Volume 39,Issue 7,2010 Table of Contents
2010, 39(7):1129-1134.
Abstract:
Three micro-arc oxidization coatings were prepared on magnesium substrates in fluorozirconate electrolyte (Zr-coating), aluminate electrolyte (Al-coating) and silicate electrolyte (Si-coating). Morphologies, phase components, surface roughness, bonding strength, hardness and corrosion resistance of the coatings were investigated. The results show that the Zr-coating is dense and mainly composed of tetragonal ZrO2 (t-ZrO2), MgF2 and Mg2Zr5O12. The porous Al-coating is mainly composed of MgAl2O4 and MgO. The Si-coating is porous and mainly consists of Mg2SiO4 and MgO. The coatings formed in the three electrolytes reveal relatively coarse surface and are bonded tightly to the substrates. The Al-coating possesses a higher hardness than the Si-coating and the Zr-coating. The corrosion resistances of the coatings on magnesium surface are obviously superior to that of the pure magnesium substrate in the NaCl solution, and the Zr-coating shows the best corrosion resistance.
Three micro-arc oxidization coatings were prepared on magnesium substrates in fluorozirconate electrolyte (Zr-coating), aluminate electrolyte (Al-coating) and silicate electrolyte (Si-coating). Morphologies, phase components, surface roughness, bonding strength, hardness and corrosion resistance of the coatings were investigated. The results show that the Zr-coating is dense and mainly composed of tetragonal ZrO2 (t-ZrO2), MgF2 and Mg2Zr5O12. The porous Al-coating is mainly composed of MgAl2O4 and MgO. The Si-coating is porous and mainly consists of Mg2SiO4 and MgO. The coatings formed in the three electrolytes reveal relatively coarse surface and are bonded tightly to the substrates. The Al-coating possesses a higher hardness than the Si-coating and the Zr-coating. The corrosion resistances of the coatings on magnesium surface are obviously superior to that of the pure magnesium substrate in the NaCl solution, and the Zr-coating shows the best corrosion resistance.
2010, 39(7):1135-1140.
Abstract:
The effects of joint addition of minor elements Cr, Mn, Zr, Ti and B on grain refinement of Al-Zn-Mg-Cu alloys were investigated by optical microscopy and scanning electron microscopy（SEM）as well as EDS. Results show that grains can be refined from 256 μm to 102 μm via adding (mass fraction) 0.04%Ti, 0.18%Zr and 0.008%B to the cast alloy. Joint addition of 0.20%Cr, 0.20%Mn, 0.04%Ti and 0.008%B may attain better grain refinement, and the average grain size is as fine as 55 μm. It is because atom clusters containing minor Cr and Mn help Al3Ti nucleation to become crystallization substrate. Joint adding of 0.20%Cr, 0.20%Mn, 0.03%Ti, 0.14%Zr and 0.006%B can result in a remarkable refinement with average grain size about 22 μm. This is because a part of Zr atoms enters the crystal nuclei of Al3Ti based on the atom clusters containing minor elements Cr and Mn to replace the Ti to form new crystal nuclei Al3(Tix, Zr1-x). While minor elements Cr and Mn decrease the surface tension between liquid aluminum and solid Al3Ti, Al3Zr and Al3(Tix, Zr1-x) particles, and impede the nucleation of particles to grow up.
The effects of joint addition of minor elements Cr, Mn, Zr, Ti and B on grain refinement of Al-Zn-Mg-Cu alloys were investigated by optical microscopy and scanning electron microscopy（SEM）as well as EDS. Results show that grains can be refined from 256 μm to 102 μm via adding (mass fraction) 0.04%Ti, 0.18%Zr and 0.008%B to the cast alloy. Joint addition of 0.20%Cr, 0.20%Mn, 0.04%Ti and 0.008%B may attain better grain refinement, and the average grain size is as fine as 55 μm. It is because atom clusters containing minor Cr and Mn help Al3Ti nucleation to become crystallization substrate. Joint adding of 0.20%Cr, 0.20%Mn, 0.03%Ti, 0.14%Zr and 0.006%B can result in a remarkable refinement with average grain size about 22 μm. This is because a part of Zr atoms enters the crystal nuclei of Al3Ti based on the atom clusters containing minor elements Cr and Mn to replace the Ti to form new crystal nuclei Al3(Tix, Zr1-x). While minor elements Cr and Mn decrease the surface tension between liquid aluminum and solid Al3Ti, Al3Zr and Al3(Tix, Zr1-x) particles, and impede the nucleation of particles to grow up.
2010, 39(7):1141-1146.
Abstract:
A2B7-type electrode alloys with a nominal composition of La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) were prepared by casting and melt-spinning. The influences of the substitution of Zr for La on the structures as well as the electrochemical performances of the alloys were investigated. The results obtained by XRD, SEM and TEM 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 substitution of Zr for La leads to an obvious increase of the LaNi5 phase in the alloys, and it also helps the formation of a like amorphous structure in the as-spun alloy. The results of the electrochemical measurements indicate that the substitution of Zr for La obviously decreases the discharge capacity of the as-cast and spun alloys, but significantly improves their cycle stability. With increasing the spinning rate, the discharge capacity of the alloys (x≤0.1) first increases and then decreases, while the cycle stability monotonously rises.
A2B7-type electrode alloys with a nominal composition of La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) were prepared by casting and melt-spinning. The influences of the substitution of Zr for La on the structures as well as the electrochemical performances of the alloys were investigated. The results obtained by XRD, SEM and TEM 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 substitution of Zr for La leads to an obvious increase of the LaNi5 phase in the alloys, and it also helps the formation of a like amorphous structure in the as-spun alloy. The results of the electrochemical measurements indicate that the substitution of Zr for La obviously decreases the discharge capacity of the as-cast and spun alloys, but significantly improves their cycle stability. With increasing the spinning rate, the discharge capacity of the alloys (x≤0.1) first increases and then decreases, while the cycle stability monotonously rises.
2010, 39(7):1147-1151.
Abstract:
Atomic structure and migration characteristics of ordered domain interfaces formed between DO22 (Ni3V) phases were investigated using the microscopic phase-field model. Studies show that the migration ability is related to the atomic structure of interfaces. During the migration of interfaces, V jumps to the nearest Ni site and exchanges with Ni, and the jump of atoms show site selectivity behaviors. The site selectivity behaviors of atom jumps force the atomic structure retaining the same before and after the interface migration. Transition interfaces formed during the migration are employed to denote the migration characteristics of interfaces. Each migratory interface forms only one kind of distinctive transition interface and has its own atom jump mode. The atom jump mode is the optimal thermodynamic and kinetics way to induce the migration of interfaces.
Atomic structure and migration characteristics of ordered domain interfaces formed between DO22 (Ni3V) phases were investigated using the microscopic phase-field model. Studies show that the migration ability is related to the atomic structure of interfaces. During the migration of interfaces, V jumps to the nearest Ni site and exchanges with Ni, and the jump of atoms show site selectivity behaviors. The site selectivity behaviors of atom jumps force the atomic structure retaining the same before and after the interface migration. Transition interfaces formed during the migration are employed to denote the migration characteristics of interfaces. Each migratory interface forms only one kind of distinctive transition interface and has its own atom jump mode. The atom jump mode is the optimal thermodynamic and kinetics way to induce the migration of interfaces.
2010, 39(7):1152-1156.
Abstract:
Ti-Al-C composite was fabricated by infiltration-in situ reaction. The as-cast material was prepared by pressing molten pure aluminum into the preform composed of titanium particles and carbon fibers. In situ reacted samples were obtained by heating the as-cast material from 600 to 1000 oC, and holding for 1 h at different temperatures. The morphology and elemental composition of samples were analyzed by scanning electron microscope and Energy dispersive X-ray, respectively. In addition, the phase composition of products was inspected by X-ray diffraction. Results show that TiAl3 and Al4C3 are formed at low temperature; with increasing of temperature, TiAl3 decomposes and TiC precipitates; at high temperature, the oxidation occurs resulting in the formation of Al2O3. The mechanism of Ti-Al-C system composite during in situ reaction procedure is as following: formation-decomposition-precipitation-oxidation.
Ti-Al-C composite was fabricated by infiltration-in situ reaction. The as-cast material was prepared by pressing molten pure aluminum into the preform composed of titanium particles and carbon fibers. In situ reacted samples were obtained by heating the as-cast material from 600 to 1000 oC, and holding for 1 h at different temperatures. The morphology and elemental composition of samples were analyzed by scanning electron microscope and Energy dispersive X-ray, respectively. In addition, the phase composition of products was inspected by X-ray diffraction. Results show that TiAl3 and Al4C3 are formed at low temperature; with increasing of temperature, TiAl3 decomposes and TiC precipitates; at high temperature, the oxidation occurs resulting in the formation of Al2O3. The mechanism of Ti-Al-C system composite during in situ reaction procedure is as following: formation-decomposition-precipitation-oxidation.
2010, 39(7):1157-1161.
Abstract:
The microstructure features of a kind of Ni-Cr-W superalloy after solution heat treatment at different temperatures (1230-1300 °C) for various time (10-120 min) were investigated by means of scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that the precipitated phases of the alloy after solution heat treatment are identified as W-rich fcc M6C and Cr-rich fcc M23C6 carbides. The volume fraction of carbides decreases with increasing of the solution heat treatment temperature and time. At the temperature above 1270 °C for 120 min, most of carbides are dissolved into the Ni-matrix, and the carbides distributing at twin boundaries may be dissolved into the matrix first. M6C carbide has no any fixed orientation relationship with the Ni-matrix, but the angle of M23C6 (220) to the matrix (11) is 30°.
The microstructure features of a kind of Ni-Cr-W superalloy after solution heat treatment at different temperatures (1230-1300 °C) for various time (10-120 min) were investigated by means of scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that the precipitated phases of the alloy after solution heat treatment are identified as W-rich fcc M6C and Cr-rich fcc M23C6 carbides. The volume fraction of carbides decreases with increasing of the solution heat treatment temperature and time. At the temperature above 1270 °C for 120 min, most of carbides are dissolved into the Ni-matrix, and the carbides distributing at twin boundaries may be dissolved into the matrix first. M6C carbide has no any fixed orientation relationship with the Ni-matrix, but the angle of M23C6 (220) to the matrix (11) is 30°.
2010, 39(7):1162-1165.
Abstract:
Driving forces of grain growth during dynamic recrystallization of TA15 titanium alloy were analyzed theoretically and the equivalent negative driving forces concept for dynamic recrystallization grain growth was also proposed. Based on driving forces of dynamic recrystallization grain growth, a grain growth rate model and a grain size model describing grain size evolution of TA15 titanium alloy during dynamic recrystallization were established. Taking the experimental data of dynamic recrystallization grain size of TA15 titanium alloy as an example, the size model parameters were optimized by genetic algorithm (GA). The calculated results of grains size were in good agreement with the experimental values, whose average error was 7.4%
Driving forces of grain growth during dynamic recrystallization of TA15 titanium alloy were analyzed theoretically and the equivalent negative driving forces concept for dynamic recrystallization grain growth was also proposed. Based on driving forces of dynamic recrystallization grain growth, a grain growth rate model and a grain size model describing grain size evolution of TA15 titanium alloy during dynamic recrystallization were established. Taking the experimental data of dynamic recrystallization grain size of TA15 titanium alloy as an example, the size model parameters were optimized by genetic algorithm (GA). The calculated results of grains size were in good agreement with the experimental values, whose average error was 7.4%
2010, 39(7):1166-1170.
Abstract:
The hot deformation and dynamic recrystallization (DRX) behavior of 15%SiC particle reinforced aluminum matrix composites were studied through isothermal compression test at the temperature of 713-773 K and the strain rate of 0.001-1 s-1; the hot deformation constitutive equation was established. Meanwhile, DRX grain size of the composites was measured by a Quantiment-500 automatic image analyzer. In the study, q–s and ?q/?s–s curves were plotted based on the experimental data to further obtain the critical strain and steady strain of DRX. Then the critical strain model and the steady strain model of DRX were set up by regression analysis of experimental data. Based on the results, the diagram of DRX for SiC particle reinforced aluminum matrix composites was given.
The hot deformation and dynamic recrystallization (DRX) behavior of 15%SiC particle reinforced aluminum matrix composites were studied through isothermal compression test at the temperature of 713-773 K and the strain rate of 0.001-1 s-1; the hot deformation constitutive equation was established. Meanwhile, DRX grain size of the composites was measured by a Quantiment-500 automatic image analyzer. In the study, q–s and ?q/?s–s curves were plotted based on the experimental data to further obtain the critical strain and steady strain of DRX. Then the critical strain model and the steady strain model of DRX were set up by regression analysis of experimental data. Based on the results, the diagram of DRX for SiC particle reinforced aluminum matrix composites was given.
2010, 39(7):1171-1174.
Abstract:
Doppler-broadening spectra of positron annihilation radiation for pure metals Ni, Co and Cr and Ni-Co-Cr alloys with three different chemical compositions were measured by 2-detector coincidence technique. And the effect of the 3d electrons on Ni-Co-Cr alloy formation was analyzed. The results show that the 3d electron signal for the metal Ni is relatively higher among the three pure metals. The increase of Ni atom proportion in Ni-Co-Cr alloys leads to an increase in the probability of positron annihilation with free electrons. The experimental ratio curves for three Ni-Co-Cr alloys are greatly similar to the corresponding theoretic ratio curves, which indicate that the bonding nature in Ni-Co-Cr alloys is mainly metallic. This can explain why the Ni-Co-Cr alloys have good metal ductility.
Doppler-broadening spectra of positron annihilation radiation for pure metals Ni, Co and Cr and Ni-Co-Cr alloys with three different chemical compositions were measured by 2-detector coincidence technique. And the effect of the 3d electrons on Ni-Co-Cr alloy formation was analyzed. The results show that the 3d electron signal for the metal Ni is relatively higher among the three pure metals. The increase of Ni atom proportion in Ni-Co-Cr alloys leads to an increase in the probability of positron annihilation with free electrons. The experimental ratio curves for three Ni-Co-Cr alloys are greatly similar to the corresponding theoretic ratio curves, which indicate that the bonding nature in Ni-Co-Cr alloys is mainly metallic. This can explain why the Ni-Co-Cr alloys have good metal ductility.
Xie Bin
,
Liao Shuzhi
,
Chen Jia
,
Lü Yunbin
,
Peng Haojun
,
Wang Xiaoli
,
Zhang Chun
,
Xie Haowen
,
Ouyang Yifang
,
Zhang Bangwei
2010, 39(7):1175-1179.
Abstract:
Taking account of the surface effect, the formula for the calculation of the formation enthalpy of nano Ti binary alloys was deduced by modified Miedema model. And the formula was used to study the formation enthalpy of Ti-M (M=Si, Fe, Zn, Tc, Cd, Re, Os, Pb, Bi) nano binary alloys. The results show that the formation enthalpy and structure stability are affected by the grain size for Ti binary alloys with the same composition. That is to say, the smaller the particle size, the greater the formation enthalpy and the worse the structure stability. Also, the component segregation for the nano Ti binary alloys is very clear when the grain size is less than 10 nm. The direction and the degree of aggregation are controlled by the aggregation driving energy.
Taking account of the surface effect, the formula for the calculation of the formation enthalpy of nano Ti binary alloys was deduced by modified Miedema model. And the formula was used to study the formation enthalpy of Ti-M (M=Si, Fe, Zn, Tc, Cd, Re, Os, Pb, Bi) nano binary alloys. The results show that the formation enthalpy and structure stability are affected by the grain size for Ti binary alloys with the same composition. That is to say, the smaller the particle size, the greater the formation enthalpy and the worse the structure stability. Also, the component segregation for the nano Ti binary alloys is very clear when the grain size is less than 10 nm. The direction and the degree of aggregation are controlled by the aggregation driving energy.
2010, 39(7):1180-1184.
Abstract:
Microstructures and mechanical properties of Mg-6Al-1.2Y-0.9Nd magnesium alloy with Sn addition were investigated by OM, SEM, EDS and XRD. The results show the addition of Sn can dramatically enhance the tensile strength of the alloy in the temperature range of 25-175 oC. When the content of Sn is up to 1%, the values of tensile strength of the alloy at room temperature and 175 oC are up to their maximums simultaneously, 242 MPa and 192 MPa, respectively. The fracture of the alloy is quasi-cleavage failure with plastic characteristic. It can be found that the grain of alloy is obviously refined with the addition of Sn. The high-melting phases Mg2Sn is found in the alloy with the addition of Sn. Sn can improve the mechanical properties of Mg-6Al-1.2Y-0.9Nd alloy because of the grain?refining?strengthening, solution strengthening and dispersion strengthening.
Microstructures and mechanical properties of Mg-6Al-1.2Y-0.9Nd magnesium alloy with Sn addition were investigated by OM, SEM, EDS and XRD. The results show the addition of Sn can dramatically enhance the tensile strength of the alloy in the temperature range of 25-175 oC. When the content of Sn is up to 1%, the values of tensile strength of the alloy at room temperature and 175 oC are up to their maximums simultaneously, 242 MPa and 192 MPa, respectively. The fracture of the alloy is quasi-cleavage failure with plastic characteristic. It can be found that the grain of alloy is obviously refined with the addition of Sn. The high-melting phases Mg2Sn is found in the alloy with the addition of Sn. Sn can improve the mechanical properties of Mg-6Al-1.2Y-0.9Nd alloy because of the grain?refining?strengthening, solution strengthening and dispersion strengthening.
2010, 39(7):1185-1188.
Abstract:
Based on the microscopic phase-field kinetic model, the evolution of Ni75Cr16.4Al8.6 alloy in the later stage of coarsening was studied using the structure function normalized factor and scaling function. The simulation results show that both the curves of scaling function of L12 phase and DO22 phase present scaling behavior in the coarsening process. Without elastic strain energy, the peak values of structure function normalized factor and scaling function of DO22 phase are higher than that of L12 phase. When the elastic strain energy is added, the curve peaks of both phases become smaller. It means the growth of both phases are stunted by strain energy; compared with L12 phase, the decrease extent of DO22 phase is larger; peak values of structure function factor and scaling function of L12 phase are higher than that of DO22 phase. The strain energy plays a greater role of restriction on DO22 phase.
Based on the microscopic phase-field kinetic model, the evolution of Ni75Cr16.4Al8.6 alloy in the later stage of coarsening was studied using the structure function normalized factor and scaling function. The simulation results show that both the curves of scaling function of L12 phase and DO22 phase present scaling behavior in the coarsening process. Without elastic strain energy, the peak values of structure function normalized factor and scaling function of DO22 phase are higher than that of L12 phase. When the elastic strain energy is added, the curve peaks of both phases become smaller. It means the growth of both phases are stunted by strain energy; compared with L12 phase, the decrease extent of DO22 phase is larger; peak values of structure function factor and scaling function of L12 phase are higher than that of DO22 phase. The strain energy plays a greater role of restriction on DO22 phase.
2010, 39(7):1189-1194.
Abstract:
By means of the statistical data of valence electron structure parameters of metallic phase and phase interfaces combined with the preparation technology and phase transformation, the theoretical calculation formulae for the tensile strength of high strength titanium alloys were put forward, i.e., the tensile strength of high strength titanium alloys is the sum of strength of b-Ti and the strengthening strength increments caused by solid-solution strengthening and interface strengthening including precipitation strengthening of alloying element. Based on the experimental data of the high strength metastable b titanium alloy Ti-B20 developed by Northwest Institute for Nonferrous Metal Research, its tensile strength was calculated when it was treated by solid solution above b transus, below b transus and at 780 °C followed by aging, respectively. The calculation results agree well with the experimental results.
By means of the statistical data of valence electron structure parameters of metallic phase and phase interfaces combined with the preparation technology and phase transformation, the theoretical calculation formulae for the tensile strength of high strength titanium alloys were put forward, i.e., the tensile strength of high strength titanium alloys is the sum of strength of b-Ti and the strengthening strength increments caused by solid-solution strengthening and interface strengthening including precipitation strengthening of alloying element. Based on the experimental data of the high strength metastable b titanium alloy Ti-B20 developed by Northwest Institute for Nonferrous Metal Research, its tensile strength was calculated when it was treated by solid solution above b transus, below b transus and at 780 °C followed by aging, respectively. The calculation results agree well with the experimental results.
2010, 39(7):1195-1198.
Abstract:
Quasi-static, dynamic and high-temperature tension experiments for the composite TP-650 were carried out by MTS-810, bar-bar tensile impact apparatus (SHTB) and Instron-1195 machine, respectively. The coupling effects of temperature and strain rate on the mechanical properties of TiC particle reinforced titanium matrix composite TP-650 were investigated. The results show that the TP-650 composite has excellent mechanical properties at elevated temperatures, even at 650 oC. At room temperature, TP-650 composite has higher strength and lower toughness than the matrix. TP-650 composite shows positive strain rate sensitivity below the strain rate of 1000 s-1. Based on the experiment results, the rheological mechanics model of TP-650 composite was established with Arrhenius equation in the form of hyperbolic sine function, and the model prediction agreed with the experimental results.
Quasi-static, dynamic and high-temperature tension experiments for the composite TP-650 were carried out by MTS-810, bar-bar tensile impact apparatus (SHTB) and Instron-1195 machine, respectively. The coupling effects of temperature and strain rate on the mechanical properties of TiC particle reinforced titanium matrix composite TP-650 were investigated. The results show that the TP-650 composite has excellent mechanical properties at elevated temperatures, even at 650 oC. At room temperature, TP-650 composite has higher strength and lower toughness than the matrix. TP-650 composite shows positive strain rate sensitivity below the strain rate of 1000 s-1. Based on the experiment results, the rheological mechanics model of TP-650 composite was established with Arrhenius equation in the form of hyperbolic sine function, and the model prediction agreed with the experimental results.
2010, 39(7):1199-1201.
Abstract:
Material failure usually occurs on the surface. A nanocrystallization surface layer on the rare-earth magnesium alloy was fabricated by low-temperature HVOF particles obtained from novel HVOF equipment. The microstructure of the surface layer was characterized by OM and TEM. The micro-hardness was also tested along the sample thickness direction. The results show that the surface grain refinement of rare earth magnesium alloy is obvious and the grain size is less than 20 nm; grain orientation is random and the depth of the nanocrystallization layer is about 80 μm. The grain size increases with increasing of the distance from the surface. The formation mechanism of nanocrystallization is as follows: the coordinated deformation of twins and dislocation lead to segmentation and refinement of large grains. The surface hardness is increased significantly, which is about twice as high as the hardness of the matrix.
Material failure usually occurs on the surface. A nanocrystallization surface layer on the rare-earth magnesium alloy was fabricated by low-temperature HVOF particles obtained from novel HVOF equipment. The microstructure of the surface layer was characterized by OM and TEM. The micro-hardness was also tested along the sample thickness direction. The results show that the surface grain refinement of rare earth magnesium alloy is obvious and the grain size is less than 20 nm; grain orientation is random and the depth of the nanocrystallization layer is about 80 μm. The grain size increases with increasing of the distance from the surface. The formation mechanism of nanocrystallization is as follows: the coordinated deformation of twins and dislocation lead to segmentation and refinement of large grains. The surface hardness is increased significantly, which is about twice as high as the hardness of the matrix.
2010, 39(7):1202-1205.
Abstract:
Rare-earth metal-organic frameworks, [Tb2(pydc-3,5)3(H2O)9]n3nH2O, was synthesized under a hydrothermal condition. Then the composition and the crystal structure of the compound were determined by single-crystal X-ray diffraction, element analysis and IR spectra. Results show that pyridine-3,5-dicarboxylic acid (pydc-3,5) ligand and Tb element form one-dimensional chain-like coordination polymer. Here the central rare-earth metal Tb has two typical coordination environments and each metal atom is nine-coordinated with oxygen atoms. The carboxylate groups of pydc-3,5 ligand provide two kinds of coordination ways as didentate and monodentate. The terbium complex can emit characteristic green fluorescence of Tb3+ and the solid-state photoluminescence spectra show that the complex has excellent fluorescence property.
Rare-earth metal-organic frameworks, [Tb2(pydc-3,5)3(H2O)9]n3nH2O, was synthesized under a hydrothermal condition. Then the composition and the crystal structure of the compound were determined by single-crystal X-ray diffraction, element analysis and IR spectra. Results show that pyridine-3,5-dicarboxylic acid (pydc-3,5) ligand and Tb element form one-dimensional chain-like coordination polymer. Here the central rare-earth metal Tb has two typical coordination environments and each metal atom is nine-coordinated with oxygen atoms. The carboxylate groups of pydc-3,5 ligand provide two kinds of coordination ways as didentate and monodentate. The terbium complex can emit characteristic green fluorescence of Tb3+ and the solid-state photoluminescence spectra show that the complex has excellent fluorescence property.
2010, 39(7):1206-1209.
Abstract:
Disordered-orientation TiO2 nanotube array films were prepared by constant-potential anodization of a novel near-β titanium alloy Ti-5Zr-3Sn-5Mo-25Nb (TLM). The TiO2 film can induce the deposition of the apatite to form HA in simulated body fluid (SBF), indicating that the film does not restrict early adhesion of the osteoblast and possesses good biocompatibility. By comparison, it is found that the adhesion ratio of osteoblast on TLM with disordered-orientation TiO2 nanotube array films after soaking in SBF for 3 d is obviously higher than that of Ti sheet with TiO2 nanotube arrays, and the cellular morphology is excellent. It is concluded that the anodization can further improve the biocompatibility and bioactivity of TLM titanium alloy.
Disordered-orientation TiO2 nanotube array films were prepared by constant-potential anodization of a novel near-β titanium alloy Ti-5Zr-3Sn-5Mo-25Nb (TLM). The TiO2 film can induce the deposition of the apatite to form HA in simulated body fluid (SBF), indicating that the film does not restrict early adhesion of the osteoblast and possesses good biocompatibility. By comparison, it is found that the adhesion ratio of osteoblast on TLM with disordered-orientation TiO2 nanotube array films after soaking in SBF for 3 d is obviously higher than that of Ti sheet with TiO2 nanotube arrays, and the cellular morphology is excellent. It is concluded that the anodization can further improve the biocompatibility and bioactivity of TLM titanium alloy.
2010, 39(7):1210-1214.
Abstract:
A new nickel base superalloy was prepared by spray forming process, which was then treated by hot-isostatic pressing. The hot compression tests were conducted under various testing conditions by a Gleeble-3500 thermal simulation instrument. The deformation mechanisms were studied by optical microscope, scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that the actual deformation temperature is higher than the nominal deformation temperature at the high strain rate of 10 s-1 due to the friction heating and thus the dynamic recrystallization (DRX) is promoted. The twin grain formed at the high strain rate can further excite sliding deformation, while lots of dislocation formed in subgrains can coordinate the deformation to ensure its proceeding. The model of the DRX grain size is established as lnd=8.26–0.058lnZ. It shows that at the fixed testing temperature, with the increase of Z parameter, viz. the increase of strain rate, the DRX grain is refined and the deformability is enhanced, which is consistent with the testing results.
A new nickel base superalloy was prepared by spray forming process, which was then treated by hot-isostatic pressing. The hot compression tests were conducted under various testing conditions by a Gleeble-3500 thermal simulation instrument. The deformation mechanisms were studied by optical microscope, scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that the actual deformation temperature is higher than the nominal deformation temperature at the high strain rate of 10 s-1 due to the friction heating and thus the dynamic recrystallization (DRX) is promoted. The twin grain formed at the high strain rate can further excite sliding deformation, while lots of dislocation formed in subgrains can coordinate the deformation to ensure its proceeding. The model of the DRX grain size is established as lnd=8.26–0.058lnZ. It shows that at the fixed testing temperature, with the increase of Z parameter, viz. the increase of strain rate, the DRX grain is refined and the deformability is enhanced, which is consistent with the testing results.
2010, 39(7):1215-1218.
Abstract:
The modified PbO2 electrodes doped with rare earth compounds, i.e. Nd(NO3)3, Ce(NO3)3, Gd2O3 and Sm2O3, were prepared by electrodeposition method and the influences of rare earth modification on the performances of PbO2 electrodes were investigated. XRD, SEM and EDS were employed to research the crystal phase structure, surface morphology and element composition of the modified electrodes respectively. XRD analysis reveals that the crystal form of PbO2 electrodes is not changed and the crystal purity of β-PbO2 is improved. SEM results indicate that the morphology of the electrode surface have changed at different degrees. EDS results suggest that the added rare-earth may enter PbO2 surface layer. The phenol degradation experiments and strengthened lifetime tests show that the electrocatalytic activity and stability of the modified electrodes are better.
The modified PbO2 electrodes doped with rare earth compounds, i.e. Nd(NO3)3, Ce(NO3)3, Gd2O3 and Sm2O3, were prepared by electrodeposition method and the influences of rare earth modification on the performances of PbO2 electrodes were investigated. XRD, SEM and EDS were employed to research the crystal phase structure, surface morphology and element composition of the modified electrodes respectively. XRD analysis reveals that the crystal form of PbO2 electrodes is not changed and the crystal purity of β-PbO2 is improved. SEM results indicate that the morphology of the electrode surface have changed at different degrees. EDS results suggest that the added rare-earth may enter PbO2 surface layer. The phenol degradation experiments and strengthened lifetime tests show that the electrocatalytic activity and stability of the modified electrodes are better.
2010, 39(7):1219-1223.
Abstract:
To fabricate Tritium Penetration Barrier (TBP) of aluminide coating on stainless steel, aluminum electrodeposition experiments on the HR-2 stainless steel were carried out by ambient temperature chloroaluminate melts AlCi3(aluminum chloride)/EMIC (1-ethyl-3-methylimidazolium chloride) under the protection of argon gas. The influences of pre-treatment of the substrate and the current density on the surface morphology, purity and adhesion of the aluminum coating were examined. The results show that the aluminum electrodeposition on HR-2 stainless steel by ambient temperature melts system AlCl3/MEIC is feasible. The aluminum coating on the HR-2 stainless steel substrate with conventional pretreatment is of high quality but the adherence to the substrate is not good. However, electrochemical etching of the substrate by anodic polarization prior to electroplating leads to well-adherent Al coating of HR-2 stainless steel. The deposited aluminum coating is white, smooth, uniform and dense, having the characteristics of irregular sphere particle-like growth with certain edge angle. The particle size of the aluminum coating increases with increasing current density. The preferable range of current density is 10-20 mA/cm2, and the electroplating time is 40 min at least.
To fabricate Tritium Penetration Barrier (TBP) of aluminide coating on stainless steel, aluminum electrodeposition experiments on the HR-2 stainless steel were carried out by ambient temperature chloroaluminate melts AlCi3(aluminum chloride)/EMIC (1-ethyl-3-methylimidazolium chloride) under the protection of argon gas. The influences of pre-treatment of the substrate and the current density on the surface morphology, purity and adhesion of the aluminum coating were examined. The results show that the aluminum electrodeposition on HR-2 stainless steel by ambient temperature melts system AlCl3/MEIC is feasible. The aluminum coating on the HR-2 stainless steel substrate with conventional pretreatment is of high quality but the adherence to the substrate is not good. However, electrochemical etching of the substrate by anodic polarization prior to electroplating leads to well-adherent Al coating of HR-2 stainless steel. The deposited aluminum coating is white, smooth, uniform and dense, having the characteristics of irregular sphere particle-like growth with certain edge angle. The particle size of the aluminum coating increases with increasing current density. The preferable range of current density is 10-20 mA/cm2, and the electroplating time is 40 min at least.
2010, 39(7):1224-1229.
Abstract:
Isothermal oxidation behavior of CoNiCrAlY(Re) alloy before and after heat-treatment at 1000 oC in air was investigated by X-ray diffraction, scanning microscopy and energy spectroscopy analysis. The results show that heat-treatment favors the homogeneous distribution of Al-rich phase in the alloy. Heat-treatment induces alloys to enter steady oxidation stage faster and lowers the oxidation rate. Compared with Re-undoped alloy, Re-doped alloy has higher oxidation mass gain during the initial oxidation stage and earlier phase transformation of alumina from metastable θ-Al2O3 to stable α-Al2O3.
Isothermal oxidation behavior of CoNiCrAlY(Re) alloy before and after heat-treatment at 1000 oC in air was investigated by X-ray diffraction, scanning microscopy and energy spectroscopy analysis. The results show that heat-treatment favors the homogeneous distribution of Al-rich phase in the alloy. Heat-treatment induces alloys to enter steady oxidation stage faster and lowers the oxidation rate. Compared with Re-undoped alloy, Re-doped alloy has higher oxidation mass gain during the initial oxidation stage and earlier phase transformation of alumina from metastable θ-Al2O3 to stable α-Al2O3.
2010, 39(7):1230-1234.
Abstract:
Diamond-like multilayer films were deposited on Ti6Al4V alloy substrate by filtered cathodic vacuum arc (FCVA) technique. The morphology of the films was observed with an atomic force microscope and the hardness was determined with a nano-indenter. Tribological properties and corrosion resistance of the diamond-like multilayer film in simulated body fluid were investigated using a micro-abrasion tribometer and an electrochemical testing system with three electrodes. Results show that the multilayer films consist of compact nanoparticles, and the surface roughness is about 4.86 nm; the hardness and elastic modulus of multilayer films are approximately 54.82 GPa and 342.27 GPa, respectively. In simulated body fluid, the diamond-like multilayer film remarkably improves the anti-wear ability and friction-reduction performances of the Ti6Al4V alloy substrate, and the wear rate of the multilayer film is only 11.7%-22.6% of Ti6Al4V alloy’s. With an increase of load, the corrosion potential of the film decreases and the corrosion current density increases; the deposited diamond-like multilayer films can effectively improve the corrosion resistance of Ti6Al4V alloy.
Diamond-like multilayer films were deposited on Ti6Al4V alloy substrate by filtered cathodic vacuum arc (FCVA) technique. The morphology of the films was observed with an atomic force microscope and the hardness was determined with a nano-indenter. Tribological properties and corrosion resistance of the diamond-like multilayer film in simulated body fluid were investigated using a micro-abrasion tribometer and an electrochemical testing system with three electrodes. Results show that the multilayer films consist of compact nanoparticles, and the surface roughness is about 4.86 nm; the hardness and elastic modulus of multilayer films are approximately 54.82 GPa and 342.27 GPa, respectively. In simulated body fluid, the diamond-like multilayer film remarkably improves the anti-wear ability and friction-reduction performances of the Ti6Al4V alloy substrate, and the wear rate of the multilayer film is only 11.7%-22.6% of Ti6Al4V alloy’s. With an increase of load, the corrosion potential of the film decreases and the corrosion current density increases; the deposited diamond-like multilayer films can effectively improve the corrosion resistance of Ti6Al4V alloy.
2010, 39(7):1240-1243.
Abstract:
Noble metal ruthenium-doped TiO2/Ti photoelectrodes were prepared by anodization. The photoelectrodes were characterized by EIS, XRD and SEM. And the photoelectrocatalytic degradation of methylene blue was carried out using the photoelectrodes. The results show that ruthenium doping can increase the specific surface area and enhance the photoelectrocatalytic activity of TiO2/Ti photoelectrodes. In 0.5% HF electrolyte, the optimal parameters are anodization voltage of 20 V, anodization time of 20 min and heat treatment of 600 oC for ruthenium-doped TiO2/Ti photoelectrode preparation. With bias voltage of 0.2 V, methylene blue were decolored completely in 120 min by ruthenium-doped TiO2/Ti photoelectrodes under UV light(125 W).
Noble metal ruthenium-doped TiO2/Ti photoelectrodes were prepared by anodization. The photoelectrodes were characterized by EIS, XRD and SEM. And the photoelectrocatalytic degradation of methylene blue was carried out using the photoelectrodes. The results show that ruthenium doping can increase the specific surface area and enhance the photoelectrocatalytic activity of TiO2/Ti photoelectrodes. In 0.5% HF electrolyte, the optimal parameters are anodization voltage of 20 V, anodization time of 20 min and heat treatment of 600 oC for ruthenium-doped TiO2/Ti photoelectrode preparation. With bias voltage of 0.2 V, methylene blue were decolored completely in 120 min by ruthenium-doped TiO2/Ti photoelectrodes under UV light(125 W).
2010, 39(7):1244-1247.
Abstract:
The application of Ti powder as active filler in the ceramic preparation by polysilazane (PSN-1) precursor pyrolysis was researched by means of IR, TG and XRD. Results show that Ti powder can effectively improve the ceramic yield of the precursor. In the experiment, the ceramic yield of the pure PSN-1 precursor pyrolyzed at 1300 oC was only 37.3%; while after adding Ti powder (Ti/PSN-1=3/10, mass fraction), the yield after 1300 oC pyrolysis was 78.7%, increasing by 40%. IR spectra reveal Ti powder addition to the precursor can accelerate the transformation from organic precursor to inorganic ceramic. XRD analysis show Ti powder as an active filler in the precursor can react with the cracker-volatile and the protective atmosphere, generating TiC, TiN and other new phases, which favors the increase of the ceramic yield.
The application of Ti powder as active filler in the ceramic preparation by polysilazane (PSN-1) precursor pyrolysis was researched by means of IR, TG and XRD. Results show that Ti powder can effectively improve the ceramic yield of the precursor. In the experiment, the ceramic yield of the pure PSN-1 precursor pyrolyzed at 1300 oC was only 37.3%; while after adding Ti powder (Ti/PSN-1=3/10, mass fraction), the yield after 1300 oC pyrolysis was 78.7%, increasing by 40%. IR spectra reveal Ti powder addition to the precursor can accelerate the transformation from organic precursor to inorganic ceramic. XRD analysis show Ti powder as an active filler in the precursor can react with the cracker-volatile and the protective atmosphere, generating TiC, TiN and other new phases, which favors the increase of the ceramic yield.
2010, 39(7):1248-1250.
Abstract:
Ti12Zr10Si5Fe2Sn amorphous alloy was prepared by rapid solidification. Its microstructure and mechanical properties were investigated by XRD, TEM, SEM and a tensile testing machine. The results show that the Ti12Zr10Si5Fe2Sn amorphous alloy has good mechanical properties. Its tensile strength is up to 399 MPa, yield stress is 329 MPa, and elongation at break is 2.5%. Moreover, its elastic modulus is 39 GPa, which is closer to elastic modulus of human bone than that of crystal metal. In addition, the fracture morphology was also analyzed.
Ti12Zr10Si5Fe2Sn amorphous alloy was prepared by rapid solidification. Its microstructure and mechanical properties were investigated by XRD, TEM, SEM and a tensile testing machine. The results show that the Ti12Zr10Si5Fe2Sn amorphous alloy has good mechanical properties. Its tensile strength is up to 399 MPa, yield stress is 329 MPa, and elongation at break is 2.5%. Moreover, its elastic modulus is 39 GPa, which is closer to elastic modulus of human bone than that of crystal metal. In addition, the fracture morphology was also analyzed.
2010, 39(7):1251-1255.
Abstract:
Diamond-like carbon films (DLC) doped with W for different time on Si substrate surface were prepared by KrF pulsed excimer laser ablution deposition (PLD) technique. The surface morphology, microstructure and some properties of the films were researched by AFM, XRD, Raman spectra and nano indenter. Results show that α-W2C and WC phases were formed after W doping, but the content of sp2 and sp3 in the film did not change obviously. The surface roughness was not sensitive to the W doping time. W doping resulted in the decrease of the residual stress by a magnitude (from higher than 20 GPa to several GPa). Meanwhile, the hardness and modulus of the films were decreased with increasing of W doping time.
Diamond-like carbon films (DLC) doped with W for different time on Si substrate surface were prepared by KrF pulsed excimer laser ablution deposition (PLD) technique. The surface morphology, microstructure and some properties of the films were researched by AFM, XRD, Raman spectra and nano indenter. Results show that α-W2C and WC phases were formed after W doping, but the content of sp2 and sp3 in the film did not change obviously. The surface roughness was not sensitive to the W doping time. W doping resulted in the decrease of the residual stress by a magnitude (from higher than 20 GPa to several GPa). Meanwhile, the hardness and modulus of the films were decreased with increasing of W doping time.
2010, 39(7):1256-1259.
Abstract:
Fatigue properties and deformation mechanism of Ti2.5Cu alloy were studied after solution and two-step aging at 293 K and 77 K. The results show that the fatigue plastic index of Ti2.5Cu alloy at 293 K and 77 K were –0.68 and –0.5, respectively. At 293 K dislocation slip mechanism was dominant. However, at 77 K twinning shear was rather active and various types of twins were found. Meanwhile, needle-like Ti2Cu strengthening phases hindered movement of dislocation and brought about obvious cyclic hardening, but they had little effect on the twinning process.
Fatigue properties and deformation mechanism of Ti2.5Cu alloy were studied after solution and two-step aging at 293 K and 77 K. The results show that the fatigue plastic index of Ti2.5Cu alloy at 293 K and 77 K were –0.68 and –0.5, respectively. At 293 K dislocation slip mechanism was dominant. However, at 77 K twinning shear was rather active and various types of twins were found. Meanwhile, needle-like Ti2Cu strengthening phases hindered movement of dislocation and brought about obvious cyclic hardening, but they had little effect on the twinning process.
2010, 39(7):1260-1264.
Abstract:
The combinatorial material chip approach is an advanced method for inorganic functional materials and it can rapidly discover and optimize novel materials. In this paper, the approach was used to study flourescent material gadolinium aluminate phosphors (Gd1-xAlyOz:Eux). The Gd1-xAlyOz:Eux gradational combinatorial material chips were prepared by ion beam sputtering deposition and two-step annealing. XRD patterns and SEM second electron images indicate that different gadolinium aluminate phases were formed in the combinatorial material chips corresponding to the different Gd:Al stoichiometry. Gd4Al2O9(GAM) and GdAlO3(GAP) were stable phases in Gd2O3-Al2O3 system, and their single phase polycrystal films were easy to synthesize. Under UV light excitation (λex=254 nm), the gradational material library showed all Gd1-xAlyOz:Eux phosphors gave bright red emission (Eu3+5, D0–7F2, 615 nm) and the best matrix for Eu3+ dopant should be GdAlO3. This library screening result was also verified by photoluminescence spectra and absorption spectra.
The combinatorial material chip approach is an advanced method for inorganic functional materials and it can rapidly discover and optimize novel materials. In this paper, the approach was used to study flourescent material gadolinium aluminate phosphors (Gd1-xAlyOz:Eux). The Gd1-xAlyOz:Eux gradational combinatorial material chips were prepared by ion beam sputtering deposition and two-step annealing. XRD patterns and SEM second electron images indicate that different gadolinium aluminate phases were formed in the combinatorial material chips corresponding to the different Gd:Al stoichiometry. Gd4Al2O9(GAM) and GdAlO3(GAP) were stable phases in Gd2O3-Al2O3 system, and their single phase polycrystal films were easy to synthesize. Under UV light excitation (λex=254 nm), the gradational material library showed all Gd1-xAlyOz:Eux phosphors gave bright red emission (Eu3+5, D0–7F2, 615 nm) and the best matrix for Eu3+ dopant should be GdAlO3. This library screening result was also verified by photoluminescence spectra and absorption spectra.
2010, 39(7):1265-1269.
Abstract:
Ti based oxide anode with SnO2+SbOx was prepared by a thermal decomposition method. The SnO2+SbOx solid solution was characterized with TG/DTA, XRD and XPS. The growth activation energy of SnO2+SbOx solid solution was calculated and its activation mechanism was discussed. Meanwhile the expected lifetime of the oxide anode under high current density of 2 A/cm2 and in 0.5 mol/L H2SO4 solution was determined by a fast life method. The results show that the free electrons and oxygen vacancy produced by the N-type semiconductor and P-type semiconductor from Sb-doped SnO2 enhance the electrode conductivity and increase its expected lifetime to 30 h. The oxygen vacancy and too low intergranular rotary driving force are the main reasons for the decrease to 12.63 kJ/mol of the growth activation energy of SnO2+SbOx solid solution. Thus, SnO2+SbOx electrode solid solution is a fine electrode material with good conductivity and high stability.
Ti based oxide anode with SnO2+SbOx was prepared by a thermal decomposition method. The SnO2+SbOx solid solution was characterized with TG/DTA, XRD and XPS. The growth activation energy of SnO2+SbOx solid solution was calculated and its activation mechanism was discussed. Meanwhile the expected lifetime of the oxide anode under high current density of 2 A/cm2 and in 0.5 mol/L H2SO4 solution was determined by a fast life method. The results show that the free electrons and oxygen vacancy produced by the N-type semiconductor and P-type semiconductor from Sb-doped SnO2 enhance the electrode conductivity and increase its expected lifetime to 30 h. The oxygen vacancy and too low intergranular rotary driving force are the main reasons for the decrease to 12.63 kJ/mol of the growth activation energy of SnO2+SbOx solid solution. Thus, SnO2+SbOx electrode solid solution is a fine electrode material with good conductivity and high stability.
2010, 39(7):1270-1274.
Abstract:
Surface of porous NiTi alloys was modified by direct current-pulse anodic oxidation technology at low temperature. The process of direct current-pulse anodic oxidation was analyzed. The phase composition, morphology and anti-corrosion behavior of the anodic oxidation film were studied by XPS, SEM and potentiodynamic polarization, respectively. The Ni release of porous NiTi alloys before and after anodic oxidation was investigated in simulated body fluid. The results show a uniform porous oxidation film with a thickness of about 190 nm on the surface of the porous NiTi alloy was obtained after anodic oxidation at direct current of 3 A and pulse current of 6 A. The oxidation film was mainly composed of the oxides of Ti. The corrosion resistance of porous NiTi alloys was obviously improved and the rate of Ni release was significantly reduced after anodic oxidation.
Surface of porous NiTi alloys was modified by direct current-pulse anodic oxidation technology at low temperature. The process of direct current-pulse anodic oxidation was analyzed. The phase composition, morphology and anti-corrosion behavior of the anodic oxidation film were studied by XPS, SEM and potentiodynamic polarization, respectively. The Ni release of porous NiTi alloys before and after anodic oxidation was investigated in simulated body fluid. The results show a uniform porous oxidation film with a thickness of about 190 nm on the surface of the porous NiTi alloy was obtained after anodic oxidation at direct current of 3 A and pulse current of 6 A. The oxidation film was mainly composed of the oxides of Ti. The corrosion resistance of porous NiTi alloys was obviously improved and the rate of Ni release was significantly reduced after anodic oxidation.
2010, 39(7):1275-1278.
Abstract:
The cast AZ31 magnesium alloys were treated by a single-pass friction stir processing (FSP), and the microstructure and mechanical properties of the processed region were studied. The results show that severe plastic deformation occurs and the coarse eutectic β-Mg17Al12 phase was broken, forming a refined and homogeneous dynamic recrystallized microstructure during the FSP period. XRD patterns indicate that a large amount of β phase dissolve into the magnesium matrix because of FSP, resulting in solid solution strengthening. The average microhardness (HV) of the FSPed AZ31 sample is 810 MPa higher than that of the cast AZ31 alloy, and the ultimate tensile strength and elongation of FSPed sample increase by 43 MPa and by 4.3% compared with those of the cast AZ31 alloy, respectively. Moreover, the fracture surface of FSPed AZ31 sample exhibits a typical ductile dimple-fracture.
The cast AZ31 magnesium alloys were treated by a single-pass friction stir processing (FSP), and the microstructure and mechanical properties of the processed region were studied. The results show that severe plastic deformation occurs and the coarse eutectic β-Mg17Al12 phase was broken, forming a refined and homogeneous dynamic recrystallized microstructure during the FSP period. XRD patterns indicate that a large amount of β phase dissolve into the magnesium matrix because of FSP, resulting in solid solution strengthening. The average microhardness (HV) of the FSPed AZ31 sample is 810 MPa higher than that of the cast AZ31 alloy, and the ultimate tensile strength and elongation of FSPed sample increase by 43 MPa and by 4.3% compared with those of the cast AZ31 alloy, respectively. Moreover, the fracture surface of FSPed AZ31 sample exhibits a typical ductile dimple-fracture.
2010, 39(7):1279-1283.
Abstract:
By means of SEM, XRD, DSC and a materials testing machine, the effects of γ phase on the martensitic transformation temperature Ms, mechanical properties and shape memory effect of Co44Ni26Ga30 alloy with different heat-treatments were investigated. Results show that the volume fraction of γ phase increased with prolonging the holding time during the heat treatment, giving rise to the decrease of Ms. The introduction of γ phase improved the ductility of the alloy greatly while deteriorated the shape memory recovery ratio. Upon appropriate thermo-mechanical training, the shape recovery ratio can be enhanced significantly to 93%.
By means of SEM, XRD, DSC and a materials testing machine, the effects of γ phase on the martensitic transformation temperature Ms, mechanical properties and shape memory effect of Co44Ni26Ga30 alloy with different heat-treatments were investigated. Results show that the volume fraction of γ phase increased with prolonging the holding time during the heat treatment, giving rise to the decrease of Ms. The introduction of γ phase improved the ductility of the alloy greatly while deteriorated the shape memory recovery ratio. Upon appropriate thermo-mechanical training, the shape recovery ratio can be enhanced significantly to 93%.
2010, 39(7):1284-1288.
Abstract:
Anisotropic magnets were synthesized by spark plasma sintering Nd11Dy2Gd2FebalAl4.0Nb0.8Zr0.8B6/Dy2O3 powder. The analyses of microstructure and magnetic property indicate that the sintering temperature determines the distribution of grain boundary phase in the magnets. After spark plasma sintering of 870 oC, 12 min (40 MPa) followed by tempering of 970 oC, 2 h + 600 oC, 1 h, the average density of samples reaches 7.39 g/cm3, residual magnetization is 1.08 T, and intrinsic coercive force is 1181 kA·m-1. The coercivity of the SPSed magnet is smaller than that of traditional sintered magnet with the same compositions, which is attributed to the discontinuous distribution of grain boundary phases, obvious decrease of rare earth relative contents in grain boundary phase because of their loss during the process, and some non-equilibrium structures in them.
Anisotropic magnets were synthesized by spark plasma sintering Nd11Dy2Gd2FebalAl4.0Nb0.8Zr0.8B6/Dy2O3 powder. The analyses of microstructure and magnetic property indicate that the sintering temperature determines the distribution of grain boundary phase in the magnets. After spark plasma sintering of 870 oC, 12 min (40 MPa) followed by tempering of 970 oC, 2 h + 600 oC, 1 h, the average density of samples reaches 7.39 g/cm3, residual magnetization is 1.08 T, and intrinsic coercive force is 1181 kA·m-1. The coercivity of the SPSed magnet is smaller than that of traditional sintered magnet with the same compositions, which is attributed to the discontinuous distribution of grain boundary phases, obvious decrease of rare earth relative contents in grain boundary phase because of their loss during the process, and some non-equilibrium structures in them.
2010, 39(7):1289-1292.
Abstract:
Magnesium hydride (MgH2) was synthesized by a direct-hydriding method, and its structure was characterized by XRD, SEM and ICP. The thermal decomposition behavior of ammonium perchlorate (AP) in the presence of MgH2 was investigated by DSC. Results show that 5% MgH2 can decrease low-temperature and high-temperature thermal-decomposition peak-temperatures of AP by 35.0 oC and 44.2 oC respectively, and increase the DSC apparent heat release of AP from 0.44 kJ·g-1 to 1.20 kJ·g-1, which indicates that MgH2 has a remarkable catalytic effect on AP thermal decomposition. The catalytic effect of MgH2 was enhanced gradually with increasing of MgH2 content. However, the effect went down when the MgH2 content reached 30%. The catalytic effect of MgH2 on the thermal decomposition of AP was obviously better than that of pure magnesium powder. The mechanism of MgH2 for catalyzing the thermal decomposition of AP was also studied.
Magnesium hydride (MgH2) was synthesized by a direct-hydriding method, and its structure was characterized by XRD, SEM and ICP. The thermal decomposition behavior of ammonium perchlorate (AP) in the presence of MgH2 was investigated by DSC. Results show that 5% MgH2 can decrease low-temperature and high-temperature thermal-decomposition peak-temperatures of AP by 35.0 oC and 44.2 oC respectively, and increase the DSC apparent heat release of AP from 0.44 kJ·g-1 to 1.20 kJ·g-1, which indicates that MgH2 has a remarkable catalytic effect on AP thermal decomposition. The catalytic effect of MgH2 was enhanced gradually with increasing of MgH2 content. However, the effect went down when the MgH2 content reached 30%. The catalytic effect of MgH2 on the thermal decomposition of AP was obviously better than that of pure magnesium powder. The mechanism of MgH2 for catalyzing the thermal decomposition of AP was also studied.
2010, 39(7):1293-1297.
Abstract:
The continuous gradient porous stainless steel material was fabricated by compression moulding forming technique. The shrinkage ratio and the microstructure of the prepared samples with different thickness were analyzed. The results indicate that the continuous gradient porous samples were deformed after sintering confirmed by their geometric contour, i.e. the initial cylinder samples became truncated cone shape due to different sintering stress between the adjacent gradient layers. The stress between two adjacent layers can promote powder sintering and influences the sintering shrinkage during sintering. In particular, the smaller the particle size is, the more obvious the influence is. The proper particle size distribution and the reasonable match of the bulk or mass of powders between different gradient layers can avoid the sintering deformation and cracks by the mutual suppression of the sintering stress among the different gradient layers to realize synchronous shrank sintering.
The continuous gradient porous stainless steel material was fabricated by compression moulding forming technique. The shrinkage ratio and the microstructure of the prepared samples with different thickness were analyzed. The results indicate that the continuous gradient porous samples were deformed after sintering confirmed by their geometric contour, i.e. the initial cylinder samples became truncated cone shape due to different sintering stress between the adjacent gradient layers. The stress between two adjacent layers can promote powder sintering and influences the sintering shrinkage during sintering. In particular, the smaller the particle size is, the more obvious the influence is. The proper particle size distribution and the reasonable match of the bulk or mass of powders between different gradient layers can avoid the sintering deformation and cracks by the mutual suppression of the sintering stress among the different gradient layers to realize synchronous shrank sintering.
2010, 39(7):1298-1301.
Abstract:
With induction of external magnetic fields, ultrafine Ni fibers with length up to 100 μm and diameter of about 250 nm were fabricated by a liquid phase reduction method under normal pressure. Then the obtained Ni fibers and commercial microsized Ni powder were used as filler to fabricate resin-based conductive composites, respectively. The electromagnetic shielding effectiveness (SE) of the resultant resin-based conductive composites was measured as a function of nickel content in the frequency range from 130 MHz to 1.5 GHz. Results indicate that compared with the composite with microsized Ni powder, the resin-based composite with ultrafine Ni fibers shows better electromagnetic shielding effectiveness. The composite with 33.3% (mass fraction) Ni fibers possesses an average SE of 15.7 dB.
With induction of external magnetic fields, ultrafine Ni fibers with length up to 100 μm and diameter of about 250 nm were fabricated by a liquid phase reduction method under normal pressure. Then the obtained Ni fibers and commercial microsized Ni powder were used as filler to fabricate resin-based conductive composites, respectively. The electromagnetic shielding effectiveness (SE) of the resultant resin-based conductive composites was measured as a function of nickel content in the frequency range from 130 MHz to 1.5 GHz. Results indicate that compared with the composite with microsized Ni powder, the resin-based composite with ultrafine Ni fibers shows better electromagnetic shielding effectiveness. The composite with 33.3% (mass fraction) Ni fibers possesses an average SE of 15.7 dB.
2010, 39(7):1302-1305.
Abstract:
Bi2-xSbxTe3 thermoelectric films were deposited on ITO-coated glass and Ti sheet substrates by an electrochemical method. The deposition process and the morphology, phase structure and composition of the films were studied by cyclic voltammetry, SEM, XRD and EDX, respectively. The thermoelectric properties of the films were measured at room temperature. Results show that pure Bi2-xSbxTe3 films can be obtained on ITO-coated glass whereas the film grown on the Ti sheet contains a little amount of Te. The film has smoother and more compact surface with cold isostatic pressing before annealing. The electrical conductivity is greatly increased and the Seebeck coefficient almost does not change, which indicates that treating with cold isostatic pressing is an effective means to improve the thermoelectric properties of the films.
Bi2-xSbxTe3 thermoelectric films were deposited on ITO-coated glass and Ti sheet substrates by an electrochemical method. The deposition process and the morphology, phase structure and composition of the films were studied by cyclic voltammetry, SEM, XRD and EDX, respectively. The thermoelectric properties of the films were measured at room temperature. Results show that pure Bi2-xSbxTe3 films can be obtained on ITO-coated glass whereas the film grown on the Ti sheet contains a little amount of Te. The film has smoother and more compact surface with cold isostatic pressing before annealing. The electrical conductivity is greatly increased and the Seebeck coefficient almost does not change, which indicates that treating with cold isostatic pressing is an effective means to improve the thermoelectric properties of the films.
2010, 39(7):1306-1309.
Abstract:
The (Fe0.5Co0.5)71-xNbxZr3Nd4B22 bulk alloys (x=0-10) were prepared by suction casting into a copper mould. The effects of Nb addition on glass-forming ability (GFA) and magnetic properties of the alloys were investigated. Results show that proper addition of Nb can increase the GFA of the alloy effectively. When the Nb content reached 5at%, a new bulk amorphous alloy, (Fe0.5Co0.5)66Nb5Zr3Nd4B22 with fully amorphous structure was obtained. The amorphous alloy exhibits typical soft magnetic property, and the saturation magnetization (Ms) is 79 Am2/kg. Its crystallization temperature (Tx) and crystallization activation energy of the alloy are 957 K and 538.30 kJ/mol, respectively.
The (Fe0.5Co0.5)71-xNbxZr3Nd4B22 bulk alloys (x=0-10) were prepared by suction casting into a copper mould. The effects of Nb addition on glass-forming ability (GFA) and magnetic properties of the alloys were investigated. Results show that proper addition of Nb can increase the GFA of the alloy effectively. When the Nb content reached 5at%, a new bulk amorphous alloy, (Fe0.5Co0.5)66Nb5Zr3Nd4B22 with fully amorphous structure was obtained. The amorphous alloy exhibits typical soft magnetic property, and the saturation magnetization (Ms) is 79 Am2/kg. Its crystallization temperature (Tx) and crystallization activation energy of the alloy are 957 K and 538.30 kJ/mol, respectively.
2010, 39(7):1310-1316.
Abstract:
Li3V2(PO4)3 is considered as the most promising cathode material for Li-ion batteries because of its high energy density, excellent electrochemical performance and thermal stability. Recent research progress in Li3V2(PO4)3 was reviewed with the focus on the electrochemical performance, micro-structural characteristics, the main preparation methods, modification study and so on. The existing problems in research of the materials were pointed out and the development prospect of the material was forecast.
Li3V2(PO4)3 is considered as the most promising cathode material for Li-ion batteries because of its high energy density, excellent electrochemical performance and thermal stability. Recent research progress in Li3V2(PO4)3 was reviewed with the focus on the electrochemical performance, micro-structural characteristics, the main preparation methods, modification study and so on. The existing problems in research of the materials were pointed out and the development prospect of the material was forecast.
