Volume 40,Issue 5,2011 Table of Contents
2011, 40(5):753-756.
Abstract:
Ti/Al diffusion couples fabricated by hot pressing were annealed at 525, 550, 575 and 600 oC. TiAl3 was the only observed phase at the Ti/Al interface when the unreacted Al foils remained. TiAl3 grew towards Al foil side. Few Al atoms were detected in Ti foils. The first formation of TiAl3 is explained on the basis of solubility limits of terminal solid solution, lattice mismatch among Al, Ti and TiAl3, and the increasing interfacial energy caused by newly formed interface. The first saturation of Al (Ti) solid solution due to the little solubility of Ti in Al, and the slight misfit among the close-packed planes of Al, Ti and TiAl3, advance the nucleation of TiAl3. TiAl3, rather than other compounds, has the lowest increasing interfacial energy, indicating its preferential formation. The formation of other titanium aluminides is suppressed due to their growth which is kinetically unstable
Ti/Al diffusion couples fabricated by hot pressing were annealed at 525, 550, 575 and 600 oC. TiAl3 was the only observed phase at the Ti/Al interface when the unreacted Al foils remained. TiAl3 grew towards Al foil side. Few Al atoms were detected in Ti foils. The first formation of TiAl3 is explained on the basis of solubility limits of terminal solid solution, lattice mismatch among Al, Ti and TiAl3, and the increasing interfacial energy caused by newly formed interface. The first saturation of Al (Ti) solid solution due to the little solubility of Ti in Al, and the slight misfit among the close-packed planes of Al, Ti and TiAl3, advance the nucleation of TiAl3. TiAl3, rather than other compounds, has the lowest increasing interfacial energy, indicating its preferential formation. The formation of other titanium aluminides is suppressed due to their growth which is kinetically unstable
2011, 40(5):757-760.
Abstract:
The microstructure evolution of NiAl-2.5Ta-7.5Cr alloy during annealing at different temperatures was investigated. It is found that the microstructure of the as-cast alloy consists of coarse Laves phase Ta(CrNiAl)2 with C14 structure at grain boundaries and Cr-rich particles with sizes in the range of 400-500 nm in the NiAl matrix. The Ta and Cr concentrations in the NiAl are ~0.6% and ~2.5% (at%), respectively. When the alloy is annealed at the temperature above 1000 °C, fine rod-like Laves phases with C15 structure begin to precipitate dispersively in the NiAl. After annealing at 1200 °C for 2 h, the volume fraction of the particles increases, and in the mean time, the Ta concentration in NiAl matrix reduces to ~0.2at%. As the annealing temperature further increases to 1400 °C, the Laves phase precipitates dissolve in the NiAl matrix completely. Therefore, the precipitation of Laves phase in NiAl during the annealing in the temperature range of 1000~1300 °C may be attributed to the diffusing followed by the supersaturation of Ta in NiAl after the solidification
The microstructure evolution of NiAl-2.5Ta-7.5Cr alloy during annealing at different temperatures was investigated. It is found that the microstructure of the as-cast alloy consists of coarse Laves phase Ta(CrNiAl)2 with C14 structure at grain boundaries and Cr-rich particles with sizes in the range of 400-500 nm in the NiAl matrix. The Ta and Cr concentrations in the NiAl are ~0.6% and ~2.5% (at%), respectively. When the alloy is annealed at the temperature above 1000 °C, fine rod-like Laves phases with C15 structure begin to precipitate dispersively in the NiAl. After annealing at 1200 °C for 2 h, the volume fraction of the particles increases, and in the mean time, the Ta concentration in NiAl matrix reduces to ~0.2at%. As the annealing temperature further increases to 1400 °C, the Laves phase precipitates dissolve in the NiAl matrix completely. Therefore, the precipitation of Laves phase in NiAl during the annealing in the temperature range of 1000~1300 °C may be attributed to the diffusing followed by the supersaturation of Ta in NiAl after the solidification
2011, 40(5):761-764.
Abstract:
The growth of zinc oxide (ZnO) nanostructures on Au-, Cu- and Zn-filled (111) and (100) porous silicons (PSs) has been investigated. The results indicate that the ZnO nanostructures grown on Au-filled (111) PS are possessed of rod-shapes with hexagonal end faces, those on the Cu-filled (100) or (111) PS are possessed of belt-shapes or rod-shapes, and those on the Zn-filled (100) or (111) PS are possessed of wire-shapes. The ZnO growth on the Au- and Cu-filled PS are mainly along c-axis orientation, while its growth on the Zn-filled PS are mainly along [] orientation, and it possesses a single crystal hexagonal structure without dislocations and stacking faults. In addition, the green emission intensity of the ZnO grown on Zn-filled PS caused by oxygen vacancies of the ZnO is weaker than that of the ZnO grown on Au (Cu)-filled PS,. It could be concluded that the ZnO grown on Zn-filled PS produces a better quality. After annealing in air, the positions of the green emission peaks do not vary, while the intensities are weakened
The growth of zinc oxide (ZnO) nanostructures on Au-, Cu- and Zn-filled (111) and (100) porous silicons (PSs) has been investigated. The results indicate that the ZnO nanostructures grown on Au-filled (111) PS are possessed of rod-shapes with hexagonal end faces, those on the Cu-filled (100) or (111) PS are possessed of belt-shapes or rod-shapes, and those on the Zn-filled (100) or (111) PS are possessed of wire-shapes. The ZnO growth on the Au- and Cu-filled PS are mainly along c-axis orientation, while its growth on the Zn-filled PS are mainly along [] orientation, and it possesses a single crystal hexagonal structure without dislocations and stacking faults. In addition, the green emission intensity of the ZnO grown on Zn-filled PS caused by oxygen vacancies of the ZnO is weaker than that of the ZnO grown on Au (Cu)-filled PS,. It could be concluded that the ZnO grown on Zn-filled PS produces a better quality. After annealing in air, the positions of the green emission peaks do not vary, while the intensities are weakened
2011, 40(5):765-768.
Abstract:
The microstructure and fracture behavior of Zr55Cu30Al10Ni5 monolithic glass and Zr55Cu30Al10Ni5 reinforced with 5%-7% ZrO2 particles composites have been studied. Vein-like pattern is the main fracture morphology of the matrix, while the smooth regions can be observed on the composites fracture surface besides vein-like pattern. The fracture strength increases from 1716 MPa to 2138 MPa after adding 7vol% ZrO2 particles with average particle size of 1 μm into the matrix, but the composites show no visible plasticity due to formation of Cu10Zr7 and CuZr phases in the matrix
The microstructure and fracture behavior of Zr55Cu30Al10Ni5 monolithic glass and Zr55Cu30Al10Ni5 reinforced with 5%-7% ZrO2 particles composites have been studied. Vein-like pattern is the main fracture morphology of the matrix, while the smooth regions can be observed on the composites fracture surface besides vein-like pattern. The fracture strength increases from 1716 MPa to 2138 MPa after adding 7vol% ZrO2 particles with average particle size of 1 μm into the matrix, but the composites show no visible plasticity due to formation of Cu10Zr7 and CuZr phases in the matrix
2011, 40(5):769-772.
Abstract:
The corrosion behavior of LaFe11.6Si1.4 alloy was investigated in benzotriazole and sodium benzoate mixed solution. Polarization measurements and electrochemical impendence spectroscopy techniques were used to measure the electrochemical parameters. Experiment results show that the inhibition efficiency is influenced strongly by the concentration of benzotriazole and pH value. The high concentration benzotriazole and high pH value are beneficial to form a compact oxidation layer and thus prevent the dissolution of Fe
The corrosion behavior of LaFe11.6Si1.4 alloy was investigated in benzotriazole and sodium benzoate mixed solution. Polarization measurements and electrochemical impendence spectroscopy techniques were used to measure the electrochemical parameters. Experiment results show that the inhibition efficiency is influenced strongly by the concentration of benzotriazole and pH value. The high concentration benzotriazole and high pH value are beneficial to form a compact oxidation layer and thus prevent the dissolution of Fe
2011, 40(5):773-777.
Abstract:
The age-hardening behavior and the mechanism of an experimental low gold content casting Ag-Pd alloy were studied by means of hardness test, XRD, SEM and EPMA, The results show that the hardness of specimens isothermal-aged at 400 oC after solution treated at 900 oC for 30 min increases unidirectionally from 1540 MPa to 3160 MPa with the prolongation of time. However, the hardness of the specimens isothermal-aged at 600 oC after solution treated at 900 oC for 30 min increases quickly and reaches the maximun 2870 MPa at 2 min aging time. Then the hardness decreases unidirectionally and remains at 1600-1700 MPa from 10 to 50 min aging time. Obvious precipitation takes place in the specimens isothermal-aged at 400 and 600 oC revealed by XRD. By SEM and EPMA, the precipitation particles can be seen in the specimens aged at 600 oC for 2 min after solution treated at 900 oC for 30 min. However, the time-FWMH curve shows that the increase of hardness after isothermal-aging is closely related with coherency stain from phase transformation. It is hard to define whether the phase transformation at 400 oC makes a contribution to the change of hardness
The age-hardening behavior and the mechanism of an experimental low gold content casting Ag-Pd alloy were studied by means of hardness test, XRD, SEM and EPMA, The results show that the hardness of specimens isothermal-aged at 400 oC after solution treated at 900 oC for 30 min increases unidirectionally from 1540 MPa to 3160 MPa with the prolongation of time. However, the hardness of the specimens isothermal-aged at 600 oC after solution treated at 900 oC for 30 min increases quickly and reaches the maximun 2870 MPa at 2 min aging time. Then the hardness decreases unidirectionally and remains at 1600-1700 MPa from 10 to 50 min aging time. Obvious precipitation takes place in the specimens isothermal-aged at 400 and 600 oC revealed by XRD. By SEM and EPMA, the precipitation particles can be seen in the specimens aged at 600 oC for 2 min after solution treated at 900 oC for 30 min. However, the time-FWMH curve shows that the increase of hardness after isothermal-aging is closely related with coherency stain from phase transformation. It is hard to define whether the phase transformation at 400 oC makes a contribution to the change of hardness
2011, 40(5):778-783.
Abstract:
A numerical simulation method based on coupling of isothermal multi-plastic deformation mechanism was put forward with isothermal forging for Ti-6Al-4V alloy as example. By investigating the plastic deformation mechanism and analyzing the strain rate sensitivity exponent m and dynamic recrystallization (DRX) of Ti-6Al-4V alloy during isothermal forging, the criteria of common plastic deformation, superplastic deformation and creep deformation were obtained. According to the criteria of the multi-plastic deformation mechanism, the real-time plastic deformation mechanism of material elements was determined and the corresponding constitutive equation was applied. This method can make simulation result more reasonable and can truly reflect the isothermal forging process of aerial materials difficult to deform: common plastic deformation, bulk superplastic deformation and isothermal pressure holding. The simulation results show that during isothermal forging process, the three kinds of plastic deformation mechanism co-exist and the deformation mechanisms of the elements change with the deformation proceeding. And the change of plastic deformation mechanism is closely related to DRX
A numerical simulation method based on coupling of isothermal multi-plastic deformation mechanism was put forward with isothermal forging for Ti-6Al-4V alloy as example. By investigating the plastic deformation mechanism and analyzing the strain rate sensitivity exponent m and dynamic recrystallization (DRX) of Ti-6Al-4V alloy during isothermal forging, the criteria of common plastic deformation, superplastic deformation and creep deformation were obtained. According to the criteria of the multi-plastic deformation mechanism, the real-time plastic deformation mechanism of material elements was determined and the corresponding constitutive equation was applied. This method can make simulation result more reasonable and can truly reflect the isothermal forging process of aerial materials difficult to deform: common plastic deformation, bulk superplastic deformation and isothermal pressure holding. The simulation results show that during isothermal forging process, the three kinds of plastic deformation mechanism co-exist and the deformation mechanisms of the elements change with the deformation proceeding. And the change of plastic deformation mechanism is closely related to DRX
2011, 40(5):784-787.
Abstract:
Modelling has now become a routine part of materials science. A model is developed for quantitative analysis and prediction of the correlation between the microstructure and mechanical properties in titanium alloys through the use of soft computing, based on quantifying microstructural features in titanium alloys. The input parameters of the model are the microstructural feature parameters, and the output parameters are some mechanical properties of the alloys. To achieve a good performance of the model, the input microstructural feature parameters must be chosen when designing model in terms of three rules: the qualitative effect of the microstructure on mechanical properties, correlative work processing and the operational efficiency of the model. A model for the analysis and prediction of the correlation between the microstructure and room-temperature tensile properties in Ti-17 titanium alloy is developed by applying artificial neural network, which is given as an example to discuss the modelling methods and approach. The model achieves the desirable predicting performance, so the modelling principle is correct and its implementation is feasible.
Modelling has now become a routine part of materials science. A model is developed for quantitative analysis and prediction of the correlation between the microstructure and mechanical properties in titanium alloys through the use of soft computing, based on quantifying microstructural features in titanium alloys. The input parameters of the model are the microstructural feature parameters, and the output parameters are some mechanical properties of the alloys. To achieve a good performance of the model, the input microstructural feature parameters must be chosen when designing model in terms of three rules: the qualitative effect of the microstructure on mechanical properties, correlative work processing and the operational efficiency of the model. A model for the analysis and prediction of the correlation between the microstructure and room-temperature tensile properties in Ti-17 titanium alloy is developed by applying artificial neural network, which is given as an example to discuss the modelling methods and approach. The model achieves the desirable predicting performance, so the modelling principle is correct and its implementation is feasible.
2011, 40(5):788-792.
Abstract:
The Johnson-Cook model and gradient-dependent plasticity were used to investigate the adiabatic shear band (ASB) width and the ambient temperature effect for Ti-6Al-4V. The ASB width was defined as the width (w5%) of the region surrounding the band center over which the temperature differed from its peak value by less than 5%, which was similar to the viewpoint proposed by Batra and Kim. Theoretical results show that at higher ambient temperatures, the ASB is wider, as is in agreement with many experimental observations. At higher total ASB widths, the ASB width-ambient temperature curve is slightly concave-upward. However, at lower total ASB widths, the ASB width-ambient temperature curve is approximately linear. These new phenomena cannot be predicted by the famous Dodd and Bai’s model. The calculated ASB widths are closer to the measured results by Liao and Duffy. A simple expression for the ASB width was derived under the condition of neglecting the strain-hardening effect and adopting the linear softening model and gradient-dependent plasticity. It is found that higher ambient temperature, density, heat capacity, softening modulus and shear stress, or lower work to heat conversion factor and shear strength lead to lower adiabatic shear sensitivity and wider adiabatic shear band
The Johnson-Cook model and gradient-dependent plasticity were used to investigate the adiabatic shear band (ASB) width and the ambient temperature effect for Ti-6Al-4V. The ASB width was defined as the width (w5%) of the region surrounding the band center over which the temperature differed from its peak value by less than 5%, which was similar to the viewpoint proposed by Batra and Kim. Theoretical results show that at higher ambient temperatures, the ASB is wider, as is in agreement with many experimental observations. At higher total ASB widths, the ASB width-ambient temperature curve is slightly concave-upward. However, at lower total ASB widths, the ASB width-ambient temperature curve is approximately linear. These new phenomena cannot be predicted by the famous Dodd and Bai’s model. The calculated ASB widths are closer to the measured results by Liao and Duffy. A simple expression for the ASB width was derived under the condition of neglecting the strain-hardening effect and adopting the linear softening model and gradient-dependent plasticity. It is found that higher ambient temperature, density, heat capacity, softening modulus and shear stress, or lower work to heat conversion factor and shear strength lead to lower adiabatic shear sensitivity and wider adiabatic shear band
10 Influence of Surface Texture and Surface Film on Cavitation Erosion Characteristics of Ti6Al4V Alloy
2011, 40(5):793-796.
Abstract:
Surface texture manufacturing to Ti6Al4V alloy by a laser surface modification method and self-assembled monolayers (SAMs) prepared on the texturing surface by a self-assembled method were conducted in order to study the effect of surface texture and surface film on the characteristics of cavitation erosion resistance of materials. The surface properties of the specimens were characterized by measurement of contact angles. Cavitation erosion mechanism of the specimens was analyzed by measurement of cavitation erosion characteristics and topography observation before and after cavitation erosion occurrence. The results indicate that cavitation erosion resistance of Ti6Al4V specimens are significantly enhanced by laser texture manufacturing. The cavitation erosion resistance is further improved by self-assembled monolayers prepared on texturing surface because of the hydrophobicity. The cavitation erosion resistance of specimens with grid texture is bigger than that of specimens with line texture because the former possesses higher hardness, higher hardness gradient and even protrudent hard point distribution. The cavitation erosion resistance of specimens with FOTS SAMs for both grid texture and line texture increases with space increasing. The cavitation erosion resistance of specimens without FOTS SAMs for both two textures decreases with space increasing
Surface texture manufacturing to Ti6Al4V alloy by a laser surface modification method and self-assembled monolayers (SAMs) prepared on the texturing surface by a self-assembled method were conducted in order to study the effect of surface texture and surface film on the characteristics of cavitation erosion resistance of materials. The surface properties of the specimens were characterized by measurement of contact angles. Cavitation erosion mechanism of the specimens was analyzed by measurement of cavitation erosion characteristics and topography observation before and after cavitation erosion occurrence. The results indicate that cavitation erosion resistance of Ti6Al4V specimens are significantly enhanced by laser texture manufacturing. The cavitation erosion resistance is further improved by self-assembled monolayers prepared on texturing surface because of the hydrophobicity. The cavitation erosion resistance of specimens with grid texture is bigger than that of specimens with line texture because the former possesses higher hardness, higher hardness gradient and even protrudent hard point distribution. The cavitation erosion resistance of specimens with FOTS SAMs for both grid texture and line texture increases with space increasing. The cavitation erosion resistance of specimens without FOTS SAMs for both two textures decreases with space increasing
2011, 40(5):797-801.
Abstract:
The hot extrusion deformation process of TA15 titanium alloy was simulated by the FEM software MSC Marc. The distribution of equivalent stress field and the equivalent strain field was obtained. The post treatment for the data based on the simulation results including stress and strain was carried out. The division of deformation was proposed by employing the characteristic quantity such as Lode parameter and invariant of the deviator (J2). Based on the simulation results, the divisions of deformation and the divisions of the plastic deformation types, the sampling to the samples of the hot extrusion was made. Microstructure observation was carried out at different temperatures and the evolution rule of the microstructure was analyzed. It has great significance for the metal hot extrusion forming analysis and its application
The hot extrusion deformation process of TA15 titanium alloy was simulated by the FEM software MSC Marc. The distribution of equivalent stress field and the equivalent strain field was obtained. The post treatment for the data based on the simulation results including stress and strain was carried out. The division of deformation was proposed by employing the characteristic quantity such as Lode parameter and invariant of the deviator (J2). Based on the simulation results, the divisions of deformation and the divisions of the plastic deformation types, the sampling to the samples of the hot extrusion was made. Microstructure observation was carried out at different temperatures and the evolution rule of the microstructure was analyzed. It has great significance for the metal hot extrusion forming analysis and its application
2011, 40(5):803-806.
Abstract:
The influence of zirconium nitride (ZrN) deposited by magnetron sputtering under different N2 partial pressure on the bonding strength of titanium porcelain was investigated. 60 commercially pure cast titanium specimens were randomly subjected to 1 contrast group and 3 test groups, named Ta, Tb and Tc. All test groups were treated with ZrN deposited under different N2 partial pressure by magnetron sputtering (group Ta 1.0×10-2 Pa, group Tb 5.0×10-2 Pa and group Tc 10.0×10-2 Pa). The pure titanium specimens were sintered after surface treatment. The compositions of the deposits were analyzed by X-ray diffraction (XRD). A universal testing machine was used to perform the three-point bending test to evaluate the bonding strength of Ti and porcelain. The microstructure of ZrN, the interface of Ti/porcelain and the fractured Ti surface were observed by scanning electron microscopy (SEM) and digital microscope. The XRD results prove that the ZrN deposits are cubic crystalline phases. The bonding strength of Ti and porcelain of each group are as following: group contrast (26.67±0.88) MPa, group Ta (49.41±0.55) MPa, group Tb (54.55±0.69) MPa and group Tc (46.24±0.53) MPa. Statistical differences were recorded (P<0.05). The results of SEM show that the Ti/porcelain interface of contrast group possesses pre-cracks, while samples of test group have better combinations. ZrN film deposited by magnetron sputtering can enhance Ti/porcelain bonding. ZrN films deposited under the N2 partial pressure of 5.0×10-2 Pa bring the highest Ti/porcelain bonding strength
The influence of zirconium nitride (ZrN) deposited by magnetron sputtering under different N2 partial pressure on the bonding strength of titanium porcelain was investigated. 60 commercially pure cast titanium specimens were randomly subjected to 1 contrast group and 3 test groups, named Ta, Tb and Tc. All test groups were treated with ZrN deposited under different N2 partial pressure by magnetron sputtering (group Ta 1.0×10-2 Pa, group Tb 5.0×10-2 Pa and group Tc 10.0×10-2 Pa). The pure titanium specimens were sintered after surface treatment. The compositions of the deposits were analyzed by X-ray diffraction (XRD). A universal testing machine was used to perform the three-point bending test to evaluate the bonding strength of Ti and porcelain. The microstructure of ZrN, the interface of Ti/porcelain and the fractured Ti surface were observed by scanning electron microscopy (SEM) and digital microscope. The XRD results prove that the ZrN deposits are cubic crystalline phases. The bonding strength of Ti and porcelain of each group are as following: group contrast (26.67±0.88) MPa, group Ta (49.41±0.55) MPa, group Tb (54.55±0.69) MPa and group Tc (46.24±0.53) MPa. Statistical differences were recorded (P<0.05). The results of SEM show that the Ti/porcelain interface of contrast group possesses pre-cracks, while samples of test group have better combinations. ZrN film deposited by magnetron sputtering can enhance Ti/porcelain bonding. ZrN films deposited under the N2 partial pressure of 5.0×10-2 Pa bring the highest Ti/porcelain bonding strength
2011, 40(5):807-812.
Abstract:
By means of the measurement of creep curves and microstructure observation, the creep behavior and influencing factors of FGH95 nickel-base superalloy has been investigated. Results show that after the solution treatment at 1150 oC and aging, some coarse g ￠ precipitates are discontinuously distributed in the grain boundary region and around them is the depleted zone of the finer g ￠ phase. However, after the solution treatment at 1165 oC and aging, the grains are obviously grown up, and the films of the carbide are continuously precipitated along the boundaries. After the solution treatment at 1160 oC and aging, the coarse g ￠ phase in the alloy is fully dissolved, the finer g ￠ phase is dispersedly distributed within the grains, and some particles of (Nb,Ti)C phase are discontinuously precipitated in the grains and along the boundaries, which is thought to be the main reason for better creep resistance due to the pinning effect of them to restrain the boundaries slipping. The deformation mechanism of the alloy during creep is the dislocation shearing or bypassing the g ￠ phase. In the later creep stage, the deformation features of the alloy are the single-orientation and double-orientations slipping of dislocations activated in the alloy, which brings out the stress concentration to promote the initiation and propagation of the micro-cracks along the boundaries, and it is thought to be the fracture mechanism of the alloy during creep
By means of the measurement of creep curves and microstructure observation, the creep behavior and influencing factors of FGH95 nickel-base superalloy has been investigated. Results show that after the solution treatment at 1150 oC and aging, some coarse g ￠ precipitates are discontinuously distributed in the grain boundary region and around them is the depleted zone of the finer g ￠ phase. However, after the solution treatment at 1165 oC and aging, the grains are obviously grown up, and the films of the carbide are continuously precipitated along the boundaries. After the solution treatment at 1160 oC and aging, the coarse g ￠ phase in the alloy is fully dissolved, the finer g ￠ phase is dispersedly distributed within the grains, and some particles of (Nb,Ti)C phase are discontinuously precipitated in the grains and along the boundaries, which is thought to be the main reason for better creep resistance due to the pinning effect of them to restrain the boundaries slipping. The deformation mechanism of the alloy during creep is the dislocation shearing or bypassing the g ￠ phase. In the later creep stage, the deformation features of the alloy are the single-orientation and double-orientations slipping of dislocations activated in the alloy, which brings out the stress concentration to promote the initiation and propagation of the micro-cracks along the boundaries, and it is thought to be the fracture mechanism of the alloy during creep
2011, 40(5):813-816.
Abstract:
Second phase particles (SPPs) of N18 zirconium alloys during seven manufacturing processes were investigated by means of quantitative metallography. The manufacturing processes include ingot-breaking, hot rolling, annealing, cold rolling, annealing, final rolling, and final annealing. The results of size, volume fraction, and distribution of SPPs were obtained after the software analysis. The key factors and control methods of SPPs growth in the rolling processing and the interaction between SPPs and grain boundaries in the later annealing process were also discussed.
Second phase particles (SPPs) of N18 zirconium alloys during seven manufacturing processes were investigated by means of quantitative metallography. The manufacturing processes include ingot-breaking, hot rolling, annealing, cold rolling, annealing, final rolling, and final annealing. The results of size, volume fraction, and distribution of SPPs were obtained after the software analysis. The key factors and control methods of SPPs growth in the rolling processing and the interaction between SPPs and grain boundaries in the later annealing process were also discussed.
2011, 40(5):817-819.
Abstract:
Deformation behavior of dual-phase Ni-31Al intermetallics at high temperature was investigated. Results show that the alloy exhibits superplastic deformation behavior at the initial strain rate of 1.25×10-4- 8×10-3 s-1 and in the temperature range of 950-1075 oC. A maximum elongation of 281.3% is obtained at 5×10-4 s-1 and 1000 oC. Microstructure analyses show that the dual phases have excellent compatible deformability during the superplastic deformation process. The initial coarse microstructure becomes much longer and finer after superplastic deformation. The superplastic phenomenon in dual-phase Ni-31Al can be explained by continuous dynamic recovery and recrystallization
Deformation behavior of dual-phase Ni-31Al intermetallics at high temperature was investigated. Results show that the alloy exhibits superplastic deformation behavior at the initial strain rate of 1.25×10-4- 8×10-3 s-1 and in the temperature range of 950-1075 oC. A maximum elongation of 281.3% is obtained at 5×10-4 s-1 and 1000 oC. Microstructure analyses show that the dual phases have excellent compatible deformability during the superplastic deformation process. The initial coarse microstructure becomes much longer and finer after superplastic deformation. The superplastic phenomenon in dual-phase Ni-31Al can be explained by continuous dynamic recovery and recrystallization
2011, 40(5):820-823.
Abstract:
In order to improve the oxidation resistance and ablation resistance of ZrB2-SiC ultra-high temperature ceramics (UHTCs), Y2O3 particles were introduced during the fabrication process of the ZrB2 based UHTCs. The oxidation-resistance and ablation-resistance of ZrB2-SiC-Y2O3 UHTCs were investigated using oxyacetylene torch test. The microstructures and phases of ZrB2-SiC-Y2O3 before and after ablation were studied by SEM and XRD. No cracks are found on the ablated surface during the process of heating and cooling, indicating that ZrB2-SiC-Y2O3 UHTCs have good thermal shock resistance. Microstructure analysis shows that the oxidation layer is composed of 4 layers and there is no obvious exfoliation between the oxidation layer and the substrate layer. The results show that high temperature stable phase t-ZrO2 in the oxidation product can be kept at low temperature by the addition of Y2O3, thus reducing the volume expansion owing to transformation and improving coherent properties of oxidation layers
In order to improve the oxidation resistance and ablation resistance of ZrB2-SiC ultra-high temperature ceramics (UHTCs), Y2O3 particles were introduced during the fabrication process of the ZrB2 based UHTCs. The oxidation-resistance and ablation-resistance of ZrB2-SiC-Y2O3 UHTCs were investigated using oxyacetylene torch test. The microstructures and phases of ZrB2-SiC-Y2O3 before and after ablation were studied by SEM and XRD. No cracks are found on the ablated surface during the process of heating and cooling, indicating that ZrB2-SiC-Y2O3 UHTCs have good thermal shock resistance. Microstructure analysis shows that the oxidation layer is composed of 4 layers and there is no obvious exfoliation between the oxidation layer and the substrate layer. The results show that high temperature stable phase t-ZrO2 in the oxidation product can be kept at low temperature by the addition of Y2O3, thus reducing the volume expansion owing to transformation and improving coherent properties of oxidation layers
2011, 40(5):824-828.
Abstract:
Zr46.3Cu43.3Al8.9Si1.5 (at%) bulk metallic glass was prepared by copper mould casting. The crystallization behavior of the alloy in continuous heating was investigated by differential canning calorimeter (DSC). The characteristic temperature apparent activation energy and the local activation energy were calculated by the Kissinger and Doyle equations, respectively. The results show that the activation energies of glass transition (Eg), crystallization (Ex) and peak crystallization (Ep) are 395.4 kJ/mol, 343.2 kJ/mol and 343.0 kJ/mol, respectively. With the increase of the crystallized volume fraction, the crystallization activation energy increases to the largest energy barrier, and then decreases. Zr46.3Cu43.3Al8.9Si1.5 bulk metallic glass has desirable thermal stability
Zr46.3Cu43.3Al8.9Si1.5 (at%) bulk metallic glass was prepared by copper mould casting. The crystallization behavior of the alloy in continuous heating was investigated by differential canning calorimeter (DSC). The characteristic temperature apparent activation energy and the local activation energy were calculated by the Kissinger and Doyle equations, respectively. The results show that the activation energies of glass transition (Eg), crystallization (Ex) and peak crystallization (Ep) are 395.4 kJ/mol, 343.2 kJ/mol and 343.0 kJ/mol, respectively. With the increase of the crystallized volume fraction, the crystallization activation energy increases to the largest energy barrier, and then decreases. Zr46.3Cu43.3Al8.9Si1.5 bulk metallic glass has desirable thermal stability
2011, 40(5):829-832.
Abstract:
(Al86Ni9La5)100-xZrx alloy ribbons (x=0, 3, 5, 7, 10) were prepared by melt-spinning. The amorphous characteristics and thermal stability of the ribbons were analyzed by X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The corrosion behavior of (Al86Ni9La5)100-xZrx (x=0, 3, 5, 7) amorphous samples were investigated by electrochemical techniques in 0.01 mol/L NaCl alkaline solution. The results reveal that among the (Al86Ni9La5)100-xZrx (x=0, 3, 5, 7, 10) ribbons the (Al86Ni9La5)95Zr5 exhibits the best thermal stability, and with the content of Zr increasing, the electrochemical corrosion resistance is also enhanced
(Al86Ni9La5)100-xZrx alloy ribbons (x=0, 3, 5, 7, 10) were prepared by melt-spinning. The amorphous characteristics and thermal stability of the ribbons were analyzed by X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The corrosion behavior of (Al86Ni9La5)100-xZrx (x=0, 3, 5, 7) amorphous samples were investigated by electrochemical techniques in 0.01 mol/L NaCl alkaline solution. The results reveal that among the (Al86Ni9La5)100-xZrx (x=0, 3, 5, 7, 10) ribbons the (Al86Ni9La5)95Zr5 exhibits the best thermal stability, and with the content of Zr increasing, the electrochemical corrosion resistance is also enhanced
2011, 40(5):833-838.
Abstract:
The hydrogen uptake behavior of Zircaloy-2 and Zircaloy-4 containing different second phase particles (SPPs) in size and category during corrosion test in super-heated steam at 400 oC/10.3 MPa was investigated. The amount of hydrogen uptake was not always corresponding to the corrosion resistance, while it was closely related to the SPPs size and category. At the same mass gain, the difference is significant in the amount of hydrogen uptake between the Zircaloy-2 and Zircaloy-4 specimens with coarse SPPs, while the difference is negligible in the amount of hydrogen uptake between the Zircaloy-2 specimens SPPs and Zircaloy-4 specimens with fine SPPs. The contribution of SPPs category to the hydrogen uptake is more notable to the specimens with coarse SPPs than specimens with fine SPPs. The tests, containing absorption pressure-composition-temperature (PCT), absorption and desorption kinetics, were proceeded in zirconium, Zr(Fe,Cr)2 and Zr2(Fe,Ni) intermetallic specimens. Results indicate that Zr(Fe,Cr)2 and Zr2(Fe,Ni) specimens could absorb and desorb hydrogen easily with high speed, while zirconium could only absorb hydrogen easily but desorb hydrogen difficultly. Based on these results, the hydrogen uptake behavior of Zircaloy corroded in super-heated steam at 400 oC /10.3 MPa were successfully explained with the model that the hydrogen generating from the reaction of zirconium and OH- at metal/oxide film interface can be captured by Zr(Fe,Cr)2 and Zr2(Fe,Ni) SPPs embedding at the metal/oxide interface. These SPPs with higher reversible absorbing and desorbing ability acted as a preferred path for hydrogen uptake.
The hydrogen uptake behavior of Zircaloy-2 and Zircaloy-4 containing different second phase particles (SPPs) in size and category during corrosion test in super-heated steam at 400 oC/10.3 MPa was investigated. The amount of hydrogen uptake was not always corresponding to the corrosion resistance, while it was closely related to the SPPs size and category. At the same mass gain, the difference is significant in the amount of hydrogen uptake between the Zircaloy-2 and Zircaloy-4 specimens with coarse SPPs, while the difference is negligible in the amount of hydrogen uptake between the Zircaloy-2 specimens SPPs and Zircaloy-4 specimens with fine SPPs. The contribution of SPPs category to the hydrogen uptake is more notable to the specimens with coarse SPPs than specimens with fine SPPs. The tests, containing absorption pressure-composition-temperature (PCT), absorption and desorption kinetics, were proceeded in zirconium, Zr(Fe,Cr)2 and Zr2(Fe,Ni) intermetallic specimens. Results indicate that Zr(Fe,Cr)2 and Zr2(Fe,Ni) specimens could absorb and desorb hydrogen easily with high speed, while zirconium could only absorb hydrogen easily but desorb hydrogen difficultly. Based on these results, the hydrogen uptake behavior of Zircaloy corroded in super-heated steam at 400 oC /10.3 MPa were successfully explained with the model that the hydrogen generating from the reaction of zirconium and OH- at metal/oxide film interface can be captured by Zr(Fe,Cr)2 and Zr2(Fe,Ni) SPPs embedding at the metal/oxide interface. These SPPs with higher reversible absorbing and desorbing ability acted as a preferred path for hydrogen uptake.
2011, 40(5):839-843.
Abstract:
The lattice constants, total energies and densities of states of transition metals Cr, Mo and W in ⅥB group with different crystalline structures were calculated by the total energy pseudopotential plane-wave method. The results show that the order of lattice stability of Cr, Mo and W is , in which bcc structure is the most stable phase, agreeing with the experimental result. The results of electronic structure calculation show that most of the electrons in s state are transferred into p state and part of s state electrons are transferred into d state. These transferences of electrons from s state to p state or d state form stronger cohesion, higher cohesive energy and more stable lattice of heavy metals.
The lattice constants, total energies and densities of states of transition metals Cr, Mo and W in ⅥB group with different crystalline structures were calculated by the total energy pseudopotential plane-wave method. The results show that the order of lattice stability of Cr, Mo and W is , in which bcc structure is the most stable phase, agreeing with the experimental result. The results of electronic structure calculation show that most of the electrons in s state are transferred into p state and part of s state electrons are transferred into d state. These transferences of electrons from s state to p state or d state form stronger cohesion, higher cohesive energy and more stable lattice of heavy metals.
2011, 40(5):844-848.
Abstract:
The principle of chemical vapor deposition (CVD) tantalum was introduced through hydrogen reduction of tantalum chloride. The influences of chlorination temperatures, Cl2 flow, H2 flow and deposition temperatures on deposition rate and crystal structure were studied. The results show that the influence of chlorination temperatures on deposition rate is minimum, while that of deposition temperatures is maximum. Microstructure is composed of small grains and columnar grains. The columnar grain sizes change with deposition parameters
The principle of chemical vapor deposition (CVD) tantalum was introduced through hydrogen reduction of tantalum chloride. The influences of chlorination temperatures, Cl2 flow, H2 flow and deposition temperatures on deposition rate and crystal structure were studied. The results show that the influence of chlorination temperatures on deposition rate is minimum, while that of deposition temperatures is maximum. Microstructure is composed of small grains and columnar grains. The columnar grain sizes change with deposition parameters
2011, 40(5):849-852.
Abstract:
Sb element was substituted for Ga in the Ga2Te3 alloy with the same molar fraction and Ga1.9Sb 0.1Te3 alloy was prepared by spark plasma sintering. The microstructure and the thermoelectric (TE) property of the alloy were investigated. Results show that after Se doping the Seebeck coefficient of the sample is about 130-240 mV/K, much lower than that of single crystal Ga2Te3, and the electrical conductivity decreases from 3600 to 1740 W-1·m-1 with temperature elevation to 649 K, being at least 16 times higher than that of single crystal Ga2Te3 at the corresponding temperature. The thermal conductivity increases by about 25% after Sb doping. The maximum TE figure of merit (ZT) value of 0.1 is obtained at 649 K, which is approximately 3 times as large as that of single crystal Ga2Te3 at the corresponding temperature
Sb element was substituted for Ga in the Ga2Te3 alloy with the same molar fraction and Ga1.9Sb 0.1Te3 alloy was prepared by spark plasma sintering. The microstructure and the thermoelectric (TE) property of the alloy were investigated. Results show that after Se doping the Seebeck coefficient of the sample is about 130-240 mV/K, much lower than that of single crystal Ga2Te3, and the electrical conductivity decreases from 3600 to 1740 W-1·m-1 with temperature elevation to 649 K, being at least 16 times higher than that of single crystal Ga2Te3 at the corresponding temperature. The thermal conductivity increases by about 25% after Sb doping. The maximum TE figure of merit (ZT) value of 0.1 is obtained at 649 K, which is approximately 3 times as large as that of single crystal Ga2Te3 at the corresponding temperature
2011, 40(5):853-857.
Abstract:
Ag/Ni20 fiber electrical composites were prepared by severe plastic deformation including coating extrusion, bunched extrusion, and drawing. The arc erosion phenomena of this composite contact in direct current state were studied. The microstructure and element distribution in contact surface after arc erosion were analyzed by SEM and EDS. It can be concluded that in Ag/Ni20 fiber electrical composites, there are five arc erosion morphological characters, i.e. starchiness coagulum, coral-like structure, framework structure, pores/air holes, and cracks
Ag/Ni20 fiber electrical composites were prepared by severe plastic deformation including coating extrusion, bunched extrusion, and drawing. The arc erosion phenomena of this composite contact in direct current state were studied. The microstructure and element distribution in contact surface after arc erosion were analyzed by SEM and EDS. It can be concluded that in Ag/Ni20 fiber electrical composites, there are five arc erosion morphological characters, i.e. starchiness coagulum, coral-like structure, framework structure, pores/air holes, and cracks
2011, 40(5):858-862.
Abstract:
Pre-deformation to various degrees was imposed to the U-Nb alloy; afterwards the strain-recovery behavior of the alloy was investigated by the self-made strain-measuring equipment. The deformation mechanism and shape memory effect (SME) of the U-Nb alloy were investigated by TEM and XRD. The results show that growth, swallow and preferred orientation of high density twins is the primary deformation mechanism for U-Nb alloy at the initial stage of deformation, and it is considered that U-Nb alloy possesses excellent shape memory effect. The maximum reversible strain reaches to 3.2% during heating; reorientation and splitting through phase reversion of enlarged twins during reheating is the main reason for the shape memory effect of U-Nb alloy
Pre-deformation to various degrees was imposed to the U-Nb alloy; afterwards the strain-recovery behavior of the alloy was investigated by the self-made strain-measuring equipment. The deformation mechanism and shape memory effect (SME) of the U-Nb alloy were investigated by TEM and XRD. The results show that growth, swallow and preferred orientation of high density twins is the primary deformation mechanism for U-Nb alloy at the initial stage of deformation, and it is considered that U-Nb alloy possesses excellent shape memory effect. The maximum reversible strain reaches to 3.2% during heating; reorientation and splitting through phase reversion of enlarged twins during reheating is the main reason for the shape memory effect of U-Nb alloy
2011, 40(5):863-866.
Abstract:
A series of MgxB2 (x=0.9, 0.95, 1.0, 1.05, 1.10) bulks samples were prepared by the in-situ solid-state reaction method, and then the effects of Mg/B stoichiometry on superconductivity and flux pinning properties of MgB2 were discussed. Phase purity, microstructure and superconducting properties were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and magnetic properties measurement system (MPMS), respectively. The results show that the sample with a nominal composition, Mg0.95B2 has the highest Jc value among all the samples. In the Mg-deficient MgB2, the degraded grains grow and lack of Mg sites are responsible to significant enhancement of the Hirr and Hc2 and the enlarged △Tc and FWHM, resulting in the great improvement of flux pinning properties of MgB2
A series of MgxB2 (x=0.9, 0.95, 1.0, 1.05, 1.10) bulks samples were prepared by the in-situ solid-state reaction method, and then the effects of Mg/B stoichiometry on superconductivity and flux pinning properties of MgB2 were discussed. Phase purity, microstructure and superconducting properties were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and magnetic properties measurement system (MPMS), respectively. The results show that the sample with a nominal composition, Mg0.95B2 has the highest Jc value among all the samples. In the Mg-deficient MgB2, the degraded grains grow and lack of Mg sites are responsible to significant enhancement of the Hirr and Hc2 and the enlarged △Tc and FWHM, resulting in the great improvement of flux pinning properties of MgB2
2011, 40(5):867-870.
Abstract:
The SiC fiber tensile strength and mechanical properties of 2D-SiCf/SiC composites, the fiber surface morphology, composite fracture surface morphology and composite interface characteristics before and after removing carbon coating were analyzed and characterized by bundle tensile test, three-point bending test, SEM and HRTEM. The results show that inherent defects on the surface of SiC fiber are exposed after the carbon coating removal, and the tensile strength of SiC fiber decreases by about 15%. The flexural strength of 2D-SiCf/SiC composites after the carbon coating removal is only 30 MPa, which is the 1/6 times of that of composites prepared by the original fiber. The fracture surface of 2D-SiCf/SiC composites after the carbon coating removal is very even, which proves the fiber reinforced effects to be poor. The analyzed results indicate that because of the increase of defects after the carbon coating removal, the interfacial physical bonding strength and the fiber physical damage will all increase. At the same time, after the carbon coating removal, the chemical action active centers and the oxygen contents on the fiber surface will increase, the situation of that will bring about the interfacial chemical bonding strength and the fiber chemical damage increasing, which has been proved by HRTEM test. The strongly bonded interface and serious fiber damage result in the mechanical properties of 2D-SiCf/SiC composites degrading badly after the carbon coating removal.
The SiC fiber tensile strength and mechanical properties of 2D-SiCf/SiC composites, the fiber surface morphology, composite fracture surface morphology and composite interface characteristics before and after removing carbon coating were analyzed and characterized by bundle tensile test, three-point bending test, SEM and HRTEM. The results show that inherent defects on the surface of SiC fiber are exposed after the carbon coating removal, and the tensile strength of SiC fiber decreases by about 15%. The flexural strength of 2D-SiCf/SiC composites after the carbon coating removal is only 30 MPa, which is the 1/6 times of that of composites prepared by the original fiber. The fracture surface of 2D-SiCf/SiC composites after the carbon coating removal is very even, which proves the fiber reinforced effects to be poor. The analyzed results indicate that because of the increase of defects after the carbon coating removal, the interfacial physical bonding strength and the fiber physical damage will all increase. At the same time, after the carbon coating removal, the chemical action active centers and the oxygen contents on the fiber surface will increase, the situation of that will bring about the interfacial chemical bonding strength and the fiber chemical damage increasing, which has been proved by HRTEM test. The strongly bonded interface and serious fiber damage result in the mechanical properties of 2D-SiCf/SiC composites degrading badly after the carbon coating removal.
2011, 40(5):871-874.
Abstract:
The microstructure and properties of the joint were studied, based on the trial of twin spot laser welding of 2 mm thick 1420 aluminium-lithium alloy. The characteristics of microstructure, micro-hardness, room-temperature tensile strength and fractography of both twin spot and single spot laser welded joints were compared. The results indicate that the microstructures of the joints by twin spot and single spot laser welding are similar. Equiaxed grains, columnar crystals, and equiaxed dendrite crystals can be found from fusion zone to the weld center in the twin spot welded joint, which are finer than that of single spot welded joint. The microhardness of twin spot laser welded joint is higher than that of single spot laser welded joint, but lower than that of base metal. Meanwhile, the tensile properties of twin spot laser welded joint is decreased to 86% of that of base metal, but a little higher than that of single spot laser welded joint
The microstructure and properties of the joint were studied, based on the trial of twin spot laser welding of 2 mm thick 1420 aluminium-lithium alloy. The characteristics of microstructure, micro-hardness, room-temperature tensile strength and fractography of both twin spot and single spot laser welded joints were compared. The results indicate that the microstructures of the joints by twin spot and single spot laser welding are similar. Equiaxed grains, columnar crystals, and equiaxed dendrite crystals can be found from fusion zone to the weld center in the twin spot welded joint, which are finer than that of single spot welded joint. The microhardness of twin spot laser welded joint is higher than that of single spot laser welded joint, but lower than that of base metal. Meanwhile, the tensile properties of twin spot laser welded joint is decreased to 86% of that of base metal, but a little higher than that of single spot laser welded joint
2011, 40(5):875-879.
Abstract:
Finite element models of thin-walled cylindrical aluminum alloy tube and the thin-walled cylindrical aluminum alloy tube with aluminum foam filler were established by ABAQUS software. The vertical compressing mechanical behavior of the two structures was simulated numerically and the simulation results were compared with the experimental. Results show that the numerical simulation results are in good agreement with the experimental. According to the stress-strain drawings of thin-walled cylindrical aluminum alloy tube and thin-walled cylindrical aluminum alloy tube with aluminum foam filler, it is concluded that the fully foam-filled tube can endure more stress than the empty tubes
Finite element models of thin-walled cylindrical aluminum alloy tube and the thin-walled cylindrical aluminum alloy tube with aluminum foam filler were established by ABAQUS software. The vertical compressing mechanical behavior of the two structures was simulated numerically and the simulation results were compared with the experimental. Results show that the numerical simulation results are in good agreement with the experimental. According to the stress-strain drawings of thin-walled cylindrical aluminum alloy tube and thin-walled cylindrical aluminum alloy tube with aluminum foam filler, it is concluded that the fully foam-filled tube can endure more stress than the empty tubes
2011, 40(5):880-884.
Abstract:
Fine-grained Ti-47Al (at%) alloy was prepared by double mechanical milling and spark plasma sintering (SPS). The morphology, microstructure and phase composition of the Ti-47Al composite powder and the microstructure of the bulk Ti-47Al alloy samples were studied by SEM, XRD and TEM. The results show that the double mechanical milled powder is composed of TiAl and Ti3Al phases, with regular particle shape and 20-40 μm particle size, as well as uniform interstructure. The SPSed bulk of Ti-47Al alloy consists of main phase TiAl and few phases Ti3Al and Ti2Al. With the sintering temperature increasing, the Ti3Al phase becomes more. For the bulk sintered at 1000 oC, the equiaxed grain microstructure is achieved with sizes in the range of 100-250 nm. For the bulk sintered at 1100 oC, the sizes of equiaxed grain significantly are increased. The SPSed bulk samples exhibit dense microstructure without pores, consisting of equiaxed TiAl phase and lamellar Ti3Al phase
Fine-grained Ti-47Al (at%) alloy was prepared by double mechanical milling and spark plasma sintering (SPS). The morphology, microstructure and phase composition of the Ti-47Al composite powder and the microstructure of the bulk Ti-47Al alloy samples were studied by SEM, XRD and TEM. The results show that the double mechanical milled powder is composed of TiAl and Ti3Al phases, with regular particle shape and 20-40 μm particle size, as well as uniform interstructure. The SPSed bulk of Ti-47Al alloy consists of main phase TiAl and few phases Ti3Al and Ti2Al. With the sintering temperature increasing, the Ti3Al phase becomes more. For the bulk sintered at 1000 oC, the equiaxed grain microstructure is achieved with sizes in the range of 100-250 nm. For the bulk sintered at 1100 oC, the sizes of equiaxed grain significantly are increased. The SPSed bulk samples exhibit dense microstructure without pores, consisting of equiaxed TiAl phase and lamellar Ti3Al phase
2011, 40(5):885-888.
Abstract:
Vickers microhardness of TA15 titanium alloy after equal channel angular pressing (ECAP) and its variation was investigated. The results indicate that the microhardness is increased observably after ECAP, and the microhardness level of the outer layer is slightly higher than that of the core in the same cylinder sample. The microhardness of ECAPed alloy is closely related to microstructure distortion, dislocation density, grain size and phase composition. There is a decrease in microhardness with the increasing pressing temperature below Tβ. As a result of the acicular martensite precipitation, the microhardness after ECAP above Tβ is much higher than that below Tβ. A lower die angle means a better hardness. The microhardness increases first and then remains at a certain level with the increasing passes, while the route effects on hardness are related to the pass number and the refinement effects. The annealing after ECAP can effectively reduce the microhardness
Vickers microhardness of TA15 titanium alloy after equal channel angular pressing (ECAP) and its variation was investigated. The results indicate that the microhardness is increased observably after ECAP, and the microhardness level of the outer layer is slightly higher than that of the core in the same cylinder sample. The microhardness of ECAPed alloy is closely related to microstructure distortion, dislocation density, grain size and phase composition. There is a decrease in microhardness with the increasing pressing temperature below Tβ. As a result of the acicular martensite precipitation, the microhardness after ECAP above Tβ is much higher than that below Tβ. A lower die angle means a better hardness. The microhardness increases first and then remains at a certain level with the increasing passes, while the route effects on hardness are related to the pass number and the refinement effects. The annealing after ECAP can effectively reduce the microhardness
2011, 40(5):889-891.
Abstract:
The bioactivity of alkali treated TLM (Ti-25Nb-3Zr-2Sn-3Mo) alloy was evaluated by the simulated body fluid (SBF) soaking method. Sodium titanate (niobate) gel layer was formed on the TLM alloy after alkali treatment, and the gel layer thickness was increased with higher alkali concentration. After soaking in SBF for 43 h, only a small quantity of apatite nucleus were formed on alkali treated pure titanium, while Ca8H2(PO4)6·5H2O crystals were detected and there were more apatite nucleus on the alkali treated TLM alloy. Results show that the alkali treated TLM alloy has thicker sodium titanate (niobate) gel layer and consequently possesses higher bioactivity than the alkali treated pure titanium.
The bioactivity of alkali treated TLM (Ti-25Nb-3Zr-2Sn-3Mo) alloy was evaluated by the simulated body fluid (SBF) soaking method. Sodium titanate (niobate) gel layer was formed on the TLM alloy after alkali treatment, and the gel layer thickness was increased with higher alkali concentration. After soaking in SBF for 43 h, only a small quantity of apatite nucleus were formed on alkali treated pure titanium, while Ca8H2(PO4)6·5H2O crystals were detected and there were more apatite nucleus on the alkali treated TLM alloy. Results show that the alkali treated TLM alloy has thicker sodium titanate (niobate) gel layer and consequently possesses higher bioactivity than the alkali treated pure titanium.
2011, 40(5):892-896.
Abstract:
由热模拟压缩实验数据分别建立铸态和锻态2种组织状态的TiNiNb合金的本构方程，并采用多项式构建Arrhenius双曲正弦型本构方程参数A、n、、Q与的函数关系。从热变形激活能随不同影响因子的变化规律出发，探究该合金在不同组织状态下的热加工性能。结果表明：铸态TiNiNb合金的流变应力略高于锻态，这主要与金属间化合物的长程有序点阵结构有关，铸态合金的适宜加工参数范围为应变速率小于0.1 s-1，最大应变小于0.4，锻态合金的适宜加工参数范围为应变速率小于0.56 s-1，最大应变小于0.5
由热模拟压缩实验数据分别建立铸态和锻态2种组织状态的TiNiNb合金的本构方程，并采用多项式构建Arrhenius双曲正弦型本构方程参数A、n、、Q与的函数关系。从热变形激活能随不同影响因子的变化规律出发，探究该合金在不同组织状态下的热加工性能。结果表明：铸态TiNiNb合金的流变应力略高于锻态，这主要与金属间化合物的长程有序点阵结构有关，铸态合金的适宜加工参数范围为应变速率小于0.1 s-1，最大应变小于0.4，锻态合金的适宜加工参数范围为应变速率小于0.56 s-1，最大应变小于0.5
2011, 40(5):897-901.
Abstract:
High energy ball milling method was employed to prepare the amorphous Ti50Ni22Cu25Sn3 alloy powders, and the effects of the ball milling parameters on the formation of the amorphous alloy were investigated. Results indicate that the rotation speed and ball diameter have a significant influence on the formation efficiency of the amorphous phase. High rotation speed and proper ball diameter can shorten the time to form the amorphous phase. At the rotation speed of 400 r/min and the mass ratio 20:1 of the ball to the powders, the completely amorphous Ti50Ni22Cu25Sn3 alloy powders can be obtained after ball milling for 30 h
High energy ball milling method was employed to prepare the amorphous Ti50Ni22Cu25Sn3 alloy powders, and the effects of the ball milling parameters on the formation of the amorphous alloy were investigated. Results indicate that the rotation speed and ball diameter have a significant influence on the formation efficiency of the amorphous phase. High rotation speed and proper ball diameter can shorten the time to form the amorphous phase. At the rotation speed of 400 r/min and the mass ratio 20:1 of the ball to the powders, the completely amorphous Ti50Ni22Cu25Sn3 alloy powders can be obtained after ball milling for 30 h
2011, 40(5):902-905.
Abstract:
Mo-50%Cu alloy was fabricated by mechanical milling and pressure-assisted solid state sintering under vacuum. Both the microstructure/morphology of the as-milled Mo/Cu composite powders and the microstructure and physical, mechanical properties of the as-sintered alloy were investigated. The results show that the pressure-assisted solid state sintering process is a feasible way to fabricate highly-densified Mo-Cu alloy product with high content of Cu. By mechanical milling, the Mo phases can be refined markedly and distributed more uniformly in the Mo/Cu composite powders and the as-sintered Mo-Cu alloy. For the Mo-50%Cu alloy fabricated by the present study, the Mo phases are found to be very fine and dispersed homogeneously in the Cu matrix, with no connecting skeleton structure of Mo observed. Therefore, the negative effect of Mo on the conductivity is weakened, and the strengthening effect of Mo is increased, resulting in a good combination of physical and mechanical properties
Mo-50%Cu alloy was fabricated by mechanical milling and pressure-assisted solid state sintering under vacuum. Both the microstructure/morphology of the as-milled Mo/Cu composite powders and the microstructure and physical, mechanical properties of the as-sintered alloy were investigated. The results show that the pressure-assisted solid state sintering process is a feasible way to fabricate highly-densified Mo-Cu alloy product with high content of Cu. By mechanical milling, the Mo phases can be refined markedly and distributed more uniformly in the Mo/Cu composite powders and the as-sintered Mo-Cu alloy. For the Mo-50%Cu alloy fabricated by the present study, the Mo phases are found to be very fine and dispersed homogeneously in the Cu matrix, with no connecting skeleton structure of Mo observed. Therefore, the negative effect of Mo on the conductivity is weakened, and the strengthening effect of Mo is increased, resulting in a good combination of physical and mechanical properties
2011, 40(5):906-910.
Abstract:
With MnO2 as microwave absorbent, double perovskite Sr2FeMoO6 powder was synthesized by microwave processing using SrCO3, Fe2O3 and MoO3 as starting materials. XRD patterns reveal that the as-synthesized product is Sr2FeMoO6 with tetragonal crystal structure and I4/mmm space group, and the unit cell parameter is a =0.5571 nm as well as c = 0.7872 nm. The grain size of the sample is about 20 nm, calculated by the Scherrer formula using the diffraction data. Magnetism testing results show that the sample is ferromagnet, the transition temperature is higher than room temperature and the saturation magnetization is 17.949 (A·m2)/kg under 1 T at room temperature. Electrical performance testing results show that the sample exhibit typical semiconductor behavior and the conductive mechanism can be described by adiabatic small polaron model. The room temperature magnetoresistance of the sample under 1 T field is up to –15.63%
With MnO2 as microwave absorbent, double perovskite Sr2FeMoO6 powder was synthesized by microwave processing using SrCO3, Fe2O3 and MoO3 as starting materials. XRD patterns reveal that the as-synthesized product is Sr2FeMoO6 with tetragonal crystal structure and I4/mmm space group, and the unit cell parameter is a =0.5571 nm as well as c = 0.7872 nm. The grain size of the sample is about 20 nm, calculated by the Scherrer formula using the diffraction data. Magnetism testing results show that the sample is ferromagnet, the transition temperature is higher than room temperature and the saturation magnetization is 17.949 (A·m2)/kg under 1 T at room temperature. Electrical performance testing results show that the sample exhibit typical semiconductor behavior and the conductive mechanism can be described by adiabatic small polaron model. The room temperature magnetoresistance of the sample under 1 T field is up to –15.63%
2011, 40(5):911-916.
Abstract:
Ceramic coatings were prepared on 20vol% Al2O3-SiO2(sf)/AZ91D magnesium matrix composites by microarc oxidation (MAO) technique in a phosphate electrolyte. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were employed to analyze the surface morphology, cross-section microstructure and phase composition of the coated composites. The electrochemical corrosion property of coatings was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results show that the ceramic coating mainly consists of MgO and MgAl2O4. The corrosion current density of ceramic coating decreases nearly by three orders of magnitude compared with magnesium matrix composite substrate while its electrochemical impedance increases greatly. The magnesium matrix composites treated by microarc oxidation display good corrosion resistance
Ceramic coatings were prepared on 20vol% Al2O3-SiO2(sf)/AZ91D magnesium matrix composites by microarc oxidation (MAO) technique in a phosphate electrolyte. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were employed to analyze the surface morphology, cross-section microstructure and phase composition of the coated composites. The electrochemical corrosion property of coatings was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results show that the ceramic coating mainly consists of MgO and MgAl2O4. The corrosion current density of ceramic coating decreases nearly by three orders of magnitude compared with magnesium matrix composite substrate while its electrochemical impedance increases greatly. The magnesium matrix composites treated by microarc oxidation display good corrosion resistance
2011, 40(5):917-920.
Abstract:
The lithium-ion battery cathode material LiFe1-xYxPO4 (x=0, 0.01, 0.02, 0.03, 0.04) were synthesized by solid-state reaction. The crystalline structure, morphology, electronic conductivity and electrochemical properties of the samples were investigated by X-ray diffraction, scanning electron microscope, powder specific resistance method and galvanostatic charge-discharge tests, respectively. The results show that a small amount of Y3+ doping does not change the crystalline structure of the material but considerably modifies the microstructure, thus increasing the electronic conductivity and improving reverse capacity and electrochemical properties. The sample of LiFe0.97Y0.03PO4 delivers an initial discharge capacity of 146.54 mAh/g at the current density of 10 mA/g
The lithium-ion battery cathode material LiFe1-xYxPO4 (x=0, 0.01, 0.02, 0.03, 0.04) were synthesized by solid-state reaction. The crystalline structure, morphology, electronic conductivity and electrochemical properties of the samples were investigated by X-ray diffraction, scanning electron microscope, powder specific resistance method and galvanostatic charge-discharge tests, respectively. The results show that a small amount of Y3+ doping does not change the crystalline structure of the material but considerably modifies the microstructure, thus increasing the electronic conductivity and improving reverse capacity and electrochemical properties. The sample of LiFe0.97Y0.03PO4 delivers an initial discharge capacity of 146.54 mAh/g at the current density of 10 mA/g
2011, 40(5):921-926.
Abstract:
The rare-earth doped strontium aluminate phosphors Sr4-xBaxAl14O25:Eu2+,Dy3+ (x=0, 0.8, 1.6, 2.4, 3.2, 4) were synthesized by a high temperature solid-state reaction method. The phase structures of the phosphors were characterized by X-ray diffraction. The results show that the monoclinic SrAl2O4 and hexagonal SrAl12O19 co-exist in the sample with x=0.8. The major phase of phosphors is hexagonal BaAl2O4 when x>1.6. It is indicated that the phase structure of the samples changes from Sr4Al14O25 to BaAl2O4 when the value of x changes from 0 to 4. The emission spectra of 360 nm irradiation reveal that Eu2+ is the luminescence center of the samples due to 4f65d-4f7 transition of Eu2+ electron. With the Ba doping content increasing, the shift of emission spectra peak occurs, because the lattice shrinkage caused by Sr2+ substitution for Ba2+ affects the 5d level cleavage of Eu2+ and thus influences the 4f65d-4f7 transition. The afterglow spectra show that Eu2+ of BaAl2O4 is the luminescence center for the products when x>1.6. The decay characteristics show that the phosphor samples with different Ba2+ content have different afterglow time, and the afterglow time also changes with the value of x. The measurement of thermoluminescence reveals that the trap depth of the phosphor samples with different Ba2+ content is different, and the samples with deeper traps have longer afterglow time.
The rare-earth doped strontium aluminate phosphors Sr4-xBaxAl14O25:Eu2+,Dy3+ (x=0, 0.8, 1.6, 2.4, 3.2, 4) were synthesized by a high temperature solid-state reaction method. The phase structures of the phosphors were characterized by X-ray diffraction. The results show that the monoclinic SrAl2O4 and hexagonal SrAl12O19 co-exist in the sample with x=0.8. The major phase of phosphors is hexagonal BaAl2O4 when x>1.6. It is indicated that the phase structure of the samples changes from Sr4Al14O25 to BaAl2O4 when the value of x changes from 0 to 4. The emission spectra of 360 nm irradiation reveal that Eu2+ is the luminescence center of the samples due to 4f65d-4f7 transition of Eu2+ electron. With the Ba doping content increasing, the shift of emission spectra peak occurs, because the lattice shrinkage caused by Sr2+ substitution for Ba2+ affects the 5d level cleavage of Eu2+ and thus influences the 4f65d-4f7 transition. The afterglow spectra show that Eu2+ of BaAl2O4 is the luminescence center for the products when x>1.6. The decay characteristics show that the phosphor samples with different Ba2+ content have different afterglow time, and the afterglow time also changes with the value of x. The measurement of thermoluminescence reveals that the trap depth of the phosphor samples with different Ba2+ content is different, and the samples with deeper traps have longer afterglow time.
2011, 40(5):927-929.
Abstract:
In order to improve the electrocatalytic activity of Pt based catalyst to ethanol oxidation, the PMo12 modified Pt electrodes were prepared. Cyclic voltammetry was employed to evaluate the electrocatalytic activity to ethanol oxidation and anti-poisoning characters to CO of the modified electrodes. Results show that PMo12 modified Pt electrodes can improve the electrocatalytic activity to ethanol oxidation and anti-poisoning characters to CO of Pt based electrode
In order to improve the electrocatalytic activity of Pt based catalyst to ethanol oxidation, the PMo12 modified Pt electrodes were prepared. Cyclic voltammetry was employed to evaluate the electrocatalytic activity to ethanol oxidation and anti-poisoning characters to CO of the modified electrodes. Results show that PMo12 modified Pt electrodes can improve the electrocatalytic activity to ethanol oxidation and anti-poisoning characters to CO of Pt based electrode
2011, 40(5):930-934.
Abstract:
Hollow hydroxyapatite (HAP) microspheres with pores on their surfaces were prepared by in situ conversion reaction of Li-Ca-B glass in phosphate solution. The morphology and phase composition of the microspheres were investigated using SEM, SEM-EDS, XRD and FTIR. The formation and conversion mechanism of the hollow HAP microspheres during the immersion process was studied. The results show that the prepared microspheres possess good hollow structures. The phase of the microspheres is calcium-deficient hydroxyapatite containing B-type CO32-, which is biomimetic. After 600 oC heat treatment, hollow microspheres’ shells are completely composed of calcium-deficient hydroxyapatite containing CO32- and exhibit the necessary mechanical strength. In the phosphate solution, Ca-P-OH hydrate is in-situ formed on the surface of the Li-Ca-B glass and precipitates at the positions occupied by Ca2+ to form microsphere shell, while the pores are formed at the positions occupied by Li+ and B3+. Such structures are good for the preparation of hollow HAP as the carriers of the porous reservoir drug release system
Hollow hydroxyapatite (HAP) microspheres with pores on their surfaces were prepared by in situ conversion reaction of Li-Ca-B glass in phosphate solution. The morphology and phase composition of the microspheres were investigated using SEM, SEM-EDS, XRD and FTIR. The formation and conversion mechanism of the hollow HAP microspheres during the immersion process was studied. The results show that the prepared microspheres possess good hollow structures. The phase of the microspheres is calcium-deficient hydroxyapatite containing B-type CO32-, which is biomimetic. After 600 oC heat treatment, hollow microspheres’ shells are completely composed of calcium-deficient hydroxyapatite containing CO32- and exhibit the necessary mechanical strength. In the phosphate solution, Ca-P-OH hydrate is in-situ formed on the surface of the Li-Ca-B glass and precipitates at the positions occupied by Ca2+ to form microsphere shell, while the pores are formed at the positions occupied by Li+ and B3+. Such structures are good for the preparation of hollow HAP as the carriers of the porous reservoir drug release system
2011, 40(5):935-940.
Abstract:
Ag/SnO2 composite materials were prepared by reaction synthesis, and the transformation of the alloy intermediate compound to the alloy-rich region, looking for a stable transition state to generate the final phase, was elaborated from the electron-atom level. The results indicate that the activation properties of Sn are higher than Ag, and the participation of oxygen source plays a leading role to the reaction process. The free state O decomposition in the initial reactive mixture is another important way to make the oxidation reaction proceed continually and thoroughly. Finally the complete reaction path was predicted.
Ag/SnO2 composite materials were prepared by reaction synthesis, and the transformation of the alloy intermediate compound to the alloy-rich region, looking for a stable transition state to generate the final phase, was elaborated from the electron-atom level. The results indicate that the activation properties of Sn are higher than Ag, and the participation of oxygen source plays a leading role to the reaction process. The free state O decomposition in the initial reactive mixture is another important way to make the oxidation reaction proceed continually and thoroughly. Finally the complete reaction path was predicted.
