Volume 40,Issue 8,2011 Table of Contents
2011, 40(8):1317-1322.
Abstract:
Hydroxycarbonate apatite/polyaniline composite coatings (HCp/PANI coatings) with mesoporous structure were fabricated by the electrophoretic deposition of calcium carbonate particles and polyaniline (PANI) nanofibers on Ti6Al4V substrates followed by treatment with phosphate buffer solutions (PBS) at 37 ○C. After soaking in PBS, the perfect crack-free CaCO3/PANI coatings are converted to HCp/PANI coatings with platelet-like structure via a dissolution-precipitation reaction. The mesopores and the macropores (or apertures) are formed within and among the platelets, respectively. Simulated body fluid (SBF) immersion tests reveal that the porous structure can improve the in vitro apatite forming ability of coatings. In SBF, the bone-like apatite nanocrystals are firstly deposited around the mesopores, and then fill the macropores with the increase of immersion time. Moreover, the superior in vitro apatite forming ability of HCp/PANI coatings is related to the PANI nanofibers. The functional groups () in PANI not only increase the local supersaturation, but also induce the heterogeneous nucleation and the growth of bone-like apatites.
Hydroxycarbonate apatite/polyaniline composite coatings (HCp/PANI coatings) with mesoporous structure were fabricated by the electrophoretic deposition of calcium carbonate particles and polyaniline (PANI) nanofibers on Ti6Al4V substrates followed by treatment with phosphate buffer solutions (PBS) at 37 ○C. After soaking in PBS, the perfect crack-free CaCO3/PANI coatings are converted to HCp/PANI coatings with platelet-like structure via a dissolution-precipitation reaction. The mesopores and the macropores (or apertures) are formed within and among the platelets, respectively. Simulated body fluid (SBF) immersion tests reveal that the porous structure can improve the in vitro apatite forming ability of coatings. In SBF, the bone-like apatite nanocrystals are firstly deposited around the mesopores, and then fill the macropores with the increase of immersion time. Moreover, the superior in vitro apatite forming ability of HCp/PANI coatings is related to the PANI nanofibers. The functional groups () in PANI not only increase the local supersaturation, but also induce the heterogeneous nucleation and the growth of bone-like apatites.
2011, 40(8):1323-1328.
Abstract:
The effects of adding cerium to lithium on the properties of lithium anode were studied in alkaline aqueous LiOH electrolyte at 30 °C. Self-corrosion hydrogen evolution rate at open circuit potential and electrochemical experiments show that the magnitude of hydrogen evolution rate is reduced obviously by adding cerium to lithium. As the content of Ce increases to 0.08 wt%, the inhibition efficiency reaches approximately 83.3%. SEM results show that the surface of Li-Ce alloy forms more compact and less porous film than that of pure lithium after discharge. XRD examination proves the presence of Ce(OH)3 in the lithium-cerium alloy film besides LiOH and LiOH·H2O. It is suggested that Ce(OH)3 plays a key role in inhibiting the hydrogen evolution and affecting discharge potential on the surface of lithium-cerium alloy anode in aqueous alkaline LiOH electrolyte.
The effects of adding cerium to lithium on the properties of lithium anode were studied in alkaline aqueous LiOH electrolyte at 30 °C. Self-corrosion hydrogen evolution rate at open circuit potential and electrochemical experiments show that the magnitude of hydrogen evolution rate is reduced obviously by adding cerium to lithium. As the content of Ce increases to 0.08 wt%, the inhibition efficiency reaches approximately 83.3%. SEM results show that the surface of Li-Ce alloy forms more compact and less porous film than that of pure lithium after discharge. XRD examination proves the presence of Ce(OH)3 in the lithium-cerium alloy film besides LiOH and LiOH·H2O. It is suggested that Ce(OH)3 plays a key role in inhibiting the hydrogen evolution and affecting discharge potential on the surface of lithium-cerium alloy anode in aqueous alkaline LiOH electrolyte.
2011, 40(8):1329-1333.
Abstract:
In order to improve the electrochemical cycle stability of the La-Mg-Ni system A2B7-type electrode alloys, La in the alloy was partially substituted by Pr. The melt-spinning technology was used for preparing La0.75-xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys. The microstructures of the as-cast and spun alloys were investigated by XRD, SEM and TEM. The results show that the as-cast and spun alloys have a multiphase structure, consisting of two main phases (La,Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The melt spinning leads to an obvious increase of the LaNi5 phase and a decrease of the (La,Mg)Ni3 phase in the alloys. The melt spinning significantly improves the cycle stability of the alloys. The capacity retaining rate at 100th charging and discharging cycle (S100) is enhanced from 65.32% to 73.97% for the x = 0 alloy and from 79.36% to 93.08% for the x = 0.4 alloy with increasing of spinning rate from 0 m/s (as-cast was defined as spinning rate of 0 m/s) to 20 m/s.
In order to improve the electrochemical cycle stability of the La-Mg-Ni system A2B7-type electrode alloys, La in the alloy was partially substituted by Pr. The melt-spinning technology was used for preparing La0.75-xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys. The microstructures of the as-cast and spun alloys were investigated by XRD, SEM and TEM. The results show that the as-cast and spun alloys have a multiphase structure, consisting of two main phases (La,Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The melt spinning leads to an obvious increase of the LaNi5 phase and a decrease of the (La,Mg)Ni3 phase in the alloys. The melt spinning significantly improves the cycle stability of the alloys. The capacity retaining rate at 100th charging and discharging cycle (S100) is enhanced from 65.32% to 73.97% for the x = 0 alloy and from 79.36% to 93.08% for the x = 0.4 alloy with increasing of spinning rate from 0 m/s (as-cast was defined as spinning rate of 0 m/s) to 20 m/s.
2011, 40(8):1334-1338.
Abstract:
The micro-crater texture of TiNi alloy was voluminously indented by a mold. Results show that the geometrical parameters of the texture will modify the tribological properties. With increasing of the circumferential pitch and the radial spacing of texture, the friction coefficient and wear rate of TiNi alloy present a decrease at the start, and then an increase after a minimum point. With gradual increasing of the ratio of depth to diameter, the friction coefficient and wear rate of TiNi alloy increase initially and then tend to decrease. When the sliding speed increases, the friction coefficient of TiNi alloy decreases firstly and then increases, following Stribeck curve. With the selected texture parameters such as micro-crater ratio of depth to diameter of 0.06, the radial distance of 1.5 mm, circumferential pitch of 15°, the surface show the best tribological properties of the friction coefficient of 0.098 and wear rate of 0.87× 10-5 mm3/N·m. It is concluded that the texture with appropriate parameters and shapes can reduce the friction coefficient and wear because of micro-hydrodynamic lubrication and the capture of wear debris from micro-crater texture.
The micro-crater texture of TiNi alloy was voluminously indented by a mold. Results show that the geometrical parameters of the texture will modify the tribological properties. With increasing of the circumferential pitch and the radial spacing of texture, the friction coefficient and wear rate of TiNi alloy present a decrease at the start, and then an increase after a minimum point. With gradual increasing of the ratio of depth to diameter, the friction coefficient and wear rate of TiNi alloy increase initially and then tend to decrease. When the sliding speed increases, the friction coefficient of TiNi alloy decreases firstly and then increases, following Stribeck curve. With the selected texture parameters such as micro-crater ratio of depth to diameter of 0.06, the radial distance of 1.5 mm, circumferential pitch of 15°, the surface show the best tribological properties of the friction coefficient of 0.098 and wear rate of 0.87× 10-5 mm3/N·m. It is concluded that the texture with appropriate parameters and shapes can reduce the friction coefficient and wear because of micro-hydrodynamic lubrication and the capture of wear debris from micro-crater texture.
2011, 40(8):1339-1343.
Abstract:
The TiB2/AZ31 magnesium based composite was fabricated by the in-situ synthesis-semisolid stirring technique, and its microstructure and mechanical property were studied. The results show that hot extrusion not only significantly refines the microstructure of the alloy, but also effectively improves the uniformity of TiB2 particles distribution. Compared with as-cast AZ31 magnesium alloy, the hardness and tensile strength of as-cast TiB2/AZ31 magnesium based composites increase to some extent (unobvious), but the elongation decreases. However, after extrusion, the hardness and the tensile strength of the as-extruded TiB2/AZ31 magnesium based composite increase by 126.2% and 98.8%, reaching 950 MPa and 322 MPa, respectively, and the elongation is also higher. Adding of TiB2 particles to AZ31 alloy and hot extrusion are effective ways to improve the wear resistance of AZ31 magnesium alloy.
The TiB2/AZ31 magnesium based composite was fabricated by the in-situ synthesis-semisolid stirring technique, and its microstructure and mechanical property were studied. The results show that hot extrusion not only significantly refines the microstructure of the alloy, but also effectively improves the uniformity of TiB2 particles distribution. Compared with as-cast AZ31 magnesium alloy, the hardness and tensile strength of as-cast TiB2/AZ31 magnesium based composites increase to some extent (unobvious), but the elongation decreases. However, after extrusion, the hardness and the tensile strength of the as-extruded TiB2/AZ31 magnesium based composite increase by 126.2% and 98.8%, reaching 950 MPa and 322 MPa, respectively, and the elongation is also higher. Adding of TiB2 particles to AZ31 alloy and hot extrusion are effective ways to improve the wear resistance of AZ31 magnesium alloy.
2011, 40(8):1344-1347.
Abstract:
The thermal stability and the electrical reliability of HfO2 films with a blocking layer (BL) of Al2O3 on strained Si0.8Ge0.2 were studied. High-resolution transmission electron microscopy (HRTEM) indicates that BL keeps HfO2 amorphous after 700 °C annealing treatment. Energy dispersive X-ray spectroscopy (EDS) shows that BL can suppress Si diffusion in HfO2 films effectively. X-ray photoelectron spectroscopy (XPS) suggests that BL suppresses the growth of HfSiO and GeOx. Electrical measurements show that the reliability of the sample with BL is improved, including high capacitance density, low interface defect density, and small shift of flatband voltage after total-dose 60Co γ-ray irradiation.
The thermal stability and the electrical reliability of HfO2 films with a blocking layer (BL) of Al2O3 on strained Si0.8Ge0.2 were studied. High-resolution transmission electron microscopy (HRTEM) indicates that BL keeps HfO2 amorphous after 700 °C annealing treatment. Energy dispersive X-ray spectroscopy (EDS) shows that BL can suppress Si diffusion in HfO2 films effectively. X-ray photoelectron spectroscopy (XPS) suggests that BL suppresses the growth of HfSiO and GeOx. Electrical measurements show that the reliability of the sample with BL is improved, including high capacitance density, low interface defect density, and small shift of flatband voltage after total-dose 60Co γ-ray irradiation.
2011, 40(8):1348-1354.
Abstract:
A novel method proposed by the author has been explicated, which means to analyze and study the atomic occupation problem of Li and Ni on 3a and 3b sites (belong to space group) in Li(Ni,Me)O2 (Me=Co, Mn or Co＋Mn) for Li-ion battery. This method is that with the help of the mixing occupation model of Li(Ni,Me)O2 and Power Cell 1.0 simulated computing program, the linear relationship between X-ray diffraction intensity ratio and the mixing occupation parameter x were obtained, and then using the data of the ratio of integrated diffraction intensity derived by the XRD experiment, the corresponding parameter x can be got from the simulated curves directly. Based on this method, the linear relationship between the square root of diffraction intensity ratio and the mixing occupation parameter x for 5 kinds of Li(Ni,Me)O2 materials were obtained. Applying this method to the study of the atomic occupation problem in the synthesis process of Li(Ni0.6Co0.2Mn0.2)O2, the relation of the mixing occupation parameter x and baking temperature has been found. Meanwhile, this method has been also used to investigate the transformation of the crystal structure and microstructure of Li(Ni1/3Co1/3Mn1/3)O2 in a 2H-graphite/Li (Ni1/3Co1/3Mn1/3)O2 lithium ion battery during charge-discharge process.
A novel method proposed by the author has been explicated, which means to analyze and study the atomic occupation problem of Li and Ni on 3a and 3b sites (belong to space group) in Li(Ni,Me)O2 (Me=Co, Mn or Co＋Mn) for Li-ion battery. This method is that with the help of the mixing occupation model of Li(Ni,Me)O2 and Power Cell 1.0 simulated computing program, the linear relationship between X-ray diffraction intensity ratio and the mixing occupation parameter x were obtained, and then using the data of the ratio of integrated diffraction intensity derived by the XRD experiment, the corresponding parameter x can be got from the simulated curves directly. Based on this method, the linear relationship between the square root of diffraction intensity ratio and the mixing occupation parameter x for 5 kinds of Li(Ni,Me)O2 materials were obtained. Applying this method to the study of the atomic occupation problem in the synthesis process of Li(Ni0.6Co0.2Mn0.2)O2, the relation of the mixing occupation parameter x and baking temperature has been found. Meanwhile, this method has been also used to investigate the transformation of the crystal structure and microstructure of Li(Ni1/3Co1/3Mn1/3)O2 in a 2H-graphite/Li (Ni1/3Co1/3Mn1/3)O2 lithium ion battery during charge-discharge process.
8 Valence Electron Structure Calculation and Interface Reaction Prediction of Phases in Ni-Al System
2011, 40(8):1355-1360.
Abstract:
The valence electron structures, theoretical binding energies and forming enthalpy of phases in Ni-Al system were calculated based on the empirical electron theory of solids and molecules, and the interfacial reaction was predicted through comparison of the forming enthalpy of phases. The calculated binding energy values of Ni, Al, Ni3Al, Ni5Al3, NiAl, Ni2Al3 and NiAl3 are 427.44, 324.58, 441.11, 440.10, 435.51, 432.66 and 395.05 kJ/mol, which are in good agreement with experimental values. At the Ni/Al interface, Ni2Al3 phase has a minimum enthalpy of formation, so it will be the first to precipitate in heat process; then, the NiAl phase may be formed at the Ni2Al3/Ni interface, while the Ni3Al phase may be formed at the NiAl/Ni interface. At the NiAl/Ni3Al interface, the absolute value of forming enthalpy of Ni5Al3 is small, so its formation needs high temperature and long time. The predicted results agree well with the experimental.
The valence electron structures, theoretical binding energies and forming enthalpy of phases in Ni-Al system were calculated based on the empirical electron theory of solids and molecules, and the interfacial reaction was predicted through comparison of the forming enthalpy of phases. The calculated binding energy values of Ni, Al, Ni3Al, Ni5Al3, NiAl, Ni2Al3 and NiAl3 are 427.44, 324.58, 441.11, 440.10, 435.51, 432.66 and 395.05 kJ/mol, which are in good agreement with experimental values. At the Ni/Al interface, Ni2Al3 phase has a minimum enthalpy of formation, so it will be the first to precipitate in heat process; then, the NiAl phase may be formed at the Ni2Al3/Ni interface, while the Ni3Al phase may be formed at the NiAl/Ni interface. At the NiAl/Ni3Al interface, the absolute value of forming enthalpy of Ni5Al3 is small, so its formation needs high temperature and long time. The predicted results agree well with the experimental.
2011, 40(8):1361-1366.
Abstract:
The effect of strain energy on pre-precipitation phase in Ni75Al15V10 alloy was studied using the microscopic phase-field method. It is found that the initial state of strain energy in the alloy has an effect on precipitation of L10 phase. L10 phase does not precipitate unless the effect of strain energy is considered. The larger the strain energy is, the shorter the nucleation incubation periods of L10 phase are, and the more obvious the characteristics of precipitated L10 phase are. Meantime the volume fraction and the lifetime of precipitated L10 phase also increase as the strain energy increases. When the strain energy is small, L10 phase precipitates in some areas of the disordered matrix firstly, and then the transformation from L10 to L12 phase occurs; however, in other regions L12 phase precipitate directly. When the strain energy becomes larger, L10 phase precipitate in most areas of the matrix, followed by part of these L10 phase dissolving, and the undissolved L10 phase would transform into L12 phase finally.
The effect of strain energy on pre-precipitation phase in Ni75Al15V10 alloy was studied using the microscopic phase-field method. It is found that the initial state of strain energy in the alloy has an effect on precipitation of L10 phase. L10 phase does not precipitate unless the effect of strain energy is considered. The larger the strain energy is, the shorter the nucleation incubation periods of L10 phase are, and the more obvious the characteristics of precipitated L10 phase are. Meantime the volume fraction and the lifetime of precipitated L10 phase also increase as the strain energy increases. When the strain energy is small, L10 phase precipitates in some areas of the disordered matrix firstly, and then the transformation from L10 to L12 phase occurs; however, in other regions L12 phase precipitate directly. When the strain energy becomes larger, L10 phase precipitate in most areas of the matrix, followed by part of these L10 phase dissolving, and the undissolved L10 phase would transform into L12 phase finally.
2011, 40(8):1367-1371.
Abstract:
Tensile strength of the SiC/Ti-6Al-4V composites under the conditions of preparation and heat treatment at 900 oC for different time was measured and calculated by means of Global Load-Sharing model. It is found that after long-time heat treatment, the calculated strength is in accordance with the measured one. But the former is higher than the later for the as-prepared sample. SEM and TEM observations show that with prolonging the holding time at 900 oC, the interfacial reaction zone of the SiC/Ti-6Al-4V becomes thicker and the C-coating of the SiC fiber thinner, leading to the decrease of the tensile strength and the increase of the interfacial shear strength. It is identified that the main interfacial reaction product is TiC. However, when the C-coating is consumed entirely Ti5Si3 forms in the interfacial reaction zone adjacent to the SiC fiber. Interfacial reaction is the main reason for the decrease of mechanical properties of composites.
Tensile strength of the SiC/Ti-6Al-4V composites under the conditions of preparation and heat treatment at 900 oC for different time was measured and calculated by means of Global Load-Sharing model. It is found that after long-time heat treatment, the calculated strength is in accordance with the measured one. But the former is higher than the later for the as-prepared sample. SEM and TEM observations show that with prolonging the holding time at 900 oC, the interfacial reaction zone of the SiC/Ti-6Al-4V becomes thicker and the C-coating of the SiC fiber thinner, leading to the decrease of the tensile strength and the increase of the interfacial shear strength. It is identified that the main interfacial reaction product is TiC. However, when the C-coating is consumed entirely Ti5Si3 forms in the interfacial reaction zone adjacent to the SiC fiber. Interfacial reaction is the main reason for the decrease of mechanical properties of composites.
2011, 40(8):1372-1376.
Abstract:
The microstructure evolution of laser multi-layer deposited Ti-XAl-YV (X￡11, Y￡10, mass fraction, %, similarly hereinafter) alloys from blended elemental powders with the content of Al and V was studied. Results show that the size and quantity of a colony in the prior b grains are decreased gradually with the increase of Al and V, and the microstructure in prior b grains changes from widmanst?tten structure to basketweave structure with the a laths and b phase braided. Meanwhile, the size and aspect ratio of a laths are decreased obviously. The nucleation and growth conditions of a phase in single-line laser multi-layer deposited Ti-XAl-YV alloys were analyzed and the microstructure evolution mechanism was revealed on the basis of thermal history modeling, a→b transformation temperature computation and the phase diagram analysis of Ti-XAl-YV alloys.
The microstructure evolution of laser multi-layer deposited Ti-XAl-YV (X￡11, Y￡10, mass fraction, %, similarly hereinafter) alloys from blended elemental powders with the content of Al and V was studied. Results show that the size and quantity of a colony in the prior b grains are decreased gradually with the increase of Al and V, and the microstructure in prior b grains changes from widmanst?tten structure to basketweave structure with the a laths and b phase braided. Meanwhile, the size and aspect ratio of a laths are decreased obviously. The nucleation and growth conditions of a phase in single-line laser multi-layer deposited Ti-XAl-YV alloys were analyzed and the microstructure evolution mechanism was revealed on the basis of thermal history modeling, a→b transformation temperature computation and the phase diagram analysis of Ti-XAl-YV alloys.
2011, 40(8):1377-1381.
Abstract:
The effects of stress, electron beam irradiation and second phase particles on zirconium hydride precipitation and growth in Zircaloy-4 were investigated using in-situ transmission electron microscope observation. Results show that with the tensile stress the cracks are likely to propagate along hydrides and new hydrides are formed at the crack tip along the vertical direction of the applied stress. A process of precipitation, cracking, re-precipitation and so on, induced by tensile stress, causes delayed hydride cracking (DHC). Under the high irradiation of converged electron beam, the hydrides decompose in the Zircaloy-4, and new hydrides prefer to precipitate around the unoxidized Zr(Fe, Cr)2 particles, and the re-precipitated hydrides are fcc-structure δ phase.
The effects of stress, electron beam irradiation and second phase particles on zirconium hydride precipitation and growth in Zircaloy-4 were investigated using in-situ transmission electron microscope observation. Results show that with the tensile stress the cracks are likely to propagate along hydrides and new hydrides are formed at the crack tip along the vertical direction of the applied stress. A process of precipitation, cracking, re-precipitation and so on, induced by tensile stress, causes delayed hydride cracking (DHC). Under the high irradiation of converged electron beam, the hydrides decompose in the Zircaloy-4, and new hydrides prefer to precipitate around the unoxidized Zr(Fe, Cr)2 particles, and the re-precipitated hydrides are fcc-structure δ phase.
2011, 40(8):1382-1386.
Abstract:
TiNi shape memory alloy (SMA) and stainless steel (SUS304) were joined by transient liquid phase (TLP) diffusion bonding using Ag-Cu foil as interlayer. The microstructure, the element profile and the phase composition of the joint were analyzed, and the shear strength and the fracture mode of the joint were also investigated. The results show that the interface zone of the joint is composed of TiNi transition zone, middle zone and stainless steel transition zone, and their main phases are Ti(Cu,Ni,Fe), AgCu and TiFe, respectively. The maximum shear strength is about 239 MPa for the specimens joined at 860 °C for 60 min under a specific pressure of 0.05 MPa. The fracture occurs at the diffusion interface between TiNi alloy and AgCu interlayer, and the joint presents a characteristic of ductile-brittle mixed fracture. Based on interface morphology and element diffusion analysis, the kinetics of isothermal solidification was studied. It indicates that the process of TLP diffusion bonding of TiNi SMA and stainless steel shows a typical characteristic of asymmetry.
TiNi shape memory alloy (SMA) and stainless steel (SUS304) were joined by transient liquid phase (TLP) diffusion bonding using Ag-Cu foil as interlayer. The microstructure, the element profile and the phase composition of the joint were analyzed, and the shear strength and the fracture mode of the joint were also investigated. The results show that the interface zone of the joint is composed of TiNi transition zone, middle zone and stainless steel transition zone, and their main phases are Ti(Cu,Ni,Fe), AgCu and TiFe, respectively. The maximum shear strength is about 239 MPa for the specimens joined at 860 °C for 60 min under a specific pressure of 0.05 MPa. The fracture occurs at the diffusion interface between TiNi alloy and AgCu interlayer, and the joint presents a characteristic of ductile-brittle mixed fracture. Based on interface morphology and element diffusion analysis, the kinetics of isothermal solidification was studied. It indicates that the process of TLP diffusion bonding of TiNi SMA and stainless steel shows a typical characteristic of asymmetry.
2011, 40(8):1387-1391.
Abstract:
Mg+10%Ni2P composite (mass fraction, similarly hereinafter) and pure magnesium samples were prepared by reactive ball-milling under hydrogen atmosphere, and their phase-structure and hydrogen storage behavior were investigated systemically. The results show that the hydrogen absorption/desorption kinetics of pure Mg are markedly improved by adding 10% Ni2P. Furthermore, the catalytically enhanced kinetic property is found to persist in the de-/hydrogenation cycles. The size of crystal grains of the composite is reduced by prolonging the ball-milling time. Ni2P is effective in inhibiting the aggregation of Mg during the de-/hydrogenation processes. The doping of Ni2P can lower the dehydriding temperatures of the hydriding Mg-Ni2P composites.
Mg+10%Ni2P composite (mass fraction, similarly hereinafter) and pure magnesium samples were prepared by reactive ball-milling under hydrogen atmosphere, and their phase-structure and hydrogen storage behavior were investigated systemically. The results show that the hydrogen absorption/desorption kinetics of pure Mg are markedly improved by adding 10% Ni2P. Furthermore, the catalytically enhanced kinetic property is found to persist in the de-/hydrogenation cycles. The size of crystal grains of the composite is reduced by prolonging the ball-milling time. Ni2P is effective in inhibiting the aggregation of Mg during the de-/hydrogenation processes. The doping of Ni2P can lower the dehydriding temperatures of the hydriding Mg-Ni2P composites.
2011, 40(8):1392-1396.
Abstract:
The FePt(2 nm)/Au(t nm) multilayer films were deposited on SiO2<0001> substrates by magnetron sputtering system at room temperature, and then the as-deposited films were annealed at various temperatures. The structure and properties of the films were investigated by X-ray fluorescence spectrometer, X-ray diffraction, the vibrating sample magnetometer and atomic force microscopy. The results indicate the as-deposited FePt/Au multilayer films show a superlattice structure for the coherent growth between fcc FePt and Au. And the films annealed at a lower temperature are still of superlattice structure. The transformation in FePt film from disorder to order phase takes place when the films are annealed at 400 oC. After annealing at 600 oC, the in-plane and out-of-plane coercivity of the film is 811.7 and 829.2 kA·m-1, respectively. It is optimal to form the L10-FePt when the Au layer thickness is 2.5 nm. Domain wall motion and moment rotation exist in the magnetizing process at the same time for all the films. Uniform films are formed for the samples after annealing.
The FePt(2 nm)/Au(t nm) multilayer films were deposited on SiO2<0001> substrates by magnetron sputtering system at room temperature, and then the as-deposited films were annealed at various temperatures. The structure and properties of the films were investigated by X-ray fluorescence spectrometer, X-ray diffraction, the vibrating sample magnetometer and atomic force microscopy. The results indicate the as-deposited FePt/Au multilayer films show a superlattice structure for the coherent growth between fcc FePt and Au. And the films annealed at a lower temperature are still of superlattice structure. The transformation in FePt film from disorder to order phase takes place when the films are annealed at 400 oC. After annealing at 600 oC, the in-plane and out-of-plane coercivity of the film is 811.7 and 829.2 kA·m-1, respectively. It is optimal to form the L10-FePt when the Au layer thickness is 2.5 nm. Domain wall motion and moment rotation exist in the magnetizing process at the same time for all the films. Uniform films are formed for the samples after annealing.
2011, 40(8):1397-1401.
Abstract:
The microstructure of a Ni-based P/M superalloy FGH95 after long-term aging at 650 oC was observed by SEM and TEM and its microstructure stability was also investigated. The results show that the microstructure of the alloy is stable at 650 oC. The major precipitated phases of the alloy are γ′ phase and carbides of MC and M23C6 without TCP phase precipitating after aging for 500-5000 h. The γ′ phase is precipitated in the matrix in three kinds of sizes during different heat treatment processes. The size of bulk γ′ phase is about 1 to 3 μm, which is precipitated on grain boundary. The size of intragranular γ′ phase is about 500 nm, with the shape of butterfly, which changes a little in size, morphology and distribution in matrix during the aging process. And the smaller γ′ phase experiences a series of changes such as growing up, splitting and growing up again and splitting again in long-term aging. Its size is in a range of 60 to 200 nm. A kind of carbide M23C6 is found on the grain boundary in the alloy aged for 3000 h.
The microstructure of a Ni-based P/M superalloy FGH95 after long-term aging at 650 oC was observed by SEM and TEM and its microstructure stability was also investigated. The results show that the microstructure of the alloy is stable at 650 oC. The major precipitated phases of the alloy are γ′ phase and carbides of MC and M23C6 without TCP phase precipitating after aging for 500-5000 h. The γ′ phase is precipitated in the matrix in three kinds of sizes during different heat treatment processes. The size of bulk γ′ phase is about 1 to 3 μm, which is precipitated on grain boundary. The size of intragranular γ′ phase is about 500 nm, with the shape of butterfly, which changes a little in size, morphology and distribution in matrix during the aging process. And the smaller γ′ phase experiences a series of changes such as growing up, splitting and growing up again and splitting again in long-term aging. Its size is in a range of 60 to 200 nm. A kind of carbide M23C6 is found on the grain boundary in the alloy aged for 3000 h.
17 Effects of Sr and Nd Addition on Microstructure and Mechanical Properties of Mg-9Al-1Si-0.3Zn Alloy
2011, 40(8):1402-1406.
Abstract:
A large amount of coarse Chinese-script-like Mg2Si particles in the magnesium alloys containing much silicon is harmful to the mechanical properties of the alloys. Sr and Nd were added in Mg-9Al-1Si-0.3Zn alloy to refine the coarse Mg2Si, and the effect of the added elements on microstructures and mechanical properties of the alloy were studied. The refining mechanism of Sr and Nd to Mg2Si was analyzed. The results show that the Chinese-script-like morphology of the Mg2Si particles is improved and uniform polygonal block are formed with the addition of Sr element. When the Sr addition is 0.16 wt%, the particles appear in a completely polygonal morphology. When both Sr and Nd elements are added to the alloy, an intermetallic compound of Mg, Al, Nd and Si elements precipitate; the more added Nd, the more new phases, which act as the heterogeneous nuclei for the growth of the Mg2Si particles. The Mg2Si particles are refined as an irregular shape under the combination effects of Sr and Nd elements. The grain-refinement on Mg2Si particles improves the mechanical properties of the alloy.
A large amount of coarse Chinese-script-like Mg2Si particles in the magnesium alloys containing much silicon is harmful to the mechanical properties of the alloys. Sr and Nd were added in Mg-9Al-1Si-0.3Zn alloy to refine the coarse Mg2Si, and the effect of the added elements on microstructures and mechanical properties of the alloy were studied. The refining mechanism of Sr and Nd to Mg2Si was analyzed. The results show that the Chinese-script-like morphology of the Mg2Si particles is improved and uniform polygonal block are formed with the addition of Sr element. When the Sr addition is 0.16 wt%, the particles appear in a completely polygonal morphology. When both Sr and Nd elements are added to the alloy, an intermetallic compound of Mg, Al, Nd and Si elements precipitate; the more added Nd, the more new phases, which act as the heterogeneous nuclei for the growth of the Mg2Si particles. The Mg2Si particles are refined as an irregular shape under the combination effects of Sr and Nd elements. The grain-refinement on Mg2Si particles improves the mechanical properties of the alloy.
2011, 40(8):1407-1411.
Abstract:
The effect of carbon addition on the solidification microstructure of the first generation single crystal Ni-based superalloy AM3 was studied. The results indicate that with increasing of carbon content, dendrite morphology and dendrite arm spacings have no obvious change, volume fraction of eutectic is significantly decreased, and the primary carbide is gradually increased. The primary carbide morphologies in this alloy commonly are blocky, framework-like and Chinese-script-like. When the carbon level is high, the carbide morphology becomes net-like by frame-like carbides connecting each other (Chinese script morphology).
The effect of carbon addition on the solidification microstructure of the first generation single crystal Ni-based superalloy AM3 was studied. The results indicate that with increasing of carbon content, dendrite morphology and dendrite arm spacings have no obvious change, volume fraction of eutectic is significantly decreased, and the primary carbide is gradually increased. The primary carbide morphologies in this alloy commonly are blocky, framework-like and Chinese-script-like. When the carbon level is high, the carbide morphology becomes net-like by frame-like carbides connecting each other (Chinese script morphology).
2011, 40(8):1412-1416.
Abstract:
The microstructure, transformation, shape memory effect (SME) and superelasticity (SE) characteristics of Ti-50.8Ni shape memory alloy were investigated by thermal gravimetry, X-ray diffraction, optical microscopy, differential scanning calorimetry and tensile testing. The results show that the microstructure of Ti-50.8Ni alloy is fibrous after annealing below 600 oC, while it is equiaxed after annealing over 600 oC. The alloy oxidation speeds up when the heating temperature is over 600 oC. With the annealing temperature Ta increasing, the transformation types of Ti-50.8Ni alloy change from A→R→M/M→R→A to A→R→M/M→A to A→R/R→A (A—parent phase, R—R phase, M—martensite), the M transformation temperature increases, the R transformation temperature decreases, the M transformation temperature hysteresis decreases, and the alloy’s characteristics at room temperature change from SME+SE to SE. Ti-50.8Ni alloy spring shows SME+SE with deforming temperature Td＜20 oC, and it shows SE with Td＞30 oC. The stress-induced martensite stress of the alloy spring increases with increasing Td.
The microstructure, transformation, shape memory effect (SME) and superelasticity (SE) characteristics of Ti-50.8Ni shape memory alloy were investigated by thermal gravimetry, X-ray diffraction, optical microscopy, differential scanning calorimetry and tensile testing. The results show that the microstructure of Ti-50.8Ni alloy is fibrous after annealing below 600 oC, while it is equiaxed after annealing over 600 oC. The alloy oxidation speeds up when the heating temperature is over 600 oC. With the annealing temperature Ta increasing, the transformation types of Ti-50.8Ni alloy change from A→R→M/M→R→A to A→R→M/M→A to A→R/R→A (A—parent phase, R—R phase, M—martensite), the M transformation temperature increases, the R transformation temperature decreases, the M transformation temperature hysteresis decreases, and the alloy’s characteristics at room temperature change from SME+SE to SE. Ti-50.8Ni alloy spring shows SME+SE with deforming temperature Td＜20 oC, and it shows SE with Td＞30 oC. The stress-induced martensite stress of the alloy spring increases with increasing Td.
2011, 40(8):1417-1421.
Abstract:
The crystallization behavior of the spray-formed La62Al15.7(Cu,Ni)22.3 bulk amorphous alloys and the suction-cast alloys was studied. The results show that the crystallization processes of both the La62Al15.7(Cu,Ni)22.3 amorphous alloys include three stages. La, Al3La and an unknown phase containing much Cu and Ni are precipitated in the amorphous matrix, respectively. Calculating of the activation energy and annealing experimental results for the La62Al15.7(Cu,Ni)22.3 amorphous alloys show that the thermal stability of the spray-formed bulk La62Al15.7(Cu,Ni)22.3 amorphous alloy is better than that of the suction-cast amorphous alloy below 503 K, while above 553 K it is inverse.
The crystallization behavior of the spray-formed La62Al15.7(Cu,Ni)22.3 bulk amorphous alloys and the suction-cast alloys was studied. The results show that the crystallization processes of both the La62Al15.7(Cu,Ni)22.3 amorphous alloys include three stages. La, Al3La and an unknown phase containing much Cu and Ni are precipitated in the amorphous matrix, respectively. Calculating of the activation energy and annealing experimental results for the La62Al15.7(Cu,Ni)22.3 amorphous alloys show that the thermal stability of the spray-formed bulk La62Al15.7(Cu,Ni)22.3 amorphous alloy is better than that of the suction-cast amorphous alloy below 503 K, while above 553 K it is inverse.
2011, 40(8):1422-1425.
Abstract:
The oxidation characteristics and the effect of oxidation on mechanical properties of Ti600 alloy at 600 oC were researched. The results show that the increase of oxide skin is nearly controlled by the diffusion of O element. After 600 oC thermal exposure for a long time, the surface is mainly composed of TiO2 and Al2O3. The solution O element mainly exists inside octahedral interstice, which leads to almost changeless “a” and “b” and obviously increased “c” of hcp a-Ti crystal lattice. Through the comparison of mechanical properties between the samples with oxide skin and without oxide skin, it can be concluded that the decrease of plasticity is mainly due to the oxidation of the alloy. Thus it is very necessary to adopt surface protection for Ti600 alloy for 600 oC application.
The oxidation characteristics and the effect of oxidation on mechanical properties of Ti600 alloy at 600 oC were researched. The results show that the increase of oxide skin is nearly controlled by the diffusion of O element. After 600 oC thermal exposure for a long time, the surface is mainly composed of TiO2 and Al2O3. The solution O element mainly exists inside octahedral interstice, which leads to almost changeless “a” and “b” and obviously increased “c” of hcp a-Ti crystal lattice. Through the comparison of mechanical properties between the samples with oxide skin and without oxide skin, it can be concluded that the decrease of plasticity is mainly due to the oxidation of the alloy. Thus it is very necessary to adopt surface protection for Ti600 alloy for 600 oC application.
2011, 40(8):1426-1429.
Abstract:
Fe/Ru multilayers were prepared by high vacuum e-gun evaporation system and the samples were studied by HRTEM and VSM. The interface structure of Fe/Ru multilayers with different thickness and its effects on magnetic properties were analyzed. Results show that the Fe/Ru multilayers have good periodic structure. When Fe layer is very thin, Fe layer is not continuous and the multilayer show a superparamagnetic property due to the Fe particles distributed as islands. HRTEM of Fe/Ru interface shows the difference in roughness between the two interfaces of Fe/Ru. The origin of the positive magnetoresistance (MR) is related to the difference in roughness, in which the scattering spin asymmetry is less than one. After annealing in vacuum, the negative MR of multilayer is increased greatly, indicating that it is originated from the roughness of the interlayer.
Fe/Ru multilayers were prepared by high vacuum e-gun evaporation system and the samples were studied by HRTEM and VSM. The interface structure of Fe/Ru multilayers with different thickness and its effects on magnetic properties were analyzed. Results show that the Fe/Ru multilayers have good periodic structure. When Fe layer is very thin, Fe layer is not continuous and the multilayer show a superparamagnetic property due to the Fe particles distributed as islands. HRTEM of Fe/Ru interface shows the difference in roughness between the two interfaces of Fe/Ru. The origin of the positive magnetoresistance (MR) is related to the difference in roughness, in which the scattering spin asymmetry is less than one. After annealing in vacuum, the negative MR of multilayer is increased greatly, indicating that it is originated from the roughness of the interlayer.
2011, 40(8):1430-1433.
Abstract:
The rare earth oxides (REO) doped molybdenum powder was prepared by solid-solid doping, solid-liquid doping and liquid-liquid doping, respectively; afterwards, the powder was sintered by spark plasma sintering and traditional sintering combined with cold isostatic compaction method for fabricating REO-Mo cermet cathodes. OM and emission property tests were used to research the microstructure and the secondary electron emission properties of the samples. The results show that the emission properties of the material can be enhanced through the uniform distribution of rare earth oxides and the refinement of structure. The activation temperature can be decreased greatly by annealing in hydrogen at high temperature, and the secondary emission yield is also enhanced apparently.
The rare earth oxides (REO) doped molybdenum powder was prepared by solid-solid doping, solid-liquid doping and liquid-liquid doping, respectively; afterwards, the powder was sintered by spark plasma sintering and traditional sintering combined with cold isostatic compaction method for fabricating REO-Mo cermet cathodes. OM and emission property tests were used to research the microstructure and the secondary electron emission properties of the samples. The results show that the emission properties of the material can be enhanced through the uniform distribution of rare earth oxides and the refinement of structure. The activation temperature can be decreased greatly by annealing in hydrogen at high temperature, and the secondary emission yield is also enhanced apparently.
2011, 40(8):1434-1437.
Abstract:
The saturation capacity and reaction probability of N2, CO2 and O2 adsorption on clean uranium surface at 323 K were quantitatively measured by the low pressure PVT method, and their reactivity and kinetics property were compared and analyzed. Results show that N2, CO2 and O2 exhibit the common reaction characteristics of adsorbed gas amount (coverage) approaching a maximum value and reaction probability decreasing with a rise in adsorbed gas amount. The reactivity ordering of gases with uranium is O2>CO2>N2 and saturation capacity follows the relation of NO2≈2.4NCO2≈7NN2. The initial reaction kinetics relies on the impacts of both product layer composition and thickness on the molecular dissociation and dissociative particles diffusion process, and the uranium nitride, carbide or oxycarbide have a stronger repression effect than uranium oxide on the above process.
The saturation capacity and reaction probability of N2, CO2 and O2 adsorption on clean uranium surface at 323 K were quantitatively measured by the low pressure PVT method, and their reactivity and kinetics property were compared and analyzed. Results show that N2, CO2 and O2 exhibit the common reaction characteristics of adsorbed gas amount (coverage) approaching a maximum value and reaction probability decreasing with a rise in adsorbed gas amount. The reactivity ordering of gases with uranium is O2>CO2>N2 and saturation capacity follows the relation of NO2≈2.4NCO2≈7NN2. The initial reaction kinetics relies on the impacts of both product layer composition and thickness on the molecular dissociation and dissociative particles diffusion process, and the uranium nitride, carbide or oxycarbide have a stronger repression effect than uranium oxide on the above process.
2011, 40(8):1438-1441.
Abstract:
A series of 90W-7Ni-3Fe alloys with different yttrium contents were fabricated via liquid phase sintering of nano-composite powder prepared by spray drying with subsequent thermal reduction process. The rare earth Y content was 0, 0.4% and 5% (mass fraction). XRD, SEM and EDX were used to analyze the existence state and distribution characteristics of yttrium added in the 90W-7Ni-3Fe alloys. The results show that the added yttrium exists in the form of Y2O3 and Y is not detected within the W particles. When the content of yttrium is 0.4%, a new phase rich in yttrium locates between the tungsten particles and the matrix material; with the content of yttrium increasing to 5%, the yttrium-rich region appears in the matrix and the particle size of W is refined effectively.
A series of 90W-7Ni-3Fe alloys with different yttrium contents were fabricated via liquid phase sintering of nano-composite powder prepared by spray drying with subsequent thermal reduction process. The rare earth Y content was 0, 0.4% and 5% (mass fraction). XRD, SEM and EDX were used to analyze the existence state and distribution characteristics of yttrium added in the 90W-7Ni-3Fe alloys. The results show that the added yttrium exists in the form of Y2O3 and Y is not detected within the W particles. When the content of yttrium is 0.4%, a new phase rich in yttrium locates between the tungsten particles and the matrix material; with the content of yttrium increasing to 5%, the yttrium-rich region appears in the matrix and the particle size of W is refined effectively.
2011, 40(8):1442-1445.
Abstract:
The self-discharge property of La0.65Mg0.35Nix (x=3.0~3.5) hydrogen storage alloy electrodes was studied systematically. The results show that with the Ni content increasing, the maximum discharge capacity of the alloy electrodes increases from 350.6 mAh·g-1 (x=3.0) to 351.2 mAh·g-1 (x=3.1) and then decreases to 244.1 mAh·g-1 (x=3.5). Moreover, the capacity retention rate of 72 h self-discharge increases from 77.7% (x=3.0) to 79.5% (x=3.1), and then decreases to 63.5% (x=3.5), which indicates that the self-discharge property of the alloy electrodes is improved by the appropriate Ni content. The variety of the self-discharge property of the alloy electrodes with x value was analyzed by testing the electrochemical pressure-component-temperature (P-C-T) curves and corrosion curves of the alloy electrodes.
The self-discharge property of La0.65Mg0.35Nix (x=3.0~3.5) hydrogen storage alloy electrodes was studied systematically. The results show that with the Ni content increasing, the maximum discharge capacity of the alloy electrodes increases from 350.6 mAh·g-1 (x=3.0) to 351.2 mAh·g-1 (x=3.1) and then decreases to 244.1 mAh·g-1 (x=3.5). Moreover, the capacity retention rate of 72 h self-discharge increases from 77.7% (x=3.0) to 79.5% (x=3.1), and then decreases to 63.5% (x=3.5), which indicates that the self-discharge property of the alloy electrodes is improved by the appropriate Ni content. The variety of the self-discharge property of the alloy electrodes with x value was analyzed by testing the electrochemical pressure-component-temperature (P-C-T) curves and corrosion curves of the alloy electrodes.
2011, 40(8):1446-1449.
Abstract:
A dealloying treatment method was applied to the surface modification of nearly equiatomic NiTi alloy so as to remove the harmful element of nickel selectively from NiTi alloys and form a Ni-free titanium oxide layer on the surface. Sample surfaces were analyzed by SEM, XRD, AES, FTIR and XPS, and then samples were immersed in SBF solution for 14 d in order to observe the bioactivity. The results show that the dealloying treatment of NiTi alloy at low temperature leads to 400 nm thick Ni-free surface layer that possesses a nanometer grid structure, and titania surface is in situ formed that possesses a degree of bioactivity because of the combination of hydroxyl (OH-) group in the process of dealloying treatment simultaneously. As-prepared titania layer was changed into anatase after heated at 500 oC for 1 h. As a consequence, the dealloying treatment method could improve biocompatibility of NiTi alloys.
A dealloying treatment method was applied to the surface modification of nearly equiatomic NiTi alloy so as to remove the harmful element of nickel selectively from NiTi alloys and form a Ni-free titanium oxide layer on the surface. Sample surfaces were analyzed by SEM, XRD, AES, FTIR and XPS, and then samples were immersed in SBF solution for 14 d in order to observe the bioactivity. The results show that the dealloying treatment of NiTi alloy at low temperature leads to 400 nm thick Ni-free surface layer that possesses a nanometer grid structure, and titania surface is in situ formed that possesses a degree of bioactivity because of the combination of hydroxyl (OH-) group in the process of dealloying treatment simultaneously. As-prepared titania layer was changed into anatase after heated at 500 oC for 1 h. As a consequence, the dealloying treatment method could improve biocompatibility of NiTi alloys.
2011, 40(8):1450-1453.
Abstract:
Nanocomposite Nd8.5Fe77.7Nb2Co5Ga0.6B6.2 bonded magnets were prepared by melt-spun and vacuum annealing processes. The dependence on the melt-spun speed of magnetic properties and temperature coefficients of the magnets was investigated. The results show that a proper melt-spun speed is beneficial to the grain refinement and the exchange coupling effect between the Nd2Fe14B and α-Fe phases of the alloys annealed is greatly improved. It is also shown that the temperature coefficients are significantly influenced by the melt-spun speed. With the increase of the melt-spun speed, the temperature coefficient β of coercivity is continuously decreased. The temperature coefficient α of remanence is decreased first and then increased with the increase of the melt-spun speed. It might be closely related to the exchange coupling effect between the Nd2Fe14B and α-Fe phases.
Nanocomposite Nd8.5Fe77.7Nb2Co5Ga0.6B6.2 bonded magnets were prepared by melt-spun and vacuum annealing processes. The dependence on the melt-spun speed of magnetic properties and temperature coefficients of the magnets was investigated. The results show that a proper melt-spun speed is beneficial to the grain refinement and the exchange coupling effect between the Nd2Fe14B and α-Fe phases of the alloys annealed is greatly improved. It is also shown that the temperature coefficients are significantly influenced by the melt-spun speed. With the increase of the melt-spun speed, the temperature coefficient β of coercivity is continuously decreased. The temperature coefficient α of remanence is decreased first and then increased with the increase of the melt-spun speed. It might be closely related to the exchange coupling effect between the Nd2Fe14B and α-Fe phases.
2011, 40(8):1454-1457.
Abstract:
Dynamic shearing experiment on TC18 titanium alloy was carried out by using a split Hopkinson bar process. Refining mechanism of grains in the adiabatic shear band of TC18 titanium alloy deformed under the conditions of high strain-rate were investigated by means of OM, SEM and TEM. The results of TEM observation show that the grains in the adiabatic shear band of TC18 titanium alloy are refined due to the combined action of three mechanisms. The first mechanism is that dislocations were rapidly reproduced, moved and clogged at the obstacles such as grain boundary, second-phase particles, and so on; then, cracks were generated in the head of clogging of dislocation due to huge stress resulted from the clogging of dislocation; finally, smaller grains were formed due to breakdown of elongation grain. The second refining mechanism of grains, which is presented by us first, is inner-necking mode. The third one is dynamic recrystallization.
Dynamic shearing experiment on TC18 titanium alloy was carried out by using a split Hopkinson bar process. Refining mechanism of grains in the adiabatic shear band of TC18 titanium alloy deformed under the conditions of high strain-rate were investigated by means of OM, SEM and TEM. The results of TEM observation show that the grains in the adiabatic shear band of TC18 titanium alloy are refined due to the combined action of three mechanisms. The first mechanism is that dislocations were rapidly reproduced, moved and clogged at the obstacles such as grain boundary, second-phase particles, and so on; then, cracks were generated in the head of clogging of dislocation due to huge stress resulted from the clogging of dislocation; finally, smaller grains were formed due to breakdown of elongation grain. The second refining mechanism of grains, which is presented by us first, is inner-necking mode. The third one is dynamic recrystallization.
2011, 40(8):1458-1461.
Abstract:
Nb-21Ti-4C (βNb-Ti) alloys with different Al contents were fabricated by a vacuum non-consumable arc-melting method. The effects of Al content on the microstructure and lattice parameters of the alloys were studied. The results indicate that the as-cast alloys contain dendritic-growth niobium solid solution Nbss, carbide (Nb, Ti)C, Nb3Al and interdendritic eutectic of Nbss/MC. The nucleation and growth of Nb3Al are in dendritic Nbss, and other Al elements dissolve into Nbss and MC. The Nbss dendritic size increases first and then decreases with Al content increasing. After heat treatment at 1100 oC for 24 h, Nbss of interdendritic eutectic grows further as a discontinuous precipitation process, and needle-like or plate-like MC and Nb3Al precipitate from Nbss, resulting in lattice parameters becoming larger; the lattice parameters of MC changes with Al content change and Nb precipitation.
Nb-21Ti-4C (βNb-Ti) alloys with different Al contents were fabricated by a vacuum non-consumable arc-melting method. The effects of Al content on the microstructure and lattice parameters of the alloys were studied. The results indicate that the as-cast alloys contain dendritic-growth niobium solid solution Nbss, carbide (Nb, Ti)C, Nb3Al and interdendritic eutectic of Nbss/MC. The nucleation and growth of Nb3Al are in dendritic Nbss, and other Al elements dissolve into Nbss and MC. The Nbss dendritic size increases first and then decreases with Al content increasing. After heat treatment at 1100 oC for 24 h, Nbss of interdendritic eutectic grows further as a discontinuous precipitation process, and needle-like or plate-like MC and Nb3Al precipitate from Nbss, resulting in lattice parameters becoming larger; the lattice parameters of MC changes with Al content change and Nb precipitation.
31 Giant Magneto-Impedance Effect and Thermal Properties of the Co67.5Fe4.5Ni3Si10B15 Amorphous Wires
2011, 40(8):1462-1465.
Abstract:
The giant magneto-impedance (GMI) effect and thermal properties of the Co67.5Fe4.5Ni3Si10B15 amorphous wires, which were prepared by the in-rotating water spinning technique and annealed by passing through a direct current with a tensile stress in N2 atmosphere were investigated. After annealing in N2, the amorphous wire sample exhibits preferable brightness, soft magnetic properties and giant magneto-impedance effect. When the measurement was carried out with an exciting power of 6 dBm and an exciting frequency of 70 MHz, the samples were characterized with the largest impedance change of 125% and the biggest sensitivity of 3.92%/A·m-1. The Co67.5Fe4.5Ni3Si10B15 amorphous wires have the excellent thermal stability in the temperature range of 233-353 K, which makes this kind of amorphous wires promising materials in magnetic sensor application fields.
The giant magneto-impedance (GMI) effect and thermal properties of the Co67.5Fe4.5Ni3Si10B15 amorphous wires, which were prepared by the in-rotating water spinning technique and annealed by passing through a direct current with a tensile stress in N2 atmosphere were investigated. After annealing in N2, the amorphous wire sample exhibits preferable brightness, soft magnetic properties and giant magneto-impedance effect. When the measurement was carried out with an exciting power of 6 dBm and an exciting frequency of 70 MHz, the samples were characterized with the largest impedance change of 125% and the biggest sensitivity of 3.92%/A·m-1. The Co67.5Fe4.5Ni3Si10B15 amorphous wires have the excellent thermal stability in the temperature range of 233-353 K, which makes this kind of amorphous wires promising materials in magnetic sensor application fields.
2011, 40(8):1466-1469.
Abstract:
Effect of calcium content on corrosion rate of AZ61-1.2Y magnesium alloys in 0.5% and 3.5% NaCl solution was studied by the static mass-loss tests. The microstructures of the alloys were observed by optical microscope and the morphologies of corrosion surface were analyzed with scanning electron microscopy. The results indicate that with the addition of 1wt% calcium, the grain size of the AZ61-1.2Y alloys is obviously refined, and the microstructure and component is more homogeneous. But when the addition of calcium is more than 1wt%, the precipitates of the alloys increase and they cause the phenomenon of coarsening and segregation. Furthermore, in 0.5% and 3.5% NaCl solution, the corrosion rates of the alloys decrease firstly and then increase with the increase of calcium content. With the addition of 1wt% calcium, the corrosion rate of the alloys is lowest, and the corrosion resistance is improved remarkably.
Effect of calcium content on corrosion rate of AZ61-1.2Y magnesium alloys in 0.5% and 3.5% NaCl solution was studied by the static mass-loss tests. The microstructures of the alloys were observed by optical microscope and the morphologies of corrosion surface were analyzed with scanning electron microscopy. The results indicate that with the addition of 1wt% calcium, the grain size of the AZ61-1.2Y alloys is obviously refined, and the microstructure and component is more homogeneous. But when the addition of calcium is more than 1wt%, the precipitates of the alloys increase and they cause the phenomenon of coarsening and segregation. Furthermore, in 0.5% and 3.5% NaCl solution, the corrosion rates of the alloys decrease firstly and then increase with the increase of calcium content. With the addition of 1wt% calcium, the corrosion rate of the alloys is lowest, and the corrosion resistance is improved remarkably.
2011, 40(8):1470-1472.
Abstract:
Pure vanadium samples were prepared by hot isostatic pressing (HIP) technology. High temperature mechanical properties of the as-prepared samples in the range of 700-1100 oC were tested by means of high temperature tensile testing. The fracture surfaces and microstructures were analyzed using scanning electron microscope (SEM) and optical microscope (OM). The results show that the tensile strength, elongation and reduction in area are temperature-dependent and show approximately linear decrease with increasing the temperature. Vanadium possesses good tensile strength and ductility as the tensile temperature is 700-800 oC, and shows a feature of ductile fracture. However, a mixed ductile-brittle fracture surface is observed at the testing temperature 900-1100 oC and the cleavage face is increased with the tensile temperature rising.
Pure vanadium samples were prepared by hot isostatic pressing (HIP) technology. High temperature mechanical properties of the as-prepared samples in the range of 700-1100 oC were tested by means of high temperature tensile testing. The fracture surfaces and microstructures were analyzed using scanning electron microscope (SEM) and optical microscope (OM). The results show that the tensile strength, elongation and reduction in area are temperature-dependent and show approximately linear decrease with increasing the temperature. Vanadium possesses good tensile strength and ductility as the tensile temperature is 700-800 oC, and shows a feature of ductile fracture. However, a mixed ductile-brittle fracture surface is observed at the testing temperature 900-1100 oC and the cleavage face is increased with the tensile temperature rising.
2011, 40(8):1473-1477.
Abstract:
AZ31 Mg alloy was rolled at the temperature ranging from 603 K to 703 K with reduction from 20% to 40% and strain rate from 4 s-1 to 16 s-1. The effect of reduction per pass, strain rate and rolling temperature on the microstructure of the deformed Mg alloy was studied. The dynamic recrystallization (DRX) mechanism of AZ31 Mg alloy during hot rolling was investigated. The results demonstrate that the strain rate and the temperature not only affect the extent of DRX, but also change the mode of DRX or nucleation mechanism. When the strain rate is = 13.9 s-1, the DRX mode is twinning-induced DRX at T=603 K; but there appear some new chain-like grains along the original grain boundaries at T=703 K. When the temperature is T= 673 K, DRX is mainly twinning-induced DRX at the strain rate = 11.35 s-1, while with the strain rate decreasing to = 4 s-1, the DRX mode turns into rotation DRX.
AZ31 Mg alloy was rolled at the temperature ranging from 603 K to 703 K with reduction from 20% to 40% and strain rate from 4 s-1 to 16 s-1. The effect of reduction per pass, strain rate and rolling temperature on the microstructure of the deformed Mg alloy was studied. The dynamic recrystallization (DRX) mechanism of AZ31 Mg alloy during hot rolling was investigated. The results demonstrate that the strain rate and the temperature not only affect the extent of DRX, but also change the mode of DRX or nucleation mechanism. When the strain rate is = 13.9 s-1, the DRX mode is twinning-induced DRX at T=603 K; but there appear some new chain-like grains along the original grain boundaries at T=703 K. When the temperature is T= 673 K, DRX is mainly twinning-induced DRX at the strain rate = 11.35 s-1, while with the strain rate decreasing to = 4 s-1, the DRX mode turns into rotation DRX.
2011, 40(8):1478-1482.
Abstract:
Ti foil was put into the NaOH solution and TiO2 nanowire array films were prepared by a hydrothermal method. The effects of hydrothermal parameters on the nano-structured TiO2 and its growth mechanism were systematically studied. The samples were characterized by FESEM, XRD and TEM. The results show that the dynamic equilibrium between the dissolution of Ti and crystal growth of titanate is the main influencing factor for structures and morphologies of the products. At the same temperature, the decreased concentration of the NaOH solution leads to the increased dimension of the hydrothermal products. The temperature rise can accelerate the dissolution of Ti and the diffusion of titanate, and the products grow along linear dimension. Meantime the high temperature makes more complete crystal structure. The prepared TiO2 nanowire array exhibits good optical and electrical properties.
Ti foil was put into the NaOH solution and TiO2 nanowire array films were prepared by a hydrothermal method. The effects of hydrothermal parameters on the nano-structured TiO2 and its growth mechanism were systematically studied. The samples were characterized by FESEM, XRD and TEM. The results show that the dynamic equilibrium between the dissolution of Ti and crystal growth of titanate is the main influencing factor for structures and morphologies of the products. At the same temperature, the decreased concentration of the NaOH solution leads to the increased dimension of the hydrothermal products. The temperature rise can accelerate the dissolution of Ti and the diffusion of titanate, and the products grow along linear dimension. Meantime the high temperature makes more complete crystal structure. The prepared TiO2 nanowire array exhibits good optical and electrical properties.
2011, 40(8):1483-1487.
Abstract:
Five kinds of nano-metal carbon-supported catalysts M/C (M=Pt, Pd, Ni, Ag, Au) were prepared by a chemical reduction method. The crystal structure, surface composition and element valence state were characterized by X-ray diffraction and X-ray photoelectron spectroscopy, respectively, the morphology of the catalysts was observed by TEM, and the electro-catalytic activity to methanol oxidation was measured by cyclic voltammetry. The results show that the nano-particles with high purity are well dispersed on active black carbon and their sizes are from 3 nm to 11 nm; Pd/C catalyst exhibits high activity to methanol electro-oxidation; Ni/C possesses certain activity to methanol oxidation, but Ag/C and Au/C almost do not have activity. In 1.0 mol·L-1CH3OH+1.0 mol·L-1NaOH, the peak current density of Pd/C to methanol oxidation is 890 mA·mg-1, about 66% of that of Pt/C, and the peak current density of Ni/C is 6.3 mA·mg-1, only 0.46% of that of Pt/C.
Five kinds of nano-metal carbon-supported catalysts M/C (M=Pt, Pd, Ni, Ag, Au) were prepared by a chemical reduction method. The crystal structure, surface composition and element valence state were characterized by X-ray diffraction and X-ray photoelectron spectroscopy, respectively, the morphology of the catalysts was observed by TEM, and the electro-catalytic activity to methanol oxidation was measured by cyclic voltammetry. The results show that the nano-particles with high purity are well dispersed on active black carbon and their sizes are from 3 nm to 11 nm; Pd/C catalyst exhibits high activity to methanol electro-oxidation; Ni/C possesses certain activity to methanol oxidation, but Ag/C and Au/C almost do not have activity. In 1.0 mol·L-1CH3OH+1.0 mol·L-1NaOH, the peak current density of Pd/C to methanol oxidation is 890 mA·mg-1, about 66% of that of Pt/C, and the peak current density of Ni/C is 6.3 mA·mg-1, only 0.46% of that of Pt/C.
2011, 40(8):1488-1491.
Abstract:
The bovine serum albumin (BSA) adsorption character of pure porous titanium (PPT), acid-alkali treated porous titanium (AAPT) and alkali-heat treated porous titanium (AHPT) was investigated. The effect of surface modification on the protein adsorption behavior of porous titanium was discussed. In addition, the surface properties of the samples, including surface morphology, phase composition, roughness and contact angles, were examined by SEM, XRD, stylus profiler and contact equipment, respectively. Results show that after surface modification all the surface properties of the porous titanium change obviously, and the protein adsorption ability is enhanced evidently.
The bovine serum albumin (BSA) adsorption character of pure porous titanium (PPT), acid-alkali treated porous titanium (AAPT) and alkali-heat treated porous titanium (AHPT) was investigated. The effect of surface modification on the protein adsorption behavior of porous titanium was discussed. In addition, the surface properties of the samples, including surface morphology, phase composition, roughness and contact angles, were examined by SEM, XRD, stylus profiler and contact equipment, respectively. Results show that after surface modification all the surface properties of the porous titanium change obviously, and the protein adsorption ability is enhanced evidently.
2011, 40(8):1492-1495.
Abstract:
The ultrafine Ag powders with relatively high tap density were prepared by a chemical reduction method using AgNO3 as raw material. Hydroquinone and chain triacontanol amine were chosen as reductant and dispersant agent, respectively. The laser fineness gage was used to investigate the grain size distribution and the average diameter of Ag powders. The morphology, grain size and agglomerating state of Ag powders was examined by SEM and TEM. The phase composition of Ag powders was characterized by XRD. The results show that the grain size of Ag powders can be controlled by adjusting the concentration of AgNO3, the ratio of AgNO3 to reductant and dispersant agent dosage. The Ag powder obtained is of face-centered cubic crystal structure with quasi-orbicular morphology. The average tap density of the silver powders is up to 4.0 g/cm3.
The ultrafine Ag powders with relatively high tap density were prepared by a chemical reduction method using AgNO3 as raw material. Hydroquinone and chain triacontanol amine were chosen as reductant and dispersant agent, respectively. The laser fineness gage was used to investigate the grain size distribution and the average diameter of Ag powders. The morphology, grain size and agglomerating state of Ag powders was examined by SEM and TEM. The phase composition of Ag powders was characterized by XRD. The results show that the grain size of Ag powders can be controlled by adjusting the concentration of AgNO3, the ratio of AgNO3 to reductant and dispersant agent dosage. The Ag powder obtained is of face-centered cubic crystal structure with quasi-orbicular morphology. The average tap density of the silver powders is up to 4.0 g/cm3.
2011, 40(8):1496-1499.
Abstract:
HFC125 gas is an effective ignition-proof protection to high temperature magnesium alloy melt. The surface films from the reaction between HFC125/N2 gas mixture and Mg alloy melt was studied under the weak or strong air convection condition. The results show that under the condition of weak air convection, almost no oxygen ion exists in the obtained surface film, while under the condition of strong air convection, the surface film contains a small amount of oxygen ion. The protection effect does not change obviously for the both working conditions.
HFC125 gas is an effective ignition-proof protection to high temperature magnesium alloy melt. The surface films from the reaction between HFC125/N2 gas mixture and Mg alloy melt was studied under the weak or strong air convection condition. The results show that under the condition of weak air convection, almost no oxygen ion exists in the obtained surface film, while under the condition of strong air convection, the surface film contains a small amount of oxygen ion. The protection effect does not change obviously for the both working conditions.
2011, 40(8):1500-1504.
Abstract:
The research progress of the HITPERM soft magnetic alloys Fe(Co)-M-B-Cu (M=Nb, Zr, Hf, etc.) was summarized. The alloy design, fabrication, microstructure analysis, property test and optimization were explored. At the same time, the application of HITPERM for high temperature condition was also simply introduced.
The research progress of the HITPERM soft magnetic alloys Fe(Co)-M-B-Cu (M=Nb, Zr, Hf, etc.) was summarized. The alloy design, fabrication, microstructure analysis, property test and optimization were explored. At the same time, the application of HITPERM for high temperature condition was also simply introduced.
