Volume 38,Issue 10,2009 Table of Contents
2009, 38(10):1693-1697.
Abstract:
Nanocrystalline Mo-18Cu, Mo-30Cu and Mo-40Cu (wt%) composite powders were fabricated by sol-spray drying, calcinating and subsequent hydrogen reduction process. The sintering behavior of nanocrystalline Mo-Cu composite powder and the influence of the copper content on the sintering densification process were investigated. The result shows that nanocrystalline Mo-Cu composite can obtain a fully dense structure. Particularly, Mo-30Cu and Mo-40Cu sintered at 1050-1200 °C can achieve relative densities over 98% and attain fine-grain structures. The relative density of Mo-18Cu sintered at 1350-1400 °C can also reach 98%, while a coarse structure with a mean grain size of 5 μm is obtained due to the remarkable grain growth in the compact. According to the compositional analysis, metastable Mo (Cu) solid solution forms in the composite powder. However, with the increase of the sintering temperature, Cu precipitates gradually from the metastable Mo (Cu) solid solution.
Nanocrystalline Mo-18Cu, Mo-30Cu and Mo-40Cu (wt%) composite powders were fabricated by sol-spray drying, calcinating and subsequent hydrogen reduction process. The sintering behavior of nanocrystalline Mo-Cu composite powder and the influence of the copper content on the sintering densification process were investigated. The result shows that nanocrystalline Mo-Cu composite can obtain a fully dense structure. Particularly, Mo-30Cu and Mo-40Cu sintered at 1050-1200 °C can achieve relative densities over 98% and attain fine-grain structures. The relative density of Mo-18Cu sintered at 1350-1400 °C can also reach 98%, while a coarse structure with a mean grain size of 5 μm is obtained due to the remarkable grain growth in the compact. According to the compositional analysis, metastable Mo (Cu) solid solution forms in the composite powder. However, with the increase of the sintering temperature, Cu precipitates gradually from the metastable Mo (Cu) solid solution.
2009, 38(10):1698-1702.
Abstract:
The Co-Gd film was prepared in urea-acetamide-NaBr melt at 393 K by an electrodeposition method. The cyclic voltammetry was used to investigate the co-deposition behavior of Gd and Co. Using the techniques, such as scanning electron microscope (SEM), energy-dispersive X-ray spectral analysis (EDS) and X-ray diffraction (XRD), the effects of the cathodic current density on the composition, the surface morphology and the structure of the coating were studied. Results show that the content of Gd in the coating increases at first and decreases later with the increasing current density, and reaches the maximum value of 54.97% (mass fraction, similarly hereinafter) at 12.5 mA/cm2. The surface morphology of the deposit becomes rough with the increase of the content of Gd in the coating. The as-plated deposit consists of amorphous phase, and the deposit is converted into cobalt (Fm3m) phase at 300 °C, and transformed into GdCo5 (P6/mmm) at 600 °C. The magnetic properties of the coating were measured by vibrating sample magnetometer(VSM). The experimental results reveal that the Gd content has great influence on magnetic properties of the alloy films. During heat treatment, the film saturation magnetization come to the maximum value of 550.43 kA/m at 600 °C, and the film coercive force reaches the maximum of 34.97 kA/m at 400 °C.
The Co-Gd film was prepared in urea-acetamide-NaBr melt at 393 K by an electrodeposition method. The cyclic voltammetry was used to investigate the co-deposition behavior of Gd and Co. Using the techniques, such as scanning electron microscope (SEM), energy-dispersive X-ray spectral analysis (EDS) and X-ray diffraction (XRD), the effects of the cathodic current density on the composition, the surface morphology and the structure of the coating were studied. Results show that the content of Gd in the coating increases at first and decreases later with the increasing current density, and reaches the maximum value of 54.97% (mass fraction, similarly hereinafter) at 12.5 mA/cm2. The surface morphology of the deposit becomes rough with the increase of the content of Gd in the coating. The as-plated deposit consists of amorphous phase, and the deposit is converted into cobalt (Fm3m) phase at 300 °C, and transformed into GdCo5 (P6/mmm) at 600 °C. The magnetic properties of the coating were measured by vibrating sample magnetometer(VSM). The experimental results reveal that the Gd content has great influence on magnetic properties of the alloy films. During heat treatment, the film saturation magnetization come to the maximum value of 550.43 kA/m at 600 °C, and the film coercive force reaches the maximum of 34.97 kA/m at 400 °C.
2009, 38(10):1703-1706.
Abstract:
The SiC fiber reinforced Ti55 composite (SiCf/Ti55) was fabricated by Fiber Coating Method (FCM) and Hot Isostatic Pressing (HIP). After the composites were thermally exposed in vacuum under different conditions, the study on the order of interfacial reaction products and the kinetics of interfacial reaction was performed. The results show that only C, Ti and Si elements take part in the interfacial reaction. The order of interfacial reaction products of SiCf/Ti55 composite exposed at 1000 °C can be identified as SiC | Ti3SiC2 | Ti5Si3+TiC | TiC | Ti55. However, the Ti3SiC2 does not exist in the composites exposed at low temperature. The interfacial reaction layer growth is controlled by diffusion and follows a role of parabolic rate, and the activation energy Qk and the pre-exponential factor k0 of SiCf/Ti55 composite are 198.16 kJ·mol-1 and 1.79′10-3 m·s-1/2, respectively. Compared with the SiCf/Ti composite and SiCf/Ti2AlNb composite, there is an interface with higher stability in SiCf/Ti55 composite. However, the interfacial reaction between SiC fiber and matrix takes place easier in SiCf/Ti55 composite than in the SiCf/Ti600 composite and SCS-6 SiCf/super а2 composite.
The SiC fiber reinforced Ti55 composite (SiCf/Ti55) was fabricated by Fiber Coating Method (FCM) and Hot Isostatic Pressing (HIP). After the composites were thermally exposed in vacuum under different conditions, the study on the order of interfacial reaction products and the kinetics of interfacial reaction was performed. The results show that only C, Ti and Si elements take part in the interfacial reaction. The order of interfacial reaction products of SiCf/Ti55 composite exposed at 1000 °C can be identified as SiC | Ti3SiC2 | Ti5Si3+TiC | TiC | Ti55. However, the Ti3SiC2 does not exist in the composites exposed at low temperature. The interfacial reaction layer growth is controlled by diffusion and follows a role of parabolic rate, and the activation energy Qk and the pre-exponential factor k0 of SiCf/Ti55 composite are 198.16 kJ·mol-1 and 1.79′10-3 m·s-1/2, respectively. Compared with the SiCf/Ti composite and SiCf/Ti2AlNb composite, there is an interface with higher stability in SiCf/Ti55 composite. However, the interfacial reaction between SiC fiber and matrix takes place easier in SiCf/Ti55 composite than in the SiCf/Ti600 composite and SCS-6 SiCf/super а2 composite.
2009, 38(10):1707-1710.
Abstract:
Nanosized particles of (La0.57Dy0.1)Sr0.33MnO3 perovskite-type oxides were successfully synthesized at relatively low calcinated temperature of 800 °C for 10 h using amorphous molecular alloy as precursor. X-ray diffraction (XRD) and electron diffraction (ED) revealed that the resulting product is of pure single-phase rhombohedral structure. From the measurements and calculation of isothermal magnetization at different temperatures, we discovered that the maximum magnetic entropy change at TC (358 K) increases near linearly with magnetic field increasing and shows no sign of saturation even under 5 T; moreover, a comparatively large magnetic entropy change with broader peak temperature range around the Curie temperature is also observed, and this good performance may be related to the large surface and interface of nanoparticles.
Nanosized particles of (La0.57Dy0.1)Sr0.33MnO3 perovskite-type oxides were successfully synthesized at relatively low calcinated temperature of 800 °C for 10 h using amorphous molecular alloy as precursor. X-ray diffraction (XRD) and electron diffraction (ED) revealed that the resulting product is of pure single-phase rhombohedral structure. From the measurements and calculation of isothermal magnetization at different temperatures, we discovered that the maximum magnetic entropy change at TC (358 K) increases near linearly with magnetic field increasing and shows no sign of saturation even under 5 T; moreover, a comparatively large magnetic entropy change with broader peak temperature range around the Curie temperature is also observed, and this good performance may be related to the large surface and interface of nanoparticles.
2009, 38(10):1711-1717.
Abstract:
The microstructures of as-cast Ti-Al-Nb-W-B alloy were investigated to assess the possibility of eliminating the triaxial β(B2) phase on the crystal boundary through heat treatment and multi-step forging thermal mechanical treatment. The microstructure evolution and growth mechanism were studied according to Ti-Al-Nb ternary phase diagram, and then the process of eliminating of the triaxial β(B2) phase on the crystal boundary was assessed. The results of the experiments indicate that the best way to eliminate β(B2) phase is holding at the 1260 °C for 8 h or 1220 °C for 36 h followed by furnace cooling, but the grains grow appreciably. On the other hand, after multi-step forging with a total deformation of more than 80%, the as-cast nearly lamellar structure can be refined obviously to the duplex microstructure, and the β(B2) phase is basically eliminated.
The microstructures of as-cast Ti-Al-Nb-W-B alloy were investigated to assess the possibility of eliminating the triaxial β(B2) phase on the crystal boundary through heat treatment and multi-step forging thermal mechanical treatment. The microstructure evolution and growth mechanism were studied according to Ti-Al-Nb ternary phase diagram, and then the process of eliminating of the triaxial β(B2) phase on the crystal boundary was assessed. The results of the experiments indicate that the best way to eliminate β(B2) phase is holding at the 1260 °C for 8 h or 1220 °C for 36 h followed by furnace cooling, but the grains grow appreciably. On the other hand, after multi-step forging with a total deformation of more than 80%, the as-cast nearly lamellar structure can be refined obviously to the duplex microstructure, and the β(B2) phase is basically eliminated.
2009, 38(10):1718-1721.
Abstract:
The HfCx absent solid solutions are formed easily resulting from C absence when HfC is being prepared or used. To forecast HfCx macroscopical properties, the valence electron structure of the absent solid-solutions with different x value was analyzed based on solid and molecule empirical theory (EET), and compared with that of the HfC matrix. The results shows that with the decrease of x value, i.e. the increase of the carbon atom absence, the crystal cell constant of the HfCx solid solutions decreased gradually; the number and the bond energy of the max covalent bond and the covalent bond number percent decreased gradually, too. This shows that the hardness, strength, bond energy and melting point were all decreased little by little; while, the toughness, conductivity and sintering properties were improved by degrees.
The HfCx absent solid solutions are formed easily resulting from C absence when HfC is being prepared or used. To forecast HfCx macroscopical properties, the valence electron structure of the absent solid-solutions with different x value was analyzed based on solid and molecule empirical theory (EET), and compared with that of the HfC matrix. The results shows that with the decrease of x value, i.e. the increase of the carbon atom absence, the crystal cell constant of the HfCx solid solutions decreased gradually; the number and the bond energy of the max covalent bond and the covalent bond number percent decreased gradually, too. This shows that the hardness, strength, bond energy and melting point were all decreased little by little; while, the toughness, conductivity and sintering properties were improved by degrees.
2009, 38(10):1722-1726.
Abstract:
The crystallization behaviors of Cu-mold suction-cast La62Al15.7(Cu,Ni)22.3 bulk amorphous alloy were studied by isothermal and non-isothermal crystallization annealing method. The results show that the crystallization process of the amorphous alloys includes three stages; the products for the different stages are La, Al3La and Cu-and-Ni rich unknown phases, respectively. The activation energies Eg, Ep1, Ep2 and Ep3, corresponding to characteristic temperatures Tg, Tp1, Tp2 and Tp3, respectively, were obtained from the Kissinger and Ozawa equations. The relation of activation energies has the sequence of Eg
The crystallization behaviors of Cu-mold suction-cast La62Al15.7(Cu,Ni)22.3 bulk amorphous alloy were studied by isothermal and non-isothermal crystallization annealing method. The results show that the crystallization process of the amorphous alloys includes three stages; the products for the different stages are La, Al3La and Cu-and-Ni rich unknown phases, respectively. The activation energies Eg, Ep1, Ep2 and Ep3, corresponding to characteristic temperatures Tg, Tp1, Tp2 and Tp3, respectively, were obtained from the Kissinger and Ozawa equations. The relation of activation energies has the sequence of Eg
2009, 38(10):1727-1730.
Abstract:
The powders and bulks product composed of TiC, Ti3SiC2, TiSi2 and Ti5Si3 were synthesized by mechanically induced self-propagation reaction (MSR) during mechanical alloying of 3Ti/Si/2C powders. The Ti3SiC2 content of the powders and bulks was about 17.6% and 58.2% (mass fraction, similarly hereinafter), respectively. A reaction mechanism for the synthesis of Ti3SiC2 by MSR was proposed. The mechanism indicated that Ti3SiC2 nucleated and grew in solid TiC and Ti-Si liquid. The effects of MSR and self-propagation high temperature sintering on the content and microstructure of Ti3SiC2 in products were discussed finally.
The powders and bulks product composed of TiC, Ti3SiC2, TiSi2 and Ti5Si3 were synthesized by mechanically induced self-propagation reaction (MSR) during mechanical alloying of 3Ti/Si/2C powders. The Ti3SiC2 content of the powders and bulks was about 17.6% and 58.2% (mass fraction, similarly hereinafter), respectively. A reaction mechanism for the synthesis of Ti3SiC2 by MSR was proposed. The mechanism indicated that Ti3SiC2 nucleated and grew in solid TiC and Ti-Si liquid. The effects of MSR and self-propagation high temperature sintering on the content and microstructure of Ti3SiC2 in products were discussed finally.
2009, 38(10):1731-1735.
Abstract:
The application of fractal scanning pattern in laser solid forming (LSF) of TC4 alloy was investigated through experiments. The forming characteristics of the fractal scanning path were discussed and the influence of process parameters (laser power, overlap rate etc) on the forming quality of TC4 alloy was studied. A method of eliminating the formation defects under fractal scanning pattern was proposed. Study shows that under fractal scanning pattern, the main defects of TC4 alloy formed by the LSF process are ill bonding and porosity, because the height of deposition at the corner of the fractal path is larger than that under linear scanning pattern resulting in the concave on the formation surface. The defects including ill bonding and porosity are relieved to some extent with the increase of the laser power and overlap rate, but still obvious. According to the obtained conclusion and formation characteristics of fractal scanning pattern, a “semi-spot vibration” strategy is proposed. The strategy means that the beginning scanning position of each layer offset by half a laser spot along x and y direction to make the concave; therefore the convex formed by two adjacent deposition layers respectively overlap each other and thus the deterioration of surface quality is restricted effectively.
The application of fractal scanning pattern in laser solid forming (LSF) of TC4 alloy was investigated through experiments. The forming characteristics of the fractal scanning path were discussed and the influence of process parameters (laser power, overlap rate etc) on the forming quality of TC4 alloy was studied. A method of eliminating the formation defects under fractal scanning pattern was proposed. Study shows that under fractal scanning pattern, the main defects of TC4 alloy formed by the LSF process are ill bonding and porosity, because the height of deposition at the corner of the fractal path is larger than that under linear scanning pattern resulting in the concave on the formation surface. The defects including ill bonding and porosity are relieved to some extent with the increase of the laser power and overlap rate, but still obvious. According to the obtained conclusion and formation characteristics of fractal scanning pattern, a “semi-spot vibration” strategy is proposed. The strategy means that the beginning scanning position of each layer offset by half a laser spot along x and y direction to make the concave; therefore the convex formed by two adjacent deposition layers respectively overlap each other and thus the deterioration of surface quality is restricted effectively.
2009, 38(10):1736-1739.
Abstract:
The microstructures and thermoelectric properties of AgSb1-xGaxTe2 (x=0-0.2) alloys prepared by spark plasma sintering (SPS) were examined. Results show that the AgSb1-xGaxTe2 alloys possess the same crystal structure with AgSbTe2, and formed secondary phase AgGaTe. After the alloy was doped with Ga, Seebeck coefficients were higher than that of the reference sample without Ga doping, but the thermal conductivity was lower than that of AgSbTe2. When x=0.1, i.e. the alloy was AgSb0.9Ga0.1Te2, the maximum ZT was 0.29 at 375 K, which was approximately 0.08 higher than that of AgSbTe2.
The microstructures and thermoelectric properties of AgSb1-xGaxTe2 (x=0-0.2) alloys prepared by spark plasma sintering (SPS) were examined. Results show that the AgSb1-xGaxTe2 alloys possess the same crystal structure with AgSbTe2, and formed secondary phase AgGaTe. After the alloy was doped with Ga, Seebeck coefficients were higher than that of the reference sample without Ga doping, but the thermal conductivity was lower than that of AgSbTe2. When x=0.1, i.e. the alloy was AgSb0.9Ga0.1Te2, the maximum ZT was 0.29 at 375 K, which was approximately 0.08 higher than that of AgSbTe2.
2009, 38(10):1740-1744.
Abstract:
The conventional and nanostructured Al2O3-13TiO2 composite ceramic coatings(ω/%, similarly hereinafter) were fabricated by plasma spraying on TiAl alloy surface with conventional and nanostructured agglomerated powders as starting materials. The morphology, microstructure and phase composition of the powder and the coating were investigated by means of scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Meanwhile, the formation mechanism of the coating microstructure was discussed. The results show that the conventional composite ceramic coating presents typical plasma-spraying lamellar accumulation structure. However, the nanostructured ceramic coating consists of not only fully melted regions but also partially melted regions, and the fully melted region has a lamellar-like structure as conventional coating. According to the different microstructure, the partially melted regions can be divided into liquid-phase sintered regions (three-dimensional net or skeleton-like structure: submicron Al2O3 particles distributed in the TiO2 matrix) and solid-phase sintered regions (residual nanoparticles have grown to some extent but still remained nano-scale). The different partially melted regions come from the difference of the melting point between A12O3 and TiO2. The main phase, in both the conventional and nanostructured coating, is the metastable phase of γ-Al2O3 due to the rapid solidification during the deposition of plasma spraying.
The conventional and nanostructured Al2O3-13TiO2 composite ceramic coatings(ω/%, similarly hereinafter) were fabricated by plasma spraying on TiAl alloy surface with conventional and nanostructured agglomerated powders as starting materials. The morphology, microstructure and phase composition of the powder and the coating were investigated by means of scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Meanwhile, the formation mechanism of the coating microstructure was discussed. The results show that the conventional composite ceramic coating presents typical plasma-spraying lamellar accumulation structure. However, the nanostructured ceramic coating consists of not only fully melted regions but also partially melted regions, and the fully melted region has a lamellar-like structure as conventional coating. According to the different microstructure, the partially melted regions can be divided into liquid-phase sintered regions (three-dimensional net or skeleton-like structure: submicron Al2O3 particles distributed in the TiO2 matrix) and solid-phase sintered regions (residual nanoparticles have grown to some extent but still remained nano-scale). The different partially melted regions come from the difference of the melting point between A12O3 and TiO2. The main phase, in both the conventional and nanostructured coating, is the metastable phase of γ-Al2O3 due to the rapid solidification during the deposition of plasma spraying.
2009, 38(10):1745-1748.
Abstract:
Adopting the undercooling technique combined molten glass denucleating with cyclical superheating, the solidification microstructures of undercooled and hypercooled Fe-B eutectic alloy melts were investigated by the thermal analysis of the cooling curves. The results show that the variations of cooling curves of alloy melts reveal the undercooling extent of melts, i.e. according to the analysis of the characteristic parameters in cooling curves the achievement of undercooled and hypercooled microstructures can be determined directly. And the corresponding relation between the nucleation, distribution, grain size as well as eutectic morphology of the primary phase and the undercooling degree can also be reflected by the cooling curves.
Adopting the undercooling technique combined molten glass denucleating with cyclical superheating, the solidification microstructures of undercooled and hypercooled Fe-B eutectic alloy melts were investigated by the thermal analysis of the cooling curves. The results show that the variations of cooling curves of alloy melts reveal the undercooling extent of melts, i.e. according to the analysis of the characteristic parameters in cooling curves the achievement of undercooled and hypercooled microstructures can be determined directly. And the corresponding relation between the nucleation, distribution, grain size as well as eutectic morphology of the primary phase and the undercooling degree can also be reflected by the cooling curves.
2009, 38(10):1749-1751.
Abstract:
The room temperature deformation behavior of hydrogenated TC4 alloys was studied through compression tests. The hydrogen treatment on the microstructure and deformation mechanism of the TC4 alloy at room temperature was studied by OM, TEM and XRD. Results show that hydrogen, as β stabilized element, modified the metastable phase composition of as-quenched alloys, promoted the generation of orthorhombic martensite α″ and body-centered β phase. When the H content was 0.45% (mass fraction, similarly hereinafter), the alloy mainly consisted of α″ phase, and the deformation behavior was twinning, which improved the deformation limit in a small range; while when the H content was higher than 0.59%, there were much β phase, and the deformation behavior was slipping, which improved the deformation limit greatly.
The room temperature deformation behavior of hydrogenated TC4 alloys was studied through compression tests. The hydrogen treatment on the microstructure and deformation mechanism of the TC4 alloy at room temperature was studied by OM, TEM and XRD. Results show that hydrogen, as β stabilized element, modified the metastable phase composition of as-quenched alloys, promoted the generation of orthorhombic martensite α″ and body-centered β phase. When the H content was 0.45% (mass fraction, similarly hereinafter), the alloy mainly consisted of α″ phase, and the deformation behavior was twinning, which improved the deformation limit in a small range; while when the H content was higher than 0.59%, there were much β phase, and the deformation behavior was slipping, which improved the deformation limit greatly.
2009, 38(10):1752-1755.
Abstract:
Effects of Co addition on the microstructure, phase transformation behavior, shape memory effect and mechanical properties of the wide hysteresis NiTiNb alloy were investigated. The results show that the addition of Co not only restrains the appearance of brittle (Ti,Nb)2Ni phase effectively, but also decreases markedly the martensite transformation temperature (Ms) in NiTiNb alloys. The value of wide hysteresis becomes narrower from 119.3 to 111 ℃ with the addition of Co element, but still remains enough high level. Compared with the NiTiNb alloys, the yield stress, the elongation, the recovery stress and the maximum recovery strain of NiTiNbCo alloys are increased from 320 MPa, 20%, 434 MPa and 5.3% to 460 MPa, 24.5%, 486 MPa and 7.8％, respectively. Therefore, alloying is an effective method to improve the yield stress and recovery stress.
Effects of Co addition on the microstructure, phase transformation behavior, shape memory effect and mechanical properties of the wide hysteresis NiTiNb alloy were investigated. The results show that the addition of Co not only restrains the appearance of brittle (Ti,Nb)2Ni phase effectively, but also decreases markedly the martensite transformation temperature (Ms) in NiTiNb alloys. The value of wide hysteresis becomes narrower from 119.3 to 111 ℃ with the addition of Co element, but still remains enough high level. Compared with the NiTiNb alloys, the yield stress, the elongation, the recovery stress and the maximum recovery strain of NiTiNbCo alloys are increased from 320 MPa, 20%, 434 MPa and 5.3% to 460 MPa, 24.5%, 486 MPa and 7.8％, respectively. Therefore, alloying is an effective method to improve the yield stress and recovery stress.
2009, 38(10):1756-1760.
Abstract:
The influence of Ni-Al ordering energy from the first to the fourth layer on the atom long range order progress in Ni75Al13Cr12 alloy was investigated by microscopic phase field model. Results show that as the first Ni-Al ordering energy increased the ordering and the clustering degree of Al atoms increased, while that of Cr atoms alternated with time steps. As the second Ni-Al ordering energy increased, the ordering and the clustering degree of Al atoms decreased, while that of Cr atoms alternated, too, which was opposite to the change of the first layer. As the third Ni-Al ordering energy increased, the degree and speed of the ordering and the clustering of Al and Cr atoms were all increased. And the influence of the fourth Ni-Al ordering energy was contrary with the third one. Under the same change of ±10 meV, the influence of Ni-Al ordering energy on the ordering and the clustering of Al atoms became more obvious as increasing of the number of the layer; the influence of the third Ni-Al ordering energy on the ordering and the clustering of Cr atoms was maximum; while the influence of the second Ni-Al ordering energy on the Cr ordering was minimum, and the influence of the fourth ordering energy on the clustering of Cr atoms was minimum.
The influence of Ni-Al ordering energy from the first to the fourth layer on the atom long range order progress in Ni75Al13Cr12 alloy was investigated by microscopic phase field model. Results show that as the first Ni-Al ordering energy increased the ordering and the clustering degree of Al atoms increased, while that of Cr atoms alternated with time steps. As the second Ni-Al ordering energy increased, the ordering and the clustering degree of Al atoms decreased, while that of Cr atoms alternated, too, which was opposite to the change of the first layer. As the third Ni-Al ordering energy increased, the degree and speed of the ordering and the clustering of Al and Cr atoms were all increased. And the influence of the fourth Ni-Al ordering energy was contrary with the third one. Under the same change of ±10 meV, the influence of Ni-Al ordering energy on the ordering and the clustering of Al atoms became more obvious as increasing of the number of the layer; the influence of the third Ni-Al ordering energy on the ordering and the clustering of Cr atoms was maximum; while the influence of the second Ni-Al ordering energy on the Cr ordering was minimum, and the influence of the fourth ordering energy on the clustering of Cr atoms was minimum.
2009, 38(10):1761-1764.
Abstract:
The extrusion process of silver was simulated by thermal coupling elastic-plastic finite element analysis module, using the CAE (Computer Aided Engineering) simulation software package-MSC.Marc. By analyzing the flow situation of the silver in the extrusion process, it is found that the simulated extrusion flow line agrees with the experimental, which shows that it is feasible to simulate metal flowing process by the finite element software. The stress and the strain in this extrusion process were analyzed. The biggest stress of the silver is in the deforming region. However, the zone from the deforming region to the calibrating strap is the most intense deformed zone.
The extrusion process of silver was simulated by thermal coupling elastic-plastic finite element analysis module, using the CAE (Computer Aided Engineering) simulation software package-MSC.Marc. By analyzing the flow situation of the silver in the extrusion process, it is found that the simulated extrusion flow line agrees with the experimental, which shows that it is feasible to simulate metal flowing process by the finite element software. The stress and the strain in this extrusion process were analyzed. The biggest stress of the silver is in the deforming region. However, the zone from the deforming region to the calibrating strap is the most intense deformed zone.
2009, 38(10):1765-1768.
Abstract:
FeCrAl fibrous porous materials with the porosity larger than 85% were prepared using the fiber of 20 μm in diameter as starting material. Under the ordinary sound pressure and high sound intensity conditions, the sound absorption properties of FeCrAl sintering fibrous porous materials were tested. The results indicate that the sound absorption properties of FeCrAl fibrous porous materials were increased by increasing of the porosity under ordinary sound pressure. But it was not beneficial to sound absorption under high frequency when the porosity was too high or too low. The larger the thickness was, the better the sound absorption properties of FeCrAl fibrous porous materials were. Adding the airspace can improve the sound absorption properties under low frequency. Under high sound intensity (100-140 dB), the sound absorption properties of the material would not change with the sound pressure level (SPL); effects of the parameters on the sound absorption properties were in concordance with that under ordinary sound pressure. The sound absorption coefficient of FeCrAl fibrous porous materials with 94% porosity and 20 mm thickness was up to 90% at 120 dB and in the frequency range of 2.5-6.4 kHz.
FeCrAl fibrous porous materials with the porosity larger than 85% were prepared using the fiber of 20 μm in diameter as starting material. Under the ordinary sound pressure and high sound intensity conditions, the sound absorption properties of FeCrAl sintering fibrous porous materials were tested. The results indicate that the sound absorption properties of FeCrAl fibrous porous materials were increased by increasing of the porosity under ordinary sound pressure. But it was not beneficial to sound absorption under high frequency when the porosity was too high or too low. The larger the thickness was, the better the sound absorption properties of FeCrAl fibrous porous materials were. Adding the airspace can improve the sound absorption properties under low frequency. Under high sound intensity (100-140 dB), the sound absorption properties of the material would not change with the sound pressure level (SPL); effects of the parameters on the sound absorption properties were in concordance with that under ordinary sound pressure. The sound absorption coefficient of FeCrAl fibrous porous materials with 94% porosity and 20 mm thickness was up to 90% at 120 dB and in the frequency range of 2.5-6.4 kHz.
2009, 38(10):1769-1773.
Abstract:
Hypereutectic Al-20Si (mass fraction) alloy hollow tubes were prepared by centrifugal casting under an electromagnetic field (EMF). Effects of EMF on the solidification microstructure of the alloy and morphology of primary Si phases were investigated. Results show that primary Si phases in the solidification microstructure were refined after applying EMF compared with the microstructure of the Al-20Si hypereutectic alloys by conventional centrifugal casting. The segregation layer width of Si phases in the outer of the tube decreased gradually with the increase of the EMF intensity. The morphology of the Si phases in the outer of the tube changed from typical pentagram into dendrites grown along the heat flow direction. The phenomena of dulling and congregation of the Si phases in the inner of the tube were found due to EMF stirring. The size and aspect ratio of the primary Si phase decreased little by little with the increase of EMF intensity. The electromagnetic stirring destroyed the radial configuration of Si phases, eutectic Si phases distributed randomly, and the eutectic lamina spaces in the eutectic cell increased gradually.
Hypereutectic Al-20Si (mass fraction) alloy hollow tubes were prepared by centrifugal casting under an electromagnetic field (EMF). Effects of EMF on the solidification microstructure of the alloy and morphology of primary Si phases were investigated. Results show that primary Si phases in the solidification microstructure were refined after applying EMF compared with the microstructure of the Al-20Si hypereutectic alloys by conventional centrifugal casting. The segregation layer width of Si phases in the outer of the tube decreased gradually with the increase of the EMF intensity. The morphology of the Si phases in the outer of the tube changed from typical pentagram into dendrites grown along the heat flow direction. The phenomena of dulling and congregation of the Si phases in the inner of the tube were found due to EMF stirring. The size and aspect ratio of the primary Si phase decreased little by little with the increase of EMF intensity. The electromagnetic stirring destroyed the radial configuration of Si phases, eutectic Si phases distributed randomly, and the eutectic lamina spaces in the eutectic cell increased gradually.
2009, 38(10):1774-1777.
Abstract:
Cu-Nb microcomposite wire materials containing N=854 niobium filaments were prepared by bundling and drawing technique. The electrical resistivity of the materials is 0.36 μΩ·cm at 77 K. The conductivity values could be greater than 70%IACS at 293 K. The ultimate tensile strength could reach 915 MPa at room temperature when the sectional area of the materials was larger than 5 mm2. And the fracture surface morphology and the Nb filaments arrangement of Cu-Nb wires were observed by SEM.
Cu-Nb microcomposite wire materials containing N=854 niobium filaments were prepared by bundling and drawing technique. The electrical resistivity of the materials is 0.36 μΩ·cm at 77 K. The conductivity values could be greater than 70%IACS at 293 K. The ultimate tensile strength could reach 915 MPa at room temperature when the sectional area of the materials was larger than 5 mm2. And the fracture surface morphology and the Nb filaments arrangement of Cu-Nb wires were observed by SEM.
2009, 38(10):1778-1782.
Abstract:
Effects of trace Zr and Er additions on microstructures and mechanical properties of Al-4.4Zn-2.4Mg alloys (mass fraction, similarly hereinafter) were investigated by testing hardness, tensile property, resistivity, and stress corrosion cracking resistance and observing metallographic microstructure of the alloy. The results show that the grain refining effect of Zr addition alone for the alloy is better than that of Er addition alone or Zr-Er co-addition. However the Zr-Er co-addition can obviously inhibit recrystallization behavior of the alloys. The Al-4.4Zn-2.4Mg alloy with Zr-Er co-addition has nearly equal mechanical properties to that with Zr addition alone, while has better stress-corrosion cracking resistance than that with Zr or Er addition alone. The alloys with Zr-Er co-addition possess the optimum combination properties. Zr-Er co-addition can improve the stress-corrosion cracking resistance of the Al-4.4Zn-2.4Mg alloy, which is indirectly realized by the fibrous microstructure obtained from inhibiting recrystallization.
Effects of trace Zr and Er additions on microstructures and mechanical properties of Al-4.4Zn-2.4Mg alloys (mass fraction, similarly hereinafter) were investigated by testing hardness, tensile property, resistivity, and stress corrosion cracking resistance and observing metallographic microstructure of the alloy. The results show that the grain refining effect of Zr addition alone for the alloy is better than that of Er addition alone or Zr-Er co-addition. However the Zr-Er co-addition can obviously inhibit recrystallization behavior of the alloys. The Al-4.4Zn-2.4Mg alloy with Zr-Er co-addition has nearly equal mechanical properties to that with Zr addition alone, while has better stress-corrosion cracking resistance than that with Zr or Er addition alone. The alloys with Zr-Er co-addition possess the optimum combination properties. Zr-Er co-addition can improve the stress-corrosion cracking resistance of the Al-4.4Zn-2.4Mg alloy, which is indirectly realized by the fibrous microstructure obtained from inhibiting recrystallization.
2009, 38(10):1783-1786.
Abstract:
The link microstructure of P/M FGH4096 alloy was investigated by SEM, EDAX and TEM. The tensile properties and grain refining effect of the microstructure was also discussed. The results show that the link microstructure could be obtained by the standard heat treatment or the direct-aging heat treatment for the alloy after hot-die forging, where the equiaxed fine grains (about 4 μm) distributed homogeneously in the non-equiaxed coarse grains (about 10 μm). The obtained microstructure has better mechanical properties. After the multiple forging and the standard heat treatment, the non-equiaxed coarse grains have been refined completely from ASTM5-6 to above ASTM12. It reveals that the link microstructure can provide fine grain reservation for the fine microstructure.
The link microstructure of P/M FGH4096 alloy was investigated by SEM, EDAX and TEM. The tensile properties and grain refining effect of the microstructure was also discussed. The results show that the link microstructure could be obtained by the standard heat treatment or the direct-aging heat treatment for the alloy after hot-die forging, where the equiaxed fine grains (about 4 μm) distributed homogeneously in the non-equiaxed coarse grains (about 10 μm). The obtained microstructure has better mechanical properties. After the multiple forging and the standard heat treatment, the non-equiaxed coarse grains have been refined completely from ASTM5-6 to above ASTM12. It reveals that the link microstructure can provide fine grain reservation for the fine microstructure.
2009, 38(10):1791-1796.
Abstract:
The amorphous Fe78Si9B13 alloy was treated by low frequency pulse magnetic field (LFPMF) and nanocrystallized at a low temperature. The microstructures and the magnetic properties of the untreated and treated alloys were analyzed by M?ssbauer spectra and LDJ9600 vibrating sample magnetometer (VSM). The valence electron structures and the magnetic moment of the unnanocrystallized and nanocrystallized amorphous alloys were calculated using the method of Bond Length Difference (BLD) of the Empirical Electron Theory (EET) of solids and molecules. The error of the computed value in theory and experimental value of the magnetic moment is less than 7%, which satisfies the demand of first approximation, indicating that it can be realized that magnetic moment of amorphous alloy is calculated on the valence electron level.
The amorphous Fe78Si9B13 alloy was treated by low frequency pulse magnetic field (LFPMF) and nanocrystallized at a low temperature. The microstructures and the magnetic properties of the untreated and treated alloys were analyzed by M?ssbauer spectra and LDJ9600 vibrating sample magnetometer (VSM). The valence electron structures and the magnetic moment of the unnanocrystallized and nanocrystallized amorphous alloys were calculated using the method of Bond Length Difference (BLD) of the Empirical Electron Theory (EET) of solids and molecules. The error of the computed value in theory and experimental value of the magnetic moment is less than 7%, which satisfies the demand of first approximation, indicating that it can be realized that magnetic moment of amorphous alloy is calculated on the valence electron level.
Zhou Jun
,
Li Zhongkui
,
Zhang Jianjun
,
Zhu Meisheng
,
Wang Wensheng
,
Tian Feng
,
Shi Minghua
,
Zhou Lian
2009, 38(10):1797-1800.
Abstract:
Fatigue crack propagation behavior of an advanced Zr-Sn-Nb alloy NZ2 with different hydrogen contents (0, 200, 450, and 730 mg/g) was investigated by standard M(T) specimens. The results showed that stable crack propagation behavior obeyed the Paris Law, i.e. da/dN=C(DK)n, whether the hydrogen content is high or low. But the power exponent n of the Paris Law was decreased with the hydrogen content increasing; the increment of hydrogen content can decrease the ductility of NZ2 alloy and enhance the fatigue crack growth rate, especially when the specimens have higher hydrogen content.
Fatigue crack propagation behavior of an advanced Zr-Sn-Nb alloy NZ2 with different hydrogen contents (0, 200, 450, and 730 mg/g) was investigated by standard M(T) specimens. The results showed that stable crack propagation behavior obeyed the Paris Law, i.e. da/dN=C(DK)n, whether the hydrogen content is high or low. But the power exponent n of the Paris Law was decreased with the hydrogen content increasing; the increment of hydrogen content can decrease the ductility of NZ2 alloy and enhance the fatigue crack growth rate, especially when the specimens have higher hydrogen content.
2009, 38(10):1801-1806.
Abstract:
A computer simulation system of the ring pipe bending process of titanium alloys was established using MSC/Superform finite element simulation software on the basis of elastic-plastic finite element theory. The Archimedes spiral was selected as the center axis of the ox-horn die with small bending radius for maintaining the continuity of the curvature radius. Optimization simulation of die parameters such as Archimedes constant, expanding diameter ratio and bending angle was carried out by mid-frequency induction heating method. The conclusions are as follows: (1) the reasonable Archimedes constant can ensure the sound uniformity of the wall thickness and the optimized constant was 1.0 according to the simulation; (2) the too higher expanding diameter ratio would induce easily some defects such as crinkles and thickness-decrease, while the too lower ratio would induce thickness-increase of the abdomen and uniformity-decrease of the wall-thickness; thus the preferred ratio value was 1.33 for the process; (3) if the bending angle was too small, the pipe bending progress was severe and the mechanical properties of the obtained pipe could not satisfy the requirements well; if the angle was too large, the bending progress was stable, but the thrust became difficult as the increase of the thrust resistance; therefore, the preferred bending angle was 40° for the process. The titanium ring pipe with uniform wall thickness, high-voltage-resistance and equal strength was obtained using the above mentioned parameters, detected by the orthogonal test.
A computer simulation system of the ring pipe bending process of titanium alloys was established using MSC/Superform finite element simulation software on the basis of elastic-plastic finite element theory. The Archimedes spiral was selected as the center axis of the ox-horn die with small bending radius for maintaining the continuity of the curvature radius. Optimization simulation of die parameters such as Archimedes constant, expanding diameter ratio and bending angle was carried out by mid-frequency induction heating method. The conclusions are as follows: (1) the reasonable Archimedes constant can ensure the sound uniformity of the wall thickness and the optimized constant was 1.0 according to the simulation; (2) the too higher expanding diameter ratio would induce easily some defects such as crinkles and thickness-decrease, while the too lower ratio would induce thickness-increase of the abdomen and uniformity-decrease of the wall-thickness; thus the preferred ratio value was 1.33 for the process; (3) if the bending angle was too small, the pipe bending progress was severe and the mechanical properties of the obtained pipe could not satisfy the requirements well; if the angle was too large, the bending progress was stable, but the thrust became difficult as the increase of the thrust resistance; therefore, the preferred bending angle was 40° for the process. The titanium ring pipe with uniform wall thickness, high-voltage-resistance and equal strength was obtained using the above mentioned parameters, detected by the orthogonal test.
25 Effects of Strain Rate and Relative Density on Compressive Properties of SiCp/ZL104 Composite Foams
2009, 38(10):1807-1810.
Abstract:
The quasi-static and dynamic compressive properties of 5vol%SiCp/ZL104 composite foams, fabricated by the method of direct melt foaming, were tested and analyzed. The results show that under the conditions of quasi-static or dynamic compression, the stress-strain curves of 5vol%SiCp/ZL104 composite foams involves three regions: the linear elastic deformation region, the collapse plateau region and the densification region. The yield stress is sensitive to the strain rate, so it increases and the strain hardening occurs with the increase of the strain rate. Compared with that under quasi-static loading, dynamic yield stress and flow stress of 5vol%SiCp/ZL104 composite foams increase remarkably with the increase of relative density.
The quasi-static and dynamic compressive properties of 5vol%SiCp/ZL104 composite foams, fabricated by the method of direct melt foaming, were tested and analyzed. The results show that under the conditions of quasi-static or dynamic compression, the stress-strain curves of 5vol%SiCp/ZL104 composite foams involves three regions: the linear elastic deformation region, the collapse plateau region and the densification region. The yield stress is sensitive to the strain rate, so it increases and the strain hardening occurs with the increase of the strain rate. Compared with that under quasi-static loading, dynamic yield stress and flow stress of 5vol%SiCp/ZL104 composite foams increase remarkably with the increase of relative density.
2009, 38(10):1811-1814.
Abstract:
Parameters of processing (temperature, strain, strain rate and cooling method) and properties (tensile strength and elongation) of TA15 titanium alloy hot-restriction-deformed were obtained through mechanical properties examination; their relationship network model was built by BP artificial neural network. The results show that the built model can reflect the relationships between processing and properties very well and has certain accuracy. It can be used for the prediction of the properties of TA15 titanium alloy under different deformation conditions. Meanwhile, the model can also serve as a guide for the heat treatment of TA15 titanium alloy.
Parameters of processing (temperature, strain, strain rate and cooling method) and properties (tensile strength and elongation) of TA15 titanium alloy hot-restriction-deformed were obtained through mechanical properties examination; their relationship network model was built by BP artificial neural network. The results show that the built model can reflect the relationships between processing and properties very well and has certain accuracy. It can be used for the prediction of the properties of TA15 titanium alloy under different deformation conditions. Meanwhile, the model can also serve as a guide for the heat treatment of TA15 titanium alloy.
2009, 38(10):1815-1817.
Abstract:
Nitrogen-doped modified TiO2 films were prepared through sol-gel method. The thickness, surface microstructure and composition were analyzed by nano indenter, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of N-doped TiO2 films was researched through the degradation experiment of methylene blue under UV light. Results showed that nitrogen ions are doped into TiO2 films by adding urea and they are between TiO2 crystal lattices and mainly in interstitial configuration and substitution configuration. The films are very flat with the thickness of between 50-200 nm. Nitrogen ions doping improves the photocatalytic activity of TiO2 films. When N/Ti=0.015 (atom ratio) in TiO2 films, it takes single N-doped TiO2 film 2.5 h to decompose the methylene blue solution.
Nitrogen-doped modified TiO2 films were prepared through sol-gel method. The thickness, surface microstructure and composition were analyzed by nano indenter, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of N-doped TiO2 films was researched through the degradation experiment of methylene blue under UV light. Results showed that nitrogen ions are doped into TiO2 films by adding urea and they are between TiO2 crystal lattices and mainly in interstitial configuration and substitution configuration. The films are very flat with the thickness of between 50-200 nm. Nitrogen ions doping improves the photocatalytic activity of TiO2 films. When N/Ti=0.015 (atom ratio) in TiO2 films, it takes single N-doped TiO2 film 2.5 h to decompose the methylene blue solution.
2009, 38(10):1818-1821.
Abstract:
MoO3 nanofibers with 50~100 nm diameter and larger than 20 μm length were prepared at 170 ℃ constant temperature for 40 h using (NH4)6Mo7O24·4H2O and nitric acid as starting materials through hydrothermal process. Then the hydrogen reduction tests of the prepared MoO3 nanofiber were carried out at different temperatures within 450~650 ℃. The samples prepared by hydrogen reduction tests were characterized by XRD and FSEM. The results indicated that MoO3 nanofibers began to change into MoO2 at 450 ℃, and could be completely reduced to Mo powder with 0.1~2 μm particle size at 600 ℃. During the reduction process, the original fiber-like morphology of most MoO3 nanofibers was not well-retained; but in some cases, the fiber-like morphology of a small part of single MoO3 nanofibers in free space could be retained, and changed into needle-like Mo particles.
MoO3 nanofibers with 50~100 nm diameter and larger than 20 μm length were prepared at 170 ℃ constant temperature for 40 h using (NH4)6Mo7O24·4H2O and nitric acid as starting materials through hydrothermal process. Then the hydrogen reduction tests of the prepared MoO3 nanofiber were carried out at different temperatures within 450~650 ℃. The samples prepared by hydrogen reduction tests were characterized by XRD and FSEM. The results indicated that MoO3 nanofibers began to change into MoO2 at 450 ℃, and could be completely reduced to Mo powder with 0.1~2 μm particle size at 600 ℃. During the reduction process, the original fiber-like morphology of most MoO3 nanofibers was not well-retained; but in some cases, the fiber-like morphology of a small part of single MoO3 nanofibers in free space could be retained, and changed into needle-like Mo particles.
2009, 38(10):1822-1825.
Abstract:
A novel flame-retarded Ti14 alloy (α+Ti2Cu) was solid forged at 950 ℃ and semi-solid forged (SSF) at 1000 ℃, respectively. Compared with that of the solid forged alloy, the microstructure and tensile properties of the semi-solid forged alloy were investigated; meanwhile, the possible reason for the change of the microstructure and tensile properties were also discussed. The results show that the dynamic recrystallization does not occur during the SSF, which coarsened the grains at room temperature. Liquid Ti2Cu distributed along grain boundaries under pressure, and segregation was formed, coarsening grain boundaries and changing their microstructure; the microstructure change of grain boundaries induced the hardening effect, resulting in the increase of tensile strength and the decrease of plasticity at room temperature.
A novel flame-retarded Ti14 alloy (α+Ti2Cu) was solid forged at 950 ℃ and semi-solid forged (SSF) at 1000 ℃, respectively. Compared with that of the solid forged alloy, the microstructure and tensile properties of the semi-solid forged alloy were investigated; meanwhile, the possible reason for the change of the microstructure and tensile properties were also discussed. The results show that the dynamic recrystallization does not occur during the SSF, which coarsened the grains at room temperature. Liquid Ti2Cu distributed along grain boundaries under pressure, and segregation was formed, coarsening grain boundaries and changing their microstructure; the microstructure change of grain boundaries induced the hardening effect, resulting in the increase of tensile strength and the decrease of plasticity at room temperature.
2009, 38(10):1826-1830.
Abstract:
Laves phase NbCr2 alloys were prepared by mechanical alloying and hot pressing sintering technology. Influences of the milling time on the grain size and density of the hot-pressed alloys were studied. The effect mechanism of grain refinement on 1100 ℃ oxidation behavior was also discussed. Results show that the relative density of the hot-pressed alloys increased and the grain size decreased when the milling time of Cr-Nb powders was prolonged. When the milling time was 100 h, the relative density and the grain size reached 98.7% and 35 nm, respectively. The grain refinement was beneficial to the improvement of Cr atom dispersion to form Cr2O3 film. However, the excessive refinement of grains resulted in the growth stress increase of the oxides film and then the oxide films cracked and shed; as a result, the oxidation was exacerbated.
Laves phase NbCr2 alloys were prepared by mechanical alloying and hot pressing sintering technology. Influences of the milling time on the grain size and density of the hot-pressed alloys were studied. The effect mechanism of grain refinement on 1100 ℃ oxidation behavior was also discussed. Results show that the relative density of the hot-pressed alloys increased and the grain size decreased when the milling time of Cr-Nb powders was prolonged. When the milling time was 100 h, the relative density and the grain size reached 98.7% and 35 nm, respectively. The grain refinement was beneficial to the improvement of Cr atom dispersion to form Cr2O3 film. However, the excessive refinement of grains resulted in the growth stress increase of the oxides film and then the oxide films cracked and shed; as a result, the oxidation was exacerbated.
2009, 38(10):1831-1834.
Abstract:
Zr1-xTixNiSn0.975Sb0.025 (x=0, 0.15, 0.25, 0.5) based Half-Heusler thermoelectric materials were synthesized by suspension melting. X-ray diffraction results show that the obtained alloy was single phase compound. Compared with conventional melting methods, the suspension melting markedly reduced the preparation duration. Meanwhile the effects of Ti substitution and different hot-pressing conditions on thermoelectric properties of the materials were also studied. Results show that the Ti substitution for the A site of ZrNiSn0.975Sb0.025 can reduce the thermal conductivity but does not affect its thermoelectric properties obviously. The density can affect the thermoelectric properties. Proper hot-pressing condition can make ZT values reach the maximum of about 0.45.
Zr1-xTixNiSn0.975Sb0.025 (x=0, 0.15, 0.25, 0.5) based Half-Heusler thermoelectric materials were synthesized by suspension melting. X-ray diffraction results show that the obtained alloy was single phase compound. Compared with conventional melting methods, the suspension melting markedly reduced the preparation duration. Meanwhile the effects of Ti substitution and different hot-pressing conditions on thermoelectric properties of the materials were also studied. Results show that the Ti substitution for the A site of ZrNiSn0.975Sb0.025 can reduce the thermal conductivity but does not affect its thermoelectric properties obviously. The density can affect the thermoelectric properties. Proper hot-pressing condition can make ZT values reach the maximum of about 0.45.
2009, 38(10):1839-1842.
Abstract:
The effects of first annealing and sintering temperature on the microstructures and magnetic properties of Dy2O3 doped Nd-Fe-B magnets were investigated. Results show that the effect of first annealing and sintering temperature on magnetic properties is remarkable, especially on the coercive force Hcj, which is closely related to the content of Dy2O3. When the added content of Dy2O3 is 2%, the first annealing can improve Hcj obviously, whereas the effect of sintering temperature is very unconspicuous. When the added content of Dy2O3 is 5%, Hcj is improved evidently with the increase of sintering temperature; however, the first annealing increases Hcj lightly. This is mainly attributed to the following reasons: on one hand, Dy2O3 is reduced to form Nd2O3 particles affecting sintering and annealing system; on the other hand, sintering temperature impacts the diffusion of Dy atom.
The effects of first annealing and sintering temperature on the microstructures and magnetic properties of Dy2O3 doped Nd-Fe-B magnets were investigated. Results show that the effect of first annealing and sintering temperature on magnetic properties is remarkable, especially on the coercive force Hcj, which is closely related to the content of Dy2O3. When the added content of Dy2O3 is 2%, the first annealing can improve Hcj obviously, whereas the effect of sintering temperature is very unconspicuous. When the added content of Dy2O3 is 5%, Hcj is improved evidently with the increase of sintering temperature; however, the first annealing increases Hcj lightly. This is mainly attributed to the following reasons: on one hand, Dy2O3 is reduced to form Nd2O3 particles affecting sintering and annealing system; on the other hand, sintering temperature impacts the diffusion of Dy atom.
33 Comparison of Ru-Ti-Ir-Ta/Ti Quarternary Coating Prepared by Different Techniques on Titanium Anodes
2009, 38(10):1843-1847.
Abstract:
Ru-Ti-Ir-Ta/Ti quarternary metal oxide titanium anodes with sandwich coating structure were prepared by thermal decomposition and sol-gel method, respectively. The phases and micro-morphologies of the two coatings were investigated by means of XRD and SEM. The electrocatalytic activity of the coatings was studied and compared by Tafel curve and cyclic voltammetry curve. It is demonstrated that the main phases in the coatings prepared by different techniques are mainly rutile-type solid solution (Ir, Ta)O2 and (Ti, Ru)O2. Metallic Ru is found in the coating prepared by thermal decomposition. The crystals in the coating prepared by sol-gel are finer. The morphologies of the coatings by thermal decomposition and sol-gel are obviously different. The former is distinctly dry cracked-mud like, and the latter shows the detritus-type. The result indicates that the titanium anode prepared by sol-gel have the better electrocatalytic activity and corrosion resistance than that by thermal decomposition.
Ru-Ti-Ir-Ta/Ti quarternary metal oxide titanium anodes with sandwich coating structure were prepared by thermal decomposition and sol-gel method, respectively. The phases and micro-morphologies of the two coatings were investigated by means of XRD and SEM. The electrocatalytic activity of the coatings was studied and compared by Tafel curve and cyclic voltammetry curve. It is demonstrated that the main phases in the coatings prepared by different techniques are mainly rutile-type solid solution (Ir, Ta)O2 and (Ti, Ru)O2. Metallic Ru is found in the coating prepared by thermal decomposition. The crystals in the coating prepared by sol-gel are finer. The morphologies of the coatings by thermal decomposition and sol-gel are obviously different. The former is distinctly dry cracked-mud like, and the latter shows the detritus-type. The result indicates that the titanium anode prepared by sol-gel have the better electrocatalytic activity and corrosion resistance than that by thermal decomposition.
2009, 38(10):1848-1851.
Abstract:
Nanocrystalline LaFeO3 was prepared by a simple molten-salt method with La2O3 and FeCl3·6H2O as main starting materials. The nanocrystal1ine samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) for the phases and morphology. Their gas-sensing properties to triethylamine, C2H5OH, gasoline, C6H6 and CH3COCH3 were investigated. The results demonstrated that pure LaFeO3 nanocrystal1ine with uniform grain sizes and an average diameter of about 40 nm was formed when calcined at 800 ℃. Moreover, the gas sensor made of the nanocrystalline LaFeO3 sample showed high sensitivity as well as good selectivity to dilute triethylamine. The LaFeO3 sensor showed the sensitivity as high as 7.9 to even 25 μg/g triethylamine at 250 ℃, and the response and recovery time are 6 and 13 s, respectively.
Nanocrystalline LaFeO3 was prepared by a simple molten-salt method with La2O3 and FeCl3·6H2O as main starting materials. The nanocrystal1ine samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) for the phases and morphology. Their gas-sensing properties to triethylamine, C2H5OH, gasoline, C6H6 and CH3COCH3 were investigated. The results demonstrated that pure LaFeO3 nanocrystal1ine with uniform grain sizes and an average diameter of about 40 nm was formed when calcined at 800 ℃. Moreover, the gas sensor made of the nanocrystalline LaFeO3 sample showed high sensitivity as well as good selectivity to dilute triethylamine. The LaFeO3 sensor showed the sensitivity as high as 7.9 to even 25 μg/g triethylamine at 250 ℃, and the response and recovery time are 6 and 13 s, respectively.
2009, 38(10):1852-1855.
Abstract:
Corrosion resistance of cerium conversion film on Mg-Gd-Y-Zr alloy was investigated by volumetric method. The optimum deposition parameters were obtained by orthogonal table L9(43), i.e. pH value 10.0, electrochemical deposition time 30 min, accelerating agent concentration 0.05 mol/L, and temperature 25 ℃. The influence degrees on corrosion resistance were in the sequence of pH > electrochemical deposition time > accelerating agent concentration > temperature. The corrosion resistance of cerium conversion film, chromated conversion film and Mg-Gd-Y-Zr magnesium alloy in 3.5% NaCl solution was compared by measuring the rate of evolved hydrogen. Results show that cerium conversion film improves the corrosion resistance of RE-Mg alloys remarkably.
Corrosion resistance of cerium conversion film on Mg-Gd-Y-Zr alloy was investigated by volumetric method. The optimum deposition parameters were obtained by orthogonal table L9(43), i.e. pH value 10.0, electrochemical deposition time 30 min, accelerating agent concentration 0.05 mol/L, and temperature 25 ℃. The influence degrees on corrosion resistance were in the sequence of pH > electrochemical deposition time > accelerating agent concentration > temperature. The corrosion resistance of cerium conversion film, chromated conversion film and Mg-Gd-Y-Zr magnesium alloy in 3.5% NaCl solution was compared by measuring the rate of evolved hydrogen. Results show that cerium conversion film improves the corrosion resistance of RE-Mg alloys remarkably.
2009, 38(10):1856-1859.
Abstract:
Ni-based alloy sheet with the diameter of Ф1000 mm and thickness of 0.10-0.13 mm was fabricated by electron beam physical vapor deposition (EB-PVD). Microstructure, precipitated carbide composition and tensile strength were studied for the samples before and after aging heat treatment by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that crystal grains grow up after aging heat treatment; the growth speed slows down evidently with aging time prolonging. Small carbide particles precipitate at the grain boundary during aging, which are (Cr, Fe)23C6 with fcc structure by diffraction pattern analysis. The high-temperature tensile strength of the aged sample increases obviously while the elongation decreases to some extent.
Ni-based alloy sheet with the diameter of Ф1000 mm and thickness of 0.10-0.13 mm was fabricated by electron beam physical vapor deposition (EB-PVD). Microstructure, precipitated carbide composition and tensile strength were studied for the samples before and after aging heat treatment by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that crystal grains grow up after aging heat treatment; the growth speed slows down evidently with aging time prolonging. Small carbide particles precipitate at the grain boundary during aging, which are (Cr, Fe)23C6 with fcc structure by diffraction pattern analysis. The high-temperature tensile strength of the aged sample increases obviously while the elongation decreases to some extent.
2009, 38(10):1860-1863.
Abstract:
In order to find a simple and effective method to optimize the process parameter of precursor infiltration and pyrolysis (PIP) process for ceramic matrix composites, the viewpoint of characterization of the mechanical properties of 2D composites using multifilament composites was put forward. Multifilament and 2D SiCf/SiC composites were fabricated by five kinds of PIP processes, and the change rules of mechanical properties of the two kinds of composites with different PIP processes were investigated. Meanwhile, the validity of using multifilament composites to characterize the mechanical properties of 2D composites was analyzed. The results show that the change rules of mechanical properties of multifilament composites with PIP process parameters are in good agreement with that of 2D composites, because their interfaces, fiber damage and other characteristics are basically the same. The ratio of mechanical properties was employed to characterize the consistency between multifilament and 2D composites. The results indicate that the mechanical properties of those two kinds of composites have higher consistency, but it will decrease with the complexity of PIP process increasing. The mechanical properties of 2D composites can be well characterized by multifilament composites, and the process parameters of 2D composites fabricated by PIP process can be optimized primarily, which can enhance the process design efficiency obviously.
In order to find a simple and effective method to optimize the process parameter of precursor infiltration and pyrolysis (PIP) process for ceramic matrix composites, the viewpoint of characterization of the mechanical properties of 2D composites using multifilament composites was put forward. Multifilament and 2D SiCf/SiC composites were fabricated by five kinds of PIP processes, and the change rules of mechanical properties of the two kinds of composites with different PIP processes were investigated. Meanwhile, the validity of using multifilament composites to characterize the mechanical properties of 2D composites was analyzed. The results show that the change rules of mechanical properties of multifilament composites with PIP process parameters are in good agreement with that of 2D composites, because their interfaces, fiber damage and other characteristics are basically the same. The ratio of mechanical properties was employed to characterize the consistency between multifilament and 2D composites. The results indicate that the mechanical properties of those two kinds of composites have higher consistency, but it will decrease with the complexity of PIP process increasing. The mechanical properties of 2D composites can be well characterized by multifilament composites, and the process parameters of 2D composites fabricated by PIP process can be optimized primarily, which can enhance the process design efficiency obviously.
2009, 38(10):1864-1869.
Abstract:
Gamma titanium aluminide (γ-TiAl) alloys are candidate materials for lightweight high-temperature structural applications and the mechanical properties of the alloys with fully lamellar microstructure are extremely anisotropic. In the seed method of directional solidification, the seed crystal materials with special lamellar orientation are applied, the high-temperature α phases are controlled to grow along <110> direction, and finally the fully lamellar microstructures parallel to the growth direction are obtained. Another approach of controlling the orientation of lamellar microstructure is to change the solidification pathway so that the alloys solidify completely with β phases, and the obtained lamellar microstructure is aligned at 0° and 45° angles to the grow direction. This paper summarized the mechanism and recent research progress of the lamellar orientation control by the two methods in TiAl alloys, and systemically studied the effects of the alloy composition and processing parameters on the lamellar orientation control process. Finally the problems of aligned lamellar microstructure preparation in TiAl alloys at home and abroad that needed to be further investigated were presented.
Gamma titanium aluminide (γ-TiAl) alloys are candidate materials for lightweight high-temperature structural applications and the mechanical properties of the alloys with fully lamellar microstructure are extremely anisotropic. In the seed method of directional solidification, the seed crystal materials with special lamellar orientation are applied, the high-temperature α phases are controlled to grow along <110> direction, and finally the fully lamellar microstructures parallel to the growth direction are obtained. Another approach of controlling the orientation of lamellar microstructure is to change the solidification pathway so that the alloys solidify completely with β phases, and the obtained lamellar microstructure is aligned at 0° and 45° angles to the grow direction. This paper summarized the mechanism and recent research progress of the lamellar orientation control by the two methods in TiAl alloys, and systemically studied the effects of the alloy composition and processing parameters on the lamellar orientation control process. Finally the problems of aligned lamellar microstructure preparation in TiAl alloys at home and abroad that needed to be further investigated were presented.
2009, 38(10):1870-1875.
Abstract:
Effects of Severe Plastic Deformation on Microstructure and Property of Magnesium Alloys
Effects of Severe Plastic Deformation on Microstructure and Property of Magnesium Alloys
2009, 38(10):1876-1880.
Abstract:
Research progress of fabrication, properties and applications on the energy, circumstance and biomaterials of highly ordered TiO2 nanotube array films made by anodic oxidation of titanium in fluoride-based electrolytes were overviewed.
Research progress of fabrication, properties and applications on the energy, circumstance and biomaterials of highly ordered TiO2 nanotube array films made by anodic oxidation of titanium in fluoride-based electrolytes were overviewed.
2009, 38(10):1935-1838.
Abstract:
Cu58.1Zr35.9Al6 bulk metallic glass bars with a diameter of 3 mm were prepared by copper mould suction casting. The effects of temperature on the elastic property and microstructure of the alloy were studied. The results show that the changes of the elastic property and microstructure can be divided into three stages corresponding to different temperature regions. Below the glass transition temperature Tg, the structural relaxation occurred. In the temperature range from Troom to 150 ℃, the structure transition is local and short-range, so the elastic properties only change slightly. However, in the temperature range from 150 ℃ to Tg, because the intermediate-range and long-range atomic diffusion take place with aggregation and rearranging under the sufficient condition, the excess free volume is removed, and thus the elastic properties are improved greatly with the increase of temperature. Within the super-cool liquid regions, from Tg to the onset crystallization temperature Tx, the new phase Cu10Zr7 forms while the elastic properties decrease a little near Tg (490 ℃). Above Tx, the elastic properties increase further with increasing of temperature, and the small amount of Cu8Zr3 phases form besides a large amount of Cu10Zr7. The temperature has a considerable effect on the elastic property and microstructure of Cu58.1Zr35.9Al6 bulk metallic glasses. The effect is closely related to the large decrease of the free volume, the improvement of the atom order degree and the formation of separation phases.
Cu58.1Zr35.9Al6 bulk metallic glass bars with a diameter of 3 mm were prepared by copper mould suction casting. The effects of temperature on the elastic property and microstructure of the alloy were studied. The results show that the changes of the elastic property and microstructure can be divided into three stages corresponding to different temperature regions. Below the glass transition temperature Tg, the structural relaxation occurred. In the temperature range from Troom to 150 ℃, the structure transition is local and short-range, so the elastic properties only change slightly. However, in the temperature range from 150 ℃ to Tg, because the intermediate-range and long-range atomic diffusion take place with aggregation and rearranging under the sufficient condition, the excess free volume is removed, and thus the elastic properties are improved greatly with the increase of temperature. Within the super-cool liquid regions, from Tg to the onset crystallization temperature Tx, the new phase Cu10Zr7 forms while the elastic properties decrease a little near Tg (490 ℃). Above Tx, the elastic properties increase further with increasing of temperature, and the small amount of Cu8Zr3 phases form besides a large amount of Cu10Zr7. The temperature has a considerable effect on the elastic property and microstructure of Cu58.1Zr35.9Al6 bulk metallic glasses. The effect is closely related to the large decrease of the free volume, the improvement of the atom order degree and the formation of separation phases.
