Volume 42,Issue 9,2013 Table of Contents
2013, 42(9):1761-1766.
Abstract:
Hot deformation behavior of TB8 alloy near the β-transus was investigated via hot compression tests in the temperature range of 650~900 oC and at strain rates ranging from 0.01 s-1 to 10 s-1. The flow stress curves obtained in the dual phase α+β and single phase β regions were analyzed in terms of the different dependence on the flow stresses responding to different temperatures, strain rates and different microstructural evolutions. At the high strain rate of 10 s-1，the true-stress ture-strain curves have two peaks at temperature of 850 °C and 900 °C. This is a new phenomenon, which has not been reported before. The value of apparent activation energy is 233.0151 kJ/mol for dual phase microstructure and 197.8987 kJ/mol for single phase β microstructure. Furthermore, the corresponding flow stress constitutive equation of TB8 alloy in dual-phase and in single-phase regions is established.
Hot deformation behavior of TB8 alloy near the β-transus was investigated via hot compression tests in the temperature range of 650~900 oC and at strain rates ranging from 0.01 s-1 to 10 s-1. The flow stress curves obtained in the dual phase α+β and single phase β regions were analyzed in terms of the different dependence on the flow stresses responding to different temperatures, strain rates and different microstructural evolutions. At the high strain rate of 10 s-1，the true-stress ture-strain curves have two peaks at temperature of 850 °C and 900 °C. This is a new phenomenon, which has not been reported before. The value of apparent activation energy is 233.0151 kJ/mol for dual phase microstructure and 197.8987 kJ/mol for single phase β microstructure. Furthermore, the corresponding flow stress constitutive equation of TB8 alloy in dual-phase and in single-phase regions is established.
2013, 42(9):1767-1762.
Abstract:
The experiment and the simulation of the tensile properties and the fracture toughness of 7050-T7451 high strength aluminum alloy hole specimens for aircraft were conducted. The plastic dissipation energy of the crack tip associates tensile properties with fracture toughness KIC, which can be quantificationally calculated through the tensile parameters. The distribution of the deformation zone and the zone proportion of plane stress and plane strain were characterized by parameter Z, which is determined by the geometry of the hole specimen. The research shows (1) Z parameter is associated with the KIC of materials and components, and reflects the influence of the specimen geometry and hole size on the KIC of components; (2) KIC of the specimen is sensitive to the hole size perpendicular to the tensile direction, and decreases with the increase of the size; (3) the strength indexes such as yield stress and ultimate tensile strength are affected mainly by the hole size perpendicular to the tensile direction, and are almost irrelevant to the change of the hole size along the tensile direction, but the elongation is on the contrary
The experiment and the simulation of the tensile properties and the fracture toughness of 7050-T7451 high strength aluminum alloy hole specimens for aircraft were conducted. The plastic dissipation energy of the crack tip associates tensile properties with fracture toughness KIC, which can be quantificationally calculated through the tensile parameters. The distribution of the deformation zone and the zone proportion of plane stress and plane strain were characterized by parameter Z, which is determined by the geometry of the hole specimen. The research shows (1) Z parameter is associated with the KIC of materials and components, and reflects the influence of the specimen geometry and hole size on the KIC of components; (2) KIC of the specimen is sensitive to the hole size perpendicular to the tensile direction, and decreases with the increase of the size; (3) the strength indexes such as yield stress and ultimate tensile strength are affected mainly by the hole size perpendicular to the tensile direction, and are almost irrelevant to the change of the hole size along the tensile direction, but the elongation is on the contrary
2013, 42(9):1773-1778.
Abstract:
The spinodal decomposition of symmetric and asymmetric binary alloys has been studied from precipitate evolution and coarsening mechanism by a binary phase field crystal method. The calculated results indicate that when the alloy composition changes from a symmetric point to the asymmetric one, the morphology of decomposed phases transforms gradually from long stripes to spheres, with the coarsening mechanism undergoing a transition from the coalescence of neighboring particles to Ostwald ripening. Only the coarsening kinetics of the binary alloys which is close to the spinodal decomposition line is in a fair agreement with the prediction of the modified LSW theory
The spinodal decomposition of symmetric and asymmetric binary alloys has been studied from precipitate evolution and coarsening mechanism by a binary phase field crystal method. The calculated results indicate that when the alloy composition changes from a symmetric point to the asymmetric one, the morphology of decomposed phases transforms gradually from long stripes to spheres, with the coarsening mechanism undergoing a transition from the coalescence of neighboring particles to Ostwald ripening. Only the coarsening kinetics of the binary alloys which is close to the spinodal decomposition line is in a fair agreement with the prediction of the modified LSW theory
2013, 42(9):1779-1784.
Abstract:
The flow behavior of an extruded Mg-7.8Li-4.6Zn-0.96Ce-0.85Y-0.30Zr alloy was investigated by a thermo-mechanical simulator in the temperature range from 250 to 450 °C and the strain rate range from 0.001 to 10 s-1. The results indicate that the flow stress-strain curves of the alloy are characterized by an increase of the flow stress until a maximum stress value followed by the flow softening being observed. Such flow behavior is a characteristic for hot working accompanied by dynamic recrystallization. The flow behavior of the alloy can be represented by a hyperbolic sine type equation during the whole deformation temperature; however, it is not proper to fit the flow stress equation using the power and the exponential equation. The stress exponent n in the hyperbolic sine equation is high and increases with increasing of deformation temperature. The hot deformation process of the alloy is mainly controlled by dislocation climb. The average hot deformation activation energy Q of the alloy is 148 kJ/mol, which is higher than both the self-diffusion activation energy of Mg (135 kJ/mol) and the lattice diffusion activation energy of β-phase (103 kJ/mol). The results discussed above can be attributed to the addition of rare-earth (RE)
The flow behavior of an extruded Mg-7.8Li-4.6Zn-0.96Ce-0.85Y-0.30Zr alloy was investigated by a thermo-mechanical simulator in the temperature range from 250 to 450 °C and the strain rate range from 0.001 to 10 s-1. The results indicate that the flow stress-strain curves of the alloy are characterized by an increase of the flow stress until a maximum stress value followed by the flow softening being observed. Such flow behavior is a characteristic for hot working accompanied by dynamic recrystallization. The flow behavior of the alloy can be represented by a hyperbolic sine type equation during the whole deformation temperature; however, it is not proper to fit the flow stress equation using the power and the exponential equation. The stress exponent n in the hyperbolic sine equation is high and increases with increasing of deformation temperature. The hot deformation process of the alloy is mainly controlled by dislocation climb. The average hot deformation activation energy Q of the alloy is 148 kJ/mol, which is higher than both the self-diffusion activation energy of Mg (135 kJ/mol) and the lattice diffusion activation energy of β-phase (103 kJ/mol). The results discussed above can be attributed to the addition of rare-earth (RE)
2013, 42(9):1785-1789.
Abstract:
The effects of process parameters on vacuum diffusion bonding between tantalum (Ta) and copper (Cu) were studied. The interfacial structure of Ta/Cu joint was analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and microhardness test. The results indicate that under the condition of loading pressure of 10 MPa and holding time of 60 min, the number of interfacial voids decreases with increasing of bonding temperature. With the temperature up to 1000 °C, the voids at the interface disappear completely, the joint has the maximum shear strength, and its interfacial layer is about 3 to 5 μm. The microhardness test shows that the hardness in weld zone is relatively higher than that in non-weld zone due to the fact that work hardening takes place in the matrix and the joint interface
The effects of process parameters on vacuum diffusion bonding between tantalum (Ta) and copper (Cu) were studied. The interfacial structure of Ta/Cu joint was analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and microhardness test. The results indicate that under the condition of loading pressure of 10 MPa and holding time of 60 min, the number of interfacial voids decreases with increasing of bonding temperature. With the temperature up to 1000 °C, the voids at the interface disappear completely, the joint has the maximum shear strength, and its interfacial layer is about 3 to 5 μm. The microhardness test shows that the hardness in weld zone is relatively higher than that in non-weld zone due to the fact that work hardening takes place in the matrix and the joint interface
2013, 42(9):1790-1794.
Abstract:
The hydriding properties of Zr9Ni11 alloy at different temperatures (25~150 °C) and various initial hydrogen pressures (10~160 kPa) were investigated. The results show that with the increase of temperature, the equilibrium pressure of the Zr9Ni11 alloy increases significantly, but its hydrogen absorption quantity decreases dramatically. When the temperature is less than 75 °C, the hydriding reaction rate of Zr9Ni11 alloy increases with increasing of temperature; while the temperature is higher than 75 °C, the hydriding reaction rate of the alloy decreases with increasing of temperature. The initial hydrogen pressure has a great influence on the kinetic properties of the alloy. When the initial pressure is lower than 50 kPa, the hydriding reaction rate of the alloy increases obviously with the increase of the initial hydrogen pressure, and even in the case of relatively low pressure, the alloy can still absorb hydrogen dramatically. The hydrogen absorption quantity and the equilibrium pressure of the alloy increase with the increase of the initial hydrogen pressure. The samples of the alloy before and after hydrogenation were analyzed by XRD, SEM(EDS) and TEM(SAED). After several hydriding-dehydriding cycles, the surface of the alloy which is homogeneous and smooth before hydrogenation becomes rough and crannied, and the ratio of Zr and Ni on the surface is varied. It is also found the amorphous states might be increased and mischcrystal formed through hydriding-dehydriding cycles. Zr9Ni11 alloy might be a promising candidate for extracting tritium according to our investigation.
The hydriding properties of Zr9Ni11 alloy at different temperatures (25~150 °C) and various initial hydrogen pressures (10~160 kPa) were investigated. The results show that with the increase of temperature, the equilibrium pressure of the Zr9Ni11 alloy increases significantly, but its hydrogen absorption quantity decreases dramatically. When the temperature is less than 75 °C, the hydriding reaction rate of Zr9Ni11 alloy increases with increasing of temperature; while the temperature is higher than 75 °C, the hydriding reaction rate of the alloy decreases with increasing of temperature. The initial hydrogen pressure has a great influence on the kinetic properties of the alloy. When the initial pressure is lower than 50 kPa, the hydriding reaction rate of the alloy increases obviously with the increase of the initial hydrogen pressure, and even in the case of relatively low pressure, the alloy can still absorb hydrogen dramatically. The hydrogen absorption quantity and the equilibrium pressure of the alloy increase with the increase of the initial hydrogen pressure. The samples of the alloy before and after hydrogenation were analyzed by XRD, SEM(EDS) and TEM(SAED). After several hydriding-dehydriding cycles, the surface of the alloy which is homogeneous and smooth before hydrogenation becomes rough and crannied, and the ratio of Zr and Ni on the surface is varied. It is also found the amorphous states might be increased and mischcrystal formed through hydriding-dehydriding cycles. Zr9Ni11 alloy might be a promising candidate for extracting tritium according to our investigation.
2013, 42(9):1795-1799.
Abstract:
It is the hot spot that how to improve the utilization rate of Pt on membrane electrodes. In the present study, the PtCuLaOx composite membrane electrode materials were fabricated on the surface of graphite fibrous cloth by ion beam sputtering (IBS). The phase composition and the surface structure of PtCuLaOx membrane were tested by X-ray diffraction (XRD) and atomic force microscope (AFM). The cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used to analyze the influence of different acid treatment conditions on the membrane electrocatalysis performance in a tri-electrode system. The results indicate that the PtCuLaOx membrane grain sizes are in the scope about 30 nm, and after acid treatment they become bigger. The sample acid-treated at 50 °C for 30 min in the solution of H2SO4 (0.5 mol/L) has the best electrochemical activity surface area (ESA) and exchange current density (i0). Its platinum loading capacity is only 0.0802 mg/cm2, and has very high ratio of performance to price.
It is the hot spot that how to improve the utilization rate of Pt on membrane electrodes. In the present study, the PtCuLaOx composite membrane electrode materials were fabricated on the surface of graphite fibrous cloth by ion beam sputtering (IBS). The phase composition and the surface structure of PtCuLaOx membrane were tested by X-ray diffraction (XRD) and atomic force microscope (AFM). The cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used to analyze the influence of different acid treatment conditions on the membrane electrocatalysis performance in a tri-electrode system. The results indicate that the PtCuLaOx membrane grain sizes are in the scope about 30 nm, and after acid treatment they become bigger. The sample acid-treated at 50 °C for 30 min in the solution of H2SO4 (0.5 mol/L) has the best electrochemical activity surface area (ESA) and exchange current density (i0). Its platinum loading capacity is only 0.0802 mg/cm2, and has very high ratio of performance to price.
2013, 42(9):1800-1804.
Abstract:
Equal-channel angular pressing (ECAP) experiments were conducted on a Mg-12Al-0.7Si magnesium alloy to investigate the influence of extrusion pass on its microstructure and mechanical properties. Homogeneously refined grains and secondary Mg17Al12 particles have been observed after multiple pass ECAP processing at 573 K. Mg2Si phase with size of about 2~3 μm has been observed after 8-pass ECAP processing; its morphology changes from initial coarse Chinese script shape to fine granule polygonal shape and its distribution tends to dispersing. The ultimate strength and the elongation of the alloy at room temperature remarkably increase to 293 MPa (after 6-pass processing) and 5.1% (after 8-pass processing), respectively. During the high temperature (200 °C) test, 2-pass processed specimen exhibits high strength of 204 MPa, and the 6-pass processed specimen has better elongation of 34.4%. The high strength of ECAPed alloy is attributed to grain refinement and modification of the second phase during ECAP, especially the Mg2Si phase. It is also shown that the basal plane texture (0002) developed by repetitive ECAP pressing influences the mechanical behavior of the ECAP-processed alloy
Equal-channel angular pressing (ECAP) experiments were conducted on a Mg-12Al-0.7Si magnesium alloy to investigate the influence of extrusion pass on its microstructure and mechanical properties. Homogeneously refined grains and secondary Mg17Al12 particles have been observed after multiple pass ECAP processing at 573 K. Mg2Si phase with size of about 2~3 μm has been observed after 8-pass ECAP processing; its morphology changes from initial coarse Chinese script shape to fine granule polygonal shape and its distribution tends to dispersing. The ultimate strength and the elongation of the alloy at room temperature remarkably increase to 293 MPa (after 6-pass processing) and 5.1% (after 8-pass processing), respectively. During the high temperature (200 °C) test, 2-pass processed specimen exhibits high strength of 204 MPa, and the 6-pass processed specimen has better elongation of 34.4%. The high strength of ECAPed alloy is attributed to grain refinement and modification of the second phase during ECAP, especially the Mg2Si phase. It is also shown that the basal plane texture (0002) developed by repetitive ECAP pressing influences the mechanical behavior of the ECAP-processed alloy
2013, 42(9):1805-1809.
Abstract:
The pretreatment of the cyanide tailing by roasting and its effect on the followed comprehensive recovery of valuable metals were investigated. The results indicate that the leaching rate of gold reaches 46.14%, the magnetic susceptibility of iron is up to 86.27% when the roasting temperature is 750 °C, the roasting time is 1.25 h, and the dosage of reductant is 6%. Combined with mineral structure and principle of magnetic roasting, the promoting mechanism of gold leaching by roasting was explored. The gold exposed through the magnetic roasting is the foremost improvement for high leaching rate of gold
The pretreatment of the cyanide tailing by roasting and its effect on the followed comprehensive recovery of valuable metals were investigated. The results indicate that the leaching rate of gold reaches 46.14%, the magnetic susceptibility of iron is up to 86.27% when the roasting temperature is 750 °C, the roasting time is 1.25 h, and the dosage of reductant is 6%. Combined with mineral structure and principle of magnetic roasting, the promoting mechanism of gold leaching by roasting was explored. The gold exposed through the magnetic roasting is the foremost improvement for high leaching rate of gold
2013, 42(9):1810-1813.
Abstract:
The present study described the synthesis of spheroidized Nd-Fe-B powders using a radio frequency (RF) inductively coupled plasma (ICP) torch with irregular feedstock materials. The effect of the power feed rate and the particle size of the feedstock material on spheroidization was analyzed. Scanning electron microscopy was used to examine the morphologies and the cross sections of plasma-processed powders. X-ray diffraction was used to analyze the oxides formed in the spheroidization processing. The loose densities and the particle size distributions of both the raw materials and the spheroidized powders were characterized. The results show that almost 100% of spheroidization percentage could be achieved. The loose density and powder flowability are enhanced greatly after plasma-treating. The loose density rises from 2.778 g/cm3 to 3.785 g/cm3. The powder flowability increases from 43.3 s/50 g to 27.5 s/50 g. Due to the good flowabitity and high loose density of the spherical powders, plasma-treated Nd-Fe-B powders have been used as the feedstock for gel-casting and injection molding
The present study described the synthesis of spheroidized Nd-Fe-B powders using a radio frequency (RF) inductively coupled plasma (ICP) torch with irregular feedstock materials. The effect of the power feed rate and the particle size of the feedstock material on spheroidization was analyzed. Scanning electron microscopy was used to examine the morphologies and the cross sections of plasma-processed powders. X-ray diffraction was used to analyze the oxides formed in the spheroidization processing. The loose densities and the particle size distributions of both the raw materials and the spheroidized powders were characterized. The results show that almost 100% of spheroidization percentage could be achieved. The loose density and powder flowability are enhanced greatly after plasma-treating. The loose density rises from 2.778 g/cm3 to 3.785 g/cm3. The powder flowability increases from 43.3 s/50 g to 27.5 s/50 g. Due to the good flowabitity and high loose density of the spherical powders, plasma-treated Nd-Fe-B powders have been used as the feedstock for gel-casting and injection molding
2013, 42(9):1814-1819.
Abstract:
The corrosion behavior of Zircaloy-4 alloy after different heat treatments in 550 oC/25 MPa supercritical water was investigated. Microstructure of the oxide film was observed by SEM. Nodular corrosion was observed in all the alloys regardless of heat treatment. Based on the microstructure observation, the nodular corrosion mechanism of Zircaloy-4 was discussed. The initial oxide film formed on Zircaloy-4 after corrosion is dense with very few micro-pores and micro-cracks. However, densities of oxides and Zircaloy-4 substrate are different and it leads to expansion tendency of brittle oxide film which imposes complex stress on the film. Therefore, crack formation and propagation occur at oxides/metal interface and result in the rupture of the film in the weakest regions under the effect of the stress which increases with the growth of the film. Subsequently, corrosive water penetrates into the cracks and forms effective oxygen sources, which accelerate the localized corrosion. The non-uniform corrosion in the film finally evolves to nodular corrosion. The formation of the effective oxygen sources at oxides/metal interface is the most important factor for nodular corrosion. Other factors, such as alloying elements, heat treatments, size and distribution of secondary phases and anisotropy growth of oxides, could also affect the nodular corrosion behavior via changing the microstructure of oxide film.
The corrosion behavior of Zircaloy-4 alloy after different heat treatments in 550 oC/25 MPa supercritical water was investigated. Microstructure of the oxide film was observed by SEM. Nodular corrosion was observed in all the alloys regardless of heat treatment. Based on the microstructure observation, the nodular corrosion mechanism of Zircaloy-4 was discussed. The initial oxide film formed on Zircaloy-4 after corrosion is dense with very few micro-pores and micro-cracks. However, densities of oxides and Zircaloy-4 substrate are different and it leads to expansion tendency of brittle oxide film which imposes complex stress on the film. Therefore, crack formation and propagation occur at oxides/metal interface and result in the rupture of the film in the weakest regions under the effect of the stress which increases with the growth of the film. Subsequently, corrosive water penetrates into the cracks and forms effective oxygen sources, which accelerate the localized corrosion. The non-uniform corrosion in the film finally evolves to nodular corrosion. The formation of the effective oxygen sources at oxides/metal interface is the most important factor for nodular corrosion. Other factors, such as alloying elements, heat treatments, size and distribution of secondary phases and anisotropy growth of oxides, could also affect the nodular corrosion behavior via changing the microstructure of oxide film.
2013, 42(9):1820-1825.
Abstract:
Hot compression tests of Haynes230 superalloy were conducted using a Thermecmastor-Z simulator in the temperature range of 950~1250 oC and strain rates of 0.001~10 s-1. Optical microscope (OM) and transmission electron microscope (TEM) techniques were employed to investigate the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). Results show that both the size and volume fraction of DRX grains increase with the increasing of deformation temperature but decrease with the increasing of strain rate. The dominant nucleation mechanism of DRX is bulging of the original grain boundaries. The necklace structure of recrystallized grains along original grain boundaries plays an important role for nucleation and growth of DRX grains. The relationship between DRX steady state grain size and Zener-Holloman parameter can be well established by a power law function
Hot compression tests of Haynes230 superalloy were conducted using a Thermecmastor-Z simulator in the temperature range of 950~1250 oC and strain rates of 0.001~10 s-1. Optical microscope (OM) and transmission electron microscope (TEM) techniques were employed to investigate the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). Results show that both the size and volume fraction of DRX grains increase with the increasing of deformation temperature but decrease with the increasing of strain rate. The dominant nucleation mechanism of DRX is bulging of the original grain boundaries. The necklace structure of recrystallized grains along original grain boundaries plays an important role for nucleation and growth of DRX grains. The relationship between DRX steady state grain size and Zener-Holloman parameter can be well established by a power law function
2013, 42(9):1826-1831.
Abstract:
As the candidate materials for advanced ultra-supercritical power plants, 617 alloy has superior mechanical properties and resistance ability against oxidation at a high temperature. In this paper, equilibrium precipitated phases of 617 alloy were calculated by Thermo-Calc software. The results show that the equilibrium phases include γ′, σ, μ, M6C and M23C6. The amount of γ′ is more sensitive to Ti than Al. Furthermore, this paper analyzed the microstructure features of 617 alloy as standard heat-treated. It is shown that 617 alloy has equiaxed grains and continuously precipitated carbides which are observed along the grain boundary. After solution treatment (1180 oC/1 h), part of the carbides re-dissolves and carbides become discontinuously distributed at the grain boundary
As the candidate materials for advanced ultra-supercritical power plants, 617 alloy has superior mechanical properties and resistance ability against oxidation at a high temperature. In this paper, equilibrium precipitated phases of 617 alloy were calculated by Thermo-Calc software. The results show that the equilibrium phases include γ′, σ, μ, M6C and M23C6. The amount of γ′ is more sensitive to Ti than Al. Furthermore, this paper analyzed the microstructure features of 617 alloy as standard heat-treated. It is shown that 617 alloy has equiaxed grains and continuously precipitated carbides which are observed along the grain boundary. After solution treatment (1180 oC/1 h), part of the carbides re-dissolves and carbides become discontinuously distributed at the grain boundary
2013, 42(9):1832-1837.
Abstract:
To better understand the temperature field in the upsetting head of a titanium alloy rivet and its influence on the forming of ASBs, a three dimensional FE model was built on the ABAQUS platform, fully taking into consideration the strain hardening, strain rate hardening and thermal softening effect of the rivet material and friction and nonlinear behavior of the structure. Computation results show that ASBs experience a high strain concentration during the process and the high temperature zones coincide with the ASBs basically. It is observed that the temperature rise in the ASBs reaches to 500 oC, which means the highest temperature in the rivet exceeds its recrystallization?temperature
To better understand the temperature field in the upsetting head of a titanium alloy rivet and its influence on the forming of ASBs, a three dimensional FE model was built on the ABAQUS platform, fully taking into consideration the strain hardening, strain rate hardening and thermal softening effect of the rivet material and friction and nonlinear behavior of the structure. Computation results show that ASBs experience a high strain concentration during the process and the high temperature zones coincide with the ASBs basically. It is observed that the temperature rise in the ASBs reaches to 500 oC, which means the highest temperature in the rivet exceeds its recrystallization?temperature
2013, 42(9):1838-1843.
Abstract:
The polished 9Cr18Mo martensitic stainless steel was implanted with nitrogen ions at a fluence of 2×1017 ion/cm2. To investigate the surface mechanical properties of the 9Cr18Mo steel samples after nitrogen ion implantation, the surface nanohardness and tribology properties of the original and nitrogen ion implanted steel samples were investigated. At the same time, their surface morphologies were also examined. The results show that nitrogen ion implantation would improve the surface hardness and lower the friction coefficient and wear rates of 9Cr18Mo steel samples significantly, while it does not change their surface morphology and surface roughness. To elucidate the strengthening mechanism of nitrogen ion implantation, the surface structures and components were studied by X-ray diffractometer and X-ray photoelectron spectroscopy. The results indicate that nitrogen ion implantation region can be divided into two layers. One is a surface layer of around 20 nm thickness, which is composed of metal nitrides and solid solution phases besides plenty of carbon atoms and the carbon atoms accumulate at the surface in a form of CrxCy phases. The other is the subsurface layer below 20 nm depth, which is mainly composed of metal nitrides. The surface components and structures have significant contributions to the improved mechanical properties.
The polished 9Cr18Mo martensitic stainless steel was implanted with nitrogen ions at a fluence of 2×1017 ion/cm2. To investigate the surface mechanical properties of the 9Cr18Mo steel samples after nitrogen ion implantation, the surface nanohardness and tribology properties of the original and nitrogen ion implanted steel samples were investigated. At the same time, their surface morphologies were also examined. The results show that nitrogen ion implantation would improve the surface hardness and lower the friction coefficient and wear rates of 9Cr18Mo steel samples significantly, while it does not change their surface morphology and surface roughness. To elucidate the strengthening mechanism of nitrogen ion implantation, the surface structures and components were studied by X-ray diffractometer and X-ray photoelectron spectroscopy. The results indicate that nitrogen ion implantation region can be divided into two layers. One is a surface layer of around 20 nm thickness, which is composed of metal nitrides and solid solution phases besides plenty of carbon atoms and the carbon atoms accumulate at the surface in a form of CrxCy phases. The other is the subsurface layer below 20 nm depth, which is mainly composed of metal nitrides. The surface components and structures have significant contributions to the improved mechanical properties.
2013, 42(9):1844-1848.
Abstract:
Hot compression tests of die-cast AZ91D magnesium alloy were performed on Gleeblle-1500D at strain rates ranging in 0.01~10 s-1 and deformation temperatures ranging in 250~450 oC. The constitutive equation, =1.41×1012 [sinh(0.014σ)]5.295exp (–159 449.509/RT), which is described by Zener-Hollomom parameters for hot compression deformation of die-cast AZ91D magnesium alloy was established. Compared to gravity cast AZ91D magnesium alloy, the deformation activation energy of die-cast AZ91D magnesium alloy, Q=159.45 kJ·mol-1, determined by hyperbolic sine function is lower
Hot compression tests of die-cast AZ91D magnesium alloy were performed on Gleeblle-1500D at strain rates ranging in 0.01~10 s-1 and deformation temperatures ranging in 250~450 oC. The constitutive equation, =1.41×1012 [sinh(0.014σ)]5.295exp (–159 449.509/RT), which is described by Zener-Hollomom parameters for hot compression deformation of die-cast AZ91D magnesium alloy was established. Compared to gravity cast AZ91D magnesium alloy, the deformation activation energy of die-cast AZ91D magnesium alloy, Q=159.45 kJ·mol-1, determined by hyperbolic sine function is lower
2013, 42(9):1849-1853.
Abstract:
ficient, entropy, helmholtz free energy, heat capacity at constant pressure and heat capacity at constant volume were calculated. The results show the calculated linear thermal expansion coefficient, entropy, helmholtz free energy, heat capacity at constant pressure and heat capacity at constant volume with taking into account the electronic contribution are in good agreement with experimental measurements for temperatures up to 2000 K. On the basis of the above results, elastic properties of cubic tungsten are obtained. The temperature dependences of elastic coefficient, bulk modulus, shear modulus and young's modulus are also got, which are in good agreement with experimental data
ficient, entropy, helmholtz free energy, heat capacity at constant pressure and heat capacity at constant volume were calculated. The results show the calculated linear thermal expansion coefficient, entropy, helmholtz free energy, heat capacity at constant pressure and heat capacity at constant volume with taking into account the electronic contribution are in good agreement with experimental measurements for temperatures up to 2000 K. On the basis of the above results, elastic properties of cubic tungsten are obtained. The temperature dependences of elastic coefficient, bulk modulus, shear modulus and young's modulus are also got, which are in good agreement with experimental data
2013, 42(9):1854-1858.
Abstract:
Hot compressing tests on powder metallurgy (P/M) TA15 titanium alloy have been conducted by a Gleeble-1500 simulator. A processing map for P/M TA15 titanium alloy in the temperature range of 850~1050 oC and the strain rate range of 0.001~10 s-1 was developed on the basis of a dynamic materials model and interpreted by microstructure observation. The results show that the alloy possesses superplasticity at the peak of power dissipation efficiency when deformed at T=1000 oC/=0.001 ~0.01 s-1. The alloy exhibits instability regime at T=850 oC/=0.001~0.01 s-1, T=900 oC/=1~10 s-1, T=950 oC/=0.01~1 s-1 and T=1050 oC/=1~10 s-1 with the power dissipation efficiency lower than 30%. Surface cracks and coarse β grains are observed. The deformation characteristics of P/M TA15 alloy at T=900 ~950 oC/=0.001~0.01 s-1, T=950 ~1000 oC/=1~10 s-1 and T=1000~1050 oC/=0.01~0.1 s-1, are recrystallization with the power dissipation efficiency of 30%~60%. Dynamic recrystallization or dynamic recovery can be observed in these domains.
Hot compressing tests on powder metallurgy (P/M) TA15 titanium alloy have been conducted by a Gleeble-1500 simulator. A processing map for P/M TA15 titanium alloy in the temperature range of 850~1050 oC and the strain rate range of 0.001~10 s-1 was developed on the basis of a dynamic materials model and interpreted by microstructure observation. The results show that the alloy possesses superplasticity at the peak of power dissipation efficiency when deformed at T=1000 oC/=0.001 ~0.01 s-1. The alloy exhibits instability regime at T=850 oC/=0.001~0.01 s-1, T=900 oC/=1~10 s-1, T=950 oC/=0.01~1 s-1 and T=1050 oC/=1~10 s-1 with the power dissipation efficiency lower than 30%. Surface cracks and coarse β grains are observed. The deformation characteristics of P/M TA15 alloy at T=900 ~950 oC/=0.001~0.01 s-1, T=950 ~1000 oC/=1~10 s-1 and T=1000~1050 oC/=0.01~0.1 s-1, are recrystallization with the power dissipation efficiency of 30%~60%. Dynamic recrystallization or dynamic recovery can be observed in these domains.
2013, 42(9):1859-1863.
Abstract:
The effect of microstructures on noise level in ultrasonic testing of TC4 titanium alloy was investigated. A comparative study of microstructures for different noise levels was performed using optical microscopy. A new characterization of microstructure inhomogeneity was developed and used to explain the reason for different noise levels. The EBSD technique was used to provide orientation information about these inhomogeneous microstructures. Results show that the region with high noise level presents obvious microstructure inhomogeneity. With the principle of ultrasonic testing, it is concluded that the variation of crystallography orientation would essentially give rise to the noise in ultrasonic testing. Finally ultrasonic response of TC4 alloy with different β grain sizes was investigated, and it is shown that the specimen with more microstructure interfaces exhibits a higher noise level
The effect of microstructures on noise level in ultrasonic testing of TC4 titanium alloy was investigated. A comparative study of microstructures for different noise levels was performed using optical microscopy. A new characterization of microstructure inhomogeneity was developed and used to explain the reason for different noise levels. The EBSD technique was used to provide orientation information about these inhomogeneous microstructures. Results show that the region with high noise level presents obvious microstructure inhomogeneity. With the principle of ultrasonic testing, it is concluded that the variation of crystallography orientation would essentially give rise to the noise in ultrasonic testing. Finally ultrasonic response of TC4 alloy with different β grain sizes was investigated, and it is shown that the specimen with more microstructure interfaces exhibits a higher noise level
2013, 42(9):1869-1873.
Abstract:
Li1+x(Fey/2Niy/2Mn1-y)1-xO2 was synthesized by a coprecipitation-hydrothermal-calcinations method. The crystal structure and charge/discharge performance of Li1+x(Fey/2Niy/2Mn1-y)1-xO2 were analyzed by X-ray diffraction (XRD), inductively coupled plasma (ICP) and electrochemical performance measurement. The XRD tests and ICP analyses demonstrate that Fe and Ni substitute a part of Mn of Li2MnO3 to form the good solid solution structure yLiFe1/2Ni1/2O2-(1-y)Li2MnO3 (y= 0.1, 0.2, 0.3, 0.4, 0.5). SEM images show that different y values lead to different apparent morphologies of the materials. When y=0.4, the particles are spherical with uniform and small size. The electrochemical tests indicate that when y=0.4, the cathode material has the best electrochemical performance with the discharge capacity of 195.0 mAh/g after 50 cycles
Li1+x(Fey/2Niy/2Mn1-y)1-xO2 was synthesized by a coprecipitation-hydrothermal-calcinations method. The crystal structure and charge/discharge performance of Li1+x(Fey/2Niy/2Mn1-y)1-xO2 were analyzed by X-ray diffraction (XRD), inductively coupled plasma (ICP) and electrochemical performance measurement. The XRD tests and ICP analyses demonstrate that Fe and Ni substitute a part of Mn of Li2MnO3 to form the good solid solution structure yLiFe1/2Ni1/2O2-(1-y)Li2MnO3 (y= 0.1, 0.2, 0.3, 0.4, 0.5). SEM images show that different y values lead to different apparent morphologies of the materials. When y=0.4, the particles are spherical with uniform and small size. The electrochemical tests indicate that when y=0.4, the cathode material has the best electrochemical performance with the discharge capacity of 195.0 mAh/g after 50 cycles
2013, 42(9):1874-1878.
Abstract:
The thermal fatigue behavior and mechanical fatigue behavior of board level solder joint were investigated by experimental testing and numerical simulation. And two kinds of solder materials, including traditional eutectic lead-tin solder and SAC305 lead-free solder, were considered. Results show that the lead-free solder (SAC305) joint has a longer thermal fatigue lifetime, but a shorter mechanical fatigue lifetime than the eutectic solder joint. Therefore, the evolutions of inelastic strains, including creep and plastic strain, caused by thermal fatigue and mechanical fatigue loading in the solder joint were analyzed by a finite element method. And the difference of solder joint’s thermal fatigue and mechanical fatigue behavior was presented
The thermal fatigue behavior and mechanical fatigue behavior of board level solder joint were investigated by experimental testing and numerical simulation. And two kinds of solder materials, including traditional eutectic lead-tin solder and SAC305 lead-free solder, were considered. Results show that the lead-free solder (SAC305) joint has a longer thermal fatigue lifetime, but a shorter mechanical fatigue lifetime than the eutectic solder joint. Therefore, the evolutions of inelastic strains, including creep and plastic strain, caused by thermal fatigue and mechanical fatigue loading in the solder joint were analyzed by a finite element method. And the difference of solder joint’s thermal fatigue and mechanical fatigue behavior was presented
2013, 42(9):1879-1882.
Abstract:
Fe44Co20Nd7Nb4B25 bulk amorphous alloy was prepared by copper mold casting. The microstructure, glass-forming ability, thermal stability and magnetic properties were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM). It is found that Fe44Co20Nd7Nb4B25 alloy with amorphous structure exhibits good soft magnetic property, excellent glass-forming ability and thermal stability. The value of activation energy, Ep, is 642 kJ/mol. The annealed sample shows hard magnetic behavior, and the maximum value of intrinsic coercivity (iHc) is 1164 kA/m after annealing at 1003 K. When annealed at 963 K, the values of remanence (Br) and maximum energy product ((BH)max) reaches a maximum of 0.27 T and 15.79 kJ/m3, respectively
Fe44Co20Nd7Nb4B25 bulk amorphous alloy was prepared by copper mold casting. The microstructure, glass-forming ability, thermal stability and magnetic properties were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM). It is found that Fe44Co20Nd7Nb4B25 alloy with amorphous structure exhibits good soft magnetic property, excellent glass-forming ability and thermal stability. The value of activation energy, Ep, is 642 kJ/mol. The annealed sample shows hard magnetic behavior, and the maximum value of intrinsic coercivity (iHc) is 1164 kA/m after annealing at 1003 K. When annealed at 963 K, the values of remanence (Br) and maximum energy product ((BH)max) reaches a maximum of 0.27 T and 15.79 kJ/m3, respectively
2013, 42(9):1884-1888.
Abstract:
A thermal spike model has been established and the high energy damage of UO2 was simulated by a molecular dynamics method. Different input temperatures and different input radii were set in single thermal spike simulation. The atoms in the central zone are activated by the thermal energy and passes to the outer layer with pressure wave style fast. The recovery happens simultaneously with a vast number of departure atoms. The final configurations are three types including amorphous, semi-amorphous and crystal. The simulation results can reproduce the physical process of thermal spike irradiation well. The affected zone which is too tiny to be viewed by experimental instruments can be observed directly
A thermal spike model has been established and the high energy damage of UO2 was simulated by a molecular dynamics method. Different input temperatures and different input radii were set in single thermal spike simulation. The atoms in the central zone are activated by the thermal energy and passes to the outer layer with pressure wave style fast. The recovery happens simultaneously with a vast number of departure atoms. The final configurations are three types including amorphous, semi-amorphous and crystal. The simulation results can reproduce the physical process of thermal spike irradiation well. The affected zone which is too tiny to be viewed by experimental instruments can be observed directly
2013, 42(9):1889-1892.
Abstract:
The effect of substrate surface treatments on structures and sorption properties of ZrCoRE thin film getters were analyzed by SEM, SPI, XRD and dynamic gas sorption tests. The results show that nanostructures of ZrCoRE thin films are strongly affected by the substrate surface. Both surface roughness and structure disorder degree grow with the increase of substrate surface roughness. After activation at 300 oC for 30 min, the sorption property of I-type getter film (Ra=5 nm) decreases quickly with the time. While II-type (Ra=7 nm), III-type (Ra=59 nm) and type-Ⅳ(Ra=125 nm) getter films exhibit stable gas sorption plateaus and increasing sorption speeds in sequence. Ⅳ-type getter film shows the best sorption property
The effect of substrate surface treatments on structures and sorption properties of ZrCoRE thin film getters were analyzed by SEM, SPI, XRD and dynamic gas sorption tests. The results show that nanostructures of ZrCoRE thin films are strongly affected by the substrate surface. Both surface roughness and structure disorder degree grow with the increase of substrate surface roughness. After activation at 300 oC for 30 min, the sorption property of I-type getter film (Ra=5 nm) decreases quickly with the time. While II-type (Ra=7 nm), III-type (Ra=59 nm) and type-Ⅳ(Ra=125 nm) getter films exhibit stable gas sorption plateaus and increasing sorption speeds in sequence. Ⅳ-type getter film shows the best sorption property
2013, 42(9):1893-1896.
Abstract:
The elastic properties and electronic structure of Ta-doped γ′-Ni3Al Phase have been investigated by the pseudo-potential plane wave (PP-PW) method within density functional theory. The calculated results show that Ta can effectively strengthen the elastic properties of Ni3Al alloys, which makes the Young’s modulus increase by 12.86%. The Ni3(Al,Ta) intermetallic compound behaves in ductile, but is more brittle than Ni3Al in nature. Using a sum of overlap populations of all bonds in the supercell, the covalent bonding of intermetallic compounds was evaluated quantitatively. It is found that Ta can increase the covalent bonding of γ′-Ni3Al. The bond characters were also analyzed using valence charge densities and total density of states, and the results indicate the chemical bonds in γ′-Ni3(Al,Ta) can be classified as a mixture of directional covalent and metallic characteristic
The elastic properties and electronic structure of Ta-doped γ′-Ni3Al Phase have been investigated by the pseudo-potential plane wave (PP-PW) method within density functional theory. The calculated results show that Ta can effectively strengthen the elastic properties of Ni3Al alloys, which makes the Young’s modulus increase by 12.86%. The Ni3(Al,Ta) intermetallic compound behaves in ductile, but is more brittle than Ni3Al in nature. Using a sum of overlap populations of all bonds in the supercell, the covalent bonding of intermetallic compounds was evaluated quantitatively. It is found that Ta can increase the covalent bonding of γ′-Ni3Al. The bond characters were also analyzed using valence charge densities and total density of states, and the results indicate the chemical bonds in γ′-Ni3(Al,Ta) can be classified as a mixture of directional covalent and metallic characteristic
2013, 42(9):1897-1900.
Abstract:
The effect of nano-particles TiO2 on the microstructures and properties of SnAgCu solders was investigated. The results indicate that adding a small amount of nano-particles TiO2 can improve the wettability of SnAgCu solders, and the mechanical properties of solder joints can be enhanced significantly; however, excessive nano-particles would reduce the properties. It can be found that the optimum content of nano-particles is 0.1 wt% for SnAgCu solders, when the matrix microstructure of solders may be refined obviously, and the dendrite-arm spacing of SnAgCu solders is decreased by 62.5% after soldering. Moreover, during thermal cycling tests, the SnAgCu solder joints show superior thermal fatigue resistance with the addition of 0.1wt% TiO2 because the particles restrict the movement of dislocations, thus hindering the propagation of cracks in matrix microstructure.
The effect of nano-particles TiO2 on the microstructures and properties of SnAgCu solders was investigated. The results indicate that adding a small amount of nano-particles TiO2 can improve the wettability of SnAgCu solders, and the mechanical properties of solder joints can be enhanced significantly; however, excessive nano-particles would reduce the properties. It can be found that the optimum content of nano-particles is 0.1 wt% for SnAgCu solders, when the matrix microstructure of solders may be refined obviously, and the dendrite-arm spacing of SnAgCu solders is decreased by 62.5% after soldering. Moreover, during thermal cycling tests, the SnAgCu solder joints show superior thermal fatigue resistance with the addition of 0.1wt% TiO2 because the particles restrict the movement of dislocations, thus hindering the propagation of cracks in matrix microstructure.
2013, 42(9):1901-1904.
Abstract:
Through the high temperature tensile creep experiments, the TC6 alloy creep strain-time curves were obtained, and the steady creep rate, the stress exponent and the apparent creep activation energy were calculated in the temperature range of 350~450 oC and different stresses. Microstructures of the alloy before and after creeping were analyzed by OM and TEM. On this basis the creep deformation mechanism was also studied. The results show that the steady creep rate increases with the increase of temperature or stress. The creep behavior of TC6 alloy in the range of 350~450 oC is controlled by double mechanisms of dislocation and diffusion. The boundary slip also has some effects on creeping.
Through the high temperature tensile creep experiments, the TC6 alloy creep strain-time curves were obtained, and the steady creep rate, the stress exponent and the apparent creep activation energy were calculated in the temperature range of 350~450 oC and different stresses. Microstructures of the alloy before and after creeping were analyzed by OM and TEM. On this basis the creep deformation mechanism was also studied. The results show that the steady creep rate increases with the increase of temperature or stress. The creep behavior of TC6 alloy in the range of 350~450 oC is controlled by double mechanisms of dislocation and diffusion. The boundary slip also has some effects on creeping.
2013, 42(9):1905-1907.
Abstract:
Mg-Zn-Ca alloys were prepared by a casting technique, and some of as-cast alloys were solution treated at 470 oC for 24 h. The corrosion resistance of the alloys in simulated body fluid was investigated. The results show that positive shift occurs in the electrochemical corrosion potential of solution treated alloys in the simulated body fluid (Hank’s). And the resistance to soak corrosion is also greatly improved. The maximum corrosion rate of as-cast alloys is 5.3265 mm/a in the simulated body fluid. After solution treatment the rate is reduced to 0.8632 mm/a. It indicates that after solution treatment, the alloy shows a better corrosion resistance
Mg-Zn-Ca alloys were prepared by a casting technique, and some of as-cast alloys were solution treated at 470 oC for 24 h. The corrosion resistance of the alloys in simulated body fluid was investigated. The results show that positive shift occurs in the electrochemical corrosion potential of solution treated alloys in the simulated body fluid (Hank’s). And the resistance to soak corrosion is also greatly improved. The maximum corrosion rate of as-cast alloys is 5.3265 mm/a in the simulated body fluid. After solution treatment the rate is reduced to 0.8632 mm/a. It indicates that after solution treatment, the alloy shows a better corrosion resistance
2013, 42(9):1908-1914.
Abstract:
Nickel-based superalloy GH4700 ingots of vacuum-induction-melting and electroslag-remelting were prepared and their dendrite morphology, segregation and precipitation were investigated. Kinetic homogenizing curves were calculated by Dictra software through a residual segregation parameter model. Based on the theoretical results, five homogenizing treatments were tested and validated by microstructural analysis and thermal compressions. The results show that Nb and Ti are the principal segregated elements of GH4700 ingots. The precipitated phases of casting ingots include γ, γ′, Laves and primary carbide. After homogenization at 1170 oC/48 h, the segregation of elements Nb and Ti are almost eliminated. The phase of Laves, which is detrimental to plasticity, dissolves to the matrix. GH4700 alloy exhibits excellent workability after homogenizing heat treatment
Nickel-based superalloy GH4700 ingots of vacuum-induction-melting and electroslag-remelting were prepared and their dendrite morphology, segregation and precipitation were investigated. Kinetic homogenizing curves were calculated by Dictra software through a residual segregation parameter model. Based on the theoretical results, five homogenizing treatments were tested and validated by microstructural analysis and thermal compressions. The results show that Nb and Ti are the principal segregated elements of GH4700 ingots. The precipitated phases of casting ingots include γ, γ′, Laves and primary carbide. After homogenization at 1170 oC/48 h, the segregation of elements Nb and Ti are almost eliminated. The phase of Laves, which is detrimental to plasticity, dissolves to the matrix. GH4700 alloy exhibits excellent workability after homogenizing heat treatment
2013, 42(9):1915-1920.
Abstract:
Micro-fine spherical TiAl alloy powder was prepared by high-energy ball milling and subsequent radio frequency plasma spheroidization from atomized TiAl alloy powder with big particle size. The fabrication process and powder characteristics were investigated. The results show that the obtained powder exhibits good sphericity. The number-average particle size of the powder can be accurately controlled in the range of 10~60 μm, and the powder presents a narrow size distribution with a uniformity level of about 0.63. The powder oxygen content acts as a decreasing function of the particle size, which increases from 2.44‰ to 3.51‰ when the number-average particle size decreases from 31.5 μm to 15.6 μm. The spherical TiAl alloy power is composed of α2-Ti3Al and a small amount of γ-TiAl. The powder possesses homogeneous chemical composition and uniform equiaxed grain microstructure, and the grain size tends to be refined with the decrease of the particle size
Micro-fine spherical TiAl alloy powder was prepared by high-energy ball milling and subsequent radio frequency plasma spheroidization from atomized TiAl alloy powder with big particle size. The fabrication process and powder characteristics were investigated. The results show that the obtained powder exhibits good sphericity. The number-average particle size of the powder can be accurately controlled in the range of 10~60 μm, and the powder presents a narrow size distribution with a uniformity level of about 0.63. The powder oxygen content acts as a decreasing function of the particle size, which increases from 2.44‰ to 3.51‰ when the number-average particle size decreases from 31.5 μm to 15.6 μm. The spherical TiAl alloy power is composed of α2-Ti3Al and a small amount of γ-TiAl. The powder possesses homogeneous chemical composition and uniform equiaxed grain microstructure, and the grain size tends to be refined with the decrease of the particle size
2013, 42(9):1921-1925.
Abstract:
To solve the problems in the compact tensile tests of the 7050 high strength aluminum alloy, such as oversized crack angle, low mission success rate and substandard of the fracture toughness, the comparisons were conducted between the traditional process and the modified process. The result shows that the modified process enhances the level of the fracture toughness and the mission success rate. Besides, the reasons of the low mission success rate are shown at two main aspects which are the anisotropy and the length of the precrack. Reducing the level of the anisotropy or increasing the length of the precrack can effectively decrease the crack angle; meanwhile, the reference range of the precrack length is given for 7050 high strength aluminum alloy
To solve the problems in the compact tensile tests of the 7050 high strength aluminum alloy, such as oversized crack angle, low mission success rate and substandard of the fracture toughness, the comparisons were conducted between the traditional process and the modified process. The result shows that the modified process enhances the level of the fracture toughness and the mission success rate. Besides, the reasons of the low mission success rate are shown at two main aspects which are the anisotropy and the length of the precrack. Reducing the level of the anisotropy or increasing the length of the precrack can effectively decrease the crack angle; meanwhile, the reference range of the precrack length is given for 7050 high strength aluminum alloy
2013, 42(9):1926-1930.
Abstract:
The Cr2O3 and C powder with polyvinyl alcohol were mixed and pressed to form the pellets. The pellets of the Cr2O3-C mixtures were self-sintered and directly electrochemically reduced to Cr3C2 at the same time in molten CaCl2 at 800 oC and 3.2 V with a graphite anode. The samples were characterized by XRD, SEM, and EDX. The results show that the Cr2O3-C mixtures satisfy the bond strength requirement when electrolyzing. High purity Cr3C2 powder with the excellent sintering nature is obtained. The current efficiency is no less than 37.3%. The results of the cyclic voltammetry measurement and the potentiostatic electrolysis reveal that the reaction mechanism of Cr3C2 formation by the directly electrochemical reduction is two steps: Cr2O3+e-→Cr + O2 and Cr+C→Cr3C2.
The Cr2O3 and C powder with polyvinyl alcohol were mixed and pressed to form the pellets. The pellets of the Cr2O3-C mixtures were self-sintered and directly electrochemically reduced to Cr3C2 at the same time in molten CaCl2 at 800 oC and 3.2 V with a graphite anode. The samples were characterized by XRD, SEM, and EDX. The results show that the Cr2O3-C mixtures satisfy the bond strength requirement when electrolyzing. High purity Cr3C2 powder with the excellent sintering nature is obtained. The current efficiency is no less than 37.3%. The results of the cyclic voltammetry measurement and the potentiostatic electrolysis reveal that the reaction mechanism of Cr3C2 formation by the directly electrochemical reduction is two steps: Cr2O3+e-→Cr + O2 and Cr+C→Cr3C2.
2013, 42(9):1931-1935.
Abstract:
The experimental method of composite electroforming under CO2 supercritical fluids (SCF-CO2) was brief introduced. The experiment of nickel-Al2O3 and nickel-diamond composite electroforming were investigated using scanning electron microscope (SEM) and digital microscope hardness tester. The surface microstructures of nickel-Al2O3 and nickel-diamond composite electroforming films were analyzed. The effect of strengthening particles (nano Al2O3 particle and micro diamond particle) and pressure on microhardness of nickel-Al2O3 and nickel-diamond composite electroforming films were discussed. The results show that the bright and uniform surface of nickel-Al2O3 composite electroforming coating can be prepared under SCF-CO2 environment, and the dispersion of Al2O3 grains has optimal state. The microhardness of nickel-Al2O3 composite electroforming films gradually increases and then rapidly decreases with the increasing of Al2O3 addition. Its maximum can reach 11.4 GPa when the addition is 60 g/L and the pressure is 14 MPa, which is twice as much as that of the nickel-Al2O3 conventional composite electroforming layer. The content of Al2O3 grain in nickel-Al2O3 composite electroforming film under SCF-CO2 is 9.9 wt%. The microstructure of nickel-diamond composite electroforming films with black diamond grains and cellular distribution can be prepared under SCF-CO2. The microhardness of nickel-diamond composite electroforming films rises fast and then decreases gradually with the increasing of diamond particles. Its maximum can reach 9.1 GPa when the diamond grains content and working pressure are 60 g/L and 10 MPa respectively, but the microhardness will rapidly decrease when the pressure is higher than 14 MPa
The experimental method of composite electroforming under CO2 supercritical fluids (SCF-CO2) was brief introduced. The experiment of nickel-Al2O3 and nickel-diamond composite electroforming were investigated using scanning electron microscope (SEM) and digital microscope hardness tester. The surface microstructures of nickel-Al2O3 and nickel-diamond composite electroforming films were analyzed. The effect of strengthening particles (nano Al2O3 particle and micro diamond particle) and pressure on microhardness of nickel-Al2O3 and nickel-diamond composite electroforming films were discussed. The results show that the bright and uniform surface of nickel-Al2O3 composite electroforming coating can be prepared under SCF-CO2 environment, and the dispersion of Al2O3 grains has optimal state. The microhardness of nickel-Al2O3 composite electroforming films gradually increases and then rapidly decreases with the increasing of Al2O3 addition. Its maximum can reach 11.4 GPa when the addition is 60 g/L and the pressure is 14 MPa, which is twice as much as that of the nickel-Al2O3 conventional composite electroforming layer. The content of Al2O3 grain in nickel-Al2O3 composite electroforming film under SCF-CO2 is 9.9 wt%. The microstructure of nickel-diamond composite electroforming films with black diamond grains and cellular distribution can be prepared under SCF-CO2. The microhardness of nickel-diamond composite electroforming films rises fast and then decreases gradually with the increasing of diamond particles. Its maximum can reach 9.1 GPa when the diamond grains content and working pressure are 60 g/L and 10 MPa respectively, but the microhardness will rapidly decrease when the pressure is higher than 14 MPa
2013, 42(9):1936-1940.
Abstract:
Palladium nanoparticles were synthesized by the reduction of palladium nitrate through a water bath method in the presence of 12- tungstosilicate with Keggin structure. The morphology, particle size and structure of the palladium nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD). In addition, the palladium nanoparticles were used to modify Au electrode. Electrocatalytic properties of nano Pd in hydrazine were studied through the cyclic voltammetry. The result shows that the spherical palladium nanoparticles with the grain diameter about 3~4 nm are obtained. The electron diffraction pattern indicates that the palladium nanoparticles are face-centered cubic polycrystalline. The Pd nanoparticles modified electrodes display excellent electrocatalytic performance for the hydrazine electrooxidation. The oxidation peak current (Ipa) increases almost linearly with the increasing of concentration of the hydrazine at pH=6
Palladium nanoparticles were synthesized by the reduction of palladium nitrate through a water bath method in the presence of 12- tungstosilicate with Keggin structure. The morphology, particle size and structure of the palladium nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD). In addition, the palladium nanoparticles were used to modify Au electrode. Electrocatalytic properties of nano Pd in hydrazine were studied through the cyclic voltammetry. The result shows that the spherical palladium nanoparticles with the grain diameter about 3~4 nm are obtained. The electron diffraction pattern indicates that the palladium nanoparticles are face-centered cubic polycrystalline. The Pd nanoparticles modified electrodes display excellent electrocatalytic performance for the hydrazine electrooxidation. The oxidation peak current (Ipa) increases almost linearly with the increasing of concentration of the hydrazine at pH=6
2013, 42(9):1941-1944.
Abstract:
t is suggested that the modified polyol method is efficient for Pt/C catalyst preparation
t is suggested that the modified polyol method is efficient for Pt/C catalyst preparation
2013, 42(9):1945-1948.
Abstract:
A 50 mm thick TC4-DT alloy plate was welded using electron beam. Ultimate tensile tests of base metal, weld metal and the whole joint were carried out to collect the tensile property data. Moreover, microstructure and fracture morphology after tensile tests were observed to study the effect of electron beam welding on tensile properties of TC4-DT alloy. The results indicate that both the base metal and weld metal exhibit high strength and weak strain hardening ability. Electron beam welding makes the weld strength and strain hardening ability increase, while the plasticity and ductility decrease. Base metal is the weakest part of the whole joint, and the fracture occurs on the base metal away from the weld metal during the tensile tests of the joints. In addition, fractography of both the weld metal and base metal is found to be dimple, which means that the fracture feature of both the base and weld metal is ductile. The tensile property difference between the base metal and weld metal is related to the microstructure change of weld metal after welding. The increase of strength and decrease of plasticity and ductility for weld metal is mostly dependent on the formation of coarse β columnar grain and martensite in the weld metal due to the very fast cooling speed during electron beam welding
A 50 mm thick TC4-DT alloy plate was welded using electron beam. Ultimate tensile tests of base metal, weld metal and the whole joint were carried out to collect the tensile property data. Moreover, microstructure and fracture morphology after tensile tests were observed to study the effect of electron beam welding on tensile properties of TC4-DT alloy. The results indicate that both the base metal and weld metal exhibit high strength and weak strain hardening ability. Electron beam welding makes the weld strength and strain hardening ability increase, while the plasticity and ductility decrease. Base metal is the weakest part of the whole joint, and the fracture occurs on the base metal away from the weld metal during the tensile tests of the joints. In addition, fractography of both the weld metal and base metal is found to be dimple, which means that the fracture feature of both the base and weld metal is ductile. The tensile property difference between the base metal and weld metal is related to the microstructure change of weld metal after welding. The increase of strength and decrease of plasticity and ductility for weld metal is mostly dependent on the formation of coarse β columnar grain and martensite in the weld metal due to the very fast cooling speed during electron beam welding
2013, 42(9):1949-1952.
Abstract:
2024-T4 aluminum alloy plate was jointed by friction stir welding (FSW) under air and cooling water circulation separately, and the effect of the cooling water on the microstructure and mechanical properties of the FSW joint was investigated. The results show that the cooling water circulation medium has a significant instantaneous cooling effect. Cooling water causes remarkable grain refinement with an average grain size of 700 nm in the nugget zone. The growth of precipitates is restrained by cooling water, and the size of precipitates is 30~200 nm in the nugget zone. Cooling water decreases the thermal softening effect on the FSW joint, thus improving the microstructure and properties of the joint. HV microhardness and tensile strength of SFSW joint are increased by 234 MPa and 52.2 MPa, respectively, but the elongation is decreased a little
2024-T4 aluminum alloy plate was jointed by friction stir welding (FSW) under air and cooling water circulation separately, and the effect of the cooling water on the microstructure and mechanical properties of the FSW joint was investigated. The results show that the cooling water circulation medium has a significant instantaneous cooling effect. Cooling water causes remarkable grain refinement with an average grain size of 700 nm in the nugget zone. The growth of precipitates is restrained by cooling water, and the size of precipitates is 30~200 nm in the nugget zone. Cooling water decreases the thermal softening effect on the FSW joint, thus improving the microstructure and properties of the joint. HV microhardness and tensile strength of SFSW joint are increased by 234 MPa and 52.2 MPa, respectively, but the elongation is decreased a little
2013, 42(9):1953-1956.
Abstract:
Deposition of La2Zr2O7 (LZO) buffer layer by a reel-to-reel method was studied. The results indicate that it is a better way for fabricating a long tape that Ar-4%H2 mixed gas flows along the transversal direction of NiW substrate, and the pryolysed gases could be dissipated rapidly by this way, and the texture homogeneity of each part in the LZO film can be improved. It is also found that a small angle between the gas flow direction with the normal direction of the sample is beneficial to improve the texture of LZO film. The influence of the sample moving speed is due to the change of heat treatment time. After the treatment is optimized, a smooth and dense LZO film with sharp texture is deposited on a NiW substrate by a reel-to-reel method, and the texture sharpness of LZO film is similar to that of NiW substrate
Deposition of La2Zr2O7 (LZO) buffer layer by a reel-to-reel method was studied. The results indicate that it is a better way for fabricating a long tape that Ar-4%H2 mixed gas flows along the transversal direction of NiW substrate, and the pryolysed gases could be dissipated rapidly by this way, and the texture homogeneity of each part in the LZO film can be improved. It is also found that a small angle between the gas flow direction with the normal direction of the sample is beneficial to improve the texture of LZO film. The influence of the sample moving speed is due to the change of heat treatment time. After the treatment is optimized, a smooth and dense LZO film with sharp texture is deposited on a NiW substrate by a reel-to-reel method, and the texture sharpness of LZO film is similar to that of NiW substrate
2013, 42(9):1957-1960.
Abstract:
Bi3.25La0.75Ti3O12 (BLT) nanotubes were synthesized by dipping BLT sol precursor into an anodic aluminum oxide template (AAO). The results indicate that using 4BiNO3(OH)2×BiO(OH), La(NO3)3×6H2O and Ti(C4H9O)4 as starting materials, stable BLT sol can be prepared with solvent of acetic acid and ethylene glycol monomethyl ether. Pure perovskite BLT can be synthesized after calcining the gel that comes from sol with acetic acid and ethylene glycol monomethyl ether as solvent at 500 °C for 1 h and 750 °C for 30 min. BLT nanotubes are stacks of BLT polycrystalline of 8~12 nm and they have a wall thickness of 25 nm and diameter of 300 nm
Bi3.25La0.75Ti3O12 (BLT) nanotubes were synthesized by dipping BLT sol precursor into an anodic aluminum oxide template (AAO). The results indicate that using 4BiNO3(OH)2×BiO(OH), La(NO3)3×6H2O and Ti(C4H9O)4 as starting materials, stable BLT sol can be prepared with solvent of acetic acid and ethylene glycol monomethyl ether. Pure perovskite BLT can be synthesized after calcining the gel that comes from sol with acetic acid and ethylene glycol monomethyl ether as solvent at 500 °C for 1 h and 750 °C for 30 min. BLT nanotubes are stacks of BLT polycrystalline of 8~12 nm and they have a wall thickness of 25 nm and diameter of 300 nm
2013, 42(9):1961-1964.
Abstract:
The Y2SiO5:Ce3+/PMMA composites were prepared by in-situ polymerization with blue photoluminescent powder Y2SiO5:Ce3+ and poly methyl methacrylate (PMMA) as starting materials. The obtained samples were characterized by XRD, FT-IR, SEM, etc. Results show that the Y2SiO5:Ce3+ luminescent powder with particle size of 0.7~2.0 μm has the X2-monoclinic crystal structure and is homogeneously distributed in the PMMA. Excited by the ultraviolet light with the wavelength of 365 nm, the Y2SiO5:Ce3+/PMMA composites exhibit the blue photoluminescence and the transparency of blue photoluminescence achieves a high value of 75%. Consequently, the obtained Y2SiO5:Ce3+/PMMA composites can be used to fabricate the transparent luminescent apparatus.
The Y2SiO5:Ce3+/PMMA composites were prepared by in-situ polymerization with blue photoluminescent powder Y2SiO5:Ce3+ and poly methyl methacrylate (PMMA) as starting materials. The obtained samples were characterized by XRD, FT-IR, SEM, etc. Results show that the Y2SiO5:Ce3+ luminescent powder with particle size of 0.7~2.0 μm has the X2-monoclinic crystal structure and is homogeneously distributed in the PMMA. Excited by the ultraviolet light with the wavelength of 365 nm, the Y2SiO5:Ce3+/PMMA composites exhibit the blue photoluminescence and the transparency of blue photoluminescence achieves a high value of 75%. Consequently, the obtained Y2SiO5:Ce3+/PMMA composites can be used to fabricate the transparent luminescent apparatus.
2013, 42(9):1965-1968.
Abstract:
The orthogonal design approach and range analysis were used to investigate the preparation parameters optimization of ultrasonic arc spray (UAS) AgNiCu15-5 powder. The prepared global AgNiCu15-5 powder was characterized by SEM and XRD. The results show that both the spray length (L) and the arc current (I) have great effects, while both the arc voltage (U) and the pressure of atomization gases (P) have less effects on the powder size in the range of 25~38 μm. The optimal process parameters of the fine AgNiCu15-5 alloy powder preparation are given as follows: the spray length is 250 mm, the arc current is 100 A, the arc voltage is 32 V, and the pressure of atomization gases is 0.8 MPa. Under the optimized conditions the prepared AgNiCu15-5 powder possesses global particles with uniform size, more than 94% of which is less than 38 μm
The orthogonal design approach and range analysis were used to investigate the preparation parameters optimization of ultrasonic arc spray (UAS) AgNiCu15-5 powder. The prepared global AgNiCu15-5 powder was characterized by SEM and XRD. The results show that both the spray length (L) and the arc current (I) have great effects, while both the arc voltage (U) and the pressure of atomization gases (P) have less effects on the powder size in the range of 25~38 μm. The optimal process parameters of the fine AgNiCu15-5 alloy powder preparation are given as follows: the spray length is 250 mm, the arc current is 100 A, the arc voltage is 32 V, and the pressure of atomization gases is 0.8 MPa. Under the optimized conditions the prepared AgNiCu15-5 powder possesses global particles with uniform size, more than 94% of which is less than 38 μm
2013, 42(9):1969-1972.
Abstract:
An even and compact iridium layer was prepared on a platinum substrate by electrodeposition under a constant voltage in an ionic liquid of 1-butyl-3-methylimidazolium chloride (BMIC). The surface morphology and composition of the iridium layer were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). Results show that iridium layer can’t be prepared in pure BMIC. Adidtion of ethylene glycol and an evaluated temperature could effectively improve the solubility of IrCl3 in BMIC, which is useful in preparing iridium layer. Iridium layer is obtained at the right voltage and no iridium is got on platinum under a low voltage. When the voltage is too high, the iridium layer becomes loose. When the molar ratio of BMIC to ethylene glycol increases, the surface of the iridium layer becomes rough. Iridium layer can not be achieved at lower temperature while at higher temperature a larger crack appears on the iridium layer
An even and compact iridium layer was prepared on a platinum substrate by electrodeposition under a constant voltage in an ionic liquid of 1-butyl-3-methylimidazolium chloride (BMIC). The surface morphology and composition of the iridium layer were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). Results show that iridium layer can’t be prepared in pure BMIC. Adidtion of ethylene glycol and an evaluated temperature could effectively improve the solubility of IrCl3 in BMIC, which is useful in preparing iridium layer. Iridium layer is obtained at the right voltage and no iridium is got on platinum under a low voltage. When the voltage is too high, the iridium layer becomes loose. When the molar ratio of BMIC to ethylene glycol increases, the surface of the iridium layer becomes rough. Iridium layer can not be achieved at lower temperature while at higher temperature a larger crack appears on the iridium layer
2013, 42(9):1973-1975.
Abstract:
Ni(OH)2 nanoplate arrays grown on Ti substrate were synthesized via a hydrothermal method in solution containing nickel. The as-prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of Ni(OH)2/Ti in NaOH solution were studied. The results show that the electrode exhibits good electrocatalytic activity toward the oxidation of glucose. The linear range for the determination of gluose is 4.5×10-5~1.05×10-3 mol/L with a detection limit of 5 μmol/L (S/N = 3)
Ni(OH)2 nanoplate arrays grown on Ti substrate were synthesized via a hydrothermal method in solution containing nickel. The as-prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of Ni(OH)2/Ti in NaOH solution were studied. The results show that the electrode exhibits good electrocatalytic activity toward the oxidation of glucose. The linear range for the determination of gluose is 4.5×10-5~1.05×10-3 mol/L with a detection limit of 5 μmol/L (S/N = 3)
