundary and inside of the subgrain in the interior of tungsten within the shear band
2010, 39(12):2088-2090.
Abstract:
α-HgI2 crystal was grown using a static sublimation method in a self-designed vertical two-zone growth furnace. After 23 days growth, a single crystal of about 15 mm×12 mm×5 mm was obtained. The as-grown crystal was characterized by means of XRD and 4155 CVIV instrument, and the performance of the detector made with the as-grown HgI2 crystal was tested. The results indicate that excess iodine exists in the as-grown crystal, which can be removed effectively by heating at a feasible temperature. The resistivity of the as-grown crystal is about 1012 Ω·cm. The spectroscopy response to gamma ray (an uncollimated 241Am radiative source with the principal energy of 59.5 keV) of the detectors shows that the energy resolution is 14.6% corresponding to FWHM8.69 keV at room temperature
α-HgI2 crystal was grown using a static sublimation method in a self-designed vertical two-zone growth furnace. After 23 days growth, a single crystal of about 15 mm×12 mm×5 mm was obtained. The as-grown crystal was characterized by means of XRD and 4155 CVIV instrument, and the performance of the detector made with the as-grown HgI2 crystal was tested. The results indicate that excess iodine exists in the as-grown crystal, which can be removed effectively by heating at a feasible temperature. The resistivity of the as-grown crystal is about 1012 Ω·cm. The spectroscopy response to gamma ray (an uncollimated 241Am radiative source with the principal energy of 59.5 keV) of the detectors shows that the energy resolution is 14.6% corresponding to FWHM8.69 keV at room temperature
2010, 39(12):2091-2094.
Abstract:
The surfaces of Ti17 alloy were strengthened by an electric spark treatment (EST), then an ultrasonic surface treatment was used in order to improve the fatigue life. The surface morphology was observed by SEM. The surface residual stress was analyzed by a X-ray diffractometer. Tension-tension fatigue tests were carried out in a HT-100 fatigue testing machine at 350 oC. The results show that the surface roughness and the residual stress are reduced for the specimens after the ultrasonic treatment. The fatigue life of the specimens strengthened by ultrasonic treatments is about twice that of the specimens treated by EST only. The fatigue life of the specimen strengthened by YG8 electrode EST combination with ultrasonic treatment is the longest
The surfaces of Ti17 alloy were strengthened by an electric spark treatment (EST), then an ultrasonic surface treatment was used in order to improve the fatigue life. The surface morphology was observed by SEM. The surface residual stress was analyzed by a X-ray diffractometer. Tension-tension fatigue tests were carried out in a HT-100 fatigue testing machine at 350 oC. The results show that the surface roughness and the residual stress are reduced for the specimens after the ultrasonic treatment. The fatigue life of the specimens strengthened by ultrasonic treatments is about twice that of the specimens treated by EST only. The fatigue life of the specimen strengthened by YG8 electrode EST combination with ultrasonic treatment is the longest
2010, 39(12):2095-2100.
Abstract:
The nanoindentation in single crystal Ag thin film was simulated by a multiscale quasicontinuum (QC) method. The influences of the indenter width on the contact stress distribution, the load necessary for first dislocation emission and the nanohardness were investigated in the nanoindentation deformation process. In addition, all results of the simulation were analyzed with Rice-Thomson (R-T) dislocation model. Results show that the sharp drops of the load-displacement curves are due to the collective dislocation activities. The indenter width can greatly influence the contact stress distribution, the load necessary for first dislocation emission and the nanohardness. Normal contact stress, shear contact stress and nanohardness are decreased as the indenter width is increased, indicating an obvious indenter size effect in nanoindentation of single crystal Ag thin film; whereas the load necessary for first dislocation emission is increased as the indenter width is increased, and is in direct proportion to the square root of the indenter half-width. The simulation results are in good agreement with experimental results and R-T dislocation model
The nanoindentation in single crystal Ag thin film was simulated by a multiscale quasicontinuum (QC) method. The influences of the indenter width on the contact stress distribution, the load necessary for first dislocation emission and the nanohardness were investigated in the nanoindentation deformation process. In addition, all results of the simulation were analyzed with Rice-Thomson (R-T) dislocation model. Results show that the sharp drops of the load-displacement curves are due to the collective dislocation activities. The indenter width can greatly influence the contact stress distribution, the load necessary for first dislocation emission and the nanohardness. Normal contact stress, shear contact stress and nanohardness are decreased as the indenter width is increased, indicating an obvious indenter size effect in nanoindentation of single crystal Ag thin film; whereas the load necessary for first dislocation emission is increased as the indenter width is increased, and is in direct proportion to the square root of the indenter half-width. The simulation results are in good agreement with experimental results and R-T dislocation model
2010, 39(12):2101-2106.
Abstract:
The quasistatic and dynamic compressive mechanical properties of textured polycrystal sheet of hot rolled TB2-titanium alloy were investigated by Instron apparatus and Split-Hopkinson pressure bar (SHPB) technology, respectively. Cylindrical specimens of textured titanium alloy sheet, which were cut with the cylinder axis along the rolling direction (RD), transverse direction (TD) and 45o direction (RD-45o) from the rolling direction lying in the rolling plane, were compressed at strain rates in the range of 10-3 to 103 s-1. The compressive stress-strain curves show that the flow stresses for different directions of hot rolled TB2-titanium alloy sheet increase with increase of the strain rate and the obvious effect of strain rate hardening is observed. Both the quasistatic and dynamical compressive mechanical properties exhibit anisotropy. Furthermore, the behavior for quasistatic compression is different from that for dynamical compression. Taking into account of possible mechanisms for quasistatic and dynamic plastic deformation, the mechanical anisotropy of textured polycrystal titanium alloy sheets was discussed based on the microscope crystal plasticity deformation theory
The quasistatic and dynamic compressive mechanical properties of textured polycrystal sheet of hot rolled TB2-titanium alloy were investigated by Instron apparatus and Split-Hopkinson pressure bar (SHPB) technology, respectively. Cylindrical specimens of textured titanium alloy sheet, which were cut with the cylinder axis along the rolling direction (RD), transverse direction (TD) and 45o direction (RD-45o) from the rolling direction lying in the rolling plane, were compressed at strain rates in the range of 10-3 to 103 s-1. The compressive stress-strain curves show that the flow stresses for different directions of hot rolled TB2-titanium alloy sheet increase with increase of the strain rate and the obvious effect of strain rate hardening is observed. Both the quasistatic and dynamical compressive mechanical properties exhibit anisotropy. Furthermore, the behavior for quasistatic compression is different from that for dynamical compression. Taking into account of possible mechanisms for quasistatic and dynamic plastic deformation, the mechanical anisotropy of textured polycrystal titanium alloy sheets was discussed based on the microscope crystal plasticity deformation theory
2010, 39(12):2107-2111.
Abstract:
The effect of pre-deformation on the aging precipitation process of 2E12 aluminum alloy was investigated by DSC analysis, microhardness test and transmission electron microscope (TEM). The results show that the peak aging of 2E12 alloy exhibits two distinct stages. Pre-deformation weakens the hardening effect of the first aging stage, enhances the peak aging hardness and accelerates the aging process. The peak aging hardness increases and peak aging time decreases with more pre-deformation amount. Increase in pre-deformation degree also leads to finer and more dispersive S-lath in 2E12 alloy. The dislocations introduced by the pre-deformation provide preferential sites for the heterogeneous nucleation of S phase. The edge dislocation sites in dislocation loops are beneficial for nucleation of spherical S phase. Pre-deformation accelerates the precipitation of Type I S phase and delays the precipitation of Type II S phase
The effect of pre-deformation on the aging precipitation process of 2E12 aluminum alloy was investigated by DSC analysis, microhardness test and transmission electron microscope (TEM). The results show that the peak aging of 2E12 alloy exhibits two distinct stages. Pre-deformation weakens the hardening effect of the first aging stage, enhances the peak aging hardness and accelerates the aging process. The peak aging hardness increases and peak aging time decreases with more pre-deformation amount. Increase in pre-deformation degree also leads to finer and more dispersive S-lath in 2E12 alloy. The dislocations introduced by the pre-deformation provide preferential sites for the heterogeneous nucleation of S phase. The edge dislocation sites in dislocation loops are beneficial for nucleation of spherical S phase. Pre-deformation accelerates the precipitation of Type I S phase and delays the precipitation of Type II S phase
10 Effects of Calcium Addition on High Temperature Creep Resistance of Magnesium Alloys with High Zinc
2010, 39(12):2112-2116.
Abstract:
The effects of trace Ca addition on microstructure and high-temperature creep resistance of as-cast Mg-12Zn-4Al-0.3Mn alloy were investigated. Results show that the as-cast microstructure of the base alloy consists of α-Mg matrix and block quasicrystalline phase at gain boundaries. The composition of this quasicrystalline phase is closed to that of the equilibrium t phase (Mg32(Al,Zn)49) in the Mg-Zn-Al ternary system. A small amount of Ca addition to the base alloy results in the formation of a lamellar eutectic j (Al2Mg5Zn2) and the transformation of the quasicrystalline phase to the equilibrium t phase in the as-cast microstructure of the alloy. The volume fraction of the j phase increases with the increase of Ca addition. The creep resistance of the alloys is significantly improved by Ca addition. The optimum creep resistance of the alloy is obtained by 0.6% Ca addition under the creep condition of 175 oC, 70 MPa, whose steady state creep rate is approximately one order of magnitude lower than that of its base alloy.
The effects of trace Ca addition on microstructure and high-temperature creep resistance of as-cast Mg-12Zn-4Al-0.3Mn alloy were investigated. Results show that the as-cast microstructure of the base alloy consists of α-Mg matrix and block quasicrystalline phase at gain boundaries. The composition of this quasicrystalline phase is closed to that of the equilibrium t phase (Mg32(Al,Zn)49) in the Mg-Zn-Al ternary system. A small amount of Ca addition to the base alloy results in the formation of a lamellar eutectic j (Al2Mg5Zn2) and the transformation of the quasicrystalline phase to the equilibrium t phase in the as-cast microstructure of the alloy. The volume fraction of the j phase increases with the increase of Ca addition. The creep resistance of the alloys is significantly improved by Ca addition. The optimum creep resistance of the alloy is obtained by 0.6% Ca addition under the creep condition of 175 oC, 70 MPa, whose steady state creep rate is approximately one order of magnitude lower than that of its base alloy.
2010, 39(12):2117-2121.
Abstract:
The directional solidification of Ni-Cu alloy was simulated numerically based on a phase filed method, and the effects of pulling speed and thermal gradient on the interface shape in a forced flow/free flow were studied comparatively. The results indicate that the growth of the solidification interface incline towards the upstream direction in the forced flow. With the forced flow velocity increasing, the cells become bigger, the inclination depth of grooves is increased gradually and the depth difference becomes more obvious. With the increase in the pulling speed, the morphological evolution mode of directional solidification is planar interface→deep cells→ shallow cellular→ planar interface, while with the increasing thermal gradients the morphological evolution mode is deep cells → shallow cellular → planar interface. In addition, the forced flow has a great effect on the primary spacing of cells formed by solidification
The directional solidification of Ni-Cu alloy was simulated numerically based on a phase filed method, and the effects of pulling speed and thermal gradient on the interface shape in a forced flow/free flow were studied comparatively. The results indicate that the growth of the solidification interface incline towards the upstream direction in the forced flow. With the forced flow velocity increasing, the cells become bigger, the inclination depth of grooves is increased gradually and the depth difference becomes more obvious. With the increase in the pulling speed, the morphological evolution mode of directional solidification is planar interface→deep cells→ shallow cellular→ planar interface, while with the increasing thermal gradients the morphological evolution mode is deep cells → shallow cellular → planar interface. In addition, the forced flow has a great effect on the primary spacing of cells formed by solidification
2010, 39(12):2122-2126.
Abstract:
The equation of oxidation growth stresses for the thermal barrier coating (TBC) was expressed based on Clark’s oxidation growth strain rate theory and Wagner’s parabolic kinetic model. The evolution regularity of oxidation growth stresses with time in the coating was predicted by calculation. The PSLS (photo-stimulated luminescence spectroscopy) method was also employed to test growth stresses in TBC samples after different oxidation time. Results show that the prediction of the growth stress model for the thermal barrier coating is consistent with the test results
The equation of oxidation growth stresses for the thermal barrier coating (TBC) was expressed based on Clark’s oxidation growth strain rate theory and Wagner’s parabolic kinetic model. The evolution regularity of oxidation growth stresses with time in the coating was predicted by calculation. The PSLS (photo-stimulated luminescence spectroscopy) method was also employed to test growth stresses in TBC samples after different oxidation time. Results show that the prediction of the growth stress model for the thermal barrier coating is consistent with the test results
2010, 39(12):2127-2131.
Abstract:
A novel bulk metallic glass, Zr60.59Cu15.78Ni10.73Al10.75Nb2.15, was obtained by micro-alloying of brittle ZrCuNiAl bulk alloys with Nb addition. The structure and thermodynamics parameters were determined by XRD, DSC and HRTEM, and the mechanical properties were studied by quasistatic compression. Although XRD and DSC results show the glass nature of the alloy rods, HRTEM surely indicates the precipitation of nanocrystals of 1-2 nm in the as-cast alloys. The Nb addition significantly reduces the crystallization activation energy of Zr-based alloy and favors the further nucleation of nanocrystals during the subsequent deformation. The nanocrystals increase the potential nucleation sites of shear bands, inhibit the propagation of shear bands, and disrupt the operating shear bands; therefore the room-temperature plasticity of the alloy is largely improved. The yield strength, the average plastic strain, and the maximum and minimum plastic strain for the Zr60.59Cu15.78Ni10.73Al10.75Nb2.15 alloy are 1850 MPa, 11.95%, 25.37% and 2.95%, respectively. There is also strain-hardening phenomenon
A novel bulk metallic glass, Zr60.59Cu15.78Ni10.73Al10.75Nb2.15, was obtained by micro-alloying of brittle ZrCuNiAl bulk alloys with Nb addition. The structure and thermodynamics parameters were determined by XRD, DSC and HRTEM, and the mechanical properties were studied by quasistatic compression. Although XRD and DSC results show the glass nature of the alloy rods, HRTEM surely indicates the precipitation of nanocrystals of 1-2 nm in the as-cast alloys. The Nb addition significantly reduces the crystallization activation energy of Zr-based alloy and favors the further nucleation of nanocrystals during the subsequent deformation. The nanocrystals increase the potential nucleation sites of shear bands, inhibit the propagation of shear bands, and disrupt the operating shear bands; therefore the room-temperature plasticity of the alloy is largely improved. The yield strength, the average plastic strain, and the maximum and minimum plastic strain for the Zr60.59Cu15.78Ni10.73Al10.75Nb2.15 alloy are 1850 MPa, 11.95%, 25.37% and 2.95%, respectively. There is also strain-hardening phenomenon
14 Numerical Simulation of Particle Flow for High Velocity Compaction Based on Discrete Element Method
2010, 39(12):2132-2136.
Abstract:
Discrete element method is applied to simulate the loose particle flowing in the process of high velocity compaction. Assuming that the powder is formed by viscoelastic metal particles, a constitutive model of viscoelastic powder in high velocity compaction described by force-displacement is deduced. The governing equation of particle flow for high velocity compaction is established. The calculation method of the contact force is improved. Based on computing software PFC for the discrete element method, the particle flow and density distribution during high velocity compaction is simulated. The simulation results are consistent with the experimental. The influence of damping coefficient variation on the convergence and divergence of solving process and the density distribution of green compact is analyzed
Discrete element method is applied to simulate the loose particle flowing in the process of high velocity compaction. Assuming that the powder is formed by viscoelastic metal particles, a constitutive model of viscoelastic powder in high velocity compaction described by force-displacement is deduced. The governing equation of particle flow for high velocity compaction is established. The calculation method of the contact force is improved. Based on computing software PFC for the discrete element method, the particle flow and density distribution during high velocity compaction is simulated. The simulation results are consistent with the experimental. The influence of damping coefficient variation on the convergence and divergence of solving process and the density distribution of green compact is analyzed
2010, 39(12):2137-2141.
Abstract:
NiCrCoAlY particles and coatings were prepared by plasma spraying technique. The oxidation behavior of NiCrCoAlY particles in the plasma spraying process and the influence of shrouding gas on high-temperature oxidation resistance of NiCrCoAlY coatings were investigated. The results show that there are two oxidation mechanisms during in-flight oxidation. One is convective oxidation, and the other is diffusion oxidation. In the plasma?zone whose distance to the nozzle is less than 55 mm, convective oxidation is the dominating oxidation mechanism; in the zone whose distance to the nozzle is?more than 55 mm, diffusion oxidation is the principal mechanism. Besides the in-flight oxidation, the oxidation after spraying also occurs for the particles. In-flight oxidation is the main oxidation mechanism for NiCrCoAlY particles in plasma spraying. Shrouding gas can decrease the oxide content of in-flight oxidation and increase the oxidation resistance of NiCrCoAlY coatings
NiCrCoAlY particles and coatings were prepared by plasma spraying technique. The oxidation behavior of NiCrCoAlY particles in the plasma spraying process and the influence of shrouding gas on high-temperature oxidation resistance of NiCrCoAlY coatings were investigated. The results show that there are two oxidation mechanisms during in-flight oxidation. One is convective oxidation, and the other is diffusion oxidation. In the plasma?zone whose distance to the nozzle is less than 55 mm, convective oxidation is the dominating oxidation mechanism; in the zone whose distance to the nozzle is?more than 55 mm, diffusion oxidation is the principal mechanism. Besides the in-flight oxidation, the oxidation after spraying also occurs for the particles. In-flight oxidation is the main oxidation mechanism for NiCrCoAlY particles in plasma spraying. Shrouding gas can decrease the oxide content of in-flight oxidation and increase the oxidation resistance of NiCrCoAlY coatings
2010, 39(12):2142-2146.
Abstract:
The phase structure and electrochemical properties of La0.8-xPrxMg0.2Ni3.8 and La0.8-xPrxMg0.2Ni3.2Al0.2Co0.4 (x=0, 0.15, 0.3, 0.4) hydrogen storage alloys were investigated systematically. The structure analyses show that the alloys are mainly composed of multiphases, such as Pr5Co19 phase, Ce5Co19 phase and CaCu5 phase. The increase of Pr content in the alloys leads to an increase of the A5B19 (Pr5Co19 +Ce5Co19)-type phases; at the same time, both the lattice parameters (a, c) and the cell volume (v) for all phases are also decreased. Al element addition favors the formation of CaCu5-type phase. The electrochemical test indicates that the A5B19-type phase alloy has good electrochemical cycle stability, and the Al and Co elements can improve the electrochemical cycle stability of A5B19-type phase alloys
The phase structure and electrochemical properties of La0.8-xPrxMg0.2Ni3.8 and La0.8-xPrxMg0.2Ni3.2Al0.2Co0.4 (x=0, 0.15, 0.3, 0.4) hydrogen storage alloys were investigated systematically. The structure analyses show that the alloys are mainly composed of multiphases, such as Pr5Co19 phase, Ce5Co19 phase and CaCu5 phase. The increase of Pr content in the alloys leads to an increase of the A5B19 (Pr5Co19 +Ce5Co19)-type phases; at the same time, both the lattice parameters (a, c) and the cell volume (v) for all phases are also decreased. Al element addition favors the formation of CaCu5-type phase. The electrochemical test indicates that the A5B19-type phase alloy has good electrochemical cycle stability, and the Al and Co elements can improve the electrochemical cycle stability of A5B19-type phase alloys
2010, 39(12):2147-2151.
Abstract:
A new severe plastic deformation (SPD) K has been explored which includes two consecutive processes, i.e. initial forward extrusion and subsequent shearing process. The process can be shortened as Extrusion-Shearing (ES). The geometrical and numerical models for the structures of ES forming die have been built. Initial and boundary conditions were exerted and FEM molding has been simulated. The structures of ES forming die have been manufactured and installed to Gleeble1500D thermo-mechanical simulator. Physical modeling of ES forming has been done by instituted procedures. Microstructure observations have been carried out on the extruded rods (as-received) and ES formed rod from simulator. From the research results, the ES forming can produce the severe plastic deformation and improve the volume fraction of dynamic recrystallization. The ES simple shear process can produce intense deformation by the combination of forward extrusion and provides a convenient procedure for introducing an ultra fine grain size into a material. The results show that the ES forming process affected both the microstructure of AZ31 Mg alloy. These results can be explained by the effects of the process on microstructure of AZ31 Mg alloy such as grain size and dislocation density caused by the change in recrystallization behavior
A new severe plastic deformation (SPD) K has been explored which includes two consecutive processes, i.e. initial forward extrusion and subsequent shearing process. The process can be shortened as Extrusion-Shearing (ES). The geometrical and numerical models for the structures of ES forming die have been built. Initial and boundary conditions were exerted and FEM molding has been simulated. The structures of ES forming die have been manufactured and installed to Gleeble1500D thermo-mechanical simulator. Physical modeling of ES forming has been done by instituted procedures. Microstructure observations have been carried out on the extruded rods (as-received) and ES formed rod from simulator. From the research results, the ES forming can produce the severe plastic deformation and improve the volume fraction of dynamic recrystallization. The ES simple shear process can produce intense deformation by the combination of forward extrusion and provides a convenient procedure for introducing an ultra fine grain size into a material. The results show that the ES forming process affected both the microstructure of AZ31 Mg alloy. These results can be explained by the effects of the process on microstructure of AZ31 Mg alloy such as grain size and dislocation density caused by the change in recrystallization behavior
Ji Shouchang
,
Li Zhengxian
,
Du Jihong
,
Wang Shaopeng
,
Wang Baoyun
,
Huang Chunliang
,
Pan Xiaolong
2010, 39(12):2152-2156.
Abstract:
Ti6Al4V alloy specimens were put into a vacuum furnace for hydrogen-free carburization. The phases, microstructure, composition and hardness of the carburized coating were analyzed by XRD, SEM, EDS and HV hardness tester, respectively. Results show that after carburization TiC phase appears in the coating, but no hybrids or H-containing phase are observed. The total carburized coating is composed of accreted layer, carburized layer and diffusion layer. The accreted layer containing Ti, Al and V elements inhibits the permeance of carbon. The carburized layer is composed of dense layer I and equiaxed-crystal-shaped layer II. The diffusion layer has a little carbon, so it is only a carburization-influenced zone. The HV microhardness of the carburized coating has a gradient change. The change of hardness reflects the change of carbon content. The hardened layer is about 900 μm thick
Ti6Al4V alloy specimens were put into a vacuum furnace for hydrogen-free carburization. The phases, microstructure, composition and hardness of the carburized coating were analyzed by XRD, SEM, EDS and HV hardness tester, respectively. Results show that after carburization TiC phase appears in the coating, but no hybrids or H-containing phase are observed. The total carburized coating is composed of accreted layer, carburized layer and diffusion layer. The accreted layer containing Ti, Al and V elements inhibits the permeance of carbon. The carburized layer is composed of dense layer I and equiaxed-crystal-shaped layer II. The diffusion layer has a little carbon, so it is only a carburization-influenced zone. The HV microhardness of the carburized coating has a gradient change. The change of hardness reflects the change of carbon content. The hardened layer is about 900 μm thick
19 Influence of Thermodynamic and Kinetic Factors on the Glass Forming Ability of Bulk Metallic Glasses
2010, 39(12):2157-2160.
Abstract:
The forming mechanisms of the bulk metallic glasses (BMGs) were investigated from the viewpoints of thermodynamics and kinetics combined with the classical theory of nucleation and growth. The influences of the enthalpy change ΔHf, entropy change ΔSf, Gibbs free energy difference ΔG, melt viscosity η and cooling rate on the glass forming ability of bulk metallic glasses and their relationships were expatiated. In addition, some criteria of BMGs’ glass forming ability were summarized
The forming mechanisms of the bulk metallic glasses (BMGs) were investigated from the viewpoints of thermodynamics and kinetics combined with the classical theory of nucleation and growth. The influences of the enthalpy change ΔHf, entropy change ΔSf, Gibbs free energy difference ΔG, melt viscosity η and cooling rate on the glass forming ability of bulk metallic glasses and their relationships were expatiated. In addition, some criteria of BMGs’ glass forming ability were summarized
2010, 39(12):2161-2164.
Abstract:
Based on the microscopic phase-field kinetic model for ternary alloys, rafting of the microstructure of Ni75AlxV25-x alloys in the cyclic temperature field and the diversification of the volume fraction with the temperature and composition change were investigated. The results show that the DO22 phase is rafted obviously in the cyclic temperature field; the L12 phase is rafted obviously on the elastic soft direction when the Al content is higher. When the temperature of the cyclic temperature field is up to a certain value, the equilibrium volume fraction value of the L12 phase is higher than that in the constant temperature field; the equilibrium volume fraction value of the L12 phase increases slowly with the aging proceeding and the temperature of the cyclic temperature field increasing
Based on the microscopic phase-field kinetic model for ternary alloys, rafting of the microstructure of Ni75AlxV25-x alloys in the cyclic temperature field and the diversification of the volume fraction with the temperature and composition change were investigated. The results show that the DO22 phase is rafted obviously in the cyclic temperature field; the L12 phase is rafted obviously on the elastic soft direction when the Al content is higher. When the temperature of the cyclic temperature field is up to a certain value, the equilibrium volume fraction value of the L12 phase is higher than that in the constant temperature field; the equilibrium volume fraction value of the L12 phase increases slowly with the aging proceeding and the temperature of the cyclic temperature field increasing
2010, 39(12):2165-2168.
Abstract:
Electrochemical impedance spectroscopy (EIS) is a useful approach to characterize the oxide film structure and its evolution behavior for zirconium alloys. Oxide films formed on Zr-4 alloys with different heat treatment in super-heated steam at 400 °C, 10.3 MPa were characterized by EIS in 10% HCl solution. Results show that the EIS plot is one capacitive arc for the initial oxide film on zircaloy surface in super-heated steam, and then it evolves into two capacitive arcs with the corrosion proceeding. The oxide film is of dual-film structure. The corrosion transition of zirconium alloys in super-heated steam is partly related to the decreased protection of the oxide film. The second phase particles in zirconium alloys play an important role in impedance response of oxide films and corrosion resistance of alloys.
Electrochemical impedance spectroscopy (EIS) is a useful approach to characterize the oxide film structure and its evolution behavior for zirconium alloys. Oxide films formed on Zr-4 alloys with different heat treatment in super-heated steam at 400 °C, 10.3 MPa were characterized by EIS in 10% HCl solution. Results show that the EIS plot is one capacitive arc for the initial oxide film on zircaloy surface in super-heated steam, and then it evolves into two capacitive arcs with the corrosion proceeding. The oxide film is of dual-film structure. The corrosion transition of zirconium alloys in super-heated steam is partly related to the decreased protection of the oxide film. The second phase particles in zirconium alloys play an important role in impedance response of oxide films and corrosion resistance of alloys.
2010, 39(12):2169-2172.
Abstract:
High-quality freestanding GaN thick films were deposited by hydride vapor phase epitaxy (HVPE) on sapphire wafer with a thin Ti film on the top. The FWHM of (0002) peaks in the X-ray rocking curve profile is 260 arcsec. The FWHM of band edge emission peaks at 5 K and room temperature are 3 meV and 20 meV, respectively. The yellow spectral region is not observed at room temperature. The surface morphology of GaN films was characterized by scanning electron microscope; results show that hexagonal pits from dislocation extension exist on the surface of freestanding GaN thick films after corrosion and their dislocation density is estimated as 2.1×l07 cm-2. All these results prove that the Ti metal interlayer improves the crystalline quality of GaN epitaxial layer. The results of Raman and PL show that the surface stress of the GaN films is released completely. Finally, the temperature-dependent PL was investigated; the result also proves that the stress-free freestanding GaN thick films have high crystalline quality and optical quality
High-quality freestanding GaN thick films were deposited by hydride vapor phase epitaxy (HVPE) on sapphire wafer with a thin Ti film on the top. The FWHM of (0002) peaks in the X-ray rocking curve profile is 260 arcsec. The FWHM of band edge emission peaks at 5 K and room temperature are 3 meV and 20 meV, respectively. The yellow spectral region is not observed at room temperature. The surface morphology of GaN films was characterized by scanning electron microscope; results show that hexagonal pits from dislocation extension exist on the surface of freestanding GaN thick films after corrosion and their dislocation density is estimated as 2.1×l07 cm-2. All these results prove that the Ti metal interlayer improves the crystalline quality of GaN epitaxial layer. The results of Raman and PL show that the surface stress of the GaN films is released completely. Finally, the temperature-dependent PL was investigated; the result also proves that the stress-free freestanding GaN thick films have high crystalline quality and optical quality
2010, 39(12):2173-2176.
Abstract:
Using the technology of split Hopkinson Bar, the dynamic shearing experimentation on Ti-5Al-2.5Sn alloy has been conducted. The specimens are hat-shaped. Formation mechanism of adiabatic shear band of Ti-5Al-2.5Sn alloy has been studied by optical microscope and transmission electron microscopy (TEM). Results show that twins play a key role in the formation process of adiabatic shear band of Ti-5Al-2.5Sn alloy. The formation process of the adiabatic shear band can be divided into three stages. In the first stage, the plastic deformation of the forced shear zone is accomplished by dislocation slip and twining shear under impacting loading. A great deal of twins are formed in the deformed area. In the second stage, the local crystal orientation is adjusted due to the formation of deformed twins so that the dislocation that is at a disadvantage orientation of slipping formerly starts up, resulting in formation of the elongated sub-grains in the shear area. In the last stage, owing to interacting of the mobile dislocation and the twins, the fine equiaxial grains are formed by fracture of the twins under dynamic loading. At the same time, the fine equiaxial orthoscopic dynamic-recrystallized grains with fewer dislocations are formed in local areas of the shear band center. Size of the fine equiaxial grains formed in the shear band of Ti-5Al-2.5Sn alloy is approximately 0.1-0.3 μm
Using the technology of split Hopkinson Bar, the dynamic shearing experimentation on Ti-5Al-2.5Sn alloy has been conducted. The specimens are hat-shaped. Formation mechanism of adiabatic shear band of Ti-5Al-2.5Sn alloy has been studied by optical microscope and transmission electron microscopy (TEM). Results show that twins play a key role in the formation process of adiabatic shear band of Ti-5Al-2.5Sn alloy. The formation process of the adiabatic shear band can be divided into three stages. In the first stage, the plastic deformation of the forced shear zone is accomplished by dislocation slip and twining shear under impacting loading. A great deal of twins are formed in the deformed area. In the second stage, the local crystal orientation is adjusted due to the formation of deformed twins so that the dislocation that is at a disadvantage orientation of slipping formerly starts up, resulting in formation of the elongated sub-grains in the shear area. In the last stage, owing to interacting of the mobile dislocation and the twins, the fine equiaxial grains are formed by fracture of the twins under dynamic loading. At the same time, the fine equiaxial orthoscopic dynamic-recrystallized grains with fewer dislocations are formed in local areas of the shear band center. Size of the fine equiaxial grains formed in the shear band of Ti-5Al-2.5Sn alloy is approximately 0.1-0.3 μm
2010, 39(12):2177-2180.
Abstract:
Re(CobalFe0.10Cu0.08Zr0.03)7.55(Re=Sm, Ho, Er) alloy ribbons were prepared by a melt-spun method. The effects of substitution of heavy rare-earth elements, Ho and Er, for Sm on the magnetic property of 2:17 type SmCo alloy were investigated. Results show that the (Sm0.5Ho0.5)(CobalFe0.10Cu0.08Zr0.03)7.55 sample exhibits an excellent magnetic property at room temperature with the Hci higher than 800 kA/m. The Hci of Sm(CobalFe0.10Cu0.08Zr0.03)7.55 alloy ribbon first decreases and then increases with the temperature increasing until 400 oC, and then presents a sharp decline. The Ms of Sm(CobalFe0.10Cu0.08Zr0.03)7.55 alloy ribbon decreases continually with increasing of the temperature. The Hci of (Sm0.5Ho0.5)(CobalFe0.10Cu0.08Zr0.03)7.55 sample decreases gradually with the temperature increasing, but its Ms increases with temperature increasing until 400 oC and then decreases. The Hci of (Sm0.5Ho0.5)(CobalFe0.10Cu0.08Zr0.03)7.55 sample is lower than that of the sample without Ho element above 250 oC, but its Ms is much higher than that of the sample without Ho element. Above 300 oC, the (Sm0.5Ho0.5)(CobalFe0.10Cu0.08Zr0.03)7.55 sample presents higher Ms. It indicates that optimized ratio of the substitution of Ho for Sm is one of the paths to obtain excellent high-temperature magnetic property
Re(CobalFe0.10Cu0.08Zr0.03)7.55(Re=Sm, Ho, Er) alloy ribbons were prepared by a melt-spun method. The effects of substitution of heavy rare-earth elements, Ho and Er, for Sm on the magnetic property of 2:17 type SmCo alloy were investigated. Results show that the (Sm0.5Ho0.5)(CobalFe0.10Cu0.08Zr0.03)7.55 sample exhibits an excellent magnetic property at room temperature with the Hci higher than 800 kA/m. The Hci of Sm(CobalFe0.10Cu0.08Zr0.03)7.55 alloy ribbon first decreases and then increases with the temperature increasing until 400 oC, and then presents a sharp decline. The Ms of Sm(CobalFe0.10Cu0.08Zr0.03)7.55 alloy ribbon decreases continually with increasing of the temperature. The Hci of (Sm0.5Ho0.5)(CobalFe0.10Cu0.08Zr0.03)7.55 sample decreases gradually with the temperature increasing, but its Ms increases with temperature increasing until 400 oC and then decreases. The Hci of (Sm0.5Ho0.5)(CobalFe0.10Cu0.08Zr0.03)7.55 sample is lower than that of the sample without Ho element above 250 oC, but its Ms is much higher than that of the sample without Ho element. Above 300 oC, the (Sm0.5Ho0.5)(CobalFe0.10Cu0.08Zr0.03)7.55 sample presents higher Ms. It indicates that optimized ratio of the substitution of Ho for Sm is one of the paths to obtain excellent high-temperature magnetic property
2010, 39(12):2181-2184.
Abstract:
NiCrAl coatings were prepared on Ni-based superalloy through Atmospheric Plasma Spray (ASP), and the corrosion resistance of the coatings under the conditions of salt spray test and high-temperature oxidation was investigated. From the Tafel polarization curve of NiCrAl coatings before and after the salt spray test, it is shown that the corrosion potential of NiCrAl coatings becomes smaller while the corrosion current density becomes larger, indicating that the corrosion resistance of NiCrAl coatings after the salt spray test is decreased obviously. SEM images show that after the salt spray test, the corrosion of surface of the NiCrAl coatings is serious resulting from the appearance of many cracks and the loose microstructure, so the coatings have no protective capability. EDX analyses reveal that corrosion products are MexOyClz. After the thermal treatment at 1000 oC for 15 h, the corrosion resistance of NiCrAl coatings is enhanced because of the formation of θ-Al2O3 film
NiCrAl coatings were prepared on Ni-based superalloy through Atmospheric Plasma Spray (ASP), and the corrosion resistance of the coatings under the conditions of salt spray test and high-temperature oxidation was investigated. From the Tafel polarization curve of NiCrAl coatings before and after the salt spray test, it is shown that the corrosion potential of NiCrAl coatings becomes smaller while the corrosion current density becomes larger, indicating that the corrosion resistance of NiCrAl coatings after the salt spray test is decreased obviously. SEM images show that after the salt spray test, the corrosion of surface of the NiCrAl coatings is serious resulting from the appearance of many cracks and the loose microstructure, so the coatings have no protective capability. EDX analyses reveal that corrosion products are MexOyClz. After the thermal treatment at 1000 oC for 15 h, the corrosion resistance of NiCrAl coatings is enhanced because of the formation of θ-Al2O3 film
2010, 39(12):2185-2188.
Abstract:
Lanthanum-doped molybdenum powder was prepared by a liquid-liquid doping method and sol-gel technique, and then the lanthanum-doped molybdenum billet was obtained by isostatic pressing and sintering. The microstructure, morphology and RE phases of the materials in different states were analyzed using XRD, SEM, EDS, TEM etc. The results show that a chemical reaction between La(NO3)3 and (NH4)6Mo7O24·4H2O generates La2(MoO4)3. After calcination and reduction, RE phase exists in the molybdenum powder in the form of La2O3 and can refine the powder particles. La2O3 distribute dispersively in the molybdenum matrix after sintering into a billet
Lanthanum-doped molybdenum powder was prepared by a liquid-liquid doping method and sol-gel technique, and then the lanthanum-doped molybdenum billet was obtained by isostatic pressing and sintering. The microstructure, morphology and RE phases of the materials in different states were analyzed using XRD, SEM, EDS, TEM etc. The results show that a chemical reaction between La(NO3)3 and (NH4)6Mo7O24·4H2O generates La2(MoO4)3. After calcination and reduction, RE phase exists in the molybdenum powder in the form of La2O3 and can refine the powder particles. La2O3 distribute dispersively in the molybdenum matrix after sintering into a billet
2010, 39(12):2189-2192.
Abstract:
In-situ synthesized TiB system ceramic particle reinforced Co-based composite coating was prepared on titanium alloy surface by transverse flow CO2 laser to improve the surface service performance of materials. The composite coating was studied by XRD, SEM and EPMA. Results show that in-situ synthesized TiB2 and TiB major ceramic phases are dispersed homogeneously in the γ-Co based alloy coating; they are very thin and uniform; there is obvious difference between the dendrites and the intergranular on the microstructure and composition. The microhardness of the coating is increased prominently, whose average value is about three times higher than that of the titanium alloy substrate. Wear resistance of the composite coating is significant improved
In-situ synthesized TiB system ceramic particle reinforced Co-based composite coating was prepared on titanium alloy surface by transverse flow CO2 laser to improve the surface service performance of materials. The composite coating was studied by XRD, SEM and EPMA. Results show that in-situ synthesized TiB2 and TiB major ceramic phases are dispersed homogeneously in the γ-Co based alloy coating; they are very thin and uniform; there is obvious difference between the dendrites and the intergranular on the microstructure and composition. The microhardness of the coating is increased prominently, whose average value is about three times higher than that of the titanium alloy substrate. Wear resistance of the composite coating is significant improved
2010, 39(12):2193-2195.
Abstract:
The adiabatic shearing behavior of TC4 alloy was simulated using LS-DYNA, and the distribution of equivalent strain, von-Mises stress and temperature rise in the hat-shaped specimen during dynamic loading were obtained. It is found that a large part of plastic strain is concentrated in a narrow deformation area. The temperatures in this area are much higher than those of the matrix material. The equivalent strain, von-Mises stress and temperature rise in each corner of the hat-shaped specimen are highest during all the loading processes. The simulation indicates that the maximum temperature in adiabatic shear band is higher than the recrystallization temperature of TC4 alloy, but lower than its phase transformation temperature, which is helpful to the research of the microstructure deformation mechanism of adiabatic shear band of TC4 alloy.
The adiabatic shearing behavior of TC4 alloy was simulated using LS-DYNA, and the distribution of equivalent strain, von-Mises stress and temperature rise in the hat-shaped specimen during dynamic loading were obtained. It is found that a large part of plastic strain is concentrated in a narrow deformation area. The temperatures in this area are much higher than those of the matrix material. The equivalent strain, von-Mises stress and temperature rise in each corner of the hat-shaped specimen are highest during all the loading processes. The simulation indicates that the maximum temperature in adiabatic shear band is higher than the recrystallization temperature of TC4 alloy, but lower than its phase transformation temperature, which is helpful to the research of the microstructure deformation mechanism of adiabatic shear band of TC4 alloy.
2010, 39(12):2196-2198.
Abstract:
Solid bonding diffusion couples of U-Mo/Nb were prepared by coating and hot rolling. The diffusion couples were heat-treated at 760 oC and 790 oC for different time. The distribution of the main diffusion elements in linear dimension was measured by Energy Dispersive Spectrometer (EDS). The model of diffusion in semi-infinite media was established according to the experiment’s initial boundary conditions. Error function solutions of the diffusion equation were also presented. The diffusion coefficient of uranium diffused in Nb base metal was calculated with the experimental data. The calculation result is considered to be correct by analyzing the method of experiment
Solid bonding diffusion couples of U-Mo/Nb were prepared by coating and hot rolling. The diffusion couples were heat-treated at 760 oC and 790 oC for different time. The distribution of the main diffusion elements in linear dimension was measured by Energy Dispersive Spectrometer (EDS). The model of diffusion in semi-infinite media was established according to the experiment’s initial boundary conditions. Error function solutions of the diffusion equation were also presented. The diffusion coefficient of uranium diffused in Nb base metal was calculated with the experimental data. The calculation result is considered to be correct by analyzing the method of experiment
2010, 39(12):2199-2204.
Abstract:
The nano-crystalline NiSi2/Ti5Si3 composite coating was prepared on TC4 alloy substrate surface by double cathode glow discharge technology. The composition and microstructure of the nano-crystalline composite coating were analyzed by XRD, SEM and TEM. Nanoindentation and scratch test were used to assess its hardness, elastic modulus and adhesion property between the coating and the substrate. The results indicate that the nano-crystalline NiSi2/Ti5Si3 composite coating is composed of two different layers, NiSi2 deposition layer with average grain size of 40 nm, which is the outer layer of 7 μm thickness, and Ti5Si3 diffusion layer with average grain size of 70 nm which is the inner layer of 3 μm thickness. A large number of twins are found in the diffusion layer. The nano-crystalline NiSi2/Ti5Si3 composite coating combines closely with TC4 alloy substrate with an adhesive strength of 49 N and the hardness of the composite coating presents gradient distribution. The specific wear rate of the nano-crystalline NiSi2/Ti5Si3 composite coating is one order of magnitude lower than that of TC4 alloy, and the composite coating is very insensitive to the test load and temperature. Compared with TC4 alloy, the corrosion current density of the nanocrystalline NiSi2/Ti5Si3 composite coating is decreased by two orders of magnitude. The Nyquist plots of the nanocrystalline NiSi2/Ti5Si3 composite coating consist of single capacitance arc with a higher value
The nano-crystalline NiSi2/Ti5Si3 composite coating was prepared on TC4 alloy substrate surface by double cathode glow discharge technology. The composition and microstructure of the nano-crystalline composite coating were analyzed by XRD, SEM and TEM. Nanoindentation and scratch test were used to assess its hardness, elastic modulus and adhesion property between the coating and the substrate. The results indicate that the nano-crystalline NiSi2/Ti5Si3 composite coating is composed of two different layers, NiSi2 deposition layer with average grain size of 40 nm, which is the outer layer of 7 μm thickness, and Ti5Si3 diffusion layer with average grain size of 70 nm which is the inner layer of 3 μm thickness. A large number of twins are found in the diffusion layer. The nano-crystalline NiSi2/Ti5Si3 composite coating combines closely with TC4 alloy substrate with an adhesive strength of 49 N and the hardness of the composite coating presents gradient distribution. The specific wear rate of the nano-crystalline NiSi2/Ti5Si3 composite coating is one order of magnitude lower than that of TC4 alloy, and the composite coating is very insensitive to the test load and temperature. Compared with TC4 alloy, the corrosion current density of the nanocrystalline NiSi2/Ti5Si3 composite coating is decreased by two orders of magnitude. The Nyquist plots of the nanocrystalline NiSi2/Ti5Si3 composite coating consist of single capacitance arc with a higher value
2010, 39(12):2204-2205.
Abstract:
By observing the microstructures and measuring mechanical properties of three kinds of Mg-6Zn-XMn wrought magnesium alloys, the effects of Mn content on microstructures and mechanical properties of Mg-Zn-Mn magnesium alloy was studied. The results show that Mn element distributes dispersively in the matrix mainly as pure Mn particles which can hamper the grain growth, i.e. the grains become finer with Mn content increasing. Mn content has a certain impact on the yield strength of the three alloys, that is, the yield strength increases with Mn content increasing, and the increment of the extruded and the two-stage aged alloys are 14% and 5%, respectively. On the other hand, Mn content has no obvious effect on the tensile strength and elongation of T6 and T4+2-stage aged alloys. The alloy with 0.68wt% Mn after two-stage aging has better overall mechanical properties, whose tensile strength is the highest, 360 MPa, and whose elongation is 5.2%
By observing the microstructures and measuring mechanical properties of three kinds of Mg-6Zn-XMn wrought magnesium alloys, the effects of Mn content on microstructures and mechanical properties of Mg-Zn-Mn magnesium alloy was studied. The results show that Mn element distributes dispersively in the matrix mainly as pure Mn particles which can hamper the grain growth, i.e. the grains become finer with Mn content increasing. Mn content has a certain impact on the yield strength of the three alloys, that is, the yield strength increases with Mn content increasing, and the increment of the extruded and the two-stage aged alloys are 14% and 5%, respectively. On the other hand, Mn content has no obvious effect on the tensile strength and elongation of T6 and T4+2-stage aged alloys. The alloy with 0.68wt% Mn after two-stage aging has better overall mechanical properties, whose tensile strength is the highest, 360 MPa, and whose elongation is 5.2%
2010, 39(12):2211-2216.
Abstract:
To explore biodegradable intravascular stents, Mg-3Zn-0.8Zr-1HA composite (mass fraction, similarly hereinafter) and Mg-3Zn-0.8Zr alloy were prepared to investigate the effects of nanohydroxyapatite (n-HA) on the mechanical and biodegradable properties of Mg-3Zn-0.8Zr alloy. Results indicate that the n-HA particles are distributed uniformly in the matrix, so the grains of the matrix are refined, and the ultimate tensile strength and elongation are increased. The immersion tests in the simulated body fluid (SBF) show that the surface morphologies of the two kinds of materials are quite different as the immersion time is prolonged. After immersion for 20 d, the surface of the composite with n-HA is still perfect and covered with Ca and P, while a lot of pitting occurs on the surface of Mg-3Zn-0.8Zr alloy. The electrical current densities of the composite and the alloy are 0.701×10-5 A·cm-2 and 1.034×10-5 A·cm-2 respectively, which demonstrates that the corrosion resistance of the Mg alloy is significantly improved by the addition of nanohydroxyapatite powders.
To explore biodegradable intravascular stents, Mg-3Zn-0.8Zr-1HA composite (mass fraction, similarly hereinafter) and Mg-3Zn-0.8Zr alloy were prepared to investigate the effects of nanohydroxyapatite (n-HA) on the mechanical and biodegradable properties of Mg-3Zn-0.8Zr alloy. Results indicate that the n-HA particles are distributed uniformly in the matrix, so the grains of the matrix are refined, and the ultimate tensile strength and elongation are increased. The immersion tests in the simulated body fluid (SBF) show that the surface morphologies of the two kinds of materials are quite different as the immersion time is prolonged. After immersion for 20 d, the surface of the composite with n-HA is still perfect and covered with Ca and P, while a lot of pitting occurs on the surface of Mg-3Zn-0.8Zr alloy. The electrical current densities of the composite and the alloy are 0.701×10-5 A·cm-2 and 1.034×10-5 A·cm-2 respectively, which demonstrates that the corrosion resistance of the Mg alloy is significantly improved by the addition of nanohydroxyapatite powders.
2010, 39(12):2217-2221.
Abstract:
Lead-free solder powder of Sn-Ag-Cu system was prepared with a supersonic atomizer designed by ourselves. Then the effects of different compositions on the properties of the powder were studied, and the microstructure of its brazed joint was observed, which was compared with that of Sn37Pb solder powder. The results show that the Sn3Ag2.8Cu powder has the highest effective atomization efficiency, the lowest oxygen content, the best sphericity and surface smoothness in the three different compositions powders under the same superheat; the diffusion layer formed between Sn3Ag2.8Cu soldering paste and the copper substrate is thicker and their intermetallics are more irregular than those of Sn37Pb and Sn3Ag2.8Cu-0.1Ce soldering paste; the Sn3Ag2.8Cu-0.1Ce powder has higher effective atomization efficiency and oxygen content than the Sn37Pb powder
Lead-free solder powder of Sn-Ag-Cu system was prepared with a supersonic atomizer designed by ourselves. Then the effects of different compositions on the properties of the powder were studied, and the microstructure of its brazed joint was observed, which was compared with that of Sn37Pb solder powder. The results show that the Sn3Ag2.8Cu powder has the highest effective atomization efficiency, the lowest oxygen content, the best sphericity and surface smoothness in the three different compositions powders under the same superheat; the diffusion layer formed between Sn3Ag2.8Cu soldering paste and the copper substrate is thicker and their intermetallics are more irregular than those of Sn37Pb and Sn3Ag2.8Cu-0.1Ce soldering paste; the Sn3Ag2.8Cu-0.1Ce powder has higher effective atomization efficiency and oxygen content than the Sn37Pb powder
2010, 39(12):2222-2226.
Abstract:
In the process of soft-contact electromagnetic continuous casting of 7050 aluminum alloy, the forced flow of molten melt is produced by the intermediate magnetic field, which can improve the microstructure and eliminate hot cracks. On one hand, the electromagnetic filed can reduce the external factors for hot cracking through improving the casting condition to decrease the temperature gradient, to release the thermal stress and strain and to make alloying brittleness zone mainly in the state of being compressed. On the other hand, it also can decrease the hot cracking tendency of alloys by reducing the size of unfeeding zone and decreasing the quantities of eutectic compounds of low melting point. As a result of the two facts above, the cracking of electromagnetic continuous casting slab is eliminated
In the process of soft-contact electromagnetic continuous casting of 7050 aluminum alloy, the forced flow of molten melt is produced by the intermediate magnetic field, which can improve the microstructure and eliminate hot cracks. On one hand, the electromagnetic filed can reduce the external factors for hot cracking through improving the casting condition to decrease the temperature gradient, to release the thermal stress and strain and to make alloying brittleness zone mainly in the state of being compressed. On the other hand, it also can decrease the hot cracking tendency of alloys by reducing the size of unfeeding zone and decreasing the quantities of eutectic compounds of low melting point. As a result of the two facts above, the cracking of electromagnetic continuous casting slab is eliminated
2010, 39(12):2227-2230.
Abstract:
Flexible TiO2 nanofibres were fabricated by electrospinning with Ti(SO4)2, polyvinyl pyrrolidone (PVP), dimethyl formamide(DMF) and deionized water as starting materials. The samples were characterized with XRD, FESEM, TEM and TG-DTA. The results reveal that the obtained TiO2 nanofibres are flexible and polycrystalline structure. The mean diameter of the TiO2 nanofibres is about 100 nm, and the length is greater than 300 μm. The influence of calcination temperatures on the photocatalytic effect for TiO2 nanofibres was investigated through methyl orange, rhodamine-B and phenol as degradation compounds. The photocatalytic experiments results indicate that flexible TiO2 nanofibres possess high degradation rates for these three degradation compounds. The formation mechanism of the flexible TiO2 nanofibres was also discussed
Flexible TiO2 nanofibres were fabricated by electrospinning with Ti(SO4)2, polyvinyl pyrrolidone (PVP), dimethyl formamide(DMF) and deionized water as starting materials. The samples were characterized with XRD, FESEM, TEM and TG-DTA. The results reveal that the obtained TiO2 nanofibres are flexible and polycrystalline structure. The mean diameter of the TiO2 nanofibres is about 100 nm, and the length is greater than 300 μm. The influence of calcination temperatures on the photocatalytic effect for TiO2 nanofibres was investigated through methyl orange, rhodamine-B and phenol as degradation compounds. The photocatalytic experiments results indicate that flexible TiO2 nanofibres possess high degradation rates for these three degradation compounds. The formation mechanism of the flexible TiO2 nanofibres was also discussed
2010, 39(12):2232-2236.
Abstract:
Nanostructured surface layer was synthesized on Zr-4 alloy surface by surface mechanical attrition treatment (SMAT), and then the alloy was annealed at different temperatures in vacuum. The effects of the annealing temperature on the thermal stabilities of microstructure and hardness, and the effect of annealing on corrosion resistance were investigated by means of optical microscope, X-ray diffraction, the transmission electron microscope, microhardness test and electrochemical testing. The results show that when the annealing temperature is below 350 oC, the microstructure, grain size and microhardness of surface nanocrystallized Zr-4 alloy have good thermal stability. The corrosion resistance in 1 mol/L H2SO4 solution for the alloy only after SMAT is decreased. However, after further annealing below 350 oC, its corrosion resistance is improved, which is better than that of Zr-4 alloy without SMAT treatment
Nanostructured surface layer was synthesized on Zr-4 alloy surface by surface mechanical attrition treatment (SMAT), and then the alloy was annealed at different temperatures in vacuum. The effects of the annealing temperature on the thermal stabilities of microstructure and hardness, and the effect of annealing on corrosion resistance were investigated by means of optical microscope, X-ray diffraction, the transmission electron microscope, microhardness test and electrochemical testing. The results show that when the annealing temperature is below 350 oC, the microstructure, grain size and microhardness of surface nanocrystallized Zr-4 alloy have good thermal stability. The corrosion resistance in 1 mol/L H2SO4 solution for the alloy only after SMAT is decreased. However, after further annealing below 350 oC, its corrosion resistance is improved, which is better than that of Zr-4 alloy without SMAT treatment
Wu Yifang
,
Liu Yongning
,
Fang Jianfeng
,
Ma Xiaobo
,
Chen Yuanzhen
,
Liu Bo
,
Zhang Yuping
,
Fang Yuan
,
Li Chengshan
,
Xi Zhengping
2010, 39(12):2237-2241.
Abstract:
he phase structures and electrochemical properties of TiV2.1Ni0.4Zr0.06Cu0.03Cr0.1 alloys at different quenching rates were investigated. XRD, EBI and EDS analyses indicate that the alloys mainly consist of a V-based solid solution main phase and a network structure of Ti2Ni secondary phase along grain boundaries of the main phase. Electrochemical measurements show that the maximum discharge capacity, the exchange current density, limiting current density and the cycling stability are all increased by higher quenching rate. The high-rate dischargeablity (HRD) is decreased because of the quick dissolution of the secondary catalytic phase in alkali solution at higher discharge current density
he phase structures and electrochemical properties of TiV2.1Ni0.4Zr0.06Cu0.03Cr0.1 alloys at different quenching rates were investigated. XRD, EBI and EDS analyses indicate that the alloys mainly consist of a V-based solid solution main phase and a network structure of Ti2Ni secondary phase along grain boundaries of the main phase. Electrochemical measurements show that the maximum discharge capacity, the exchange current density, limiting current density and the cycling stability are all increased by higher quenching rate. The high-rate dischargeablity (HRD) is decreased because of the quick dissolution of the secondary catalytic phase in alkali solution at higher discharge current density
2010, 39(12):2242-2246.
Abstract:
SiO2 sol was used to enwrap the LaNi4.8Al0.2 alloy to improve the hydriding performance of the alloy. The samples after drying were analyzed by SEM. The effects of preparation parameters on hydriding performance were studied, which include water content, silica content, granularity of the alloy and the drying techniques. Results show that most metal particles are embedded into the silica sol. The sol viscosity is reduced gradually with more water and longer time. When the ratio of water to silica is 8:1, the hydriding speed of the samples is the fastest. The hydrogen absorption capacity per unit mass solid is increased with less LaNi4.8Al0.2 alloy. It is easier for the sol to enwrap the metal when the granularity of metal particles is smaller, and the hydriding performance of the samples is better. Furthermore, the hydrogen absorption capacity and absorption speed of the samples heated and dried in Ar is worse than that heated and dried in air. Thus the hydriding performance is not much relevant with the noble gas protection. The hydrogen absorption capacity and the absorption speed of the samples are obviously superior to that of the LaNi4.8Al0.2 alloy under 0.2 MPa hydrogen pressure.
SiO2 sol was used to enwrap the LaNi4.8Al0.2 alloy to improve the hydriding performance of the alloy. The samples after drying were analyzed by SEM. The effects of preparation parameters on hydriding performance were studied, which include water content, silica content, granularity of the alloy and the drying techniques. Results show that most metal particles are embedded into the silica sol. The sol viscosity is reduced gradually with more water and longer time. When the ratio of water to silica is 8:1, the hydriding speed of the samples is the fastest. The hydrogen absorption capacity per unit mass solid is increased with less LaNi4.8Al0.2 alloy. It is easier for the sol to enwrap the metal when the granularity of metal particles is smaller, and the hydriding performance of the samples is better. Furthermore, the hydrogen absorption capacity and absorption speed of the samples heated and dried in Ar is worse than that heated and dried in air. Thus the hydriding performance is not much relevant with the noble gas protection. The hydrogen absorption capacity and the absorption speed of the samples are obviously superior to that of the LaNi4.8Al0.2 alloy under 0.2 MPa hydrogen pressure.
2010, 39(12):2247-2250.
Abstract:
TiFe alloys were prepared by ilmenite electrolysis in CaCl2 molten salt, and the reaction progress of the electrolysis was investigated. The composition of the electrolytic products and the electrolytic efficiency were analyzed. Results show that the reduction of ilmenite undergoes an alloying course of prior formation of Fe and gradual formation of TiFe2 and TiFe. The in-process products include CaTiO3, Fe2TiO4 and TiO. The alloy firstly formed in the reaction is TiFe2, and then it converts into TiFe alloy by the interdiffusion between Ti and TiFe2, indicating the diffusion is a control step of the reaction. Under the same electrolysis condition, ilmenite is more difficult to electrolyze than the mixed oxides. It is because that those ilmenite particles are big and the impurity is solid solutioned into the iron titanate, so deoxygenation is more difficult and the electrolytic efficiency is much lower
TiFe alloys were prepared by ilmenite electrolysis in CaCl2 molten salt, and the reaction progress of the electrolysis was investigated. The composition of the electrolytic products and the electrolytic efficiency were analyzed. Results show that the reduction of ilmenite undergoes an alloying course of prior formation of Fe and gradual formation of TiFe2 and TiFe. The in-process products include CaTiO3, Fe2TiO4 and TiO. The alloy firstly formed in the reaction is TiFe2, and then it converts into TiFe alloy by the interdiffusion between Ti and TiFe2, indicating the diffusion is a control step of the reaction. Under the same electrolysis condition, ilmenite is more difficult to electrolyze than the mixed oxides. It is because that those ilmenite particles are big and the impurity is solid solutioned into the iron titanate, so deoxygenation is more difficult and the electrolytic efficiency is much lower
2010, 39(12):2251-2254.
Abstract:
Friction stir processing (FSP) was summarized in detail. Its effect on properties of materials and the research on preparation of composites and alloys were also introduced. In addition, the problems of FSP research, the prospect and the future development were pointed out. The influencing factors and formation mechanism of the abnormal grain growth need further studies. FSP combined with melt welding can meet the requirement of welding of high strength materials such as titanium alloys. There will be a good application future for FSP to prepare nano-particles enforced metal matrix composites (MMCs) and intermetallic composites (IMCs). An inventive technique to fabricate materials with homogeneous microstructure by adopting the concepts of FSP is pivotal for its applications
Friction stir processing (FSP) was summarized in detail. Its effect on properties of materials and the research on preparation of composites and alloys were also introduced. In addition, the problems of FSP research, the prospect and the future development were pointed out. The influencing factors and formation mechanism of the abnormal grain growth need further studies. FSP combined with melt welding can meet the requirement of welding of high strength materials such as titanium alloys. There will be a good application future for FSP to prepare nano-particles enforced metal matrix composites (MMCs) and intermetallic composites (IMCs). An inventive technique to fabricate materials with homogeneous microstructure by adopting the concepts of FSP is pivotal for its applications
2010, 39(12):2255-2261.
Abstract:
A brief overview of the analytical methods for the determination of trace and ultra-trace platinum group elements is presented. Preconcentration/separation step of the samples and detection techniques are introduced in detail. Some suggestions are proposed and the research direction in the future is forecasted for the determination of the PGEs
A brief overview of the analytical methods for the determination of trace and ultra-trace platinum group elements is presented. Preconcentration/separation step of the samples and detection techniques are introduced in detail. Some suggestions are proposed and the research direction in the future is forecasted for the determination of the PGEs
2010, 39(12):2262-2266.
Abstract:
TiNiCu shape memory alloy melt-spun ribbons have attracted much attention as one of promising microactuator materials due to their narrow transformation hysteresis, excellent shape memory effect and superelasticity and good thermal cycling stability. In present work, the recent development of TiNiCu melt-spun ribbons is comprehensively summarized, including crystallization behavior, microstructure, martensitic transformation behavior, shape memory effect and superelasticity. The emphasis is paid on the processing-microstructure-property relationship. Some important issues on the TiNiCu melt-spun ribbons are discussed
TiNiCu shape memory alloy melt-spun ribbons have attracted much attention as one of promising microactuator materials due to their narrow transformation hysteresis, excellent shape memory effect and superelasticity and good thermal cycling stability. In present work, the recent development of TiNiCu melt-spun ribbons is comprehensively summarized, including crystallization behavior, microstructure, martensitic transformation behavior, shape memory effect and superelasticity. The emphasis is paid on the processing-microstructure-property relationship. Some important issues on the TiNiCu melt-spun ribbons are discussed
