Volume 39,Issue 11,2010 Table of Contents
2010, 39(11):1881-1887.
Abstract:
Through the empirical electron theory of solids and molecules (EET), the valence electron structure of Mg-Al alloy melt was analyzed. Based on the analysis, the basic structure model was established and the melt structural information was obtained. By analyzing the irreversible phenomenon of viscosity-temperature relationship curve V(t) of magnesium alloy melt in the temperature interval of ascent and descent, the irreversible change of the melt structural information would be judged indirectly. The results show that the number difference of covalent electron pair nα of each bond between atoms is the ultimate reason of the different melt structural information, which induces micro-inhomogeneity in alloy melt directly; at near 730 °C, Al-MgⅢ(C) bonds in the atomic clusters with relatively stable structure begin to break. At this time, the melt structure achieves a new equilibratory and relatively homogeneous state. Disappearance of micro-nonequilibrium structure inherited from solidified structure, breakage of Al-MgⅢ(C) bonds in the atomic clusters and irreversible rearrangement of atoms are the essential reason of irreversible change of curve V(t). It is very important for further understanding the melt structural information of magnesium alloy and exploring solidification micro-mechanics.
Through the empirical electron theory of solids and molecules (EET), the valence electron structure of Mg-Al alloy melt was analyzed. Based on the analysis, the basic structure model was established and the melt structural information was obtained. By analyzing the irreversible phenomenon of viscosity-temperature relationship curve V(t) of magnesium alloy melt in the temperature interval of ascent and descent, the irreversible change of the melt structural information would be judged indirectly. The results show that the number difference of covalent electron pair nα of each bond between atoms is the ultimate reason of the different melt structural information, which induces micro-inhomogeneity in alloy melt directly; at near 730 °C, Al-MgⅢ(C) bonds in the atomic clusters with relatively stable structure begin to break. At this time, the melt structure achieves a new equilibratory and relatively homogeneous state. Disappearance of micro-nonequilibrium structure inherited from solidified structure, breakage of Al-MgⅢ(C) bonds in the atomic clusters and irreversible rearrangement of atoms are the essential reason of irreversible change of curve V(t). It is very important for further understanding the melt structural information of magnesium alloy and exploring solidification micro-mechanics.
2010, 39(11):1888-1892.
Abstract:
La1.9Ti0.1MgNi9 alloys were prepared by magnetic levitation melting followed by annealing treatments. The results of XRD, PCT and electrochemical measurements show that all samples possess a multiphase structure, and LaNi5 phase is the main phase. LaMg2Ni9 phase disappears and Ti2Ni phase appears at 1173 K. Annealed alloys exhibit higher compositional homogeneity and lower absorption/desorption plateau pressures compared to as-cast alloy. The effective hydrogen storage capacity of the alloy annealed at 1073 K is the highest, and it reaches 1.25% (mass fraction) at 303 K. Annealing not only enhances the discharge capacity, but also improves the cyclic stability and the high rate dischargeability markedly. La1.9Ti0.1MgNi9 alloy annealed at 1173 K presents good electrochemical performance with the maximum discharge capacity of 377 mAh/g, the HRD1100 of 0.839 and the retention of discharge capacity of 60% after 112 charge/discharge cycles.
La1.9Ti0.1MgNi9 alloys were prepared by magnetic levitation melting followed by annealing treatments. The results of XRD, PCT and electrochemical measurements show that all samples possess a multiphase structure, and LaNi5 phase is the main phase. LaMg2Ni9 phase disappears and Ti2Ni phase appears at 1173 K. Annealed alloys exhibit higher compositional homogeneity and lower absorption/desorption plateau pressures compared to as-cast alloy. The effective hydrogen storage capacity of the alloy annealed at 1073 K is the highest, and it reaches 1.25% (mass fraction) at 303 K. Annealing not only enhances the discharge capacity, but also improves the cyclic stability and the high rate dischargeability markedly. La1.9Ti0.1MgNi9 alloy annealed at 1173 K presents good electrochemical performance with the maximum discharge capacity of 377 mAh/g, the HRD1100 of 0.839 and the retention of discharge capacity of 60% after 112 charge/discharge cycles.
2010, 39(11):1893-1898.
Abstract:
The tensile properties of TG6 titanium alloy forging disc as solution and aging treatment (STA) state and STA plus 600 °C, 100 h exposed state were tested at various temperatures. The results show that the tensile strength decreases while the ductility increases with the test temperature increasing. Compared with as STA state, the room temperature tensile plasticity of the specimen subjected to a long-term thermal exposure decreases remarkably. However, once the temperature rises over 150 °C, the tensile ductility increases rapidly, namely, the thermal stability gets a recovery to a great extent. The loss of thermal stability of TG6 titanium alloy may be mainly attributed to the coherent precipitation of a2 phase and surface oxidation. When the temperature is above 150 °C, the resumption of the thermal stability would come from the change of dislocation slip mode. Upon temperature rising, the slip mode of the dislocation changes from concentrated slip mode by cutting the coherent a2 particles to cross slip mode, which will promote a more homogeneous plastic deformation and result in the improvement of tensile ductility, showing the characteristic of the macro-transferring from a planar slip to a wave slip on the fracture surface.
The tensile properties of TG6 titanium alloy forging disc as solution and aging treatment (STA) state and STA plus 600 °C, 100 h exposed state were tested at various temperatures. The results show that the tensile strength decreases while the ductility increases with the test temperature increasing. Compared with as STA state, the room temperature tensile plasticity of the specimen subjected to a long-term thermal exposure decreases remarkably. However, once the temperature rises over 150 °C, the tensile ductility increases rapidly, namely, the thermal stability gets a recovery to a great extent. The loss of thermal stability of TG6 titanium alloy may be mainly attributed to the coherent precipitation of a2 phase and surface oxidation. When the temperature is above 150 °C, the resumption of the thermal stability would come from the change of dislocation slip mode. Upon temperature rising, the slip mode of the dislocation changes from concentrated slip mode by cutting the coherent a2 particles to cross slip mode, which will promote a more homogeneous plastic deformation and result in the improvement of tensile ductility, showing the characteristic of the macro-transferring from a planar slip to a wave slip on the fracture surface.
2010, 39(11):1903-1907.
Abstract:
The anodes of Ti/IrO2-Ta2O5 were prepared using Pechini method. The microstructure and electrochemical properties of the anodes were studied with SEM, EDX, XRD, potentiodynamic polarization, cyclic voltammetry, electrochemical impedance spectroscopy and accelerated life test. It has been shown that the prepared oxide anodes have uniform surface composition, and there is no evident aggregation of IrO2 particles. Tantalum forms solid solution in the rutile IrO2 phase. With the increase of the sintering temperature, the mutual solubility between iridium and tantalum increases, and the crystallite grains of the oxide coating become finer. Moreover, with rising of the sintering temperature, the electrocatalytic activity of the oxide electrode for oxygen evolution and the electrochemically active surface area are reduced. The Ti/IrO2-Ta2O5 anode prepared at 500 °C presents the longest service life.
The anodes of Ti/IrO2-Ta2O5 were prepared using Pechini method. The microstructure and electrochemical properties of the anodes were studied with SEM, EDX, XRD, potentiodynamic polarization, cyclic voltammetry, electrochemical impedance spectroscopy and accelerated life test. It has been shown that the prepared oxide anodes have uniform surface composition, and there is no evident aggregation of IrO2 particles. Tantalum forms solid solution in the rutile IrO2 phase. With the increase of the sintering temperature, the mutual solubility between iridium and tantalum increases, and the crystallite grains of the oxide coating become finer. Moreover, with rising of the sintering temperature, the electrocatalytic activity of the oxide electrode for oxygen evolution and the electrochemically active surface area are reduced. The Ti/IrO2-Ta2O5 anode prepared at 500 °C presents the longest service life.
2010, 39(11):1908-1911.
Abstract:
The oxidation process of a newly developed Ni-Cr-W alloy in air at 1100 °C has been investigated by varying the holding time. The microstructures and compositions of the surface scale as well as the oxide in cross-section were characterized by Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectrum (EDS). The phase identification of the surface scale was carried out using X-ray diffraction (XRD). Results show that in the initial stage of oxidation (<3 h) a single oxidation layer is formed on the alloy. Surface is mainly composed of Cr2O3. With prolonging of oxidation (>7 h), a NiCr2O4 layer with spinel structure grows out gradually in the outer layer of Cr2O3. Once the outer layer of the compact spinel is formed, the double multi-components layer NiCr2O4·Cr2O3 will further decelerate the oxidation rate of the alloy. The degradation of the alloy subsurface includes the inner oxidation of grain boundaries and the formation voids and carbides-free area. The high concentration of W in the alloy does not impair the corrosion resistance of the alloy obviously.
The oxidation process of a newly developed Ni-Cr-W alloy in air at 1100 °C has been investigated by varying the holding time. The microstructures and compositions of the surface scale as well as the oxide in cross-section were characterized by Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectrum (EDS). The phase identification of the surface scale was carried out using X-ray diffraction (XRD). Results show that in the initial stage of oxidation (<3 h) a single oxidation layer is formed on the alloy. Surface is mainly composed of Cr2O3. With prolonging of oxidation (>7 h), a NiCr2O4 layer with spinel structure grows out gradually in the outer layer of Cr2O3. Once the outer layer of the compact spinel is formed, the double multi-components layer NiCr2O4·Cr2O3 will further decelerate the oxidation rate of the alloy. The degradation of the alloy subsurface includes the inner oxidation of grain boundaries and the formation voids and carbides-free area. The high concentration of W in the alloy does not impair the corrosion resistance of the alloy obviously.
2010, 39(11):1912-1917.
Abstract:
Based on the meso- and micro-structure change and damage characteristic of Ni-based single crystal superalloys in the creep condition, a two-state-variable creep damage constitutive model considering simultaneously the rafting damage and void damage has been built. The model has been employed to investigate creep damage and crack initiation behaviour of the single crystal compact tension (CT) specimen containing a cylindrical void ahead of crack tip. The influence of the deviation and randomness of the crystallographic orientations has been considered. The analysis results have shown that creep damage and crack initiation behaviour depend strongly on the void location and crystallographic orientation. When the void is close to the notch root, a microcrack will initiate at the surface of the void in the vicinity of the notch. The time of crack initiation is short. But when the void is far from the notch root, the microcrack will initiate at the notch surface. The crack location is related to the crystallographic orientations, and the time of crack initiation is long. With increasing of the deviation of the axial crystallographic orientations of the single crystal CT specimen, the time of crack initiation is decreased obviously. The maximum amplitude variation is 34.7%. While the two uncontrolled crystallographic orientations of the CT specimens vary randomly, the time of crack initiation is longest in 45° and 80° deviations, and the maximum deviation of crack initiation time is up to 3 times.
Based on the meso- and micro-structure change and damage characteristic of Ni-based single crystal superalloys in the creep condition, a two-state-variable creep damage constitutive model considering simultaneously the rafting damage and void damage has been built. The model has been employed to investigate creep damage and crack initiation behaviour of the single crystal compact tension (CT) specimen containing a cylindrical void ahead of crack tip. The influence of the deviation and randomness of the crystallographic orientations has been considered. The analysis results have shown that creep damage and crack initiation behaviour depend strongly on the void location and crystallographic orientation. When the void is close to the notch root, a microcrack will initiate at the surface of the void in the vicinity of the notch. The time of crack initiation is short. But when the void is far from the notch root, the microcrack will initiate at the notch surface. The crack location is related to the crystallographic orientations, and the time of crack initiation is long. With increasing of the deviation of the axial crystallographic orientations of the single crystal CT specimen, the time of crack initiation is decreased obviously. The maximum amplitude variation is 34.7%. While the two uncontrolled crystallographic orientations of the CT specimens vary randomly, the time of crack initiation is longest in 45° and 80° deviations, and the maximum deviation of crack initiation time is up to 3 times.
2010, 39(11):1918-1922.
Abstract:
Microstructure and mechanical properties of Ti600 high-temperature after thermal exposure at 600 ℃ for different times were studied. The results show that there is only a little precipitation during thermal exposure, which are mainly silicides and a2 phases. During thermal exposure, the deterioration of plasticity for Ti600 alloy is mainly due to the precipitations of silicides and a2 phases, and in them, the formation of a2 phase play main role. For Ti600 high-temperature titanium alloy, the main decrease stage of plasticity is resulting from the coarsening of a2 phase during thermal exposure process.
Microstructure and mechanical properties of Ti600 high-temperature after thermal exposure at 600 ℃ for different times were studied. The results show that there is only a little precipitation during thermal exposure, which are mainly silicides and a2 phases. During thermal exposure, the deterioration of plasticity for Ti600 alloy is mainly due to the precipitations of silicides and a2 phases, and in them, the formation of a2 phase play main role. For Ti600 high-temperature titanium alloy, the main decrease stage of plasticity is resulting from the coarsening of a2 phase during thermal exposure process.
2010, 39(11):1923-1927.
Abstract:
The sound absorption performance of single layer metal rubber (MR) material was theoretically investigated. The formulae were deduced to calculate the acoustic impedance rate and sound absorption coefficient for two kinds of basic single-layer absorption structure in rigid wall and with air layer. The flow resistivity is the main parameter to determine the sound absorption performance of MR material. The influence of the thickness of MR layer, flow resistivity and thickness of the air layer on the sound absorption performance of the two kinds of structures was analyzed. The method for calculating first resonant frequency for single layer structure MR material was presented. The results indicate that the optimization of thickness of MR material, flow resistivity and the thickness of the air layer is helpful to improve the sound absorption performance of the single layer structure MR material.
The sound absorption performance of single layer metal rubber (MR) material was theoretically investigated. The formulae were deduced to calculate the acoustic impedance rate and sound absorption coefficient for two kinds of basic single-layer absorption structure in rigid wall and with air layer. The flow resistivity is the main parameter to determine the sound absorption performance of MR material. The influence of the thickness of MR layer, flow resistivity and thickness of the air layer on the sound absorption performance of the two kinds of structures was analyzed. The method for calculating first resonant frequency for single layer structure MR material was presented. The results indicate that the optimization of thickness of MR material, flow resistivity and the thickness of the air layer is helpful to improve the sound absorption performance of the single layer structure MR material.
2010, 39(11):1928-1932.
Abstract:
Nanocomposite Mo-4La2O3 (mass fraction) cathode was prepared by sol-gel method and hydrogen reduction process and then hot-pressing sintering technique. The microstructure of nanocomposite cathode is homogeneous and very fine; the lanthana particles are about 40-50 nm, while they are about 200-300 nm in the conventional Mo-4La2O3 cathode. The particle size of lanthana has a strong effect on the field electron emission ability of cathode. The nanocomposite cathode has superior field electron emission ability compared with that of the conventional cathode. The sites of field electron emission of the nanocomposite cathode nearly extend over the whole surface of cathode, whereas the emission sites of the conventional cathode concentrate on a small area of the cathode surface. By creating the electron interaction model between the metal and semiconductor, the relation curves between the tunneling probability of electrons in Mo and La2O3 and second phase size were calculated and plotted, respectively. The reasons that nanocompposite cathode has stronger electron emission performance were explained.
Nanocomposite Mo-4La2O3 (mass fraction) cathode was prepared by sol-gel method and hydrogen reduction process and then hot-pressing sintering technique. The microstructure of nanocomposite cathode is homogeneous and very fine; the lanthana particles are about 40-50 nm, while they are about 200-300 nm in the conventional Mo-4La2O3 cathode. The particle size of lanthana has a strong effect on the field electron emission ability of cathode. The nanocomposite cathode has superior field electron emission ability compared with that of the conventional cathode. The sites of field electron emission of the nanocomposite cathode nearly extend over the whole surface of cathode, whereas the emission sites of the conventional cathode concentrate on a small area of the cathode surface. By creating the electron interaction model between the metal and semiconductor, the relation curves between the tunneling probability of electrons in Mo and La2O3 and second phase size were calculated and plotted, respectively. The reasons that nanocompposite cathode has stronger electron emission performance were explained.
2010, 39(11):1933-1937.
Abstract:
The effects of Al content on microstructure and properties of Monel alloy were studied by OM, SEM, an electrochemistry method and a mass loss method. The results show that the area ratio of divorcing eutectic γ′ in the interdendritic area gradually becomes larger with increasing of Al content from 2% to 4% (mass fraction). The mechanism of corrosion in the simulative sea water is pit corrosion under the conditions of different Al contents. Meanwhile, as the Al content increases, the corrosion resistance of the alloy in the simulative sea water increases first but then decreases. The Monel alloy with 3% Al addition has the best corrosion resistance in the experimental range.
The effects of Al content on microstructure and properties of Monel alloy were studied by OM, SEM, an electrochemistry method and a mass loss method. The results show that the area ratio of divorcing eutectic γ′ in the interdendritic area gradually becomes larger with increasing of Al content from 2% to 4% (mass fraction). The mechanism of corrosion in the simulative sea water is pit corrosion under the conditions of different Al contents. Meanwhile, as the Al content increases, the corrosion resistance of the alloy in the simulative sea water increases first but then decreases. The Monel alloy with 3% Al addition has the best corrosion resistance in the experimental range.
2010, 39(11):1938-1942.
Abstract:
Ni-Cr-Al superalloys are widely used as sealing materials in new type aero-engines. Though Cr and Al contents can improve the resistance of high temperature oxidation and hot corrosion, it can affect the hot workability of alloys at the same time. The effects of Cr and Al contents (Cr, 15%-25%; Al, 4%-5%, mass fraction) on the hot workability were studied by isothermal compressive deformation at deformation temperatures of 1000 oC to 1200 oC and strain rates of 0.1, 1, 5 and 20 s-1. The results indicate that increasing of Cr or Al content can reduce the safe region of hot working to different extents. Equilibrium phase diagrams and microstructure observation show that the effects of Cr and Al contents on hot workability is mainly caused by the morphology and fraction differences of cellular carbide in grain boundary. Considering the hot workability, microstructure change and corrosion resistance at high temperature, it is concluded that 20%Cr and 4%Al is the best component for sealing materials of Ni based superalloys.
Ni-Cr-Al superalloys are widely used as sealing materials in new type aero-engines. Though Cr and Al contents can improve the resistance of high temperature oxidation and hot corrosion, it can affect the hot workability of alloys at the same time. The effects of Cr and Al contents (Cr, 15%-25%; Al, 4%-5%, mass fraction) on the hot workability were studied by isothermal compressive deformation at deformation temperatures of 1000 oC to 1200 oC and strain rates of 0.1, 1, 5 and 20 s-1. The results indicate that increasing of Cr or Al content can reduce the safe region of hot working to different extents. Equilibrium phase diagrams and microstructure observation show that the effects of Cr and Al contents on hot workability is mainly caused by the morphology and fraction differences of cellular carbide in grain boundary. Considering the hot workability, microstructure change and corrosion resistance at high temperature, it is concluded that 20%Cr and 4%Al is the best component for sealing materials of Ni based superalloys.
2010, 39(11):1943-1947.
Abstract:
The source voltage increment can influence the shape of arc spark and the thickness, surface morphology and corrosion rate of MAO coatings treated with silicate aqueous solution on AZ91D magnesium alloys. The results reveal that with the voltage increment of supply pulse increasing, the brightness and size of the arc sparks is increased but the amount is decreased accordingly, and the tendency of large arc discharge is intensified; the coating thickness is increased but the film growth rate is decreased; the surface melt grain, microspore size and surface roughness are increased; corrosion rate is first decreased and then increased. The comprehensive performances such as the process stability, film growth rate, coating appearance quality and corrosion resistance are relatively optimum when the voltage increment is within 100-150 V.
The source voltage increment can influence the shape of arc spark and the thickness, surface morphology and corrosion rate of MAO coatings treated with silicate aqueous solution on AZ91D magnesium alloys. The results reveal that with the voltage increment of supply pulse increasing, the brightness and size of the arc sparks is increased but the amount is decreased accordingly, and the tendency of large arc discharge is intensified; the coating thickness is increased but the film growth rate is decreased; the surface melt grain, microspore size and surface roughness are increased; corrosion rate is first decreased and then increased. The comprehensive performances such as the process stability, film growth rate, coating appearance quality and corrosion resistance are relatively optimum when the voltage increment is within 100-150 V.
2010, 39(11):1948-1951.
Abstract:
(La0.47Gd0.2)Sr0.33MnO3 nanoparticles were synthesized by an amorphous heteronuclear complexing method. The microstructure and magnetic properties of the synthesized nanoparticles were characterized by XRD, HRTEM and MPMS. XRD and selected area electron diffraction (SAD) analyses reveal that the products are of pure single-phase rhombohedral structure. TEM observation shows that the particle sizes of the products calcined at 600, 800 and 1000 oC for 10 h are about 40-50 nm, 90-100 nm and 140-150 nm, respectively. The Curie temperature TC (298 K) of the nanoparticles does not depend on the particle size, while the relative cooling power (RCP) is determined by the particle size. (La0.47Gd0.2)Sr0.33MnO3 with particle sizes ranging from 90 nm to 100 nm has the largest RCP, which may be a suitable candidate as working substance in magnetic refrigeration at room temperature.
(La0.47Gd0.2)Sr0.33MnO3 nanoparticles were synthesized by an amorphous heteronuclear complexing method. The microstructure and magnetic properties of the synthesized nanoparticles were characterized by XRD, HRTEM and MPMS. XRD and selected area electron diffraction (SAD) analyses reveal that the products are of pure single-phase rhombohedral structure. TEM observation shows that the particle sizes of the products calcined at 600, 800 and 1000 oC for 10 h are about 40-50 nm, 90-100 nm and 140-150 nm, respectively. The Curie temperature TC (298 K) of the nanoparticles does not depend on the particle size, while the relative cooling power (RCP) is determined by the particle size. (La0.47Gd0.2)Sr0.33MnO3 with particle sizes ranging from 90 nm to 100 nm has the largest RCP, which may be a suitable candidate as working substance in magnetic refrigeration at room temperature.
14 Photoinduced Characteristics of Mn Site Doped La0.7Ba0.3Mn0.95X0.05O3 (X=Mn, Cr, Fe, Co) Thin Films
2010, 39(11):1952-1955.
Abstract:
The compounds of La0.7Ba0.3Mn0.95X0.05O3 (X= Mn, Cr, Fe, Co) were prepared by a conventional solid reaction method and then their films were prepared on LaAlO3 single crystal substrate by a magnetron sputtering method. The effects of the Mn site doping of transition elements (Cr, Fe, Co) on the photoinduced properties of the La0.7Ba0.3MnO3 (LBMO) films were investigated. Results indicate that the transition element doping of Cr, Fe or Co causes a decrease of the insulator-metal transition temperature (Tp) and an increase of the maximum relative variation (LRmax) of resistivity and the photoinduced resistivity. Among them, Fe has the largest effect, Co comes second and Cr has the smallest. Laser induction has different influences on the resistivity of films in different temperature zones. In a low temperature zone (TTp) it is decreased. The intrinsic mechanism of the transport behavior and photoinduced properties was discussed in view of the electronic structure and lattice effect of Cr, Fe and Co.
The compounds of La0.7Ba0.3Mn0.95X0.05O3 (X= Mn, Cr, Fe, Co) were prepared by a conventional solid reaction method and then their films were prepared on LaAlO3 single crystal substrate by a magnetron sputtering method. The effects of the Mn site doping of transition elements (Cr, Fe, Co) on the photoinduced properties of the La0.7Ba0.3MnO3 (LBMO) films were investigated. Results indicate that the transition element doping of Cr, Fe or Co causes a decrease of the insulator-metal transition temperature (Tp) and an increase of the maximum relative variation (LRmax) of resistivity and the photoinduced resistivity. Among them, Fe has the largest effect, Co comes second and Cr has the smallest. Laser induction has different influences on the resistivity of films in different temperature zones. In a low temperature zone (T
2010, 39(11):1956-1959.
Abstract:
The phase transition rule of near-β Ti-3Zr-Mo-15Nb (TLE) medical titanium alloys was analyzed through DSC curves and XRD patterns; effects of the processing and the heat treatment on microstructure and mechanical properties of the TLE alloys was investigated by OM, TEM and tensile experiments. The results show that fine and equiaxed grains in the TLE alloy are formed after rolling in the (α+β) phase field and solution-treatment; quenching of the β phase filed results in the formation of a metastable martensitic structure α" (orthorhombic). After low-temperature aging, some of α" martensite is decomposed into α martensite; with the aging temperature increasing, α" martensite is absolutely decomposed into α martensite. When the aging temperature is 250 oC, high strength, low modulus and high plasticity of the alloy can match preferably with human bone. The microstructure observation of the alloy indicates that the interaction between a few α" orthorhombic martensite, α martensite and certain dislocation lead to lower elastic modulus and higher plasticity, while a lot of cross martensite which are fine and needle-like contribute greatly to biomechanical property.
The phase transition rule of near-β Ti-3Zr-Mo-15Nb (TLE) medical titanium alloys was analyzed through DSC curves and XRD patterns; effects of the processing and the heat treatment on microstructure and mechanical properties of the TLE alloys was investigated by OM, TEM and tensile experiments. The results show that fine and equiaxed grains in the TLE alloy are formed after rolling in the (α+β) phase field and solution-treatment; quenching of the β phase filed results in the formation of a metastable martensitic structure α" (orthorhombic). After low-temperature aging, some of α" martensite is decomposed into α martensite; with the aging temperature increasing, α" martensite is absolutely decomposed into α martensite. When the aging temperature is 250 oC, high strength, low modulus and high plasticity of the alloy can match preferably with human bone. The microstructure observation of the alloy indicates that the interaction between a few α" orthorhombic martensite, α martensite and certain dislocation lead to lower elastic modulus and higher plasticity, while a lot of cross martensite which are fine and needle-like contribute greatly to biomechanical property.
2010, 39(11):1960-1963.
Abstract:
The microstructure and phase structure of Zr57V36Fe7 alloy were investigated. Activation property of the Zr57V36Fe7 alloy was tested. Hydrogen absorption pressure composition temperature (P-C-T) property was investigated by a pressure reduction method at the temperatures ranging from 673 to 823 K. The results indicate that the microstructures of the alloy before hydrogen absorption are constituted of lath-shaped solid-solution grains and irregular lamellar eutectic structures. The dominant hydriding phases are ZrV2 phase and α-Zr phase. After hydrogen absorption the dominant phases are ZrH1.801 phase and V16Zr8H36.29 phase. The alloy can be fully activated by heating at 723 K for 1 h in vacuum followed by a hydrogen absorption and desorption cycle. P-C-T curve exhibits a wide and flat platform. The thermodynamic parameters of the reaction can be calculated using Van’t Hoff equation. The equilibrium hydrogen pressure can reach the level of 10-8 Pa at room temperature.
The microstructure and phase structure of Zr57V36Fe7 alloy were investigated. Activation property of the Zr57V36Fe7 alloy was tested. Hydrogen absorption pressure composition temperature (P-C-T) property was investigated by a pressure reduction method at the temperatures ranging from 673 to 823 K. The results indicate that the microstructures of the alloy before hydrogen absorption are constituted of lath-shaped solid-solution grains and irregular lamellar eutectic structures. The dominant hydriding phases are ZrV2 phase and α-Zr phase. After hydrogen absorption the dominant phases are ZrH1.801 phase and V16Zr8H36.29 phase. The alloy can be fully activated by heating at 723 K for 1 h in vacuum followed by a hydrogen absorption and desorption cycle. P-C-T curve exhibits a wide and flat platform. The thermodynamic parameters of the reaction can be calculated using Van’t Hoff equation. The equilibrium hydrogen pressure can reach the level of 10-8 Pa at room temperature.
2010, 39(11):1964-1969.
Abstract:
Direct diffusion bonding between TC4 titanium alloy and 1Cr18Ni9Ti stainless steel were implemented based on the superplastic diffusion bonding (SDB) method. The joint properties, interface microstructures and the mechanism of superplastic diffusion bonding were analyzed. The results show that for direct superplastic diffusion bonding of TC4 alloy to 1Cr18Ni9Ti stainless steel, the shear strength of TC4/1Cr18Ni9Ti joints is 125.3-148.7 MPa under optimal diffusion bonding conditions including the temperature of 760-820 oC, the bonding pressure of 6-9 MPa and the bonding time of 20-40 min. Compared with the conventional diffusion bonding, the bonding temperature can be reduced by about 100 oC while the shear strength of joints is increased by more than one time. And the bonding specimens have no distinct distortion. In the ultrafine superplastic diffusion bonding of TC4 alloy and 1Cr18Ni9Ti stainless steel, the formation process of the bonded joint can be divided into three stages: close contact forming, activation of contact surface and formation of interfacial metallurgy bonded zone nearby the activation center.
Direct diffusion bonding between TC4 titanium alloy and 1Cr18Ni9Ti stainless steel were implemented based on the superplastic diffusion bonding (SDB) method. The joint properties, interface microstructures and the mechanism of superplastic diffusion bonding were analyzed. The results show that for direct superplastic diffusion bonding of TC4 alloy to 1Cr18Ni9Ti stainless steel, the shear strength of TC4/1Cr18Ni9Ti joints is 125.3-148.7 MPa under optimal diffusion bonding conditions including the temperature of 760-820 oC, the bonding pressure of 6-9 MPa and the bonding time of 20-40 min. Compared with the conventional diffusion bonding, the bonding temperature can be reduced by about 100 oC while the shear strength of joints is increased by more than one time. And the bonding specimens have no distinct distortion. In the ultrafine superplastic diffusion bonding of TC4 alloy and 1Cr18Ni9Ti stainless steel, the formation process of the bonded joint can be divided into three stages: close contact forming, activation of contact surface and formation of interfacial metallurgy bonded zone nearby the activation center.
2010, 39(11):1970-1973.
Abstract:
Based on the microscopic phase-field theory, the calculation model of the first nearest neighbor effective interchange interaction potential (w1) for DO22 phase was deduced according to the formula for the relation of occupation probability and free energy by Khachaturyan. The temperature of phase transition and atomic concentration were required in this model. Then the first nearest neighbor effective interchange interaction potentials of Ni3V-DO22 phase were obtained. The inversion calculation of Ni3V-DO22 indicates that with the temperature or atomic concentration increasing, w1 increases. If the w1 changed with temperature and atomic concentration is put into microscopic phase-field equation, the dependence on temperature and atomic concentration is more obvious for the structure of the atomic temporal evolution.
Based on the microscopic phase-field theory, the calculation model of the first nearest neighbor effective interchange interaction potential (w1) for DO22 phase was deduced according to the formula for the relation of occupation probability and free energy by Khachaturyan. The temperature of phase transition and atomic concentration were required in this model. Then the first nearest neighbor effective interchange interaction potentials of Ni3V-DO22 phase were obtained. The inversion calculation of Ni3V-DO22 indicates that with the temperature or atomic concentration increasing, w1 increases. If the w1 changed with temperature and atomic concentration is put into microscopic phase-field equation, the dependence on temperature and atomic concentration is more obvious for the structure of the atomic temporal evolution.
2010, 39(11):1974-1978.
Abstract:
Based on the Miedema formation enthalpy model, thermodynamic properties of Al-Er, Si-Er and Al-Si binary alloy were calculated, and Er was chosen as the asymmetric component in asymmetric model. Combining with Toop model, the enthalpies of formation, excess entropies and excess free-energy of Al-Si-Er ternary alloy were calculated. The results show that the enthalpies of formation, excess entropies and excess free-energy of the ternary alloy are all negative in the whole content range, and their values change obviously in the zone where the content of Er is high or low. Through calculating partial molar excess Gibbs energy of three components (Al, Si, Er), isoactivity curves of all components of Al-Si-Er ternary alloy at 1073 K were obtained. The curves show that these values of all components of Al-Si-Er ternary alloy decreased dramatically along with the diminishing of molar fraction, and these activity values of Al, Si and Er were slight in the central zone of composition triangle of ternary system. It indicates that there was strong interaction among the three components, and they were easy to form ternary intermetalic compound, which coincided with the ternary phase diagram.
Based on the Miedema formation enthalpy model, thermodynamic properties of Al-Er, Si-Er and Al-Si binary alloy were calculated, and Er was chosen as the asymmetric component in asymmetric model. Combining with Toop model, the enthalpies of formation, excess entropies and excess free-energy of Al-Si-Er ternary alloy were calculated. The results show that the enthalpies of formation, excess entropies and excess free-energy of the ternary alloy are all negative in the whole content range, and their values change obviously in the zone where the content of Er is high or low. Through calculating partial molar excess Gibbs energy of three components (Al, Si, Er), isoactivity curves of all components of Al-Si-Er ternary alloy at 1073 K were obtained. The curves show that these values of all components of Al-Si-Er ternary alloy decreased dramatically along with the diminishing of molar fraction, and these activity values of Al, Si and Er were slight in the central zone of composition triangle of ternary system. It indicates that there was strong interaction among the three components, and they were easy to form ternary intermetalic compound, which coincided with the ternary phase diagram.
2010, 39(11):1979-1983.
Abstract:
For an optimized formula of the cementing agent good for formation, the viscosity and rheological properties of 93W-Ni-Fe PEM feeds with the same powder loading but four kinds of binder composition systems which were called A, B, C and D feedstocks were studied. By the British AR2000EX rotary rheometer, the viscosity of the tungsten-based alloy PEM feed at different shear rates and different temperatures were measured. The results indicate that among the four feedstocks, A has a low viscosity and good flow properties. The rheological properties of D feed are the most unstable. According to their relationship curves between viscosity and shear rate at the 130 oC, the shear-thinning index of A, B and C feeds can be calculated as 0.048, –0.869 and –1.717, respectively. According to the relationship curves between viscosity and temperature at the shear-rate of 11.07 s-1, the flow activation energy of A, B and C feeds can be calculated as 8.524, 8.107 and 31.310 kJ·mol-1, respectively. Through simulation, at 130 oC and the shear-rate of 11.07 s-1, the liquidity index of A, B and C feeds is 7.2×10-6, 4.8×10-6 and 1.1×10-6, respectively. The comprehensive rheological performance of A feed is the best.
For an optimized formula of the cementing agent good for formation, the viscosity and rheological properties of 93W-Ni-Fe PEM feeds with the same powder loading but four kinds of binder composition systems which were called A, B, C and D feedstocks were studied. By the British AR2000EX rotary rheometer, the viscosity of the tungsten-based alloy PEM feed at different shear rates and different temperatures were measured. The results indicate that among the four feedstocks, A has a low viscosity and good flow properties. The rheological properties of D feed are the most unstable. According to their relationship curves between viscosity and shear rate at the 130 oC, the shear-thinning index of A, B and C feeds can be calculated as 0.048, –0.869 and –1.717, respectively. According to the relationship curves between viscosity and temperature at the shear-rate of 11.07 s-1, the flow activation energy of A, B and C feeds can be calculated as 8.524, 8.107 and 31.310 kJ·mol-1, respectively. Through simulation, at 130 oC and the shear-rate of 11.07 s-1, the liquidity index of A, B and C feeds is 7.2×10-6, 4.8×10-6 and 1.1×10-6, respectively. The comprehensive rheological performance of A feed is the best.
2010, 39(11):1984-1988.
Abstract:
The in vivo bone-regenerative capacity of porous calcium acid phosphate cement (CPC) and titanium alloy scaffold with controlled porous structure were investigated in rabbit calvarial defect models. The results show that the bone-regenerative capacity of porous CPC is much better than that of porous titanium alloy scaffold. Porous CPC exhibits more bone formation and higher mineralization appositional rate than porous titanium scaffold. Moreover, bone remolding of porous CPC is in earlier stage than that of porous titanium alloy scaffold. On the other hand, highly three-dimensional interconnected porous structure is beneficial for the growth of bone tissue. The mechanical properties of titanium alloy can be adapted to those of biological systems by applying a porous structure, which may enhance the integration process and improve implant fixation in earlier stage.
The in vivo bone-regenerative capacity of porous calcium acid phosphate cement (CPC) and titanium alloy scaffold with controlled porous structure were investigated in rabbit calvarial defect models. The results show that the bone-regenerative capacity of porous CPC is much better than that of porous titanium alloy scaffold. Porous CPC exhibits more bone formation and higher mineralization appositional rate than porous titanium scaffold. Moreover, bone remolding of porous CPC is in earlier stage than that of porous titanium alloy scaffold. On the other hand, highly three-dimensional interconnected porous structure is beneficial for the growth of bone tissue. The mechanical properties of titanium alloy can be adapted to those of biological systems by applying a porous structure, which may enhance the integration process and improve implant fixation in earlier stage.
2010, 39(11):1989-1992.
Abstract:
Ni56Fe19Al25 alloys were prepared by powder metallurgy from mixing elementary and pre-alloyed Ni, Fe and Al powder. The alloys were sintered at 1280 oC after shaping under 500 MPa, and then quenched in water. The sintered and quenched alloys were studied by X-ray diffraction (XRD) and tensile strength measurement. The results show that the as-sintered Ni56Fe19Al25 alloy is of (β+γ) dual-phase, and the as-quenched alloy is of (β′+γ) dual-phase. The as-quenched Ni-Fe-Al alloy under stress presents good linear super-elasticity; the tensile strength is 850 MPa, the total deformation amount before fracture reaches to 9.2%, and the largest elastic deformation is over 4.5%.
Ni56Fe19Al25 alloys were prepared by powder metallurgy from mixing elementary and pre-alloyed Ni, Fe and Al powder. The alloys were sintered at 1280 oC after shaping under 500 MPa, and then quenched in water. The sintered and quenched alloys were studied by X-ray diffraction (XRD) and tensile strength measurement. The results show that the as-sintered Ni56Fe19Al25 alloy is of (β+γ) dual-phase, and the as-quenched alloy is of (β′+γ) dual-phase. The as-quenched Ni-Fe-Al alloy under stress presents good linear super-elasticity; the tensile strength is 850 MPa, the total deformation amount before fracture reaches to 9.2%, and the largest elastic deformation is over 4.5%.
2010, 39(11):1993-1996.
Abstract:
The flow behavior and hot deformation microstructure evolution of the 9Cr-2W heat-resistant alloy were investigated at 1000-1300 oC and strain rates of 0.005-0.5 s-1 by a hot compression test. And the textures of hot upsetting samples were determined. Characteristics of stress-strain curves of the alloy deformed in the test parameter range were analyzed. The important parameters, such as stress exponent and deformation activation energy were obtained by the kinetic equation. Results of microstructure observation and texture tests indicate that the microstructure evolution mechanism of the 9Cr-2W heat-resistant alloy is dynamic recovery accompanied by geometric dynamic recrystallization. The alloy can be produced at a higher temperature in order to reduce the flow stress and to improve the anisotropy in the practical production.
The flow behavior and hot deformation microstructure evolution of the 9Cr-2W heat-resistant alloy were investigated at 1000-1300 oC and strain rates of 0.005-0.5 s-1 by a hot compression test. And the textures of hot upsetting samples were determined. Characteristics of stress-strain curves of the alloy deformed in the test parameter range were analyzed. The important parameters, such as stress exponent and deformation activation energy were obtained by the kinetic equation. Results of microstructure observation and texture tests indicate that the microstructure evolution mechanism of the 9Cr-2W heat-resistant alloy is dynamic recovery accompanied by geometric dynamic recrystallization. The alloy can be produced at a higher temperature in order to reduce the flow stress and to improve the anisotropy in the practical production.
2010, 39(11):1997-2002.
Abstract:
The corrosion behavior of electroplastic rolled (ER) AZ31 magnesium alloys subjected to high energy electric pulse treating (EPT) and conventional heat treating (CHT) respectively in 3.5%NaCl solution (mass fraction) were investigated using potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), corrosion morphology observation and corrosion rate measurement. The results indicate that the corrosion resistance of the as-ER alloys is enhanced by EPT or CHT, which is attributed to complete recrystallization and lower dislocation density after treatments. Compared with CHT, the EPT process can increase mechanical properties of materials more significantly, but it is not good at the corrosion resistance improvement, which may result from more corrosion micro-cells caused by finer grains.
The corrosion behavior of electroplastic rolled (ER) AZ31 magnesium alloys subjected to high energy electric pulse treating (EPT) and conventional heat treating (CHT) respectively in 3.5%NaCl solution (mass fraction) were investigated using potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), corrosion morphology observation and corrosion rate measurement. The results indicate that the corrosion resistance of the as-ER alloys is enhanced by EPT or CHT, which is attributed to complete recrystallization and lower dislocation density after treatments. Compared with CHT, the EPT process can increase mechanical properties of materials more significantly, but it is not good at the corrosion resistance improvement, which may result from more corrosion micro-cells caused by finer grains.
25 Influence of Heat Treatment on YBCO Superconducting Films Prepared by a Fluorine-Free PA-MOD Method
2010, 39(11):2003-2006.
Abstract:
YBCO superconducting films with Tc of 90 K were prepared via fluorine-free polymer-assisted metal organic deposition (PA-MOD) on (001) LaAlO3 single crystal substrate. The influence of different firing temperatures and gas humidities during high-temperature heat treatment was investigated to fabricate high performance YBCO films. The degree of biaxial texture for the films by different heat treatments was analyzed by X-ray diffraction θ-2θ scan, ω scan and φ scan. Surface morphologies were studied by scanning electron microscopy (SEM). Magnetic moment versus temperature curves and magnetic hysteresis loops were measured by Quantum-Design SQUID XL (7 T). The results show that the YBCO film fired at 770 oC in dry gas has excellent biaxial texture as well as smooth and dense surface morphology. The YBCO film prepared by this optimized treatment has critical current density Jc of 2 MA/cm2 (77 K, self-field) which is 1.7 to 6.7 times of that for YBCO films by other heat treatments.
YBCO superconducting films with Tc of 90 K were prepared via fluorine-free polymer-assisted metal organic deposition (PA-MOD) on (001) LaAlO3 single crystal substrate. The influence of different firing temperatures and gas humidities during high-temperature heat treatment was investigated to fabricate high performance YBCO films. The degree of biaxial texture for the films by different heat treatments was analyzed by X-ray diffraction θ-2θ scan, ω scan and φ scan. Surface morphologies were studied by scanning electron microscopy (SEM). Magnetic moment versus temperature curves and magnetic hysteresis loops were measured by Quantum-Design SQUID XL (7 T). The results show that the YBCO film fired at 770 oC in dry gas has excellent biaxial texture as well as smooth and dense surface morphology. The YBCO film prepared by this optimized treatment has critical current density Jc of 2 MA/cm2 (77 K, self-field) which is 1.7 to 6.7 times of that for YBCO films by other heat treatments.
2010, 39(11):2007-2010.
Abstract:
A bulk nanoporous copper with thickness of 1 mm was fabricated from freely corroded Cu0.3Mn0.7 alloy by means of dealloying. The phases and microstructure of samples were analyzed by XRD, FESEM, EDS and AAS. The results indicate the nanoporous copper with a uniform monolithic structure in three-dimension can be created by free-corrosion dealloying Cu0.3Mn0.7 alloy in 0.1 mol/L HCl solution for 10 d, with an average surface pore diameter of 125 nm and an average ligament size of 80 nm, also with an average cross section pore diameter of 300 nm.
A bulk nanoporous copper with thickness of 1 mm was fabricated from freely corroded Cu0.3Mn0.7 alloy by means of dealloying. The phases and microstructure of samples were analyzed by XRD, FESEM, EDS and AAS. The results indicate the nanoporous copper with a uniform monolithic structure in three-dimension can be created by free-corrosion dealloying Cu0.3Mn0.7 alloy in 0.1 mol/L HCl solution for 10 d, with an average surface pore diameter of 125 nm and an average ligament size of 80 nm, also with an average cross section pore diameter of 300 nm.
2010, 39(11):2011-2014.
Abstract:
Nanoporous copper with nano-scale pore size was synthesized by dealloying Mn-Cu alloy using a free corrosion method in acid solution. The effect of dealloying parameters, which include the electrolyte component, temperature and time of dealloying, on the residual Mn content and micro-morphology of nanoporous Cu was investigated. The results show that the nanoporous copper with a uniform three-dimensional pore structure can be created by dealloying in 0.1 mol/L HCl solution. The pore shape grows from honeycombs to three-dimensional networks with prolonging the corrosion time from 2 d to 5 d. Then with the continually increased corrosion time, the pore wall becomes coarse gradually. By increasing the temperature of the electrolyte to 60 oC, the residual Mn content is reduced obviously. The resultant nanoporous copper possesses uniform porous structures in three-dimensional network, the porosity of 57.7%, and the average pore size of 140 nm
Nanoporous copper with nano-scale pore size was synthesized by dealloying Mn-Cu alloy using a free corrosion method in acid solution. The effect of dealloying parameters, which include the electrolyte component, temperature and time of dealloying, on the residual Mn content and micro-morphology of nanoporous Cu was investigated. The results show that the nanoporous copper with a uniform three-dimensional pore structure can be created by dealloying in 0.1 mol/L HCl solution. The pore shape grows from honeycombs to three-dimensional networks with prolonging the corrosion time from 2 d to 5 d. Then with the continually increased corrosion time, the pore wall becomes coarse gradually. By increasing the temperature of the electrolyte to 60 oC, the residual Mn content is reduced obviously. The resultant nanoporous copper possesses uniform porous structures in three-dimensional network, the porosity of 57.7%, and the average pore size of 140 nm
2010, 39(11):2015-2017.
Abstract:
The porous niobium-based materials with high strength and excellent biocompatibility were prepared by a novel foam impregnating process using polyurethane foam as the support. The porosity, microstructure and mechanical properties were characterized by XRD, SEM and so on. Results show that there are three-dimensional connected pore structure and pure phase in the prepared porous niobium-based materials. The porosity, pore size and average density is 71.4%, 500 μm and 2.45 g/cm3, respectively. The average elastic modulus of three-dimensional connected porous Nb is 815 MPa and the average compressive strength is 36.62 MPa, which coincide with cancellous bone in mechanical properties.
The porous niobium-based materials with high strength and excellent biocompatibility were prepared by a novel foam impregnating process using polyurethane foam as the support. The porosity, microstructure and mechanical properties were characterized by XRD, SEM and so on. Results show that there are three-dimensional connected pore structure and pure phase in the prepared porous niobium-based materials. The porosity, pore size and average density is 71.4%, 500 μm and 2.45 g/cm3, respectively. The average elastic modulus of three-dimensional connected porous Nb is 815 MPa and the average compressive strength is 36.62 MPa, which coincide with cancellous bone in mechanical properties.
2010, 39(11):2018-2022.
Abstract:
Conductive fiber was prepared by coating antimony-doped tin oxide (ATO) on silicon dioxide glass fiber using a heterogeneous nucleation method. The varying trend of resistivity with the calcination temperature of the ATO-coated silicon dioxide fiber was almost the same as that of the pure ATO. The resistivities of the ATO-coated silicon dioxide fibers with the coating amounts of 100%, 75%, 50%, 25%, and 12.5% and treated at 500-1200 oC were all below 200 Ω·cm. As the conductive additive, the ATO-coated silicon dioxide fiber can maximally save the ATO amount because of the bridge effect resulting from its high aspect ratio, which makes it possible to form a more completed conductive net in the ceramics for a small quantity of conductive fibers. For instance, about 77.8% of ATO amount can be saved when the ATO-coated silicon dioxide fibers with 12.5% coating material are used as conductive filler.
Conductive fiber was prepared by coating antimony-doped tin oxide (ATO) on silicon dioxide glass fiber using a heterogeneous nucleation method. The varying trend of resistivity with the calcination temperature of the ATO-coated silicon dioxide fiber was almost the same as that of the pure ATO. The resistivities of the ATO-coated silicon dioxide fibers with the coating amounts of 100%, 75%, 50%, 25%, and 12.5% and treated at 500-1200 oC were all below 200 Ω·cm. As the conductive additive, the ATO-coated silicon dioxide fiber can maximally save the ATO amount because of the bridge effect resulting from its high aspect ratio, which makes it possible to form a more completed conductive net in the ceramics for a small quantity of conductive fibers. For instance, about 77.8% of ATO amount can be saved when the ATO-coated silicon dioxide fibers with 12.5% coating material are used as conductive filler.
2010, 39(11):2023-2026.
Abstract:
Microstructures and electrochemical properties of the as-cast (Ti0.65Zr0.35)1.10(V0.5Mn0.3Cr0.4Ni0.8)Bx (x=0, 0.01, 0.05, 0.1, 0.2) alloys were analyzed by X-ray diffraction, scanning electron microscope, X-ray energy dispersive spectrum and electrochemical testing. The results show that VB phase appeared in the as-cast alloys when boron was added. Claviform VB phase is not an absorption phase. With the increase of boron addition, the activation property, the cycle stability and the high rate discharging performance are improved, and the reversible discharge capacity is decreased. Analyses show that the claviform VB phase increases the diffusion channels of hydrogen ion in the alloys. Furthermore, it increases the phase interface, and decreases the grain stress in the process of charging and discharging in alloy electrodes. Reaction resistance of the alloy electrode is decreased with boron addition increasing, and the rate property and cycle stability are optimized obviously.
Microstructures and electrochemical properties of the as-cast (Ti0.65Zr0.35)1.10(V0.5Mn0.3Cr0.4Ni0.8)Bx (x=0, 0.01, 0.05, 0.1, 0.2) alloys were analyzed by X-ray diffraction, scanning electron microscope, X-ray energy dispersive spectrum and electrochemical testing. The results show that VB phase appeared in the as-cast alloys when boron was added. Claviform VB phase is not an absorption phase. With the increase of boron addition, the activation property, the cycle stability and the high rate discharging performance are improved, and the reversible discharge capacity is decreased. Analyses show that the claviform VB phase increases the diffusion channels of hydrogen ion in the alloys. Furthermore, it increases the phase interface, and decreases the grain stress in the process of charging and discharging in alloy electrodes. Reaction resistance of the alloy electrode is decreased with boron addition increasing, and the rate property and cycle stability are optimized obviously.
2010, 39(11):2027-2029.
Abstract:
High quality MCrAlY coatings were deposited by a high velocity oxy-fuel (HVOF) spraying process as a substitute for low pressure plasma spraying (LPPS). A kerosene-driven HVOF system K2 was used with NiCoCrAlTaReSiY as powder lot. The influences of the nozzle length and spraying parameters on the deposition process and coating properties were studied. The coating porosity and oxygen content were determined. The microstructure of the coating after vacuum heat treatment and high-temperature oxidation in air was observed. The distribution of Al and O in the coating was measured. The result shows that the obtained NiCoCrAlTaReSiY coatings have excellent oxidation resistance.
High quality MCrAlY coatings were deposited by a high velocity oxy-fuel (HVOF) spraying process as a substitute for low pressure plasma spraying (LPPS). A kerosene-driven HVOF system K2 was used with NiCoCrAlTaReSiY as powder lot. The influences of the nozzle length and spraying parameters on the deposition process and coating properties were studied. The coating porosity and oxygen content were determined. The microstructure of the coating after vacuum heat treatment and high-temperature oxidation in air was observed. The distribution of Al and O in the coating was measured. The result shows that the obtained NiCoCrAlTaReSiY coatings have excellent oxidation resistance.
2010, 39(11):2030-2034.
Abstract:
TiO2-coated SiO2 (TiO2-SiO2) particles were prepared by a layer-by-layer assembly technique using TiCl4 as a precursor. Then PEG2000 was added in the particles. Effects of PEG2000 on the formation and photocatalytic activity of TiO2-SiO2 were studied. The results show that the amount of TiO2 on the surface of the particles was increased with more coating layers. With PEG addition to the precursor solution, many fine pores in the particles appeared among the TiO2 particles and the surface area of TiO2-SiO2 was increased. The mixed crystalline phases of anatase and rutile were synthesized by 550 oC calcination, and the relative content of anatase phase increased with increasing of PEG2000 amount. The catalytic activity of PEG2000-added TiO2-SiO2 was higher than that of TiO2-SiO2 without addition.
TiO2-coated SiO2 (TiO2-SiO2) particles were prepared by a layer-by-layer assembly technique using TiCl4 as a precursor. Then PEG2000 was added in the particles. Effects of PEG2000 on the formation and photocatalytic activity of TiO2-SiO2 were studied. The results show that the amount of TiO2 on the surface of the particles was increased with more coating layers. With PEG addition to the precursor solution, many fine pores in the particles appeared among the TiO2 particles and the surface area of TiO2-SiO2 was increased. The mixed crystalline phases of anatase and rutile were synthesized by 550 oC calcination, and the relative content of anatase phase increased with increasing of PEG2000 amount. The catalytic activity of PEG2000-added TiO2-SiO2 was higher than that of TiO2-SiO2 without addition.
2010, 39(11):2035-2038.
Abstract:
The preparation process of one dimensional nanostructure Pb(Zr0.52Ti0.48)O3 (PZT) using sol-gel dipping of anodized aluminium oxide (AAO) template was studied. Results show with zirconium oxynitrate, lead acetate and tetrabutyl titanate as raw materials (Zr:Pb:Ti=0.52:1:0.48) and ethylene glycol as solvent, stable and lasting PZT sol was obtained. Then the sol was injected into the hard template followed by the crystallization step at 650 oCo and corrosion of AAO; finally the PZT nanotubes were prepared. The characterization results shows the PZT nanotubes products are perovskite, with structurally integrated surface, uniform aperture and ordered arrangement, and their length is 50μm, the diameter 300 nm and the thickness 40 nm.
The preparation process of one dimensional nanostructure Pb(Zr0.52Ti0.48)O3 (PZT) using sol-gel dipping of anodized aluminium oxide (AAO) template was studied. Results show with zirconium oxynitrate, lead acetate and tetrabutyl titanate as raw materials (Zr:Pb:Ti=0.52:1:0.48) and ethylene glycol as solvent, stable and lasting PZT sol was obtained. Then the sol was injected into the hard template followed by the crystallization step at 650 oCo and corrosion of AAO; finally the PZT nanotubes were prepared. The characterization results shows the PZT nanotubes products are perovskite, with structurally integrated surface, uniform aperture and ordered arrangement, and their length is 50μm, the diameter 300 nm and the thickness 40 nm.
2010, 39(11):2039-2043.
Abstract:
The electroless nickel plating of as-cast AM60B magnesium alloy was carried out using NiCO3·3Ni(OH)2·4H2O as main salt and sodium hypophosphite as reductant. The influence of pH value on the microstructure, microhardness and electrochemical properties of the electroless Ni plating was studied using X-ray diffractometer (XRD), microhardness device, metallograph and electrochemical station. The results show that the deposition rate of the electroless Ni plating increases when the pH value increases from 6.0 to 7.0. The electroless coating is composed of cell structures. When the pH is 6.5, the electroless Ni coating is compact and the particle is smallest. The microhardness and the P content are reduced with the pH value increasing from 6.0 to 7.0. When the pH value is 6.0, the microhardness HV is highest and gets to 5400 MPa. At the three pH values, the electroless Ni coating is integrated; the main peak of Ni is wider, while there are nearly no second or third peaks. When the pH value is 6.5, the corrosion electric potential of plating is up to –0. 90 V, and the corrosion resistance is best.
The electroless nickel plating of as-cast AM60B magnesium alloy was carried out using NiCO3·3Ni(OH)2·4H2O as main salt and sodium hypophosphite as reductant. The influence of pH value on the microstructure, microhardness and electrochemical properties of the electroless Ni plating was studied using X-ray diffractometer (XRD), microhardness device, metallograph and electrochemical station. The results show that the deposition rate of the electroless Ni plating increases when the pH value increases from 6.0 to 7.0. The electroless coating is composed of cell structures. When the pH is 6.5, the electroless Ni coating is compact and the particle is smallest. The microhardness and the P content are reduced with the pH value increasing from 6.0 to 7.0. When the pH value is 6.0, the microhardness HV is highest and gets to 5400 MPa. At the three pH values, the electroless Ni coating is integrated; the main peak of Ni is wider, while there are nearly no second or third peaks. When the pH value is 6.5, the corrosion electric potential of plating is up to –0. 90 V, and the corrosion resistance is best.
2010, 39(11):2044-2047.
Abstract:
Diffusion bonding was carried out between titanium alloy (TC4) and oxygen free copper (OFC) in vacuum and good transition joints were formed. The microstructure and elements’ composition were characterized by XRD, SEM and EDX. The tensile strength of the welding joint was measured. The results show that with the welding temperature increasing, the tensile strength of the welding joint increased first and then decreased. Thus the optimum welding parameters were 800 °C , 5 MPa and 30 min. The interdiffused layer with gradually varied element composition was formed at the interface of TC4/OFC welding joint. Cu3Ti2, Cu4Ti3, CuTi and Cu4Ti were formed at the interface of titanium and copper. The fracture morphology indicates that the fracture mainly took place at the weak bond of TC4/OFC interface. And the pores at the joints and species and thickness of the intermetallics played an important role in the bond strength of TC4/OFC.
Diffusion bonding was carried out between titanium alloy (TC4) and oxygen free copper (OFC) in vacuum and good transition joints were formed. The microstructure and elements’ composition were characterized by XRD, SEM and EDX. The tensile strength of the welding joint was measured. The results show that with the welding temperature increasing, the tensile strength of the welding joint increased first and then decreased. Thus the optimum welding parameters were 800 °C , 5 MPa and 30 min. The interdiffused layer with gradually varied element composition was formed at the interface of TC4/OFC welding joint. Cu3Ti2, Cu4Ti3, CuTi and Cu4Ti were formed at the interface of titanium and copper. The fracture morphology indicates that the fracture mainly took place at the weak bond of TC4/OFC interface. And the pores at the joints and species and thickness of the intermetallics played an important role in the bond strength of TC4/OFC.
2010, 39(11):2048-2050.
Abstract:
The electrochemical behaviors of AZ magnesium alloys in 1.0 mol/L Mg(ClO4)2 solution were investigated by mass loss, linear sweep voltammetry (LSV), electrochemical impedance spectroscopy and chronopotentiometry, in order to examine their performances as negative electrode material in magnesium battery. The results of immersion and LSV show that the self-corrosion rate of AZ21 is larger than that of AZ31 and AZ61; AZ21 and AZ31 are more active than AZ61, exhibiting less anode polarization and negative open circuit potential. The EIS show Rct of AZ21, AZ31 and AZ61 magnesium alloys gradually increase. In the discharging experiment, the discharge potential of AZ31 is negative and stable. The anodic current efficiency of AZ31 is 82%, higher than that of AZ21 and AZ61 magnesium alloys. The delay time of AZ31 is 2 s, shorter than that of the AZ21 and AZ61. Thus, the AZ31 magnesium alloy is more excellent as anodic material of Mg battery.
The electrochemical behaviors of AZ magnesium alloys in 1.0 mol/L Mg(ClO4)2 solution were investigated by mass loss, linear sweep voltammetry (LSV), electrochemical impedance spectroscopy and chronopotentiometry, in order to examine their performances as negative electrode material in magnesium battery. The results of immersion and LSV show that the self-corrosion rate of AZ21 is larger than that of AZ31 and AZ61; AZ21 and AZ31 are more active than AZ61, exhibiting less anode polarization and negative open circuit potential. The EIS show Rct of AZ21, AZ31 and AZ61 magnesium alloys gradually increase. In the discharging experiment, the discharge potential of AZ31 is negative and stable. The anodic current efficiency of AZ31 is 82%, higher than that of AZ21 and AZ61 magnesium alloys. The delay time of AZ31 is 2 s, shorter than that of the AZ21 and AZ61. Thus, the AZ31 magnesium alloy is more excellent as anodic material of Mg battery.
2010, 39(11):2051-2054.
Abstract:
The sodium titanate nanorods were synthesized via hydrothermal reaction in NaOH solution. Then the Li-Ti-O compound nanorods were prepared by a molten salt method in molten LiNO3, which was involved in the ion-exchange process, and by calcination at 400-700 oC in air. It is found that Li-Ti-O compound was of nanorod morphology and underwent a phase transition to a mixture of Li-poor anatase LixTiO2 and spinel Li4Ti5O12. The electrochemical lithium storage property was tested by constant current charge/discharge. Results demonstrate that the Li-Ti-O compound nanorods calcined at 600 oC have excellent specific capacity, good reversibility and high rate discharge capability.
The sodium titanate nanorods were synthesized via hydrothermal reaction in NaOH solution. Then the Li-Ti-O compound nanorods were prepared by a molten salt method in molten LiNO3, which was involved in the ion-exchange process, and by calcination at 400-700 oC in air. It is found that Li-Ti-O compound was of nanorod morphology and underwent a phase transition to a mixture of Li-poor anatase LixTiO2 and spinel Li4Ti5O12. The electrochemical lithium storage property was tested by constant current charge/discharge. Results demonstrate that the Li-Ti-O compound nanorods calcined at 600 oC have excellent specific capacity, good reversibility and high rate discharge capability.
2010, 39(11):2055-2058.
Abstract:
The Ti/Sn-Sb anode doped with Ce was prepared by an electro-deposition and thermal oxidation method. The microstructure and morphology of the anode were examined by SEM, EMPA and XRD, and its catalytic selectivity was studied by potentiodynamic polarization and cyclic voltammetry. The result shows that the anode coating has a compact texture, whose oxide distributes uniformly with a complete coverage of the Ti matrix. Electrochemical performance test shows that the anode has high oxygen evolution potential and good catalysis for the oxidative degradation of phenol. In the simulative test of phenol degradation, the removal rates of phenol and COD (chemical oxygen demand) reach 100% and 97.7%, respectively. Therefore, the Ti/Sn-Sb anode doped with Ce possesses high ability of removing the phenol in waste water.
The Ti/Sn-Sb anode doped with Ce was prepared by an electro-deposition and thermal oxidation method. The microstructure and morphology of the anode were examined by SEM, EMPA and XRD, and its catalytic selectivity was studied by potentiodynamic polarization and cyclic voltammetry. The result shows that the anode coating has a compact texture, whose oxide distributes uniformly with a complete coverage of the Ti matrix. Electrochemical performance test shows that the anode has high oxygen evolution potential and good catalysis for the oxidative degradation of phenol. In the simulative test of phenol degradation, the removal rates of phenol and COD (chemical oxygen demand) reach 100% and 97.7%, respectively. Therefore, the Ti/Sn-Sb anode doped with Ce possesses high ability of removing the phenol in waste water.
2010, 39(11):2059-2063.
Abstract:
Iridium (Ir) is one of the most potential oxidation-resistant and thermal shock-resistant materials for carbon/carbon composites above 1800 oC in aerospace field. In this work, the current status of research of Ir coatings is reviewed. The main preparation methods, physical vapor deposition, metalorganic chemical vapor deposition, melting salt electroformed deposition and double-glow plasma deposition for the oxidation-resistant and thermal shock-resistant Ir coatings, are introduced. The interlayer between Ir coating and carbon/carbon composites which can increase bonding strength and match thermal stress is studied. The summary of engine test of Ir coatings is presented. The influencing factors of service time of Ir coatings are discussed. The practical techniques to prepare Ir coatings in China are put forward.
Iridium (Ir) is one of the most potential oxidation-resistant and thermal shock-resistant materials for carbon/carbon composites above 1800 oC in aerospace field. In this work, the current status of research of Ir coatings is reviewed. The main preparation methods, physical vapor deposition, metalorganic chemical vapor deposition, melting salt electroformed deposition and double-glow plasma deposition for the oxidation-resistant and thermal shock-resistant Ir coatings, are introduced. The interlayer between Ir coating and carbon/carbon composites which can increase bonding strength and match thermal stress is studied. The summary of engine test of Ir coatings is presented. The influencing factors of service time of Ir coatings are discussed. The practical techniques to prepare Ir coatings in China are put forward.
2010, 39(11):2064-2068.
Abstract:
The characteristics of CO2-supercritical fluids (SCF-CO2) and the features of SCF-CO2 electroplating technology are analyzed. The effects of surfactant additive content, CO2 volume fraction, as well as temperature, pressure and other operating parameters of SCF-CO2 electroplating on the preparation of nanomaterials are reviewed. The plated nanomaterial films using this new method have a uniform surface and dense structures, which are better than the materials obtained by conventional electroplating methods. The micro-hardness and wear resistance are also increased significantly. At last, the directions of development of SCF-CO2 electroplating technology in future are expected.
The characteristics of CO2-supercritical fluids (SCF-CO2) and the features of SCF-CO2 electroplating technology are analyzed. The effects of surfactant additive content, CO2 volume fraction, as well as temperature, pressure and other operating parameters of SCF-CO2 electroplating on the preparation of nanomaterials are reviewed. The plated nanomaterial films using this new method have a uniform surface and dense structures, which are better than the materials obtained by conventional electroplating methods. The micro-hardness and wear resistance are also increased significantly. At last, the directions of development of SCF-CO2 electroplating technology in future are expected.
