Volume 41,Issue 11,2012 Table of Contents
2012, 41(11):1881-1886.
Abstract:
In order to improve the hydriding and dehydriding behaviour of the Mg2Ni-type alloys, Ni in the alloy was partially substituted by Co, and melt-spinning technology was used to prepare the Mg20Ni10-xCox (x=0, 1, 2, 3, 4) hydrogen storage alloys. The structures of the as-cast and spun alloys were studied by XRD, SEM and HRTEM. The hydriding and dehydriding kinetics as well as the electrochemical performances of the alloys were measured. The results show that no amorphous phase is detected in the as-spun Co-free alloy, but the as-spun alloys substituted by Co display the presence of an amorphous phase. The substitution of Co for Ni and the melt spinning significantly improve the hydrogen absorption and desorption performances of the as-cast and spun alloys. Meanwhile, the substitution of Co for Ni enhances the discharge capacity and cycle stability of the as-spun alloys dramatically.
In order to improve the hydriding and dehydriding behaviour of the Mg2Ni-type alloys, Ni in the alloy was partially substituted by Co, and melt-spinning technology was used to prepare the Mg20Ni10-xCox (x=0, 1, 2, 3, 4) hydrogen storage alloys. The structures of the as-cast and spun alloys were studied by XRD, SEM and HRTEM. The hydriding and dehydriding kinetics as well as the electrochemical performances of the alloys were measured. The results show that no amorphous phase is detected in the as-spun Co-free alloy, but the as-spun alloys substituted by Co display the presence of an amorphous phase. The substitution of Co for Ni and the melt spinning significantly improve the hydrogen absorption and desorption performances of the as-cast and spun alloys. Meanwhile, the substitution of Co for Ni enhances the discharge capacity and cycle stability of the as-spun alloys dramatically.
2 Low-Temperature Magnetotransport and Magnetic Properties of Cobalt-Doped Amorphous Carbon Thin Films
Tang Ruihe
,
Liu Wei
,
Zhang Zhengjun
,
Yu Ronghai
,
Liu Xiaofang
,
Yang Bai
,
Mizuguchi Masaki
,
Takanashi Koki
2012, 41(11):1887-1890.
Abstract:
A series of Co-doped amorphous carbon granular thin films with various Co contents (x, at%) were deposited on n-type Si (100) substrates by a magnetron co-sputtering technique at room temperature. The microstructure, magnetotransport and magnetic properties of the Co-C films have been characterized. By optimizing Co content, giant negative magnetoresistances (MRs) were observed at low temperature, with a maximum MR ratio of 27.6% at 2 K under an applied magnetic field of 90×79.6 kA·m-1 for the film with Co content of 6.4 at%. As Co content increases from 6.4 at% to 16.4 at%, the MR ratio decreases gradually from 27.6% to 2.2%. A linear lnr-T–1/2 relationship indicates that the spin transport in Co6.4C93.6 thin film agrees well with tunneling conductance.
A series of Co-doped amorphous carbon granular thin films with various Co contents (x, at%) were deposited on n-type Si (100) substrates by a magnetron co-sputtering technique at room temperature. The microstructure, magnetotransport and magnetic properties of the Co-C films have been characterized. By optimizing Co content, giant negative magnetoresistances (MRs) were observed at low temperature, with a maximum MR ratio of 27.6% at 2 K under an applied magnetic field of 90×79.6 kA·m-1 for the film with Co content of 6.4 at%. As Co content increases from 6.4 at% to 16.4 at%, the MR ratio decreases gradually from 27.6% to 2.2%. A linear lnr-T–1/2 relationship indicates that the spin transport in Co6.4C93.6 thin film agrees well with tunneling conductance.
2012, 41(11):1891-1895.
Abstract:
Zr53.9Cu29.4Ni4.9Al9.8Fe2 alloy sample with the diameter of 3 mm was prepared by Cu mold suction casting at different temperatures. The effect of casting temperature on mechanical properties and microstructure of the as-cast alloy was investigated. It is found that there is a critical casting temperature for the fully amorphous structure, below which the crystallization phase might be precipitated. Experiment results show that the compressive strength increases and the compressive plasticity slightly decreases when the casting temperature increases to certain extent. However, the compressive strength and the compressive plasticity simultaneously increase when the casting voltage increases to 9 kV, and the compressive plasticity is 2.62%. Mechanical properties of BMG can be tailored to certain extent by controlling the casting temperature, which is correlated with free volume and residual stresses.
Zr53.9Cu29.4Ni4.9Al9.8Fe2 alloy sample with the diameter of 3 mm was prepared by Cu mold suction casting at different temperatures. The effect of casting temperature on mechanical properties and microstructure of the as-cast alloy was investigated. It is found that there is a critical casting temperature for the fully amorphous structure, below which the crystallization phase might be precipitated. Experiment results show that the compressive strength increases and the compressive plasticity slightly decreases when the casting temperature increases to certain extent. However, the compressive strength and the compressive plasticity simultaneously increase when the casting voltage increases to 9 kV, and the compressive plasticity is 2.62%. Mechanical properties of BMG can be tailored to certain extent by controlling the casting temperature, which is correlated with free volume and residual stresses.
2012, 41(11):1896-1898.
Abstract:
Rare earth metal Tb was employed as the catalyst to prepare GaN nanostructures. GaN nanorods were synthesized through ammoniating Ga2O3/Tb films sputtered on Si(111) substrates. Results of X-ray diffraction (XRD) and Fourier transform infrared spectrum (FTIR) indicate that the prepared nanorods are hexagonal GaN. Observations of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) show that the GaN nanorod is single-crystalline in structure with 80~200 nm in diameter and several tens of microns in length. The growth mechanism of GaN nanorods was also discussed briefly.
Rare earth metal Tb was employed as the catalyst to prepare GaN nanostructures. GaN nanorods were synthesized through ammoniating Ga2O3/Tb films sputtered on Si(111) substrates. Results of X-ray diffraction (XRD) and Fourier transform infrared spectrum (FTIR) indicate that the prepared nanorods are hexagonal GaN. Observations of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) show that the GaN nanorod is single-crystalline in structure with 80~200 nm in diameter and several tens of microns in length. The growth mechanism of GaN nanorods was also discussed briefly.
2012, 41(11):1899-1902.
Abstract:
Influences of temperature, initial pressure and particle size on the hydriding reaction kinetics of Ti33V20Cr47 alloy powder was analyzed and discussed. It is found that the rate-controlling step of the hydriding processes is hydrogen diffusion with the activation energy of 25.7±0.8 kJ/mol. The reaction rate can be accelerated with the increase of temperature. The Ti33V20Cr47 alloy can finish hydrogen absorption faster under the initial pressure 1.5 MPa and 2.5 MPa than under the initial pressure 3.5 MPa because it has two plateaus. The reaction rate can also be accelerated with the increase of particle size. The possible reason could be related to the fact that the large particle size is adverse for the dissipation of reaction heat, thus leading to the rise of the alloy temperature.
Influences of temperature, initial pressure and particle size on the hydriding reaction kinetics of Ti33V20Cr47 alloy powder was analyzed and discussed. It is found that the rate-controlling step of the hydriding processes is hydrogen diffusion with the activation energy of 25.7±0.8 kJ/mol. The reaction rate can be accelerated with the increase of temperature. The Ti33V20Cr47 alloy can finish hydrogen absorption faster under the initial pressure 1.5 MPa and 2.5 MPa than under the initial pressure 3.5 MPa because it has two plateaus. The reaction rate can also be accelerated with the increase of particle size. The possible reason could be related to the fact that the large particle size is adverse for the dissipation of reaction heat, thus leading to the rise of the alloy temperature.
2012, 41(11):1903-1906.
Abstract:
In order to research the plasticity of the Cu-based bulk amorphous and the influence of rare earth element on the mechanical properties of the amorphous, the Cu50-xZr42Al8Gdx (x=0, 2, 4) alloy rods with 3.0 mm in diameter were prepared by the suspend melting-copper mold suction casting. The structure and glass forming ability of the alloys were analyzed by X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. Subsequently, through the compression performance testing and the fracture morphology observation, the effect of rare earth element Gd on the mechanical performance and the fracture behavior of the samples were investigated. The results show that the structure of the rods is composed of amorphous phase. The samples possess larger thermal stability and good glass formation ability. With the increase of Gd content, the brittleness of the samples is enhanced gradually. Fracture mode presents brittle fracture.
In order to research the plasticity of the Cu-based bulk amorphous and the influence of rare earth element on the mechanical properties of the amorphous, the Cu50-xZr42Al8Gdx (x=0, 2, 4) alloy rods with 3.0 mm in diameter were prepared by the suspend melting-copper mold suction casting. The structure and glass forming ability of the alloys were analyzed by X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. Subsequently, through the compression performance testing and the fracture morphology observation, the effect of rare earth element Gd on the mechanical performance and the fracture behavior of the samples were investigated. The results show that the structure of the rods is composed of amorphous phase. The samples possess larger thermal stability and good glass formation ability. With the increase of Gd content, the brittleness of the samples is enhanced gradually. Fracture mode presents brittle fracture.
2012, 41(11):1907-1910.
Abstract:
The compressibility and forming ability of water-atomized Ni-16Cr-XAl-3Fe (X= 4.5, 9.0, 13.5, 18, wt%) alloy powders were investigated. Results show that the microhardness of the powders increases with the increasing of Al contents, and the compacting behavior of the four kinds of powders is well consisted with Huang Peiyun compacting theory. According to the compacting equations, it is found that serious work-hardening occurs for powders with relatively high Al contents during pressing, and thus the compressibility and forming ability of water-atomized Ni-16Cr-XAl-3Fe powders become poor with the increasing of Al content. Microcracks and delaminations will appear at the corners of compacts. The reason is mainly attributed to the precipitates of intermetallic compounds such as Ni3Al and NiAl.
The compressibility and forming ability of water-atomized Ni-16Cr-XAl-3Fe (X= 4.5, 9.0, 13.5, 18, wt%) alloy powders were investigated. Results show that the microhardness of the powders increases with the increasing of Al contents, and the compacting behavior of the four kinds of powders is well consisted with Huang Peiyun compacting theory. According to the compacting equations, it is found that serious work-hardening occurs for powders with relatively high Al contents during pressing, and thus the compressibility and forming ability of water-atomized Ni-16Cr-XAl-3Fe powders become poor with the increasing of Al content. Microcracks and delaminations will appear at the corners of compacts. The reason is mainly attributed to the precipitates of intermetallic compounds such as Ni3Al and NiAl.
2012, 41(11):1911-1916.
Abstract:
The effect of duplex aging on low cycle fatigue behavior of Ti-10V-2Fe-3Al alloys was investigated. The cyclic stress response curves show that the cyclic softening occurs at the high strain amplitude of 1.5%, 1.2% and 1.0%. However, when the strain amplitude decreases to 0.8% and 0.6%, cyclic stress saturation appears. Low cycle fatigue life of duplex aging is similar to that of simplex aging. The relationship between cycle total strain amplitude and fatigue life fits to classic Coffin-Manson equation. The fractography analyses suggest that transgranular fracture with well-developed fatigue striations is the predominant failure mode. The plastic deformation traces and secondary cracks are also observed. TEM examination reveals that fatigue deformed microstructures are homogeneous for both duplex aging and simplex aging. Due to shortening operated time and saving energy, duplex aging is more beneficial to actual industrial production than simplex aging.
The effect of duplex aging on low cycle fatigue behavior of Ti-10V-2Fe-3Al alloys was investigated. The cyclic stress response curves show that the cyclic softening occurs at the high strain amplitude of 1.5%, 1.2% and 1.0%. However, when the strain amplitude decreases to 0.8% and 0.6%, cyclic stress saturation appears. Low cycle fatigue life of duplex aging is similar to that of simplex aging. The relationship between cycle total strain amplitude and fatigue life fits to classic Coffin-Manson equation. The fractography analyses suggest that transgranular fracture with well-developed fatigue striations is the predominant failure mode. The plastic deformation traces and secondary cracks are also observed. TEM examination reveals that fatigue deformed microstructures are homogeneous for both duplex aging and simplex aging. Due to shortening operated time and saving energy, duplex aging is more beneficial to actual industrial production than simplex aging.
2012, 41(11):1917-1922.
Abstract:
The deformation behavior of GH625 superalloy was studied by the isothermal compression test in the temperature range of 950~ 1150 °C and the strain rate range of 0.001~5 s-1 and the effect of deformation condition on the microstructure was also investigated by OM and TEM. Results show that the dynamic recrystallization do not occur as the strain is little while the recrystallized grains appear when ε=0.1. As the deformation temperature increases, the recrystallized grain size increases and the dislocation density decreases; when the deformation temperature is low, some twins are observed in the matrix. As the strain rate increases, the nucleation rate increases and the grain size decreases, while the dislocation density increases at a constant deformation temperature; while at the low strain rate, the degree of recrystallization is high, which lead to the increase of grain size. According to stress-strain curves, the peak strain, the critical strain and the steady strain are obtained, and the relationship between the logarithmic values of the critical strain for DRX initiation () and the logarithmic value of the Zener-Hollomon parameter (lnZ) could be established as follows: lnεp= –6.022 85+0.123 85lnZ, εc=2.0×10-3·Z0.123 85. On the basis of quantitative microstructure analysis, the recrystallized volume fraction is also established as Xd=1–exp[–0.5634(ε/εp–0.79)1.313].
The deformation behavior of GH625 superalloy was studied by the isothermal compression test in the temperature range of 950~ 1150 °C and the strain rate range of 0.001~5 s-1 and the effect of deformation condition on the microstructure was also investigated by OM and TEM. Results show that the dynamic recrystallization do not occur as the strain is little while the recrystallized grains appear when ε=0.1. As the deformation temperature increases, the recrystallized grain size increases and the dislocation density decreases; when the deformation temperature is low, some twins are observed in the matrix. As the strain rate increases, the nucleation rate increases and the grain size decreases, while the dislocation density increases at a constant deformation temperature; while at the low strain rate, the degree of recrystallization is high, which lead to the increase of grain size. According to stress-strain curves, the peak strain, the critical strain and the steady strain are obtained, and the relationship between the logarithmic values of the critical strain for DRX initiation () and the logarithmic value of the Zener-Hollomon parameter (lnZ) could be established as follows: lnεp= –6.022 85+0.123 85lnZ, εc=2.0×10-3·Z0.123 85. On the basis of quantitative microstructure analysis, the recrystallized volume fraction is also established as Xd=1–exp[–0.5634(ε/εp–0.79)1.313].
2012, 41(11):1923-1928.
Abstract:
The as-cast TiAl alloys containing tungsten and niobium were exposed to 700 °C air for a long term and effects of the exposure on microstructures and mechanical properties were investigated. Results show that the γ phase is stable and the phenomena of recovery, recrystallization and disconnection are never observed during the long-term thermal exposure. However, the metastable α2 lamellar decompose to α2+γ phases, resulting in embrittlement of the alloys. The tensile and fatigue resistance of TiAl alloys are improved after “parallel decomposition” of α2 lamellar but the “perpendicular decomposition” of α2 lamellar is detrimental to tensile resistance. The heavy element additions can slow down the “perpendicular decomposition” of α2 lamellar.
The as-cast TiAl alloys containing tungsten and niobium were exposed to 700 °C air for a long term and effects of the exposure on microstructures and mechanical properties were investigated. Results show that the γ phase is stable and the phenomena of recovery, recrystallization and disconnection are never observed during the long-term thermal exposure. However, the metastable α2 lamellar decompose to α2+γ phases, resulting in embrittlement of the alloys. The tensile and fatigue resistance of TiAl alloys are improved after “parallel decomposition” of α2 lamellar but the “perpendicular decomposition” of α2 lamellar is detrimental to tensile resistance. The heavy element additions can slow down the “perpendicular decomposition” of α2 lamellar.
2012, 41(11):1929-1934.
Abstract:
In order to investigate the microstructure characteristics and the precipitation law of equilibrium phases of Incoloy 825, the microstructure was observed by the scanning electron microscopy and the simulation analysis was conducted by Thermo-Calc software. The result indicates that there is not any precipitate at the grain boundary in the original rolling state Incoloy 825 and a few Ti carbides exist within the grains. After aging at 750 °C for 4 h, block M23C6 precipitates at the grain boundary; when aging at 980 °C, MC increases with the time increasing. The main equilibrium precipitated phases of Incoloy 825 include g ￠, a-Cr, MC and M23C6. Al, Cr, Ti and C increase the precipitation start temperature and the maximum precipitation amount of g ￠, a-Cr, MC and M23C6, respectively.
In order to investigate the microstructure characteristics and the precipitation law of equilibrium phases of Incoloy 825, the microstructure was observed by the scanning electron microscopy and the simulation analysis was conducted by Thermo-Calc software. The result indicates that there is not any precipitate at the grain boundary in the original rolling state Incoloy 825 and a few Ti carbides exist within the grains. After aging at 750 °C for 4 h, block M23C6 precipitates at the grain boundary; when aging at 980 °C, MC increases with the time increasing. The main equilibrium precipitated phases of Incoloy 825 include g ￠, a-Cr, MC and M23C6. Al, Cr, Ti and C increase the precipitation start temperature and the maximum precipitation amount of g ￠, a-Cr, MC and M23C6, respectively.
2012, 41(11):1935-1939.
Abstract:
The hot tearing of K418 alloy turbocharger turbine blades was investigated. The effects of aluminum and titanium content on the microstructure of K418 alloy were analyzed by optical microscope and scanning electronic microscope (SEM). The probable equilibrium phases in K418 alloy were calculated and the effects of changing of aluminum and titanium content on the equilibrium phases were studied by Thermo-Calc software. The results show that the microstructure of K418 alloy changes obviously with the aluminum and titanium content increasing. The size of γ′ and the amount of (γ+γ′) eutectic increase, resulting in more prior forming and propagating areas of the hot tearing. The hot tearing is caused by the fracture of dendrites structures, forming and propagating along the interdendrites. The precipitation temperature and mass fraction of γ′ rise with aluminum and titanium content increasing, and especially aluminum has a more important effect. The effective crystallization temperature interval is broadened with aluminum and titanium content increasing, which leads to the hot tearing of the turbine blades.
The hot tearing of K418 alloy turbocharger turbine blades was investigated. The effects of aluminum and titanium content on the microstructure of K418 alloy were analyzed by optical microscope and scanning electronic microscope (SEM). The probable equilibrium phases in K418 alloy were calculated and the effects of changing of aluminum and titanium content on the equilibrium phases were studied by Thermo-Calc software. The results show that the microstructure of K418 alloy changes obviously with the aluminum and titanium content increasing. The size of γ′ and the amount of (γ+γ′) eutectic increase, resulting in more prior forming and propagating areas of the hot tearing. The hot tearing is caused by the fracture of dendrites structures, forming and propagating along the interdendrites. The precipitation temperature and mass fraction of γ′ rise with aluminum and titanium content increasing, and especially aluminum has a more important effect. The effective crystallization temperature interval is broadened with aluminum and titanium content increasing, which leads to the hot tearing of the turbine blades.
2012, 41(11):1940-1944.
Abstract:
The microstructures of AZ91 alloy modified by yttrium and/or erbium addition were investigated by SEM, XRD and EDS. The mechanical properties of the alloys at room temperature and 150 °C were analyzed. The results show that adding Y and/or Er can sufficiently refine α-Mg grain and decrease the amount of continuous net-like β-Mg17Al12 phase. The refining effect of co-addition is more obvious than that of Y or Er addition alone. Y-Er co-addition is more efficient in improving crystal with smaller size and better mechanical properties. Part of Y in Al2Y or Er in Al3Er is substituted by Er or Y when Y and Er are co-added in AZ91 alloy. The alloy with Y-Er co-addition has better mechanical properties than that with Y or Er addition alone. With increases of RE, the tensile strength and elongation of alloys rise at first and then drop.
The microstructures of AZ91 alloy modified by yttrium and/or erbium addition were investigated by SEM, XRD and EDS. The mechanical properties of the alloys at room temperature and 150 °C were analyzed. The results show that adding Y and/or Er can sufficiently refine α-Mg grain and decrease the amount of continuous net-like β-Mg17Al12 phase. The refining effect of co-addition is more obvious than that of Y or Er addition alone. Y-Er co-addition is more efficient in improving crystal with smaller size and better mechanical properties. Part of Y in Al2Y or Er in Al3Er is substituted by Er or Y when Y and Er are co-added in AZ91 alloy. The alloy with Y-Er co-addition has better mechanical properties than that with Y or Er addition alone. With increases of RE, the tensile strength and elongation of alloys rise at first and then drop.
2012, 41(11):1945-1949.
Abstract:
TiAl alloy and Ni-based alloy were joined by vacuum reactive brazing using Ti foil as the interlayer. Interfacial microstructure and formation phases of the brazed joint were investigated by means of scanning electron microscope and electron probe microanalysis, and shear strength of the joint was determined. The results show that the brazed joint is mainly composed of Tiss and Ti2Ni when brazed at 960 °C; when the brazing temperature increases from 960 °C to 1000 °C, Ti-Al and Al-Ni-Ti compounds form in the brazing seam and the typical interface structure of the brazed joint is GH99/(Ni,Cr)ss/Ti2Ni+AlNi2Ti+TiNi/Ti3Al+Al3NiTi2/Ti3Al+Al3NiTi2/TiAl. Further increasing the brazing temperature results in excessive growth of Ti3Al and Al3NiTi2 phase, which reduces the joining properties. The shear strength of the joint reaches a maximum of 233 MPa when brazed at 1000 oC for 10 min. With the brazing temperature increasing, the thickness of the brazing seam increases firstly and then decreases.
TiAl alloy and Ni-based alloy were joined by vacuum reactive brazing using Ti foil as the interlayer. Interfacial microstructure and formation phases of the brazed joint were investigated by means of scanning electron microscope and electron probe microanalysis, and shear strength of the joint was determined. The results show that the brazed joint is mainly composed of Tiss and Ti2Ni when brazed at 960 °C; when the brazing temperature increases from 960 °C to 1000 °C, Ti-Al and Al-Ni-Ti compounds form in the brazing seam and the typical interface structure of the brazed joint is GH99/(Ni,Cr)ss/Ti2Ni+AlNi2Ti+TiNi/Ti3Al+Al3NiTi2/Ti3Al+Al3NiTi2/TiAl. Further increasing the brazing temperature results in excessive growth of Ti3Al and Al3NiTi2 phase, which reduces the joining properties. The shear strength of the joint reaches a maximum of 233 MPa when brazed at 1000 oC for 10 min. With the brazing temperature increasing, the thickness of the brazing seam increases firstly and then decreases.
2012, 41(11):1950-1954.
Abstract:
Two kinds of Mg-based alloy nanoparticles Mg-Ni and Mg-Ni/La2O3 were prepared by the DC arc plasma discharge method, and the phase structure and the electrochemistry performances of Mg-Ni nanoparticles with rare earth oxide La2O3 superficial modification were studied. The results indicate that rare earth oxide La2O3 modification for Mg-Ni nanoparticles can effectively suppress MgO and Mg(OH)2 phases. After doping La2O3, the Mg-Ni nanoparticles’ electrochemical performances are obviously improved, and the anticorrosion performance and the electric discharge performance in the thick alkaline solution are enhanced.
Two kinds of Mg-based alloy nanoparticles Mg-Ni and Mg-Ni/La2O3 were prepared by the DC arc plasma discharge method, and the phase structure and the electrochemistry performances of Mg-Ni nanoparticles with rare earth oxide La2O3 superficial modification were studied. The results indicate that rare earth oxide La2O3 modification for Mg-Ni nanoparticles can effectively suppress MgO and Mg(OH)2 phases. After doping La2O3, the Mg-Ni nanoparticles’ electrochemical performances are obviously improved, and the anticorrosion performance and the electric discharge performance in the thick alkaline solution are enhanced.
2012, 41(11):1955-1959.
Abstract:
A deformation technique of the equal channel helix angular extrusion (ECHE) was proposed. Extrusion process, temperature field, metal flow, microstructure and mechanical properties of ECHE AZ31 magnesium alloy were investigated by Deform-3D FEM, OM, SEM, TEM and tensile experiments. The results show that metal flow is symmetrical and there is no disfigurement at the temperature of 380 oC and extrusion rate of 3 mm·s-1. The ECHE could evidently refine the grains of the alloy. The mechanism of grain refinement is grain fragmentation and dynamic recrystallization. The mean grain size after extrusion is 3~5 μm and the material is deformed homogeneously. The mechanical properties are greatly improved. The tensile strength, yield strength and elongation of the sample are increased from 209 MPa, 104 MPa and 11% to 286 MPa, 165 MPa and 26.4%, respectively. The tensile fracture combines the dimple fracture with quasi-cleavage fracture.
A deformation technique of the equal channel helix angular extrusion (ECHE) was proposed. Extrusion process, temperature field, metal flow, microstructure and mechanical properties of ECHE AZ31 magnesium alloy were investigated by Deform-3D FEM, OM, SEM, TEM and tensile experiments. The results show that metal flow is symmetrical and there is no disfigurement at the temperature of 380 oC and extrusion rate of 3 mm·s-1. The ECHE could evidently refine the grains of the alloy. The mechanism of grain refinement is grain fragmentation and dynamic recrystallization. The mean grain size after extrusion is 3~5 μm and the material is deformed homogeneously. The mechanical properties are greatly improved. The tensile strength, yield strength and elongation of the sample are increased from 209 MPa, 104 MPa and 11% to 286 MPa, 165 MPa and 26.4%, respectively. The tensile fracture combines the dimple fracture with quasi-cleavage fracture.
2012, 41(11):1960-1964.
Abstract:
D022 phase is the main strengthening phase in Ni-Al-V alloy applied at high temperature and structure transformation from fcc to D022 during the ordering process has been investigated extensively. The 3-D stress orienting effect of D022-Ni3(V,Al) was studied using microelastical phase field model in this work. The results indicate that D022 particles tend to grow along stress soft direction of [100] and be depressed along [001] which means the growing direction is perpendicular to c-axes of D022 phase, and the layer D022 microstructure is formed due to the way they grows. The fcc matrix transforms into three D022 variants during the early stage and then the strain field of D022 and L12 particles generates elastic interaction which leads to variants deletion. Different D022 variants assort and compete with each other during precipitation process, and D022-variant Ⅲ disappears while D022-variantⅠdominates in the end.
D022 phase is the main strengthening phase in Ni-Al-V alloy applied at high temperature and structure transformation from fcc to D022 during the ordering process has been investigated extensively. The 3-D stress orienting effect of D022-Ni3(V,Al) was studied using microelastical phase field model in this work. The results indicate that D022 particles tend to grow along stress soft direction of [100] and be depressed along [001] which means the growing direction is perpendicular to c-axes of D022 phase, and the layer D022 microstructure is formed due to the way they grows. The fcc matrix transforms into three D022 variants during the early stage and then the strain field of D022 and L12 particles generates elastic interaction which leads to variants deletion. Different D022 variants assort and compete with each other during precipitation process, and D022-variant Ⅲ disappears while D022-variantⅠdominates in the end.
2012, 41(11):1965-1969.
Abstract:
The precipitation of μ phase in a high W strengthening nickel-base superalloy and its effect on the tensile properties of the alloy were investigated at room temperature, 750 °C and 950 °C. The results indicate that the precipitation of μ phase firstly increases and then decreases with the increasing of temperature in the range from 850 °C to 1150 °C, with its peak around 1000 °C. The effect of μ phase on tensile properties of the alloy is related with temperature. It strengthens the alloy by impeding the motion of dislocations and increases the yield and ultimate strength at room temperature up to 750 °C, and slightly decreases the elongation. While μ phase deceases the yield and ultimate strength and increases the elongation of the alloy at 950 °C, because its precipitation consumes the solid (solution) strengthening element W which is the main strengthening form when the g￠ phase is largely dissolved.
The precipitation of μ phase in a high W strengthening nickel-base superalloy and its effect on the tensile properties of the alloy were investigated at room temperature, 750 °C and 950 °C. The results indicate that the precipitation of μ phase firstly increases and then decreases with the increasing of temperature in the range from 850 °C to 1150 °C, with its peak around 1000 °C. The effect of μ phase on tensile properties of the alloy is related with temperature. It strengthens the alloy by impeding the motion of dislocations and increases the yield and ultimate strength at room temperature up to 750 °C, and slightly decreases the elongation. While μ phase deceases the yield and ultimate strength and increases the elongation of the alloy at 950 °C, because its precipitation consumes the solid (solution) strengthening element W which is the main strengthening form when the g￠ phase is largely dissolved.
2012, 41(11):1970-1974.
Abstract:
The deformation behavior and superplasticity of Ti-6Al-4V alloy at elevated temperature have been investigated through tensile tests. The microstructures near the fracture of the specimen have been observed by optical microscopy. The results show that the flow stress of Ti-6Al-4V alloy decreases obviously with increasing of the temperature or decreasing of the initial strain rate. The temperature and the initial strain rate of optimal superplastic deformation are 880 oC and 0.001 s-1, respectively. Under this optimal condition, the maximum elongation is 689%; however, the peak stress is only 30.03 MPa. During the superplastic tensile deformation, the dynamic recrystallization occurs obviously in the deformation zone of the specimen and the lamellar α grain is broken, refined and spheroidized, so that the superplasticity can be improved. With increasing of the deformation temperature, the deformation amount and the deformation time, the recrystal α grain will merge and grow up, causing obvious coarsening of the microstructure. The temperature of optimal superplastic deformation should not exceed the ceasing temperature of lamellar α→β phase transformation for the α+β titanium alloy with primary α phase and lamellar transformed β phase.
The deformation behavior and superplasticity of Ti-6Al-4V alloy at elevated temperature have been investigated through tensile tests. The microstructures near the fracture of the specimen have been observed by optical microscopy. The results show that the flow stress of Ti-6Al-4V alloy decreases obviously with increasing of the temperature or decreasing of the initial strain rate. The temperature and the initial strain rate of optimal superplastic deformation are 880 oC and 0.001 s-1, respectively. Under this optimal condition, the maximum elongation is 689%; however, the peak stress is only 30.03 MPa. During the superplastic tensile deformation, the dynamic recrystallization occurs obviously in the deformation zone of the specimen and the lamellar α grain is broken, refined and spheroidized, so that the superplasticity can be improved. With increasing of the deformation temperature, the deformation amount and the deformation time, the recrystal α grain will merge and grow up, causing obvious coarsening of the microstructure. The temperature of optimal superplastic deformation should not exceed the ceasing temperature of lamellar α→β phase transformation for the α+β titanium alloy with primary α phase and lamellar transformed β phase.
2012, 41(11):1975-1979.
Abstract:
The electronic structure and surface energy of Li2MgN2H2 were calculated by the first principle, and then the transition state of molecular H2 adsorption and dissociation on the lowest energy (100) surface was analyzed for re-hydrogenation of Li2MgN2H2. The results show that the Mg-Mg-Li site on the lowest energy (100) surface is the most stable for molecular H2 adsorption and dissociating, where the related energies for these two reactions are about –0.1898 eV and 0.84 eV (81 kJ/mol), respectively. This indicates that the activation energy for re-hydrogenation of Li2MgN2H2 is apparently too high, and it results in the slow reaction rate of hydrogenation.
The electronic structure and surface energy of Li2MgN2H2 were calculated by the first principle, and then the transition state of molecular H2 adsorption and dissociation on the lowest energy (100) surface was analyzed for re-hydrogenation of Li2MgN2H2. The results show that the Mg-Mg-Li site on the lowest energy (100) surface is the most stable for molecular H2 adsorption and dissociating, where the related energies for these two reactions are about –0.1898 eV and 0.84 eV (81 kJ/mol), respectively. This indicates that the activation energy for re-hydrogenation of Li2MgN2H2 is apparently too high, and it results in the slow reaction rate of hydrogenation.
2012, 41(11):1980-1984.
Abstract:
The effect of preoxidation temperature on high temperature (1100 °C) cyclic oxidation resistance of GH3128 superalloy was studied by thermogravimetry combined with SEM, XRD and other analysis approaches. The results show that the high temperature cyclic oxidation resistance of GH3128 superalloy can be effectively improved by preoxidation at the appropriate temperature. The high temperature cyclic oxidation resistance of GH3128 superalloy after pre-oxidization depends on the combined effect of two factors. The first one is that the alloy element Cr in the surface of the alloys oxidizes selectively to form the protective oxide film, which is dense and uniform, to enhance the high temperature cyclic oxidation resistance of the alloy. The second one is that the alloy elements Ti and Cr segregate at grain boundaries in the surface of the alloys to accelerate the oxidation of grain boundary and to produce microscopic cracks near the boundary, and then reduce the high temperature cyclic oxidation resistance of the alloy. The samples pre-oxidized at 900 °C possess the best cyclic oxidation resistance due to that the protective oxide film is uniformly formed and the negative effect caused by the grain boundary segregation of Ti and Cr is relatively weak at 900 °C.
The effect of preoxidation temperature on high temperature (1100 °C) cyclic oxidation resistance of GH3128 superalloy was studied by thermogravimetry combined with SEM, XRD and other analysis approaches. The results show that the high temperature cyclic oxidation resistance of GH3128 superalloy can be effectively improved by preoxidation at the appropriate temperature. The high temperature cyclic oxidation resistance of GH3128 superalloy after pre-oxidization depends on the combined effect of two factors. The first one is that the alloy element Cr in the surface of the alloys oxidizes selectively to form the protective oxide film, which is dense and uniform, to enhance the high temperature cyclic oxidation resistance of the alloy. The second one is that the alloy elements Ti and Cr segregate at grain boundaries in the surface of the alloys to accelerate the oxidation of grain boundary and to produce microscopic cracks near the boundary, and then reduce the high temperature cyclic oxidation resistance of the alloy. The samples pre-oxidized at 900 °C possess the best cyclic oxidation resistance due to that the protective oxide film is uniformly formed and the negative effect caused by the grain boundary segregation of Ti and Cr is relatively weak at 900 °C.
2012, 41(11):1985-1989.
Abstract:
The pure titanium plates were modified by SAM using the organic solution with 3-aminopropyltriethoxysilane as the chief component and subsequently exposed to simulated body fluid for biomimetic mineralization. The surface morphologies and structures were characterized by attenuated total refraction-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electronic microscopy (SEM) and X-ray diffraction (XRD); Human sweat gland cells (HMSCs) were planted on the surfaces of samples before and after modification, and then the adhesion and proliferation of HMSCs on the surfaces of titanium and its action before and after modification were investigated by MTT colorimetry and SEM. The results show that HCA coating is synthesized by biomimetic method and the ratio of Ca/P is 1.3. Compared with the pure titanium samples, the adhered HMSCs on the surfaces of titanium after modification by SAM are more, and the proliferation effect is obvious.
The pure titanium plates were modified by SAM using the organic solution with 3-aminopropyltriethoxysilane as the chief component and subsequently exposed to simulated body fluid for biomimetic mineralization. The surface morphologies and structures were characterized by attenuated total refraction-Fourier transform infrared spectroscopy (ATR-FTIR), scanning electronic microscopy (SEM) and X-ray diffraction (XRD); Human sweat gland cells (HMSCs) were planted on the surfaces of samples before and after modification, and then the adhesion and proliferation of HMSCs on the surfaces of titanium and its action before and after modification were investigated by MTT colorimetry and SEM. The results show that HCA coating is synthesized by biomimetic method and the ratio of Ca/P is 1.3. Compared with the pure titanium samples, the adhered HMSCs on the surfaces of titanium after modification by SAM are more, and the proliferation effect is obvious.
2012, 41(11):1990-1994.
Abstract:
The hot corrosion process of nickel-base superalloy with different Ti content by coating with salt membrane was studied. The results show that the hot corrosion resistance of the superalloy increases greatly under the experimental condition of 900 °C after adding 0.55% Ti. Its hot corrosion resistance becomes better with the increasing of Ti content. Continuous and compact Cr2O3 layer can be formed on the surface of the superalloy by adding titanium. Thickness of Cr2O3 layer increases and Al2O3 layer transfers outward with more Ti, so that the hot corrosion resistance of the alloy increases.
The hot corrosion process of nickel-base superalloy with different Ti content by coating with salt membrane was studied. The results show that the hot corrosion resistance of the superalloy increases greatly under the experimental condition of 900 °C after adding 0.55% Ti. Its hot corrosion resistance becomes better with the increasing of Ti content. Continuous and compact Cr2O3 layer can be formed on the surface of the superalloy by adding titanium. Thickness of Cr2O3 layer increases and Al2O3 layer transfers outward with more Ti, so that the hot corrosion resistance of the alloy increases.
2012, 41(11):1995-1999.
Abstract:
The biodegradable calcium/phosphate coating on the surface of the magnesium alloy AZ31B was prepared by atmospheric plasma spraying. The phase compositions and crystallinity of the coating were quantitative investigated by XRD, and the microscopic morphology and elemental composition of the coating before and after immersion in the simulated body fluid (SBF) were investigated by SEM and EDS. The degradability of magnesium alloy with calcium/phosphorus coating in SBF solution were studied according to the pH value and the degradation rate of the coating. The results show that the high density calcium/phosphate coating is closely integrated with the magnesium alloy substrate. The coating is composed of HA with difficult degradation and Ca3(PO4)2, Ca4P2O9 and CaO with easy degradation, and the crystallinity of HA in the coating is 49.3%. In addition, the study of biodegradation shows that the pH value and the degradation rate of the calcium/phosphorus coating in SBF are less than that of magnesium alloy, and the smaller change magnitude makes the coating material’s degradation be controlled in a stable range.
The biodegradable calcium/phosphate coating on the surface of the magnesium alloy AZ31B was prepared by atmospheric plasma spraying. The phase compositions and crystallinity of the coating were quantitative investigated by XRD, and the microscopic morphology and elemental composition of the coating before and after immersion in the simulated body fluid (SBF) were investigated by SEM and EDS. The degradability of magnesium alloy with calcium/phosphorus coating in SBF solution were studied according to the pH value and the degradation rate of the coating. The results show that the high density calcium/phosphate coating is closely integrated with the magnesium alloy substrate. The coating is composed of HA with difficult degradation and Ca3(PO4)2, Ca4P2O9 and CaO with easy degradation, and the crystallinity of HA in the coating is 49.3%. In addition, the study of biodegradation shows that the pH value and the degradation rate of the calcium/phosphorus coating in SBF are less than that of magnesium alloy, and the smaller change magnitude makes the coating material’s degradation be controlled in a stable range.
2012, 41(11):2000-2004.
Abstract:
The possibility of using electron beam melting (EBM) technology to manufacture Ti600 alloy complex parts was explored by studying EBM-Ti600 alloy microstructure, strength at room temperature and fracture characteristics. The results show that the deposition microstructure of EBM-Ti600 alloy is basket weave microstructure. The α laths gradually become larger from top to bottom of the part and vast nanometer secondary phase particles precipitate in the middle of the part. Susceptible corrosion structure is also observed along α boundaries. The nanometer secondary phase particles in the microstructure of EBM-Ti600 alloy mainly include particles of Y2O3, α2, high temperature phases and low temperature phase of Si, and the precipitated phase of Si is mainly related with the Ti600 alloy composition and the EBM process. The strength of EBM-Ti600 alloy at room temperature is not uniform, the top strength is the largest, then the bottom, and the middle is the lowest, which is because of the α lath size and the different existing forms of Si. The tensile fracture of EBM-Ti600 alloy at room temperature is plastic fracture, which is mainly caused by part defects, intrinsic brittleness and not strong intergranular bonding.
The possibility of using electron beam melting (EBM) technology to manufacture Ti600 alloy complex parts was explored by studying EBM-Ti600 alloy microstructure, strength at room temperature and fracture characteristics. The results show that the deposition microstructure of EBM-Ti600 alloy is basket weave microstructure. The α laths gradually become larger from top to bottom of the part and vast nanometer secondary phase particles precipitate in the middle of the part. Susceptible corrosion structure is also observed along α boundaries. The nanometer secondary phase particles in the microstructure of EBM-Ti600 alloy mainly include particles of Y2O3, α2, high temperature phases and low temperature phase of Si, and the precipitated phase of Si is mainly related with the Ti600 alloy composition and the EBM process. The strength of EBM-Ti600 alloy at room temperature is not uniform, the top strength is the largest, then the bottom, and the middle is the lowest, which is because of the α lath size and the different existing forms of Si. The tensile fracture of EBM-Ti600 alloy at room temperature is plastic fracture, which is mainly caused by part defects, intrinsic brittleness and not strong intergranular bonding.
Ji Shouchang
,
Li Zhengxian
,
Du Jihong
,
Zha Bailin
,
Huang Chunliang
,
Wang Baoyun
,
Luo Xiaofeng
,
Hua Yunfeng
,
Wang Yanfeng
2012, 41(11):2005-2009.
Abstract:
WC-12Co coating was prepared by high-velocity oxygen fuel (HVOF) spraying on Ti6Al4V alloy. The microstructure, phase structure and composition of the coating were investigated by SEM, XRD and EDS, respectively. Results show that the whole coating is dense, of low porosity and bonds well with the substrate. There is no lamination in the coating. The agglomerated particles bond closely with each other and they are dispersively distributed. It is attributed to the high speed of supersonic particles, which can make up for the pores caused by the irregular stacking fault to decrease the porosity and increase the density. The high speed particles deform sufficiently and it is beneficial to increase the area of the active region and good for the combining between the particles and the substrate, as well as particles and the coating. There are a few of Co3W3C and trace W2C besides WC in the coating; there is no metal Co, which has become amorphous. It is thought that W2C comes from the thermal decomposition of WC during spraying while the Co3W3C is the reaction product of Co and WC in the oxygen atmosphere and its small amount is due to the short time of the powder staying in the combustion chamber.
WC-12Co coating was prepared by high-velocity oxygen fuel (HVOF) spraying on Ti6Al4V alloy. The microstructure, phase structure and composition of the coating were investigated by SEM, XRD and EDS, respectively. Results show that the whole coating is dense, of low porosity and bonds well with the substrate. There is no lamination in the coating. The agglomerated particles bond closely with each other and they are dispersively distributed. It is attributed to the high speed of supersonic particles, which can make up for the pores caused by the irregular stacking fault to decrease the porosity and increase the density. The high speed particles deform sufficiently and it is beneficial to increase the area of the active region and good for the combining between the particles and the substrate, as well as particles and the coating. There are a few of Co3W3C and trace W2C besides WC in the coating; there is no metal Co, which has become amorphous. It is thought that W2C comes from the thermal decomposition of WC during spraying while the Co3W3C is the reaction product of Co and WC in the oxygen atmosphere and its small amount is due to the short time of the powder staying in the combustion chamber.
2012, 41(11):2010-2012.
Abstract:
The microstructure and the second phases in the annealed Zr-Nb-Cu alloy were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crystal structure of the second phases was determined by selected area electron diffraction (SAD) pattern, and the quantitative analysis of second phases was preformed using TEM with energy dispersion spectroscopy (EDS). Results show that there are two kinds of second phases in the Zr-Nb-Cu alloy. The first one is β-Nb with a bcc structure, small size and a dispersive distribution in the grains, and the second one is Zr2Cu precipitates with a tetragonal structure, big size and a distribution on the grain boundary.
The microstructure and the second phases in the annealed Zr-Nb-Cu alloy were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crystal structure of the second phases was determined by selected area electron diffraction (SAD) pattern, and the quantitative analysis of second phases was preformed using TEM with energy dispersion spectroscopy (EDS). Results show that there are two kinds of second phases in the Zr-Nb-Cu alloy. The first one is β-Nb with a bcc structure, small size and a dispersive distribution in the grains, and the second one is Zr2Cu precipitates with a tetragonal structure, big size and a distribution on the grain boundary.
2012, 41(11):2013-2016.
Abstract:
The Re coating was deposited on C/C substrates by double-glow plasma technique. The microstructure, phases, Vickers hardness and interfacial bonding strength of the coating were studied. The results show that the Re coating is composed of poly-crystalline column structural grains with preferential growth orientation of (110) and (103) crystal plane. The Re coating is dense and smooth, and the size of grains ranges from 0.5 μm to 1.5 μm. The Vickers hardness of the Re coating is 6.66±0.25 GPa. The Re coating and C/C substrates inter-diffuses with each other during preparation and there is mechanical bonding and physical bonding in the interface. During the loading process of the scratch tests, the interfacial bonding strength between Re coating and C/C substrates is high even when the C/C substrate is broken due to the low hardness and ductility.
The Re coating was deposited on C/C substrates by double-glow plasma technique. The microstructure, phases, Vickers hardness and interfacial bonding strength of the coating were studied. The results show that the Re coating is composed of poly-crystalline column structural grains with preferential growth orientation of (110) and (103) crystal plane. The Re coating is dense and smooth, and the size of grains ranges from 0.5 μm to 1.5 μm. The Vickers hardness of the Re coating is 6.66±0.25 GPa. The Re coating and C/C substrates inter-diffuses with each other during preparation and there is mechanical bonding and physical bonding in the interface. During the loading process of the scratch tests, the interfacial bonding strength between Re coating and C/C substrates is high even when the C/C substrate is broken due to the low hardness and ductility.
2012, 41(11):2017-2020.
Abstract:
The silver-coated copper powder with high silver content, a silver layer of certain thickness and high density was prepared by chemistry plating reaction. The surface morphology, structure and conductivity of the coated powder and the initial powder were characterized by SEM, XRD, LSPSDA, DOM and TG-DTA. Results show that the surface of the silver-coated copper power with high silver content is dense and coated completely, and the coating thickness is up to 336 nm. The powder has good conductivity and oxidation resistance.
The silver-coated copper powder with high silver content, a silver layer of certain thickness and high density was prepared by chemistry plating reaction. The surface morphology, structure and conductivity of the coated powder and the initial powder were characterized by SEM, XRD, LSPSDA, DOM and TG-DTA. Results show that the surface of the silver-coated copper power with high silver content is dense and coated completely, and the coating thickness is up to 336 nm. The powder has good conductivity and oxidation resistance.
2012, 41(11):2021-2024.
Abstract:
The simulations of the influence of temperature on Cr atom substitution character in Ni-Cr-Al alloy were performed based on microscopic phase-field model. It is found that nonstoicheometric ordering L12 phases appear first with congruent ordering+spinodal decomposition mechanism, then followed by non-classical nucleation and growth mechanism with the rising of aging temperature, and the incubation period increases gradually at 873~1173 K. The volume fraction of L12 phases increases and that of D022 phases decreases. D022 phases disappear and only L12 phases are remained at 1173 K.
The simulations of the influence of temperature on Cr atom substitution character in Ni-Cr-Al alloy were performed based on microscopic phase-field model. It is found that nonstoicheometric ordering L12 phases appear first with congruent ordering+spinodal decomposition mechanism, then followed by non-classical nucleation and growth mechanism with the rising of aging temperature, and the incubation period increases gradually at 873~1173 K. The volume fraction of L12 phases increases and that of D022 phases decreases. D022 phases disappear and only L12 phases are remained at 1173 K.
2012, 41(11):2025-2028.
Abstract:
The microstructures of Mo-Nb alloy single crystals grown by electron beam floating zone melting were studied using the optical metallograph (OM), scanning electron microscopy (SEM), electron back scatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that molybdenum-niobium alloy single crystals consist of a mass of sub-grain microstructure. With the increasing of the growth rate of the single crystals, the size of the sub-grain decreases and the growth striations appear at the same time. But the degree of segregation of the alloying element niobium increases with increasing of the growth rate. The increasing content of alloying element Nb also decreases the size of the sub-grain. The size of the sub-grains changes after high temperature annealing process in vacuum.
The microstructures of Mo-Nb alloy single crystals grown by electron beam floating zone melting were studied using the optical metallograph (OM), scanning electron microscopy (SEM), electron back scatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that molybdenum-niobium alloy single crystals consist of a mass of sub-grain microstructure. With the increasing of the growth rate of the single crystals, the size of the sub-grain decreases and the growth striations appear at the same time. But the degree of segregation of the alloying element niobium increases with increasing of the growth rate. The increasing content of alloying element Nb also decreases the size of the sub-grain. The size of the sub-grains changes after high temperature annealing process in vacuum.
2012, 41(11):2029-2032.
Abstract:
The La-Mg-Ni alloy films were prepared by a constant-voltage electrodeposition method in acetamide-urea-NaBr-KBr. The surface morphology and structure of the films were studied by SEM and XRD. The electrochemical performance was studied by Tafel and EIS. The results show that the film has smoother surface and better hydrogen storage function with the cathode potential shifting to negative direction. △G≠ and Q of the deposition layer are determined to be 22.35 kJ·mol-1 and 7.98 μF/cm2, respectively when the voltage is –1.0 V, indicating the high hydrogen evolution activity and high hydrogen capacity.
The La-Mg-Ni alloy films were prepared by a constant-voltage electrodeposition method in acetamide-urea-NaBr-KBr. The surface morphology and structure of the films were studied by SEM and XRD. The electrochemical performance was studied by Tafel and EIS. The results show that the film has smoother surface and better hydrogen storage function with the cathode potential shifting to negative direction. △G≠ and Q of the deposition layer are determined to be 22.35 kJ·mol-1 and 7.98 μF/cm2, respectively when the voltage is –1.0 V, indicating the high hydrogen evolution activity and high hydrogen capacity.
2012, 41(11):2033-2036.
Abstract:
Electrochemical corrosion behaviours of vanadium and V-5Cr-5Ti alloy in chlorine ion solution have been studied by electrochemical techniques. The results indicate that in 50 μg/g Cl- potassium chloride solution, corrosion potential of vanadium is higher than that of V-5Cr-5Ti alloy, and therefore vanadium is more stable in thermodynamics. Relative to V-5Cr-5Ti alloy, vanadium has much higher polarization resistance and even lower corrosion current. Vanadium and V-5Cr-5Ti alloy have similar cathodic polarization behaviour. In the process of anodic polarization, vanadium manifests Tafel behaviour mainly and V-5Cr-5Ti alloy represents “pseudo-passivation” and passivation behaviours. They have negative cyclic polarization hysteresis loop. Corrosion resistant performance of vanadium is better than that of V-5Cr-5Ti alloy.
Electrochemical corrosion behaviours of vanadium and V-5Cr-5Ti alloy in chlorine ion solution have been studied by electrochemical techniques. The results indicate that in 50 μg/g Cl- potassium chloride solution, corrosion potential of vanadium is higher than that of V-5Cr-5Ti alloy, and therefore vanadium is more stable in thermodynamics. Relative to V-5Cr-5Ti alloy, vanadium has much higher polarization resistance and even lower corrosion current. Vanadium and V-5Cr-5Ti alloy have similar cathodic polarization behaviour. In the process of anodic polarization, vanadium manifests Tafel behaviour mainly and V-5Cr-5Ti alloy represents “pseudo-passivation” and passivation behaviours. They have negative cyclic polarization hysteresis loop. Corrosion resistant performance of vanadium is better than that of V-5Cr-5Ti alloy.
2012, 41(11):2037-2040.
Abstract:
The principle and method of chemical vapor deposition tantalum were proposed. Through the cold wall deposition, tantalum coatings were deposited on molybdenum substrates. The effect of CVD temperature on deposition rate, microstructure and hardness of Ta coatings was investigated. The results show that with the increasing of the deposition temperature, the deposition rate increases in the range of 1000~1200 °C; above 1200 °C, the deposition rate decreases; the microstructure of the deposition layer is of columnar grain and the grain size increases with the increasing of the deposition temperature. Meanwhile the hardness and density of the deposition layer decreases. The optimal deposition temperature of CVD tantalum layer is about 1100 °C.
The principle and method of chemical vapor deposition tantalum were proposed. Through the cold wall deposition, tantalum coatings were deposited on molybdenum substrates. The effect of CVD temperature on deposition rate, microstructure and hardness of Ta coatings was investigated. The results show that with the increasing of the deposition temperature, the deposition rate increases in the range of 1000~1200 °C; above 1200 °C, the deposition rate decreases; the microstructure of the deposition layer is of columnar grain and the grain size increases with the increasing of the deposition temperature. Meanwhile the hardness and density of the deposition layer decreases. The optimal deposition temperature of CVD tantalum layer is about 1100 °C.
2012, 41(11):2041-2044.
Abstract:
IrO2-SnO2 coatings with different Sn contents were prepared on titanium substrate by a thermal decomposition method. The relationship between the capacitance properties and microstructure was investigated by means of cyclic voltammetry, constant current discharge measurements and transmission electron microscope (TEM). Results show that the specific capacitance of IrO2-SnO2 coating electrodes increases first and then decreases with the Sn content increasing. The reversibilities and fast charging and discharging behaviors of the electrode materials are improved gradually. The maximal specific capacitance reaches 485.07 F/g when the content of Sn is 70 mol%, 7.5 times larger than that of pure IrO2 electrode. The coating is of amorphous structure, including the nanocrystalline with about 1 nm size and narrow size distribution, which increases the active site area.
IrO2-SnO2 coatings with different Sn contents were prepared on titanium substrate by a thermal decomposition method. The relationship between the capacitance properties and microstructure was investigated by means of cyclic voltammetry, constant current discharge measurements and transmission electron microscope (TEM). Results show that the specific capacitance of IrO2-SnO2 coating electrodes increases first and then decreases with the Sn content increasing. The reversibilities and fast charging and discharging behaviors of the electrode materials are improved gradually. The maximal specific capacitance reaches 485.07 F/g when the content of Sn is 70 mol%, 7.5 times larger than that of pure IrO2 electrode. The coating is of amorphous structure, including the nanocrystalline with about 1 nm size and narrow size distribution, which increases the active site area.
2012, 41(11):2045-2048.
Abstract:
The Tb0.3Dy0.7Fe1.95-xNbx (x=0, 0.03, 0.06, 0.09) alloys were prepared by a high-vacuum arc melting furnace. The crystal structure, microstructure and magnetostriction of the alloys were studied. Results demonstrate that after Nb addition the matrix phase of the Tb0.3Dy0.7Fe1.95-xNbx (x=0.03, 0.06, 0.09) alloys consists predominantly of the cubic Laves phase with MgCu2 (C15-type) structure, and the lattice parameter of the Laves phase in the alloys is least affected. Nb is soluble negligibly in the matrix RFe2 and Re-rich phases, but dissolved in the RFe3 phase and formed into Re(Nb,Fe)3 phase when x=0.03. The formation of the NbFe2 phase as the primary phase make the solidifying liquid become rich in rare earths and suppress the formation of the deleterious RFe3 phase. The hexagonal C14-type Laves phase NbFe2 does not dissolve into the matrix RFe2 (C15-type) phase. The concentration of the element Nb affects the magnetostriction significantly. The improvement in magnetostriction is maximum for the element-added alloy with a low concentration of the element Nb (x=0.03) as compared to the parent alloy Tb0.3Dy0.7Fe1.95. However, the decrease in magnetostriction occurs with the increasing of Nb content which is due to the formation of paramagnetic phases NbFe2 and Re-rich phases. Whereas the magnetostriction has a little improvement as compared to the parent alloy Tb0.3Dy0.7Fe1.95.
The Tb0.3Dy0.7Fe1.95-xNbx (x=0, 0.03, 0.06, 0.09) alloys were prepared by a high-vacuum arc melting furnace. The crystal structure, microstructure and magnetostriction of the alloys were studied. Results demonstrate that after Nb addition the matrix phase of the Tb0.3Dy0.7Fe1.95-xNbx (x=0.03, 0.06, 0.09) alloys consists predominantly of the cubic Laves phase with MgCu2 (C15-type) structure, and the lattice parameter of the Laves phase in the alloys is least affected. Nb is soluble negligibly in the matrix RFe2 and Re-rich phases, but dissolved in the RFe3 phase and formed into Re(Nb,Fe)3 phase when x=0.03. The formation of the NbFe2 phase as the primary phase make the solidifying liquid become rich in rare earths and suppress the formation of the deleterious RFe3 phase. The hexagonal C14-type Laves phase NbFe2 does not dissolve into the matrix RFe2 (C15-type) phase. The concentration of the element Nb affects the magnetostriction significantly. The improvement in magnetostriction is maximum for the element-added alloy with a low concentration of the element Nb (x=0.03) as compared to the parent alloy Tb0.3Dy0.7Fe1.95. However, the decrease in magnetostriction occurs with the increasing of Nb content which is due to the formation of paramagnetic phases NbFe2 and Re-rich phases. Whereas the magnetostriction has a little improvement as compared to the parent alloy Tb0.3Dy0.7Fe1.95.
2012, 41(11):2049-2053.
Abstract:
Tantalum is an ideal medical metal material, which can integrate with human soft/hard tissue. Chemical vapor deposition method was used to deposit tantalum film on the surface of Ti6Al4V scaffolds with controlled porous structure. The Ti6Al4V scaffolds could have ideal three-dimensional pore structure and mechanical compatibility, but also have excellent biological properties of tantalum. The investigation results show that the surface color changes of porous scaffolds before and after coating are obvious. After coating, the scaffolds show Ta metal color. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests demonstrate that the deposition on the surface of porous titanium alloy scaffolds is the tantalum metal. Compared to the Zimmer trabecular metal, the elastic modulus and compressive strength of the porous titanium alloy scaffold coated with tantalum are more similar to that of human cortical bone, which could be an ideal substitute for bone repair.
Tantalum is an ideal medical metal material, which can integrate with human soft/hard tissue. Chemical vapor deposition method was used to deposit tantalum film on the surface of Ti6Al4V scaffolds with controlled porous structure. The Ti6Al4V scaffolds could have ideal three-dimensional pore structure and mechanical compatibility, but also have excellent biological properties of tantalum. The investigation results show that the surface color changes of porous scaffolds before and after coating are obvious. After coating, the scaffolds show Ta metal color. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests demonstrate that the deposition on the surface of porous titanium alloy scaffolds is the tantalum metal. Compared to the Zimmer trabecular metal, the elastic modulus and compressive strength of the porous titanium alloy scaffold coated with tantalum are more similar to that of human cortical bone, which could be an ideal substitute for bone repair.
2012, 41(11):2054-2057.
Abstract:
Fine-grain Ti/Al composite powder was prepared by mechanical alloying. TiAl intermetallics with various grain sizes were prepared by different compacting methods and reaction sintering as well as isothermal forging. The microstructural characters of TiAl alloys were analyzed. The effects of different processes on microstructures of TiAl intermetallics were studied. The results indicate that the processing of cold isostatic pressing, reaction sintering at 630 oC and isothermal forging can effectively reduce the grain size of Ti/Al alloys, and the grain size of the TiAl intermetallics is between 5 and 8 μm. The lamellar TiAl intermetallics, which are nearly fully dense, can also be obtained by common cold pressing, reaction sintering at 1250 oC and isothermal forging, but the grain size is 20~30 μm.
Fine-grain Ti/Al composite powder was prepared by mechanical alloying. TiAl intermetallics with various grain sizes were prepared by different compacting methods and reaction sintering as well as isothermal forging. The microstructural characters of TiAl alloys were analyzed. The effects of different processes on microstructures of TiAl intermetallics were studied. The results indicate that the processing of cold isostatic pressing, reaction sintering at 630 oC and isothermal forging can effectively reduce the grain size of Ti/Al alloys, and the grain size of the TiAl intermetallics is between 5 and 8 μm. The lamellar TiAl intermetallics, which are nearly fully dense, can also be obtained by common cold pressing, reaction sintering at 1250 oC and isothermal forging, but the grain size is 20~30 μm.
2012, 41(11):2058-2063.
Abstract:
Research and development of titanium and titanium alloys for biomedical applications abroad during last years were reviewed. Several kinds of low Young’s modulus, high mechanical properties, nontoxic and allergy-free b-type titanium alloys were developed to replace the widely used Ti-6Al-4V alloy. In order to reduce the Young’s modulus of the metals to a level similar to that of cortical bone, it is very effective to make titanium and its alloys porous and to adjust their porosity. The decrease in the strength of porous titanium can be significantly inhibited by penetrating polymer into the porous titanium through pressing, by which the biocompatibility can also be further improved. In order to meet the requirements in orthopaedic surgery field, porous TiNi superelastic shape memory alloy has been developed to overcome the drawbacks like weak interfacial bonds and mismatch of Young’s modulus between bone and implants. In addition, several kinds of nontoxic and allergy-free b-type superelastic shape memory titanium alloys were developed to substitute TiNi alloy with the aim to assure a more safety use in medical field. A tremendous number of surface modification techniques related to the deposition of modified surface layer and surface hardening were developed to improve the biocompatibility and wear resistance of titanium implants.
Research and development of titanium and titanium alloys for biomedical applications abroad during last years were reviewed. Several kinds of low Young’s modulus, high mechanical properties, nontoxic and allergy-free b-type titanium alloys were developed to replace the widely used Ti-6Al-4V alloy. In order to reduce the Young’s modulus of the metals to a level similar to that of cortical bone, it is very effective to make titanium and its alloys porous and to adjust their porosity. The decrease in the strength of porous titanium can be significantly inhibited by penetrating polymer into the porous titanium through pressing, by which the biocompatibility can also be further improved. In order to meet the requirements in orthopaedic surgery field, porous TiNi superelastic shape memory alloy has been developed to overcome the drawbacks like weak interfacial bonds and mismatch of Young’s modulus between bone and implants. In addition, several kinds of nontoxic and allergy-free b-type superelastic shape memory titanium alloys were developed to substitute TiNi alloy with the aim to assure a more safety use in medical field. A tremendous number of surface modification techniques related to the deposition of modified surface layer and surface hardening were developed to improve the biocompatibility and wear resistance of titanium implants.
2012, 41(11):2064-2068.
Abstract:
A brief overview of the research progress of new cobalt-based alloys containing ordered L12 precipitates γ′-Co3(Al, W) was presented. The emphasis was on the microstructure, composition segregation and high temperature behavior of the γ-γ′ alloys with addition of different elements into ternary Co-Al-W system. The applications of new cobalt-based alloys were forecast and the research prospect required in future was pointed out.
A brief overview of the research progress of new cobalt-based alloys containing ordered L12 precipitates γ′-Co3(Al, W) was presented. The emphasis was on the microstructure, composition segregation and high temperature behavior of the γ-γ′ alloys with addition of different elements into ternary Co-Al-W system. The applications of new cobalt-based alloys were forecast and the research prospect required in future was pointed out.
