Volume 42,Issue 11,2013 Table of Contents
2013, 42(11):2012-2016.
Abstract:
The phase transformation of titania gel to anatase crystals was characterized using a high-resolution transmission electron microscopy, differential scanning calorimetry and X-ray diffractometer. It was found that the transformation behavior was determined to be inconsistent using the three measurement techniques. The transmission electron microscopic results indicated that a small amount of anatase crystals existed in the amorphous gel that was dried at 100 °C for 24 h; however, the crystals were not detected by the differential scanning calorimetry and X-ray diffraction methods. As the sintering temperature increased, the lattice constant c of tetragonal anatase crystals gradually decreased and then stabilized with the standard constant (JCPDS card No 84-1285) at the temperatures above 300 °C. The lattice constant a remained relatively unchanged, which was in good agreement with the calculated results of the transmission electron microscopy and X-ray diffraction analyses. Moreover, the anatase crystal size determined by the transmission electron microscopy was larger than that by the X-ray diffraction analysis
The phase transformation of titania gel to anatase crystals was characterized using a high-resolution transmission electron microscopy, differential scanning calorimetry and X-ray diffractometer. It was found that the transformation behavior was determined to be inconsistent using the three measurement techniques. The transmission electron microscopic results indicated that a small amount of anatase crystals existed in the amorphous gel that was dried at 100 °C for 24 h; however, the crystals were not detected by the differential scanning calorimetry and X-ray diffraction methods. As the sintering temperature increased, the lattice constant c of tetragonal anatase crystals gradually decreased and then stabilized with the standard constant (JCPDS card No 84-1285) at the temperatures above 300 °C. The lattice constant a remained relatively unchanged, which was in good agreement with the calculated results of the transmission electron microscopy and X-ray diffraction analyses. Moreover, the anatase crystal size determined by the transmission electron microscopy was larger than that by the X-ray diffraction analysis
2013, 42(11):2201-2206.
Abstract:
In order to improve the electrochemical characteristics of the La-Mg-Ni system A2B7-type electrode alloys, the partial substitution of M (M=Pr, Zr) for La has been performed. The melt spinning technology was used to prepare the La0.65M0.1Mg0.25Ni3.2Co0.2Al0.1 (M=Pr, Zr) electrode alloys. The influences of the melt spinning and substithting La with M (M=Pr, Zr) on the structures and the electrochemical hydrogen storage kinetics of the alloys were investigated. The results obtained by XRD and TEM reveal that the as-cast and spun alloys hold a multiphase structure, containing two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The as-spun (M=Pr) alloy displays an entire nanocrystalline structure, while an amorphous-like structure is detected in the as-spun (M=Zr) alloy, implying that the substitution of Zr for La facilitates the amorphous formation. The electrochemical measurement indicates that the high rate discharge ability (HRD) of the alloys first mounts up and then falls with rising of spinning rate. Furthermore, the electrochemical impedance spectrum (EIS), the Tafel polarization curves and the potential-step measurements all indicate that the electrochemical kinetics first increase and then decreases with growing of spinning rate
In order to improve the electrochemical characteristics of the La-Mg-Ni system A2B7-type electrode alloys, the partial substitution of M (M=Pr, Zr) for La has been performed. The melt spinning technology was used to prepare the La0.65M0.1Mg0.25Ni3.2Co0.2Al0.1 (M=Pr, Zr) electrode alloys. The influences of the melt spinning and substithting La with M (M=Pr, Zr) on the structures and the electrochemical hydrogen storage kinetics of the alloys were investigated. The results obtained by XRD and TEM reveal that the as-cast and spun alloys hold a multiphase structure, containing two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The as-spun (M=Pr) alloy displays an entire nanocrystalline structure, while an amorphous-like structure is detected in the as-spun (M=Zr) alloy, implying that the substitution of Zr for La facilitates the amorphous formation. The electrochemical measurement indicates that the high rate discharge ability (HRD) of the alloys first mounts up and then falls with rising of spinning rate. Furthermore, the electrochemical impedance spectrum (EIS), the Tafel polarization curves and the potential-step measurements all indicate that the electrochemical kinetics first increase and then decreases with growing of spinning rate
2013, 42(11):2207-2011.
Abstract:
The effect of hot working conditions on the stress rupture properties of Ti-24Al-15Nb-1.5Mo/TC11 dual-alloy with electron beam welds has been evaluated. Under the gradient heat treatment, the stress rupture properties of the dissimilar alloy joints with 40% deformation degree are superior to the others. The weld and heat affected zone (HAZ) are the weak areas in the stress rupture experiment. The microstructures of weld and HAZ containing grain boundary α are not beneficial to the stress rupture property. Meanwhile, the grain boundaries of Ti-24Al-15Nb-1.5Mo base alloy with coarse α2 phases have a negative effect to stress rupture property. As the atoms diffusing, the content of Nb increases obviously in the weld after stress rupture experiment.
The effect of hot working conditions on the stress rupture properties of Ti-24Al-15Nb-1.5Mo/TC11 dual-alloy with electron beam welds has been evaluated. Under the gradient heat treatment, the stress rupture properties of the dissimilar alloy joints with 40% deformation degree are superior to the others. The weld and heat affected zone (HAZ) are the weak areas in the stress rupture experiment. The microstructures of weld and HAZ containing grain boundary α are not beneficial to the stress rupture property. Meanwhile, the grain boundaries of Ti-24Al-15Nb-1.5Mo base alloy with coarse α2 phases have a negative effect to stress rupture property. As the atoms diffusing, the content of Nb increases obviously in the weld after stress rupture experiment.
2013, 42(11):2217-2221.
Abstract:
The bulk glassy cylinders with a diameter of 5 mm and the ribbons of 30 μm in thickness of Zr47Ti12.9Cu11Ni9.6Be16.7Nb2.8 metallic glass were prepared by suction casting and melt spinning，respectively. The thermal stability parameters such as glass transition temperature Tg, onset crystallization temperature Tx, glass transition and crystallization activation energies Eg, Ex, etc., were measured by Differential Scanning Calorimetry and the Kissinger equation. The results reveal that the thinner ribbon sample has higher thermal stability and the metallic glass exhibits a “the smaller, the more stable” characteristic. The crystallization behaviors of different size samples also verify the above mentioned characteristic further: in the case of the crystallization of the bulk cylinder being lower than that of the glassy ribbon, the cylinder is crystallized more easily, and its crystallization microstructure is more integral than that of the glassy ribbon.
The bulk glassy cylinders with a diameter of 5 mm and the ribbons of 30 μm in thickness of Zr47Ti12.9Cu11Ni9.6Be16.7Nb2.8 metallic glass were prepared by suction casting and melt spinning，respectively. The thermal stability parameters such as glass transition temperature Tg, onset crystallization temperature Tx, glass transition and crystallization activation energies Eg, Ex, etc., were measured by Differential Scanning Calorimetry and the Kissinger equation. The results reveal that the thinner ribbon sample has higher thermal stability and the metallic glass exhibits a “the smaller, the more stable” characteristic. The crystallization behaviors of different size samples also verify the above mentioned characteristic further: in the case of the crystallization of the bulk cylinder being lower than that of the glassy ribbon, the cylinder is crystallized more easily, and its crystallization microstructure is more integral than that of the glassy ribbon.
2013, 42(11):2232-2236.
Abstract:
Gold nanoparticles (AuNPs) were synthesized by ethanol in a base environment. Electron microscopic images characterized the sizes of AuNPs. UV-Vis spectrometer was utilized to study the absorption spectra of gold colloid and the effect of different factors for synthesis. It is found that the quantity of sodium hydroxide (NaOH) is an important factor in determining the formation of the final colloidal product. X-ray diffraction (XRD) analysis was conducted to examine the crystalline structure of the AuNPs, and indicating the nanoparticles present a face-centered-cubic (fcc) crystalline structure. Moreover, the possible mechanism of the progress and the effect of NaOH on the reduction reaction were discussed. The alcohol and hydroxyl ions (OH-) are indispensable to generate the gold particles for one-step at room temperature in just few minutes
Gold nanoparticles (AuNPs) were synthesized by ethanol in a base environment. Electron microscopic images characterized the sizes of AuNPs. UV-Vis spectrometer was utilized to study the absorption spectra of gold colloid and the effect of different factors for synthesis. It is found that the quantity of sodium hydroxide (NaOH) is an important factor in determining the formation of the final colloidal product. X-ray diffraction (XRD) analysis was conducted to examine the crystalline structure of the AuNPs, and indicating the nanoparticles present a face-centered-cubic (fcc) crystalline structure. Moreover, the possible mechanism of the progress and the effect of NaOH on the reduction reaction were discussed. The alcohol and hydroxyl ions (OH-) are indispensable to generate the gold particles for one-step at room temperature in just few minutes
2013, 42(11):2237-2241.
Abstract:
利用循环伏安法、计时电势法和计时电流等方法，研究了钨在700°C的NaCl-KCl-NaF-Na2WO4熔盐中的电化学反应机理和电结晶过程。结果表明，钨的电化学反应过程为由离子扩散速率和电子迁移速率混合控制的准可逆过程，钨的电结晶过程为瞬时形核、三维半球型形核过程，XNaCl:XKCl:XNaF: XNa2WO4= 2:2:1:0.01的实验条件下钨离子的扩散速率为2.543×10-5 cm·s-1
利用循环伏安法、计时电势法和计时电流等方法，研究了钨在700°C的NaCl-KCl-NaF-Na2WO4熔盐中的电化学反应机理和电结晶过程。结果表明，钨的电化学反应过程为由离子扩散速率和电子迁移速率混合控制的准可逆过程，钨的电结晶过程为瞬时形核、三维半球型形核过程，XNaCl:XKCl:XNaF: XNa2WO4= 2:2:1:0.01的实验条件下钨离子的扩散速率为2.543×10-5 cm·s-1
2013, 42(11):2257-2262.
Abstract:
Si-Al-Y co-deposition coatings on TiAl alloy were prepared by pack cementation processes at 1050 °C for 4 h. Scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS) and X-ray diffractmeter (XRD) were employed to investigate the surface morphologies, microstructures and phase constitutions of the coatings. Friction-wear tests of the TiAl alloy substrate and the coatings were conducted in air at normal (20 °C) and high (600 °C) temperature. The results show that the coating prepared by co-deposited Si-Al-Y has a multiple layer structure: an outer layer composed of TiSi2, a middle layer composed of (Ti,X)5Si4 (X represents Nb and Cr elements) and (Ti,X)5Si3, an inner layer composed of TiAl2 and γ-TiAl, and a Al rich-interdiffusion zone. The wear resistance of Si-Al-Y coating is obviously better than that of TiAl alloy at normal and high temperature, and it has good wear resistance performance at high temperature. The wear mechanism of the coating has no significant changes at experimental temperature that is delamination abrasion and grain-abrasion. The wear mechanisms of TiAl alloy are grinding abrasion and grain-abrasion at normal temperature, and are grinding abrasion and grain-abrasion and oxidation abrasion at 600 °C
Si-Al-Y co-deposition coatings on TiAl alloy were prepared by pack cementation processes at 1050 °C for 4 h. Scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS) and X-ray diffractmeter (XRD) were employed to investigate the surface morphologies, microstructures and phase constitutions of the coatings. Friction-wear tests of the TiAl alloy substrate and the coatings were conducted in air at normal (20 °C) and high (600 °C) temperature. The results show that the coating prepared by co-deposited Si-Al-Y has a multiple layer structure: an outer layer composed of TiSi2, a middle layer composed of (Ti,X)5Si4 (X represents Nb and Cr elements) and (Ti,X)5Si3, an inner layer composed of TiAl2 and γ-TiAl, and a Al rich-interdiffusion zone. The wear resistance of Si-Al-Y coating is obviously better than that of TiAl alloy at normal and high temperature, and it has good wear resistance performance at high temperature. The wear mechanism of the coating has no significant changes at experimental temperature that is delamination abrasion and grain-abrasion. The wear mechanisms of TiAl alloy are grinding abrasion and grain-abrasion at normal temperature, and are grinding abrasion and grain-abrasion and oxidation abrasion at 600 °C
2013, 42(11):2263-2268.
Abstract:
The annealing heat treatment of commercial-purity titanium (CP-Ti) was investigated by scanning electron microcopy (SEM), electron backscatter diffraction (EBSD) technique and orientation distribution function (ODF). It is concluded that two stages can be depicted during the primary recrystallization. The first stage is completed at 500 °C in about 60 min, when about 25% of the material recrystallizes with an orientation change. The second stage is completed from 60 to 360 min, when a large part of the material (about 75% of the material) recrystallizes without any orientation change, suggesting in situ recrystallization. The changes in texture are more pronounced at the beginning of the grain growth process. Over long-term heat treatments, the texture evolves much more slowly. The wide peak area centered by {0°, 30°, 30°} is enhanced, while the orientation near {0°, 40°, 50°} is decreased.
The annealing heat treatment of commercial-purity titanium (CP-Ti) was investigated by scanning electron microcopy (SEM), electron backscatter diffraction (EBSD) technique and orientation distribution function (ODF). It is concluded that two stages can be depicted during the primary recrystallization. The first stage is completed at 500 °C in about 60 min, when about 25% of the material recrystallizes with an orientation change. The second stage is completed from 60 to 360 min, when a large part of the material (about 75% of the material) recrystallizes without any orientation change, suggesting in situ recrystallization. The changes in texture are more pronounced at the beginning of the grain growth process. Over long-term heat treatments, the texture evolves much more slowly. The wide peak area centered by {0°, 30°, 30°} is enhanced, while the orientation near {0°, 40°, 50°} is decreased.
2013, 42(11):2274-2278.
Abstract:
Tantalum carbide (TaC) particles reinforced titanium composites were prepared by sparking plasma sintering (SPS). Microstructure and mechanical properties were analyzed by X-ray diffraction, scanning electron microscope and electron probe. The results show that densified TaC/Ti composite can be obtained when sintering above 800 ℃ by SPS. The hardness and strength of titanium can be significantly improved by adding TaC. The hardness of samples with 5%TaC addition are higher than 500 MPa and the bending strength are higher than 600 MPa. The original TaC was consumed owing to solid phase diffusion and reaction in the sintering process;. A new phase of (Ti, Ta)C1-x carbide was formed, which distributed uniformly around titanium matrix. The tantalum has been found in titanium matrix, which means solid solution is formed. The great improvement of the composite strength is associated with phase strengthening and solution strengthening mechanism
Tantalum carbide (TaC) particles reinforced titanium composites were prepared by sparking plasma sintering (SPS). Microstructure and mechanical properties were analyzed by X-ray diffraction, scanning electron microscope and electron probe. The results show that densified TaC/Ti composite can be obtained when sintering above 800 ℃ by SPS. The hardness and strength of titanium can be significantly improved by adding TaC. The hardness of samples with 5%TaC addition are higher than 500 MPa and the bending strength are higher than 600 MPa. The original TaC was consumed owing to solid phase diffusion and reaction in the sintering process;. A new phase of (Ti, Ta)C1-x carbide was formed, which distributed uniformly around titanium matrix. The tantalum has been found in titanium matrix, which means solid solution is formed. The great improvement of the composite strength is associated with phase strengthening and solution strengthening mechanism
2013, 42(11):2279-2283.
Abstract:
In order to study texture evolution and deformation mechanism during cold rolling of Zr-Sn-Nb alloys, the texture from experiments and simulations were presented and compared. Experimental texture was obtained by X-ray diffraction and simulated texture was calculated by the Taylor model with related constraints (Taylor-RC). The choice of deformation systems and their relative critical resolved shear stress (CRSS) were discussed. The results show that using a combination of slip and twinning systems with appropriate ratio of critical resolved shear stress, the simulated texture is in good agreement with the experimental one. The texture evolution of the two sheets could be interpreted by the relative activities of different slip and twinning systems, which are calculated by the Taylor-RC model.
In order to study texture evolution and deformation mechanism during cold rolling of Zr-Sn-Nb alloys, the texture from experiments and simulations were presented and compared. Experimental texture was obtained by X-ray diffraction and simulated texture was calculated by the Taylor model with related constraints (Taylor-RC). The choice of deformation systems and their relative critical resolved shear stress (CRSS) were discussed. The results show that using a combination of slip and twinning systems with appropriate ratio of critical resolved shear stress, the simulated texture is in good agreement with the experimental one. The texture evolution of the two sheets could be interpreted by the relative activities of different slip and twinning systems, which are calculated by the Taylor-RC model.
2013, 42(11):2283-2297.
Abstract:
Fine-grain 93W-4.9Ni-2.1Fe+0.03%Y alloy was fabricated by microalloying and liquid phase sintering process. The effects of the annealing temperature on the microhardness and microstructure evolution of the fine-grain 93W-4.9Ni-2.1Fe+0.03%Y after rapid hot extrusion were investigated. Meanwhile, conventional tungsten heavy alloy was also fabricated at equivalent condition for comparison. The results show that the microhardness of tungsten phase of the alloys is severely decreased with the annealing temperature increasing. EDS examination reveals that the tungsten content in the matrix of tungsten heavy alloys is gradually enhanced with elevated annealing temperature. The tungsten content in the matrix of fine-grain tungsten heavy alloy has reached a maximum level of the order of 26.11% after annealed at 1200 °C. While, the tungsten content in the matrix of conventional tungsten heavy alloy annealed at the temperature of 1350 °C is 28.14%. Microstructure observation shows that annealing treatment is preferential to the tungsten contiguity reduction and tungsten grain refinement. After high temperature annealing, the matrix is distributed more homogeneously and the volume fraction of the matrix of fine-grain tungsten heavy alloy is higher than that of coarse-grain alloy
Fine-grain 93W-4.9Ni-2.1Fe+0.03%Y alloy was fabricated by microalloying and liquid phase sintering process. The effects of the annealing temperature on the microhardness and microstructure evolution of the fine-grain 93W-4.9Ni-2.1Fe+0.03%Y after rapid hot extrusion were investigated. Meanwhile, conventional tungsten heavy alloy was also fabricated at equivalent condition for comparison. The results show that the microhardness of tungsten phase of the alloys is severely decreased with the annealing temperature increasing. EDS examination reveals that the tungsten content in the matrix of tungsten heavy alloys is gradually enhanced with elevated annealing temperature. The tungsten content in the matrix of fine-grain tungsten heavy alloy has reached a maximum level of the order of 26.11% after annealed at 1200 °C. While, the tungsten content in the matrix of conventional tungsten heavy alloy annealed at the temperature of 1350 °C is 28.14%. Microstructure observation shows that annealing treatment is preferential to the tungsten contiguity reduction and tungsten grain refinement. After high temperature annealing, the matrix is distributed more homogeneously and the volume fraction of the matrix of fine-grain tungsten heavy alloy is higher than that of coarse-grain alloy
12 Influence of Rolling Direction on Textures of Ni47Ti44Nb9 Forged, Hot-Rolled and Cold-Rolled Plates
2013, 42(11):2284-2288.
Abstract:
Ni47Ti44Nb9 alloy plate texture has important influence on the shape memory property, so it is necessary to control the texture. The different rolling direction textures of the forged plate, the hot-rolled and the cold-rolled plates were investigated. Results show that the texture of the forged plate center presents a typical γ-fiber with a peak at {111}<112>. The textures of the plate hot-rolled along rolling direction(RD), cross direction(CD) and transverse direction(TD) mainly consist of three fiber types: {114}, {223}, {332} (or{221}), among them {332} has the strongest orientation density，and γ-fibre does not appear. The strongest textures of the plate hot-rolled along RD, CD and TD, are respectively {221}<110>, {332}<113> and {332}<023>, respectively. The secondary cold-rolled plate along RD, 0o, 45o and 90o to RD, has approximately the strongest {332}<110> texture. The secondary cold-rolling texture of 90°to RD has the highest orientation density, and the γ-fibre is significantly strengthened
Ni47Ti44Nb9 alloy plate texture has important influence on the shape memory property, so it is necessary to control the texture. The different rolling direction textures of the forged plate, the hot-rolled and the cold-rolled plates were investigated. Results show that the texture of the forged plate center presents a typical γ-fiber with a peak at {111}<112>. The textures of the plate hot-rolled along rolling direction(RD), cross direction(CD) and transverse direction(TD) mainly consist of three fiber types: {114}
2013, 42(11):2289-2292.
Abstract:
The quasistatic properties and dynamic properties of 80W-Cu alloy in different loading conditions were studied, and the influence of stress state on mechanical properties of the alloy was analyzed. The results show that there exists an obvious asymmetry between compression and tensile properties of 80W-Cu alloy. In the compression process, 80W-Cu alloy exhibits good ductility while in the tensile process the material shows extremely poor ductility. Micro-analysis shows that the high W-W contiguity makes the failure easy to occur under tensile stress, which causes poor ductility of 80W-Cu alloy, while in the compression process, the whole deformation is well coordinated by the abruption of W skeleton and the plastic deformation of Cu phase, which results in good ductility of 80W-Cu alloy
The quasistatic properties and dynamic properties of 80W-Cu alloy in different loading conditions were studied, and the influence of stress state on mechanical properties of the alloy was analyzed. The results show that there exists an obvious asymmetry between compression and tensile properties of 80W-Cu alloy. In the compression process, 80W-Cu alloy exhibits good ductility while in the tensile process the material shows extremely poor ductility. Micro-analysis shows that the high W-W contiguity makes the failure easy to occur under tensile stress, which causes poor ductility of 80W-Cu alloy, while in the compression process, the whole deformation is well coordinated by the abruption of W skeleton and the plastic deformation of Cu phase, which results in good ductility of 80W-Cu alloy
2013, 42(11):2296-2273.
Abstract:
The effects of molybdenum (Mo) on the growth behavior of β-phase grain and hardness of a series of β forged Ti-Mo alloys under different solution treatment temperatures and solution treatment times were studied with an emphasis on the relationship between β-grain size and hardness. The average β-grain sizes under different solution treatment conditions were measured and analyzed．The results show that the β-grain size is not only relative to solution treatment temperatures and times but also relative to Mo contents from statistical results. The β-grain size does not always increase with increasing of solution treatment temperature, a limit value of the grain size will appear in certain temperature region and certain Mo contents. When the Ti-4Mo alloy is solution treated at the range of 900~1050 ℃, the activation energies for grain growth was 83.301 kJ/mol; and When the Ti-20Mo alloy is solution treated at the range of 750~900 ℃, the activation energies for grain growth was 272.16 kJ/mol. The growth behavior of β-phase grain is discussed in terms of grain growth thermodynamics and kinetics laws．Hardness results show that grain size has noticeable influence on hardness and hardness increases with decreasing of grain size.
The effects of molybdenum (Mo) on the growth behavior of β-phase grain and hardness of a series of β forged Ti-Mo alloys under different solution treatment temperatures and solution treatment times were studied with an emphasis on the relationship between β-grain size and hardness. The average β-grain sizes under different solution treatment conditions were measured and analyzed．The results show that the β-grain size is not only relative to solution treatment temperatures and times but also relative to Mo contents from statistical results. The β-grain size does not always increase with increasing of solution treatment temperature, a limit value of the grain size will appear in certain temperature region and certain Mo contents. When the Ti-4Mo alloy is solution treated at the range of 900~1050 ℃, the activation energies for grain growth was 83.301 kJ/mol; and When the Ti-20Mo alloy is solution treated at the range of 750~900 ℃, the activation energies for grain growth was 272.16 kJ/mol. The growth behavior of β-phase grain is discussed in terms of grain growth thermodynamics and kinetics laws．Hardness results show that grain size has noticeable influence on hardness and hardness increases with decreasing of grain size.
15 Macro and Micro Numerical Simulation of Directional Solidification of Super Alloy SX Turbine Blade
2013, 42(11):2298-2303.
Abstract:
Defect-free blades with fine microstructure and excellent high temperature performance are needed by aero-turbine. The curved shape of SX (single grain) blade is usually very complicated, and its section varies sharply at the platform, the tip shroud, etc. Thus, stray grains are difficult to avoid during directional solidification. In order to optimize the process parameter, the physical model and the mathematical model of directional solidification of SX blade were established based on Panda thermodynamic database and finite element. The temperature field, the evolution of mushy zone and the SDAS (secondary dendrite arm spacing) during solidification of SX sample by different process were simulated, and the discipline and mechanism of defect formation were investigated. The numerical results agree well with the experimental. The calculated results indicate that with the higher withdrawal rate, the SDAS gets smaller but stray grains tend to occur; with the lower withdrawal rate, the possibility of stray grains gets lower but the SDAS gets larger. The directional solidification of complicated thin-walled hollow real SX blade was simulated as well. The results show that the SDAS is nearly uniform in the blade, stray grains may appear at the platform when the withdrawal rate is up to 3.5 mm/min. By the process with varying withdrawal rate, the stray grain can be avoided while most of secondary dendrite can be refined, thus improving the productivity and percent of pass
Defect-free blades with fine microstructure and excellent high temperature performance are needed by aero-turbine. The curved shape of SX (single grain) blade is usually very complicated, and its section varies sharply at the platform, the tip shroud, etc. Thus, stray grains are difficult to avoid during directional solidification. In order to optimize the process parameter, the physical model and the mathematical model of directional solidification of SX blade were established based on Panda thermodynamic database and finite element. The temperature field, the evolution of mushy zone and the SDAS (secondary dendrite arm spacing) during solidification of SX sample by different process were simulated, and the discipline and mechanism of defect formation were investigated. The numerical results agree well with the experimental. The calculated results indicate that with the higher withdrawal rate, the SDAS gets smaller but stray grains tend to occur; with the lower withdrawal rate, the possibility of stray grains gets lower but the SDAS gets larger. The directional solidification of complicated thin-walled hollow real SX blade was simulated as well. The results show that the SDAS is nearly uniform in the blade, stray grains may appear at the platform when the withdrawal rate is up to 3.5 mm/min. By the process with varying withdrawal rate, the stray grain can be avoided while most of secondary dendrite can be refined, thus improving the productivity and percent of pass
2013, 42(11):2304-2308.
Abstract:
The effect and mechanism of Fe element addition in Cu36Zr48Ag8Al8 BMG on structure and mechanical properties were investigated. Effects of phase separation structure and nanocrystalline precipitation on mechanical behaviors were analyzed. Vickers hardness tests were used to study the effect of Fe addition on the hardness and shear band features of the BMG. The results show that Fe-enriched and Cu, Ag-enriched amorphous phase are light and dark phase in TEM contrast, respectively. Phase separation structure with different modulus and hardness in the amorphous alloy, leads to strain hardening behavior under loading. And the nanocrystallines smaller than 5 nm form and dispersion further strengthens the amorphous matrix. A few semi-circular shear bands form around Vickers indention of the amorphous phase. And more semi-circular shear bands with a smaller distance form as the indenter presses on the structure with better plasticity. The Vickers hardness of crystalline phase is lower than that of the amorphous phase, and no flaw exist around the indention
The effect and mechanism of Fe element addition in Cu36Zr48Ag8Al8 BMG on structure and mechanical properties were investigated. Effects of phase separation structure and nanocrystalline precipitation on mechanical behaviors were analyzed. Vickers hardness tests were used to study the effect of Fe addition on the hardness and shear band features of the BMG. The results show that Fe-enriched and Cu, Ag-enriched amorphous phase are light and dark phase in TEM contrast, respectively. Phase separation structure with different modulus and hardness in the amorphous alloy, leads to strain hardening behavior under loading. And the nanocrystallines smaller than 5 nm form and dispersion further strengthens the amorphous matrix. A few semi-circular shear bands form around Vickers indention of the amorphous phase. And more semi-circular shear bands with a smaller distance form as the indenter presses on the structure with better plasticity. The Vickers hardness of crystalline phase is lower than that of the amorphous phase, and no flaw exist around the indention
2013, 42(11):2309-2314.
Abstract:
The crystalline morphology and the phase evolution of Mg-6Zn-Y alloy solidified under a super-high pressure were investigated by scanning electronic microscopy (SEM) coupled with the energy disperse spectrum (EDS) and the X-ray energy diffraction (XRD). The results show that with the increase of solidification pressure, the crystalline morphology transition from a coarse equiaxed dendritic to a super-fine equiaxed dendritic, to a columnar dendritic, and to a granular “cellular” is observed in the microstructure, suggesting the solid/liquid interface is stable. The microstructure of the alloy solidified under 10-9 GPa consists of three phases, i.e. α-Mg phase, I-Mg3Zn6Y phases and S-Mg43Zn4Y3 phase, while the microstructure of the alloy solidified under 2~6 GPa consists of four phases, i.e. α-Mg phase, I-Mg3Zn6Y phase, S-Mg43Zn4Y3 phase, and ternary Mg-Zn-Y phase with high Y content
The crystalline morphology and the phase evolution of Mg-6Zn-Y alloy solidified under a super-high pressure were investigated by scanning electronic microscopy (SEM) coupled with the energy disperse spectrum (EDS) and the X-ray energy diffraction (XRD). The results show that with the increase of solidification pressure, the crystalline morphology transition from a coarse equiaxed dendritic to a super-fine equiaxed dendritic, to a columnar dendritic, and to a granular “cellular” is observed in the microstructure, suggesting the solid/liquid interface is stable. The microstructure of the alloy solidified under 10-9 GPa consists of three phases, i.e. α-Mg phase, I-Mg3Zn6Y phases and S-Mg43Zn4Y3 phase, while the microstructure of the alloy solidified under 2~6 GPa consists of four phases, i.e. α-Mg phase, I-Mg3Zn6Y phase, S-Mg43Zn4Y3 phase, and ternary Mg-Zn-Y phase with high Y content
2013, 42(11):2315-2320.
Abstract:
The Sn-Ag3.0-Cu0.5/Cu solder joint samples subjected to 2 reflows and different aging time were prepared using, SMT full-automatic reflow machine and high constant-temperature test chamber, the thicknesses of the intermetallic compounds (IMC) of the samples were measured. The results show that the thickness increment of IMC is approximately proportional to the square root of aging time. A series of thermal cycling simulations were conducted with finite element software ANSYS to examine the stress/strain behaviors of PBGA solder joints with various IMC thickness, and the solder balls were characterized by Anand unified viscoplastic constitutive model. The simulated results show that there is the most cumulative plastic strain at the top right corner of the solder ball right beneath the edge of chip, which is considered as the critical solder joint of PBGA. With increasing thickness of IMC, the equivalent stress level of the critical solder joint decreases during the thermal cycling process, the shear plastic strain range Δγ increases and the corresponding thermal fatigue life Nf decreases. The shear plastic strain increment during the heating process and holding process constitutes Δγ and the percentage of Δγ basically maintains at the level of 95% in different IMC thicknesses.
The Sn-Ag3.0-Cu0.5/Cu solder joint samples subjected to 2 reflows and different aging time were prepared using, SMT full-automatic reflow machine and high constant-temperature test chamber, the thicknesses of the intermetallic compounds (IMC) of the samples were measured. The results show that the thickness increment of IMC is approximately proportional to the square root of aging time. A series of thermal cycling simulations were conducted with finite element software ANSYS to examine the stress/strain behaviors of PBGA solder joints with various IMC thickness, and the solder balls were characterized by Anand unified viscoplastic constitutive model. The simulated results show that there is the most cumulative plastic strain at the top right corner of the solder ball right beneath the edge of chip, which is considered as the critical solder joint of PBGA. With increasing thickness of IMC, the equivalent stress level of the critical solder joint decreases during the thermal cycling process, the shear plastic strain range Δγ increases and the corresponding thermal fatigue life Nf decreases. The shear plastic strain increment during the heating process and holding process constitutes Δγ and the percentage of Δγ basically maintains at the level of 95% in different IMC thicknesses.
2013, 42(11):2321-2325.
Abstract:
Bimetallic nanoparticles (NPs) have become one of hot spots in materials science due to their unique physical and chemical properties. The alloying process of core-shell structured Ag-Au NPs has been investigated with a modified analytic embedded atom method (MAEAM) and molecular dynamics. The influence of shell thickness on alloying behavior has been studied from the viewpoint of atomic diffusion, microstructure evolution and alloying extent. For NPs with a thin shell, there is a significant atomic diffusion at the core/shell interface. The Ag core undergoes a shape evolution from initial spherical to polyhedron. The surface Au and Ag atoms are fully mixed. For NPs with a thick shell, the atomic diffusion is mainly located to the surface of NPs. The NPs exhibit polyhedron morphology with the Ag core almost unchanged. The morphology above is changed through the stacking fault growth. Compared with the thick shell, the alloying extent of NPs with a thin shell is much greater
Bimetallic nanoparticles (NPs) have become one of hot spots in materials science due to their unique physical and chemical properties. The alloying process of core-shell structured Ag-Au NPs has been investigated with a modified analytic embedded atom method (MAEAM) and molecular dynamics. The influence of shell thickness on alloying behavior has been studied from the viewpoint of atomic diffusion, microstructure evolution and alloying extent. For NPs with a thin shell, there is a significant atomic diffusion at the core/shell interface. The Ag core undergoes a shape evolution from initial spherical to polyhedron. The surface Au and Ag atoms are fully mixed. For NPs with a thick shell, the atomic diffusion is mainly located to the surface of NPs. The NPs exhibit polyhedron morphology with the Ag core almost unchanged. The morphology above is changed through the stacking fault growth. Compared with the thick shell, the alloying extent of NPs with a thin shell is much greater
2013, 42(11):2326-2331.
Abstract:
The 612 aluminates were prepared by liquid phase co-precipitation and mechanical mixing. The effect of sintering temperature on the phases of the 612 (BaO:CaO:Al2O3=6:1:2) aluminate, the sintering mechanism and some chemical reactions during the sintering process were investigated. The shape, particle size distribution and phase transform of the aluminates were studied by scanning electron microscope (SEM), Energy Dispersive Spectrometer (EDS), X-ray diffraction (XRD) and laser particle size analysis. The result shows that the submicron quasi-spherical precursor particles with the D (n, 50)(nm) of 815 nm can be produced through the method of liquid phase co-precipitation. Using the obtained precursor, the 612 aluminates with high degree of crystallization and the crystal phase of Ba5CaAl4O12 can be produced after high temperature sintering at 1500 ℃b. The emission current density for Ba-W cathode (impregnated 612 aluminates) reaches to 15.56 A/cm2 with average evaporation rate of 14.5 nm/h
The 612 aluminates were prepared by liquid phase co-precipitation and mechanical mixing. The effect of sintering temperature on the phases of the 612 (BaO:CaO:Al2O3=6:1:2) aluminate, the sintering mechanism and some chemical reactions during the sintering process were investigated. The shape, particle size distribution and phase transform of the aluminates were studied by scanning electron microscope (SEM), Energy Dispersive Spectrometer (EDS), X-ray diffraction (XRD) and laser particle size analysis. The result shows that the submicron quasi-spherical precursor particles with the D (n, 50)(nm) of 815 nm can be produced through the method of liquid phase co-precipitation. Using the obtained precursor, the 612 aluminates with high degree of crystallization and the crystal phase of Ba5CaAl4O12 can be produced after high temperature sintering at 1500 ℃b. The emission current density for Ba-W cathode (impregnated 612 aluminates) reaches to 15.56 A/cm2 with average evaporation rate of 14.5 nm/h
2013, 42(11):2332-2336.
Abstract:
To improve the wettability of silver powder in organic vehicle, a measurement of the permeating height, according to the Washburn equation, has been employed to evaluate the wetting angle of silver powder in the following three solvents, Dipropylene glycol n-propyl ether, Diethylene glycol n-butyl ether acetate and α-Terpineol. The change of the wetting angle has been observed when four dispersants, n-Caprylic acid, Triethanolamine, Sorbitan Trioleate, and BYK182 were added in different solvents. The results show that α-Terpineol has the best wettability for silver powder. As a kind of nonionic polymer surfactants, BYK182 improves the wettability in the solvents of Dipropylene glycol n-propyl ether and Diethylene glycol n-butyl ether acetate
To improve the wettability of silver powder in organic vehicle, a measurement of the permeating height, according to the Washburn equation, has been employed to evaluate the wetting angle of silver powder in the following three solvents, Dipropylene glycol n-propyl ether, Diethylene glycol n-butyl ether acetate and α-Terpineol. The change of the wetting angle has been observed when four dispersants, n-Caprylic acid, Triethanolamine, Sorbitan Trioleate, and BYK182 were added in different solvents. The results show that α-Terpineol has the best wettability for silver powder. As a kind of nonionic polymer surfactants, BYK182 improves the wettability in the solvents of Dipropylene glycol n-propyl ether and Diethylene glycol n-butyl ether acetate
2013, 42(11):2337-2340.
Abstract:
In order to study the jet and penetration performance of W-Ni-Fe alloy shaped charge liner (SCL), the W-Ni-Fe alloy SCL was subjected to static penetration experiments. The X-ray imaging system was used to study the jet forming ability. The macroscopic and microscopic phenomenon of targets was investigated. Results show that W-Ni-Fe alloy SCL can form ductility jet and the jet velocity is high, although penetration is lower, and the hole diameter is large. The microscopic analysis result shows that there is much residual jet on the surface of bullet hole and high hardness martensite is formed. The XRD result shows that the interaction is very severe between jet and steel target, and in the meantime much Fe0.95W0.05 compound is formed. The low penetration and large hole diameter about W-Ni-Fe alloy SCL is a main result of severe transverse energy dissipation of jet which is caused by martensite and intermetallic
In order to study the jet and penetration performance of W-Ni-Fe alloy shaped charge liner (SCL), the W-Ni-Fe alloy SCL was subjected to static penetration experiments. The X-ray imaging system was used to study the jet forming ability. The macroscopic and microscopic phenomenon of targets was investigated. Results show that W-Ni-Fe alloy SCL can form ductility jet and the jet velocity is high, although penetration is lower, and the hole diameter is large. The microscopic analysis result shows that there is much residual jet on the surface of bullet hole and high hardness martensite is formed. The XRD result shows that the interaction is very severe between jet and steel target, and in the meantime much Fe0.95W0.05 compound is formed. The low penetration and large hole diameter about W-Ni-Fe alloy SCL is a main result of severe transverse energy dissipation of jet which is caused by martensite and intermetallic
2013, 42(11):2341-2345.
Abstract:
TiO2 nanotubes were prepared by annealing the as-prepared samples in air at 500 ℃, and then in hydrogen atmosphere at 300 ?C. Hydrogenated TiO2 nanotube arrays were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction microscopy (XRD), and X-ray photoelectron spectroscopy (XPS). Results show that hydrogen-treated TiO2 nanotube arrays areconsisted of anatase phase TiO2 nanotube walls and disordered nanophase in the surface of TiO2 nanotube walls. It is demonstrated that the presence of the Ti-OH energy states in disordered nanophase. The hydrogenated TiO2 nanotube sample yields a photocurrent density of ~4.88 mA/cm2 vs Ag/AgCl, in 1 mol/L NaOH solution under the illumination of simulated solar light (100 mW/cm2 from lamp coupled with an AM 1.5 G filter). Remarkably, a 4-fold enhanced photocurrent density for TiO2 nanotubes after hydrogen treatment was observed
TiO2 nanotubes were prepared by annealing the as-prepared samples in air at 500 ℃, and then in hydrogen atmosphere at 300 ?C. Hydrogenated TiO2 nanotube arrays were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction microscopy (XRD), and X-ray photoelectron spectroscopy (XPS). Results show that hydrogen-treated TiO2 nanotube arrays areconsisted of anatase phase TiO2 nanotube walls and disordered nanophase in the surface of TiO2 nanotube walls. It is demonstrated that the presence of the Ti-OH energy states in disordered nanophase. The hydrogenated TiO2 nanotube sample yields a photocurrent density of ~4.88 mA/cm2 vs Ag/AgCl, in 1 mol/L NaOH solution under the illumination of simulated solar light (100 mW/cm2 from lamp coupled with an AM 1.5 G filter). Remarkably, a 4-fold enhanced photocurrent density for TiO2 nanotubes after hydrogen treatment was observed
2013, 42(11):2346-2350.
Abstract:
The effects of addition of Y with ultrasonic field assistance on as-cast microstructure of AZ91 alloy were studied. The predominant precipitated phases of AZ91-Y alloy system were worked out to be Al-Y intermetallics by Miedema’s model, and the new precipitated phases were verified to be Al2Y by the result of XRD. The phases and microstructure of the composites were also analyzed. The result shows that when the content of Y in AZ91 alloy exceeds 1.0%, the precipitated phases Al2Y grow up and agglomerate gradually, the grain refinement effect is not obvious. After the AZ91-Y melt are treated by ultrasonic for 2 min at 850 °C, Al2Y particles are refined and distribute uniformly, and the morphology of β-Mg17Al12 changes from continuous to discontinuous or spherical morphology, while the grain and microstructure of the alloy are refined obviously
The effects of addition of Y with ultrasonic field assistance on as-cast microstructure of AZ91 alloy were studied. The predominant precipitated phases of AZ91-Y alloy system were worked out to be Al-Y intermetallics by Miedema’s model, and the new precipitated phases were verified to be Al2Y by the result of XRD. The phases and microstructure of the composites were also analyzed. The result shows that when the content of Y in AZ91 alloy exceeds 1.0%, the precipitated phases Al2Y grow up and agglomerate gradually, the grain refinement effect is not obvious. After the AZ91-Y melt are treated by ultrasonic for 2 min at 850 °C, Al2Y particles are refined and distribute uniformly, and the morphology of β-Mg17Al12 changes from continuous to discontinuous or spherical morphology, while the grain and microstructure of the alloy are refined obviously
25 Optimization of Hot Deformation Parameters of Burn Resistant Titanium Alloy by Using Processing Map
2013, 42(11):2351-2355.
Abstract:
The hot compressive deformation tests of as-cast and as-extruded burn resistant titanium alloys (Ti-35V-15Cr-Si-C) were performed on the Gleeble-1500 simulator in the temperature range of 900~1200 ℃ for as-cast and 900~1150 ℃ for as-extruded alloy, over the range of strain rate from 10-3 s-1 to 1 s-1. The compressive true stress vs. true strain curves were measured, and the hot processing maps of both as-cast and as-extrude state alloys were constructed based on dynamic materials model (DMM). The results show that: (1) extrusion is the preferable ingot cogging processing technology; (2) compared to the as-cast burn resistant alloy, it is easier for the extruded alloy to generate a continuous recrystallization, and the flow localization instability for as-extruded alloy is restrained. (3) the brittleness due to carbide solution at higher temperature can not be eliminated through the processing treatment. To avoid surface cracking, the appropriate deformation temperature should be lower than 1030 ℃
The hot compressive deformation tests of as-cast and as-extruded burn resistant titanium alloys (Ti-35V-15Cr-Si-C) were performed on the Gleeble-1500 simulator in the temperature range of 900~1200 ℃ for as-cast and 900~1150 ℃ for as-extruded alloy, over the range of strain rate from 10-3 s-1 to 1 s-1. The compressive true stress vs. true strain curves were measured, and the hot processing maps of both as-cast and as-extrude state alloys were constructed based on dynamic materials model (DMM). The results show that: (1) extrusion is the preferable ingot cogging processing technology; (2) compared to the as-cast burn resistant alloy, it is easier for the extruded alloy to generate a continuous recrystallization, and the flow localization instability for as-extruded alloy is restrained. (3) the brittleness due to carbide solution at higher temperature can not be eliminated through the processing treatment. To avoid surface cracking, the appropriate deformation temperature should be lower than 1030 ℃
2013, 42(11):2356-2361.
Abstract:
Ti6Al7Nb alloys were implanted with 40 keV N+ and different implanting dosage, using in high energy ion implantation and enhanced deposition system. The torsional fretting wears of an un-treated and an ion implantation nitride Ti6Al7Nb alloy flats against Zr2O ball (with diameter of 25.2 mm) were carried out under a simulated physiological condition. Combined with the analyses of the frictional kinetics behaviours, and by means of X-ray diffraction, micro-hardness tester and SEM morphologies, the damage characteristics of the surface modification layer and its substrate were discussed in detail. The results show that the ion implantation nitride can improve the surface hardness of the alloy, its resistance of the torsional fretting wear is improved also
Ti6Al7Nb alloys were implanted with 40 keV N+ and different implanting dosage, using in high energy ion implantation and enhanced deposition system. The torsional fretting wears of an un-treated and an ion implantation nitride Ti6Al7Nb alloy flats against Zr2O ball (with diameter of 25.2 mm) were carried out under a simulated physiological condition. Combined with the analyses of the frictional kinetics behaviours, and by means of X-ray diffraction, micro-hardness tester and SEM morphologies, the damage characteristics of the surface modification layer and its substrate were discussed in detail. The results show that the ion implantation nitride can improve the surface hardness of the alloy, its resistance of the torsional fretting wear is improved also
2013, 42(11):2362-2366.
Abstract:
EuBr3, Eu(NO3)3, EuCl3, Eu(ClO4)3, Eu(AC)3 doped Sb-SnO2/Ti electrodes were prepared by thermal decomposition. The properties of electrodes for the oxidation of ethanol and the electro-catalytic decomposition of a model pollutant (methyl orange, methylene blue) were investigated. Electrodes were characterized by cyclic voltammetry, X-ray diffraction, scanning electron microscope, and X-ray photoelectron spectroscopy. It is suggested that various Eu salts doped Sb-SnO2/Ti electrodes show different catalytic properties. Eu(ClO4)3 doped electrodes show the best effect for degradation of methyl orange, EuCl3 doped electrodes provide the best degradation of methylene blue, and as for electric catalytic oxidation ethanol, Eu (NO3)3 doped electrodes show the highest catalytic activity
EuBr3, Eu(NO3)3, EuCl3, Eu(ClO4)3, Eu(AC)3 doped Sb-SnO2/Ti electrodes were prepared by thermal decomposition. The properties of electrodes for the oxidation of ethanol and the electro-catalytic decomposition of a model pollutant (methyl orange, methylene blue) were investigated. Electrodes were characterized by cyclic voltammetry, X-ray diffraction, scanning electron microscope, and X-ray photoelectron spectroscopy. It is suggested that various Eu salts doped Sb-SnO2/Ti electrodes show different catalytic properties. Eu(ClO4)3 doped electrodes show the best effect for degradation of methyl orange, EuCl3 doped electrodes provide the best degradation of methylene blue, and as for electric catalytic oxidation ethanol, Eu (NO3)3 doped electrodes show the highest catalytic activity
2013, 42(11):2367-2370.
Abstract:
Microstructure and mechanical properties were researched under different heat-treatment conditions for damage tolerance TC4-DT alloy. The relation between the different microstructure parameters with mechanical properties was analyzed, and the influence of different cooling rates on fracture toughness of TC4-DT titanium alloy was investigated. The result shows that the heat-treatment can adjust the microstructure parameters, including the content of primary α, the dimension of β grains and the dimension of lamellar α, which can affect the properties of TC4-DT alloy. The factors that influence the properties were mainly analyzed theoretically, and the fracture surface was observed
Microstructure and mechanical properties were researched under different heat-treatment conditions for damage tolerance TC4-DT alloy. The relation between the different microstructure parameters with mechanical properties was analyzed, and the influence of different cooling rates on fracture toughness of TC4-DT titanium alloy was investigated. The result shows that the heat-treatment can adjust the microstructure parameters, including the content of primary α, the dimension of β grains and the dimension of lamellar α, which can affect the properties of TC4-DT alloy. The factors that influence the properties were mainly analyzed theoretically, and the fracture surface was observed
2013, 42(11):2371-2375.
Abstract:
Nanocrystalline nickel was prepared by friction aided jet electrodeposition and traditional jet electrodeposition. The structure of two Nickel deposition layers was studied by TEM, and the corrosion behavior in 3.5wt%NaCl solution and 1 mol/LH2SO4 solution was studied by electrochemical polarization method. The results show that nano-crystalline nickel prepared by friction aided jet electrodeposition has a compact structure and an average grain size of 9.77 nm. In two corrosion solutions, the electrochemical corrosion resistance of nanocrystalline nickel prepared by friction aided jet electrodeposition can be both better than that prepared by traditional jet electrodeposition. Only nanocrystalline nickel prepared by friction aided jet electrodeposition generates passive film in the corrosion process. The grain size and micro-defects are two important factors that affect the corrosion resistance of nanocrystalline nickel
Nanocrystalline nickel was prepared by friction aided jet electrodeposition and traditional jet electrodeposition. The structure of two Nickel deposition layers was studied by TEM, and the corrosion behavior in 3.5wt%NaCl solution and 1 mol/LH2SO4 solution was studied by electrochemical polarization method. The results show that nano-crystalline nickel prepared by friction aided jet electrodeposition has a compact structure and an average grain size of 9.77 nm. In two corrosion solutions, the electrochemical corrosion resistance of nanocrystalline nickel prepared by friction aided jet electrodeposition can be both better than that prepared by traditional jet electrodeposition. Only nanocrystalline nickel prepared by friction aided jet electrodeposition generates passive film in the corrosion process. The grain size and micro-defects are two important factors that affect the corrosion resistance of nanocrystalline nickel
2013, 42(11):2376-2379.
Abstract:
The synthesis of Ni/B micro-nano composite particles was studied by diamine hydrate reducing nickel chloride in the water bath at 50°C in which nano-Ni was made to cover the surface of micron boron particles. The sample was characterized by TEM, EDS, XRD, TG-DTA and thermal conductivity instrument. The results show that this method can prepare a compact coating for Ni/B composite particles. The nano-Ni particles coated on boron particles are uniform and continuous, and the mass ratio of Ni and boron is 1:1. The average diameter of Ni crystallites is about 21.7 nm. Compared with boron powder, the high temperature of exothermic peak of Ni/B micro-nano composite particles is decreased by about 36 °C. The thermal chemistry behavior of the as-prepared composite particles is better than the superfine boron powder, and the thermal conductivity of Ni/B micro-nano composite particles is higher than that of the boron powder
The synthesis of Ni/B micro-nano composite particles was studied by diamine hydrate reducing nickel chloride in the water bath at 50°C in which nano-Ni was made to cover the surface of micron boron particles. The sample was characterized by TEM, EDS, XRD, TG-DTA and thermal conductivity instrument. The results show that this method can prepare a compact coating for Ni/B composite particles. The nano-Ni particles coated on boron particles are uniform and continuous, and the mass ratio of Ni and boron is 1:1. The average diameter of Ni crystallites is about 21.7 nm. Compared with boron powder, the high temperature of exothermic peak of Ni/B micro-nano composite particles is decreased by about 36 °C. The thermal chemistry behavior of the as-prepared composite particles is better than the superfine boron powder, and the thermal conductivity of Ni/B micro-nano composite particles is higher than that of the boron powder
2013, 42(11):2380-2383.
Abstract:
Using Ni16Cr9Al pre-alloy powder with ＜25 μm particles size as starting material, Ni16Cr9Al porous material was prepared by pressing and vacuum sintering. The effect of sintering temperature on Ni16Cr9Al porous material performance was researched. The results show that the shrinkage of the volume of Ni16Cr9Al green body will occur owing to forming and growing up of sintering-neck during the sinter. The porosity, the maximum and average pore sizes decrease and the shear strength of the Ni16Cr9Al porous materials increases with the increase of the sintering temperature. The Ni16Cr9Al porous material possesses a favorable three-dimensional meshwork after sintering at 1130 ℃. The porosity quantity decreases and the density of the Ni16Cr9Al material gradually increases after sintering over 1150 ℃
Using Ni16Cr9Al pre-alloy powder with ＜25 μm particles size as starting material, Ni16Cr9Al porous material was prepared by pressing and vacuum sintering. The effect of sintering temperature on Ni16Cr9Al porous material performance was researched. The results show that the shrinkage of the volume of Ni16Cr9Al green body will occur owing to forming and growing up of sintering-neck during the sinter. The porosity, the maximum and average pore sizes decrease and the shear strength of the Ni16Cr9Al porous materials increases with the increase of the sintering temperature. The Ni16Cr9Al porous material possesses a favorable three-dimensional meshwork after sintering at 1130 ℃. The porosity quantity decreases and the density of the Ni16Cr9Al material gradually increases after sintering over 1150 ℃
2013, 42(11):2384-2388.
Abstract:
The in-situ synthesis CrN/MoS2 solid self-lubricant composite coating was obtained by magnetron sputtering and low-temperature ion sulfuring. The XPS, AES and SEM equipped with EDS were used to observe and analyze the microstructure of the composite coating. The results show that the MoS2 is composed of sulfur which is infiltrated in 500 nm depth of the composite coating. The CETR inching tribology tester was used to analyze the tribological properties of CrN-based composite coating. The wear volume from big to small is CrMoN＞CrN/MoS2. It means that the CrN/MoS2 solid self-lubricant composite coating shows better wear resistance and antifriction. The film-forming mechanism and the frictional wear mechanism of CrN-based solid self-lubricant composite coating were discussed
The in-situ synthesis CrN/MoS2 solid self-lubricant composite coating was obtained by magnetron sputtering and low-temperature ion sulfuring. The XPS, AES and SEM equipped with EDS were used to observe and analyze the microstructure of the composite coating. The results show that the MoS2 is composed of sulfur which is infiltrated in 500 nm depth of the composite coating. The CETR inching tribology tester was used to analyze the tribological properties of CrN-based composite coating. The wear volume from big to small is CrMoN＞CrN/MoS2. It means that the CrN/MoS2 solid self-lubricant composite coating shows better wear resistance and antifriction. The film-forming mechanism and the frictional wear mechanism of CrN-based solid self-lubricant composite coating were discussed
2013, 42(11):2389-2393.
Abstract:
Effects of rolling process on bonding interface and the element thickness-ratio of Cu/Mo/Cu cladding plates prepared by hot rolling and warm rolling were studied. The results show that the Cu/Mo interface is closely bonded after rolling deformation and the bonding mechanism of Cu/Mo is dentate meshing. The grain of Cu layer near the surface and the interface is smaller than that in the center. With the increase of the deformation, the equiaxed grains of Cu layer are stretched along the rolling direction. The bonded effect of the interface is significantly improved and becomes straighter from the dentition. The deformation of Cu layer is larger than that of Mo layer. The thickness-ratio was analyzed. With the increase of the total reduction, the difference of the element deformation decreases and the element deformation gradually tends to conform. The thickness-ratio of Cu/Mo/Cu composites relation is proposed and it offers a method for base material choice
Effects of rolling process on bonding interface and the element thickness-ratio of Cu/Mo/Cu cladding plates prepared by hot rolling and warm rolling were studied. The results show that the Cu/Mo interface is closely bonded after rolling deformation and the bonding mechanism of Cu/Mo is dentate meshing. The grain of Cu layer near the surface and the interface is smaller than that in the center. With the increase of the deformation, the equiaxed grains of Cu layer are stretched along the rolling direction. The bonded effect of the interface is significantly improved and becomes straighter from the dentition. The deformation of Cu layer is larger than that of Mo layer. The thickness-ratio was analyzed. With the increase of the total reduction, the difference of the element deformation decreases and the element deformation gradually tends to conform. The thickness-ratio of Cu/Mo/Cu composites relation is proposed and it offers a method for base material choice
2013, 42(11):2394-2399.
Abstract:
The AgCuZnSn brazing filler metal was prepared on the Ag45CuZn brazing filler metal by brush electro-plating tin. The effect of current density, relative velocity of cathode and anode, bath electrolyte temperature, voltage and time on current efficiency and tin content of AgCuZnSn brazing filler metal were investigated. The surface morphology of tin coating and the brazing filler metal wettability were observed using scanning electron microscopy (SEM) and wetting test furnace. The results indicate that current efficiency and tin content initially increase and then decrease with the increase of the current density, brush electro-plating voltage and temperature. As the increase of the relative velocity of anode and cathode, the current efficiency gradually reduces, and the tin content initially increases and then decreases. With the increase of the brush electro-plating time, the current efficiency has no significant change, but the content of tin increases. SEM images show that a smooth and uniform surface morphology of the tin coating with tin grain size of about 0.3~1.8 μm and porosity of 0.82% is obtained. The non-directional tin granular parallel to the surface direction of Ag45CuZn brazing filler metal growth is better than that of perpendicular to the surface of the growth. Compared to Ag45CuZn brazing filler metal matrix, when 2.38 wt.% metal tin is brush electro-plated on Ag45CuZn brazing filler metal, the wetting area of Ag45CuZn brazing filler metal increases by about 19.5 %, and the Ag43.92Cu28.65Zn25.05Sn2.38 brazing filler metal possesses a good wettability
The AgCuZnSn brazing filler metal was prepared on the Ag45CuZn brazing filler metal by brush electro-plating tin. The effect of current density, relative velocity of cathode and anode, bath electrolyte temperature, voltage and time on current efficiency and tin content of AgCuZnSn brazing filler metal were investigated. The surface morphology of tin coating and the brazing filler metal wettability were observed using scanning electron microscopy (SEM) and wetting test furnace. The results indicate that current efficiency and tin content initially increase and then decrease with the increase of the current density, brush electro-plating voltage and temperature. As the increase of the relative velocity of anode and cathode, the current efficiency gradually reduces, and the tin content initially increases and then decreases. With the increase of the brush electro-plating time, the current efficiency has no significant change, but the content of tin increases. SEM images show that a smooth and uniform surface morphology of the tin coating with tin grain size of about 0.3~1.8 μm and porosity of 0.82% is obtained. The non-directional tin granular parallel to the surface direction of Ag45CuZn brazing filler metal growth is better than that of perpendicular to the surface of the growth. Compared to Ag45CuZn brazing filler metal matrix, when 2.38 wt.% metal tin is brush electro-plated on Ag45CuZn brazing filler metal, the wetting area of Ag45CuZn brazing filler metal increases by about 19.5 %, and the Ag43.92Cu28.65Zn25.05Sn2.38 brazing filler metal possesses a good wettability
2013, 42(11):2400-2403.
Abstract:
A linear synchronous motor prototype consisting of an excitation system made of high-Tc superconducting (HTS) coated conductor wire coils with silicon steel core and a conventional cooper coil wound armature stator has been constructed and tested. The performance of the prototype system operated at different air gaps reflecting real life operating conditions was focused on. The dependence of the reduction of the thrust and normal forces with respect to the increasing of the air gap was presented. Thrust decays rapidly with increasing air gap at low magnetic gap while having a weak decay at higher magnetic gap. The highest recorded peak thrust is 117 N/m for a magnetic gap of 15 mm, and this is achieved with less than 16 m of HTS coated conductor. This work has helped to better design superconducting linear synchronous motors.
A linear synchronous motor prototype consisting of an excitation system made of high-Tc superconducting (HTS) coated conductor wire coils with silicon steel core and a conventional cooper coil wound armature stator has been constructed and tested. The performance of the prototype system operated at different air gaps reflecting real life operating conditions was focused on. The dependence of the reduction of the thrust and normal forces with respect to the increasing of the air gap was presented. Thrust decays rapidly with increasing air gap at low magnetic gap while having a weak decay at higher magnetic gap. The highest recorded peak thrust is 117 N/m for a magnetic gap of 15 mm, and this is achieved with less than 16 m of HTS coated conductor. This work has helped to better design superconducting linear synchronous motors.
2013, 42(11):2404-2409.
Abstract:
The Mg-Nb and Mg-Nb2O5 hydrogen storage composite powders were prepared through arc plasma method followed by in-situ passivation. The composition, the phase component, the morphology, the particle size and the hydrogen storage properties of two powders were systematically analyzed by using inductive coupled plasma emission spectrometer (ICP), X-ray diffraction (XRD), transmission electron microscopy (TEM), pressure-composition-temperature (PCT) and thermogravimetry/differential thermal analysis (TG/DTA) techniques. ICP analyses reveal that the Nb contents of both powders reduce compared with their initial compositions. In addition, Nb content in Mg-Nb powder is higher than that in Mg-Nb2O5 powder. XRD results show that MgNb2O3.67 phase exists in Mg-Nb powder and NbO2.46 phase in Mg-Nb2O5 powder. TEM observations reveal that the MgNb2O3.67 particles are distributed more homogeneously and their particle sizes are smaller than those of the NbO2.46 particles in Mg-Nb2O5 powder. PCT analyses show that the hydrogen sorption plateaus of the Mg-Nb powder are wider and smoother with a smaller absorption/desorption gap compared to those of Mg-Nb2O5 powder. Based on Van’t Hoff equation, the hydrogenation enthalpy of the Mg-Nb powder is determined to be –73.33 kJ/mol H2, lower than the value of –82.45 kJ/mol H2 for Mg-Nb2O5 powder. TG-DTA measurements show that the hydrogenated Mg-Nb powder has a faster desorption rate and a sharper endothermic desorption peak compared to those of the hydrogenated Mg-Nb2O5 powder. The better hydrogen storage thermodynamic and kinetic properties of Mg-Nb powder may be attributed to the catalytic effect of MgNb2O3.67 generated in passivation. In contrast, the NbO2.46 phase can be reduced during hydrogenaing. Also, it has a low content and a heterogeneous distribution in Mg-Nb2O5 powder and thus possesses a poor catalytic effect. The above results show that the arc plasma method followed by in-situ passivation is an more efficient approach to produce metal-oxide hydrogen storage composite with a superior catalytic effect of oxide compared with the directly evaporated oxide
The Mg-Nb and Mg-Nb2O5 hydrogen storage composite powders were prepared through arc plasma method followed by in-situ passivation. The composition, the phase component, the morphology, the particle size and the hydrogen storage properties of two powders were systematically analyzed by using inductive coupled plasma emission spectrometer (ICP), X-ray diffraction (XRD), transmission electron microscopy (TEM), pressure-composition-temperature (PCT) and thermogravimetry/differential thermal analysis (TG/DTA) techniques. ICP analyses reveal that the Nb contents of both powders reduce compared with their initial compositions. In addition, Nb content in Mg-Nb powder is higher than that in Mg-Nb2O5 powder. XRD results show that MgNb2O3.67 phase exists in Mg-Nb powder and NbO2.46 phase in Mg-Nb2O5 powder. TEM observations reveal that the MgNb2O3.67 particles are distributed more homogeneously and their particle sizes are smaller than those of the NbO2.46 particles in Mg-Nb2O5 powder. PCT analyses show that the hydrogen sorption plateaus of the Mg-Nb powder are wider and smoother with a smaller absorption/desorption gap compared to those of Mg-Nb2O5 powder. Based on Van’t Hoff equation, the hydrogenation enthalpy of the Mg-Nb powder is determined to be –73.33 kJ/mol H2, lower than the value of –82.45 kJ/mol H2 for Mg-Nb2O5 powder. TG-DTA measurements show that the hydrogenated Mg-Nb powder has a faster desorption rate and a sharper endothermic desorption peak compared to those of the hydrogenated Mg-Nb2O5 powder. The better hydrogen storage thermodynamic and kinetic properties of Mg-Nb powder may be attributed to the catalytic effect of MgNb2O3.67 generated in passivation. In contrast, the NbO2.46 phase can be reduced during hydrogenaing. Also, it has a low content and a heterogeneous distribution in Mg-Nb2O5 powder and thus possesses a poor catalytic effect. The above results show that the arc plasma method followed by in-situ passivation is an more efficient approach to produce metal-oxide hydrogen storage composite with a superior catalytic effect of oxide compared with the directly evaporated oxide
2013, 42(11):2410-2415.
Abstract:
The surface treatment of AZ91D magnesium alloy was carried out in KF+KOH treatment solution using the AC micro-arc oxidation treatment technique. The relationship between coating thickness and treatment parameters was established, the structure of the coating was determined, the growth mechanism of coating was discussed and the treatment parameters for quick forming of coating was optimized. The results show that under the conditions of 979 g/L for concentration of KF, 349 g/L for concentration of KOH, 81 V for voltage and 32 ℃ for the temperature of treatment solution, a 30 μm-thick compact coating which is mainly made up of MgF2 and MgO can be formed on AZ91D magnesium alloy surface after 88 s. This forming speed of the coating is 7 times quicker than that of other treatment techniques at least
The surface treatment of AZ91D magnesium alloy was carried out in KF+KOH treatment solution using the AC micro-arc oxidation treatment technique. The relationship between coating thickness and treatment parameters was established, the structure of the coating was determined, the growth mechanism of coating was discussed and the treatment parameters for quick forming of coating was optimized. The results show that under the conditions of 979 g/L for concentration of KF, 349 g/L for concentration of KOH, 81 V for voltage and 32 ℃ for the temperature of treatment solution, a 30 μm-thick compact coating which is mainly made up of MgF2 and MgO can be formed on AZ91D magnesium alloy surface after 88 s. This forming speed of the coating is 7 times quicker than that of other treatment techniques at least
2013, 42(11):2416-2420.
Abstract:
The soldering joints of low silver solder and nano-particle composite solder were prepared by low-temperature soldering (at semi-solid state) with stirring. Researches have shown that the wettability and the filling ability of solders are improved by adding nano-Ni particles, the cavitary compounds of (CuxNi1-x) 6 Sn5 are generated by Ni with Cu6Sn5 and the micro voids formed by stirring at low temperature are the diffusion path of interface atoms, and the thickness of IMC increases compared with the soldering joints of low silver solder. The tensile strength and the shear strength is increased by 15.7% and 22.9%, respectively, and the low silver solder and its joints shift from the brittle broken to the ductile fracture after adding nano-particles. The tensile strength and the shear strength of the composites’ soldering joints are increased by 32% and 24%, respectively, compared with the soldering joints of low silver solder using stirring and flux, which is amount to or even better than the tensile strength and the shear strength of nano-particle composite solder
The soldering joints of low silver solder and nano-particle composite solder were prepared by low-temperature soldering (at semi-solid state) with stirring. Researches have shown that the wettability and the filling ability of solders are improved by adding nano-Ni particles, the cavitary compounds of (CuxNi1-x) 6 Sn5 are generated by Ni with Cu6Sn5 and the micro voids formed by stirring at low temperature are the diffusion path of interface atoms, and the thickness of IMC increases compared with the soldering joints of low silver solder. The tensile strength and the shear strength is increased by 15.7% and 22.9%, respectively, and the low silver solder and its joints shift from the brittle broken to the ductile fracture after adding nano-particles. The tensile strength and the shear strength of the composites’ soldering joints are increased by 32% and 24%, respectively, compared with the soldering joints of low silver solder using stirring and flux, which is amount to or even better than the tensile strength and the shear strength of nano-particle composite solder
2013, 42(11):2222-2227.
Abstract:
The cast structures of blade-shaped castings of DZ125 superalloy processed by liquid metal cooling (LMC) and high rate solidification (HRS) methods were studied to compare the benefits and drawbacks of these two methods. The morphologies and the growth direction of grains, primary dendrite arm spacing, γ′ size were analyzed at different cross-sections along growth directions. The results indicate that the maximum deviation angle of primary dendrites from the sample axial decreases as the withdrawal rate increases from 40 to 110 μm/s for the central zone of HRS castings. At the withdrawal rate of 70 μm/s, the grains in the central zone of LMC casting have larger deviated angles, but the overall orientations of grains become more converging. The dendrites at the top of the blade are coarser than those at the middle, especially for the HRS castings. The γ′ size becomes larger as castings solidify from the airfoil to the platform, but the difference of γ′ size between the platform and the airfoil is smaller for LMC castings when the withdrawal rate is higher than 70 μm/s.
The cast structures of blade-shaped castings of DZ125 superalloy processed by liquid metal cooling (LMC) and high rate solidification (HRS) methods were studied to compare the benefits and drawbacks of these two methods. The morphologies and the growth direction of grains, primary dendrite arm spacing, γ′ size were analyzed at different cross-sections along growth directions. The results indicate that the maximum deviation angle of primary dendrites from the sample axial decreases as the withdrawal rate increases from 40 to 110 μm/s for the central zone of HRS castings. At the withdrawal rate of 70 μm/s, the grains in the central zone of LMC casting have larger deviated angles, but the overall orientations of grains become more converging. The dendrites at the top of the blade are coarser than those at the middle, especially for the HRS castings. The γ′ size becomes larger as castings solidify from the airfoil to the platform, but the difference of γ′ size between the platform and the airfoil is smaller for LMC castings when the withdrawal rate is higher than 70 μm/s.
2013, 42(11):2228-2231.
Abstract:
In this paper, the effects of preparation process, ball-milling equipments, storing time and ball-milling time on the dehydrogenation performances were analyzed. All the samples were ball-milled by planetary ball mill except for sample 3 which was ball-milled by high-energy vibration ball mill. The results indicate that the above mentioned influence factors present obvious effect on the dehydrogenation performances of NaAlH4. The dehydrogenation amount of the samples turned up and down during ball milling increases by 50wt%. Compared to the samples prepared by planetary mill, the dehydrogenation amount of samples prepared by the high-energy vibration ball mill increases markedly. The results from studying on storing time and milling time show that the dehydrogenation amounts of the samples milled by planetary mill and laid aside for 24 h get an obvious increase. In addition, the amount of the hydrogen release of the samples milled for different time with planetary mill presents significantly difference. The amount of the hydrogen release of the sample milled for 80 min is higher than those milled for 100, 40 and 60 min. However, compared to other influence factors, the effect of ball-milling time on NaAlH4 is smaller
In this paper, the effects of preparation process, ball-milling equipments, storing time and ball-milling time on the dehydrogenation performances were analyzed. All the samples were ball-milled by planetary ball mill except for sample 3 which was ball-milled by high-energy vibration ball mill. The results indicate that the above mentioned influence factors present obvious effect on the dehydrogenation performances of NaAlH4. The dehydrogenation amount of the samples turned up and down during ball milling increases by 50wt%. Compared to the samples prepared by planetary mill, the dehydrogenation amount of samples prepared by the high-energy vibration ball mill increases markedly. The results from studying on storing time and milling time show that the dehydrogenation amounts of the samples milled by planetary mill and laid aside for 24 h get an obvious increase. In addition, the amount of the hydrogen release of the samples milled for different time with planetary mill presents significantly difference. The amount of the hydrogen release of the sample milled for 80 min is higher than those milled for 100, 40 and 60 min. However, compared to other influence factors, the effect of ball-milling time on NaAlH4 is smaller
2013, 42(11):2242-2244.
Abstract:
In the investigation of AgCuO composites, we have found a type of copper oxide particles with a superplastic deformability behavior, which is similar to that of metals. To find the reason of the deformability of the copper oxide particles. SEM, STEM and TEM were used to analyze their crystal structures in AgCuO composites, The results show that the copper oxide particles with micro-superplasticity in the composites have cubic crystal structure, and their maximum elongation can be up to 300%, The copper oxide particles with no micro-superplasticity in the composites have monoclinic crystal structure. But the micro-superplastic behavior and mechanism of the copper oxides with the cubic crystal structure are not clear for the time being, the further investigation could be needed
In the investigation of AgCuO composites, we have found a type of copper oxide particles with a superplastic deformability behavior, which is similar to that of metals. To find the reason of the deformability of the copper oxide particles. SEM, STEM and TEM were used to analyze their crystal structures in AgCuO composites, The results show that the copper oxide particles with micro-superplasticity in the composites have cubic crystal structure, and their maximum elongation can be up to 300%, The copper oxide particles with no micro-superplasticity in the composites have monoclinic crystal structure. But the micro-superplastic behavior and mechanism of the copper oxides with the cubic crystal structure are not clear for the time being, the further investigation could be needed
2013, 42(11):2245-2247.
Abstract:
Gallium oxide (β-Ga2O3) nanomaterials have been prepared from gallium and oxygen by thermal evaporation in argon atmosphere, and the electrical transport properties have been examined at high temperature. X-ray diffraction (XRD) reveals that the synthesized products are monoclinic gallium oxide, and it is further confirmed by electron diffraction of transmission electron microscope (TEM). The observation of scanning electron microscope (SEM) reveals that β-Ga2O3 nanobelt width is less than 100 nm and the length is several micrometers. The electricity property was studied at different high temperatures
Gallium oxide (β-Ga2O3) nanomaterials have been prepared from gallium and oxygen by thermal evaporation in argon atmosphere, and the electrical transport properties have been examined at high temperature. X-ray diffraction (XRD) reveals that the synthesized products are monoclinic gallium oxide, and it is further confirmed by electron diffraction of transmission electron microscope (TEM). The observation of scanning electron microscope (SEM) reveals that β-Ga2O3 nanobelt width is less than 100 nm and the length is several micrometers. The electricity property was studied at different high temperatures
2013, 42(11):2248-2252.
Abstract:
The BNi2 filler metal was used to join TiAl-based alloy to Ni-based alloy. Interfacial microstructure and formation phases of brazed joints were investigated by means of scanning electron, energy disperses spectroscopy and X-ray diffraction, and shear strength of the joints was determined. The results show that the typical interfacial microstructure of the joints is GH99/γ+Ni3B+CrB+rich Ti-boride/TiNi2Al/TiNiAl+Ti3Al/TiAl. With the increase of brazing temperature or holding time, more B and Si elements diffuse from the molten brazing filler metal into substrates, which decrease the amount of boride in the joint, while the thickness of TiNi2Al and TiNiAl+Ti3Al increases. When the brazing temperature T=1050 ℃ and the holding time t=5 min, the shear strength of the joints reaches a maximum of 205 MPa, and the joint is mainly fractured at TiNiAl intermetallic layer. Further increase the brazing temperature or holding time results in excessive growth of TiNiAl layer, which reduces the joining properties
The BNi2 filler metal was used to join TiAl-based alloy to Ni-based alloy. Interfacial microstructure and formation phases of brazed joints were investigated by means of scanning electron, energy disperses spectroscopy and X-ray diffraction, and shear strength of the joints was determined. The results show that the typical interfacial microstructure of the joints is GH99/γ+Ni3B+CrB+rich Ti-boride/TiNi2Al/TiNiAl+Ti3Al/TiAl. With the increase of brazing temperature or holding time, more B and Si elements diffuse from the molten brazing filler metal into substrates, which decrease the amount of boride in the joint, while the thickness of TiNi2Al and TiNiAl+Ti3Al increases. When the brazing temperature T=1050 ℃ and the holding time t=5 min, the shear strength of the joints reaches a maximum of 205 MPa, and the joint is mainly fractured at TiNiAl intermetallic layer. Further increase the brazing temperature or holding time results in excessive growth of TiNiAl layer, which reduces the joining properties
2013, 42(11):2253-2256.
Abstract:
Tensile testes were carried out at ambient temperature on Ti-600 alloy before and after being exposed at 600 °C for 100 h. Fracture morphologies were investigated and the fracture mechanism was also analyzed. The results indicate that the strength of the sample without oxidizing layers increases by 3% or so, the elongation decreases by about 20% for the alloy exposed at 600 °C for 100 h. While for the sample with oxidizing layers, the strength decreases a little bit, and the elongation decreases by 45% or so, which indicates that the plasticity decreases abruptly during the exposure process. For the solutioned plus aged samples, cracks originate from the center of the fracture, and dimple typed fracture can be found in the fractographies. After being exposed at 600 °C for 100 h, for the samples without oxidizing layers, dimples and cleavage facets can both be seen in the fractographies, which displays the feature of hybrid fracture. While for the samples with oxidizing layers, only cleavage facets can be observed in the fractographies, and fractures propagate along the interfaces of lamellar a phases. These results are caused by the precipitation and the existence of the brittle oxidizing layers. The cracks would be formed in the oxidizing layers first and then propagate into the matrix during the tensile tests. Oxygen permeation in the surface layer is one of the important reasons for the decrease of plasticity.
Tensile testes were carried out at ambient temperature on Ti-600 alloy before and after being exposed at 600 °C for 100 h. Fracture morphologies were investigated and the fracture mechanism was also analyzed. The results indicate that the strength of the sample without oxidizing layers increases by 3% or so, the elongation decreases by about 20% for the alloy exposed at 600 °C for 100 h. While for the sample with oxidizing layers, the strength decreases a little bit, and the elongation decreases by 45% or so, which indicates that the plasticity decreases abruptly during the exposure process. For the solutioned plus aged samples, cracks originate from the center of the fracture, and dimple typed fracture can be found in the fractographies. After being exposed at 600 °C for 100 h, for the samples without oxidizing layers, dimples and cleavage facets can both be seen in the fractographies, which displays the feature of hybrid fracture. While for the samples with oxidizing layers, only cleavage facets can be observed in the fractographies, and fractures propagate along the interfaces of lamellar a phases. These results are caused by the precipitation and the existence of the brittle oxidizing layers. The cracks would be formed in the oxidizing layers first and then propagate into the matrix during the tensile tests. Oxygen permeation in the surface layer is one of the important reasons for the decrease of plasticity.
