Volume 47,Issue 2,2018 Table of Contents
2018, 47(2):409-415.
Abstract:
The flow behavior and processing maps of homogenized AA7085 aluminum alloy were investigated by isothermal hot compression tests in the temperature range of 300-450?C and strain rate range of 0.01-10 s-1. Microstructure was characterized using Optical microscopy (OM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results show that the superimposed processing maps at different strains exhibit the optimized deformation parameters with the temperature range of 390-450 ?C and strain rate of lower than 0.1s-1. Microstructure characterization reveals that dynamic recovery and recrystallization are the main deformation mechanisms in the safe regions.In the low temperature and low strain rate regions, the coarsening of particles between ε=0.5 and ε=0.7 may be responsible for the transformation from unstability to safe domain.
The flow behavior and processing maps of homogenized AA7085 aluminum alloy were investigated by isothermal hot compression tests in the temperature range of 300-450?C and strain rate range of 0.01-10 s-1. Microstructure was characterized using Optical microscopy (OM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results show that the superimposed processing maps at different strains exhibit the optimized deformation parameters with the temperature range of 390-450 ?C and strain rate of lower than 0.1s-1. Microstructure characterization reveals that dynamic recovery and recrystallization are the main deformation mechanisms in the safe regions.In the low temperature and low strain rate regions, the coarsening of particles between ε=0.5 and ε=0.7 may be responsible for the transformation from unstability to safe domain.
2018, 47(2):416-422.
Abstract:
To clarify the globularization mechanism and model of the O-phase lamellae of Ti2AlNb-based alloys during deformation at elevated temperatures, the hot deformation behavior and microstructure evolution of Ti-22Al-25Nb (at.%) alloy during hot compression deformation in (α2+O+B2) region were investigated. The results showed that the flow softening is relevant to the dynamic globularization of O-phase lamellae and the flow instability including 45° shear deformation, 45° shear cracking and micro-cracks. The deformation constitutive model based on the exponential law was established and the deformation activation energy was calculated to be 831 kJ?mol-1. The globularization of O-phase lamellae is hard to occur at low temperatures or at high strain rates due to slow diffusion rate or insufficient diffusion time. The main globularization mechanism is the kink and shear of the O-phase lamellae, which is confirmed to be a dynamic recrystallization behavior. The dynamic globularization kinetics was also studied, which is sensitive to deformation conditions including deformation temperatures and strain rates and follows an Avrami type sigmoid equation.
To clarify the globularization mechanism and model of the O-phase lamellae of Ti2AlNb-based alloys during deformation at elevated temperatures, the hot deformation behavior and microstructure evolution of Ti-22Al-25Nb (at.%) alloy during hot compression deformation in (α2+O+B2) region were investigated. The results showed that the flow softening is relevant to the dynamic globularization of O-phase lamellae and the flow instability including 45° shear deformation, 45° shear cracking and micro-cracks. The deformation constitutive model based on the exponential law was established and the deformation activation energy was calculated to be 831 kJ?mol-1. The globularization of O-phase lamellae is hard to occur at low temperatures or at high strain rates due to slow diffusion rate or insufficient diffusion time. The main globularization mechanism is the kink and shear of the O-phase lamellae, which is confirmed to be a dynamic recrystallization behavior. The dynamic globularization kinetics was also studied, which is sensitive to deformation conditions including deformation temperatures and strain rates and follows an Avrami type sigmoid equation.
2018, 47(2):423-430.
Abstract:
Nickel-based superalloy powders have been produced by high pressure argon gas and nitrogen gas atomization, respectively. The microstructural characterization of nickel-based alloy powders has been performed with the help of a scanning electron microscope, equipped with an EDS microanalysis unit. Based on a Newtonian cooling model, the flight speed and the cooling rate of two kinds of alloy droplets are calculated. The results show that the droplet cooling rate, which depends on atomization medium and droplet size, has an effect on the solidification microstructure. For argon-gas atomized powders, the developed dendrite structure is predominant at a lower cooling rate and a mixed microstructure composed of dendrite structure and cellular structure is observed at a higher cooling rate. For nitrogen-gas atomized powders, the dendrite structure is predominant at a lower cooling rate and a full cellular structure can be observed at a higher cooling rate. According to calculation, the cooling rate of argon-gas atomized droplets is in a range from10000K/s to 424000 K/s , while the cooling rate of nitrogen-gas atomized droplets is from 10000K/sto 480000 K/s . The cooling rate increases with decreasing of droplets diameter. Two kinds of atomizing gases have a slightly influence on the cooling rate of droplets. The elements such as Cr, Co, W, Ni and Al are rich in the dendrite axis, while Ti element is rich in the inter-dendrite region.
Nickel-based superalloy powders have been produced by high pressure argon gas and nitrogen gas atomization, respectively. The microstructural characterization of nickel-based alloy powders has been performed with the help of a scanning electron microscope, equipped with an EDS microanalysis unit. Based on a Newtonian cooling model, the flight speed and the cooling rate of two kinds of alloy droplets are calculated. The results show that the droplet cooling rate, which depends on atomization medium and droplet size, has an effect on the solidification microstructure. For argon-gas atomized powders, the developed dendrite structure is predominant at a lower cooling rate and a mixed microstructure composed of dendrite structure and cellular structure is observed at a higher cooling rate. For nitrogen-gas atomized powders, the dendrite structure is predominant at a lower cooling rate and a full cellular structure can be observed at a higher cooling rate. According to calculation, the cooling rate of argon-gas atomized droplets is in a range from10000K/s to 424000 K/s , while the cooling rate of nitrogen-gas atomized droplets is from 10000K/sto 480000 K/s . The cooling rate increases with decreasing of droplets diameter. Two kinds of atomizing gases have a slightly influence on the cooling rate of droplets. The elements such as Cr, Co, W, Ni and Al are rich in the dendrite axis, while Ti element is rich in the inter-dendrite region.
2018, 47(2):430-435.
Abstract:
In the conversion coatings, some uniformly distributed micro surface cracks always occur but the surface cracks behavior is rarely studied due to the frequent initiation in the real test conditions. In this work, computer simulation of micro surface cracks behavior and internal stresses generated in the anhydrous chemical conversion coating was carried out using the finite element method with the help of ABAQUS software. The Mises stress distribution, S11 stress variation, and the stress-time curves are obtained. The results show that the internal stresses generated in the conversion coating increased obviously with increasing time, and the stresses at the center and boundary of coating pieces are bigger than the ones in other areas while the S11 stresses around the center are bigger than the ones near the boundary. The cracks at the interface of coating pieces developed gradually and were as V-type cracks finally. The width of crack mouth opened was different since the contraction degree of each coating piece is different.
In the conversion coatings, some uniformly distributed micro surface cracks always occur but the surface cracks behavior is rarely studied due to the frequent initiation in the real test conditions. In this work, computer simulation of micro surface cracks behavior and internal stresses generated in the anhydrous chemical conversion coating was carried out using the finite element method with the help of ABAQUS software. The Mises stress distribution, S11 stress variation, and the stress-time curves are obtained. The results show that the internal stresses generated in the conversion coating increased obviously with increasing time, and the stresses at the center and boundary of coating pieces are bigger than the ones in other areas while the S11 stresses around the center are bigger than the ones near the boundary. The cracks at the interface of coating pieces developed gradually and were as V-type cracks finally. The width of crack mouth opened was different since the contraction degree of each coating piece is different.
Zhao Lili
,
Yu Jinku
,
Sun Hui
,
Wang Yuehua
,
Yu Meiqi
,
Luo Hongliang
,
Xu Zhefeng
,
Kazuhiro matsugi
2018, 47(2):435-441.
Abstract:
In order to obtain NiFeW alloy coating with good performance, we studied the influence of pH value, temperature, current density, and the concentration of ascorbic acid stabilizer on the composition, deposition rate, and microhardness of NiFeW alloy coating. The results show that 1) the pH value of plating bath largely influences the concentration of W and the deposition rate of coating; 2) the temperature of plating bath largely influences the deposition rate, composition, and microhardness of coating; and 3) upon increasing the concentration of ascorbic acid, the deposition rate of coating decreases whereas the surface morphology of coating becomes more rough. With a pH of plating bath equal to 4, a temperature of 60 ℃, a current density of 4 A/dm2, and an ascorbic-acid concentration of 3 g/L, both the deposition rate and the hardness of the coating are high. In addition, both the surface quality and the corrosion resistance of the coating are good.
In order to obtain NiFeW alloy coating with good performance, we studied the influence of pH value, temperature, current density, and the concentration of ascorbic acid stabilizer on the composition, deposition rate, and microhardness of NiFeW alloy coating. The results show that 1) the pH value of plating bath largely influences the concentration of W and the deposition rate of coating; 2) the temperature of plating bath largely influences the deposition rate, composition, and microhardness of coating; and 3) upon increasing the concentration of ascorbic acid, the deposition rate of coating decreases whereas the surface morphology of coating becomes more rough. With a pH of plating bath equal to 4, a temperature of 60 ℃, a current density of 4 A/dm2, and an ascorbic-acid concentration of 3 g/L, both the deposition rate and the hardness of the coating are high. In addition, both the surface quality and the corrosion resistance of the coating are good.
2018, 47(2):442-446.
Abstract:
A series of supported nano particles catalysts, Au/γ-Al2O3, Pd/γ-Al2O3 and Au-Pd/γ-Al2O3, were prepared by the impregnation reduction method. The catalytic performance of these catalysts for direct base-free synthesis of imines by self-coupling of benzylamine was investigated. The results showed that the yield of imine could reach 93% over bimetallic alloy Au-Pd/γ-Al2O3 catalyst, much higher than monometallic Au or Pd nano particle catalyst. The used catalyst was recovered and 44% yield of imine could be obtained after 5 recycling use of Au-Pd/γ-Al2O3.
A series of supported nano particles catalysts, Au/γ-Al2O3, Pd/γ-Al2O3 and Au-Pd/γ-Al2O3, were prepared by the impregnation reduction method. The catalytic performance of these catalysts for direct base-free synthesis of imines by self-coupling of benzylamine was investigated. The results showed that the yield of imine could reach 93% over bimetallic alloy Au-Pd/γ-Al2O3 catalyst, much higher than monometallic Au or Pd nano particle catalyst. The used catalyst was recovered and 44% yield of imine could be obtained after 5 recycling use of Au-Pd/γ-Al2O3.
2018, 47(2):447-451.
Abstract:
W–30Cu/(0-4) wt.% TiC composite powders were prepared by electroless plating with simplified pretreatment. The composite powders were formed by cold compaction under 400 MPa using tablet machine and green compactions were sintered at 1,300 °C for 1 h. Micromorphology of the original W and TiC powders, simple-treated W and TiC powders, and as-received W–30Cu/(0, 0.25, 0.5, 1, 2, 3, 4) wt.% TiC composite powders after electroless plating were characterized by field emission scanning electron microscopy (FE-SEM). Microstructures of the W–30Cu/(0, 0.25, 0.5, 1, 2, 3, 4) wt.% TiC composites were also investigated by FE-SEM. The effect of TiC content on the properties of W–30Cu/(0, 0.25, 0.5, 1, 2, 3, 4) wt.% TiC composites ( such as relative density, hardness, electrical conductivity, and compressive strength) were studied. Results showed that W–30Cu/TiC composite powders with uniform structure were obtained by simplified W and TiC powder pretreatment, followed by electroless copper plating. When TiC content was less than 1wt%, the compressive strength and hardness of composite materials obviously increased and the electrical conductivity of composite materials decreased with TiC content increased, respectively. However, the electrical conductivity of composite materials was still higher than that of the national standard value. Adding a certain amount of TiC content to W–30Cu/(0, 0.25, 0.5, 1, 2, 3, 4) wt.% TiC composites, the composite materials exhibited good comprehensive performance.
W–30Cu/(0-4) wt.% TiC composite powders were prepared by electroless plating with simplified pretreatment. The composite powders were formed by cold compaction under 400 MPa using tablet machine and green compactions were sintered at 1,300 °C for 1 h. Micromorphology of the original W and TiC powders, simple-treated W and TiC powders, and as-received W–30Cu/(0, 0.25, 0.5, 1, 2, 3, 4) wt.% TiC composite powders after electroless plating were characterized by field emission scanning electron microscopy (FE-SEM). Microstructures of the W–30Cu/(0, 0.25, 0.5, 1, 2, 3, 4) wt.% TiC composites were also investigated by FE-SEM. The effect of TiC content on the properties of W–30Cu/(0, 0.25, 0.5, 1, 2, 3, 4) wt.% TiC composites ( such as relative density, hardness, electrical conductivity, and compressive strength) were studied. Results showed that W–30Cu/TiC composite powders with uniform structure were obtained by simplified W and TiC powder pretreatment, followed by electroless copper plating. When TiC content was less than 1wt%, the compressive strength and hardness of composite materials obviously increased and the electrical conductivity of composite materials decreased with TiC content increased, respectively. However, the electrical conductivity of composite materials was still higher than that of the national standard value. Adding a certain amount of TiC content to W–30Cu/(0, 0.25, 0.5, 1, 2, 3, 4) wt.% TiC composites, the composite materials exhibited good comprehensive performance.
2018, 47(2):452-456.
Abstract:
Organic-inorganic nanojunction can results in a selective scattering of charge carrier depending on their energy, which leads to a simultaneous increase in Seebeck coefficient S and power factor PF when the Fermi levels of the constituent materials are aligned appropriately. In this work, the nanojunction was successfully employed at the organic-inorganic semiconductor interface of polyparaphenylene (PPP) and Zn1-xCoxO nanoparticles through sol-gel method. The resulting Zn0.925Co0.075O/9 wt% PPP hybrids exhibited a high power factor due to the largest electrical conductivity and higher Seebeck coefficient. Moreover, organic-inorganic nano-interface effectively reduces the thermal conductivity by interface scattering of phonons. All these effects finally lead to a thermoelectric figure of merit, ZT up to 0.22 in these inorganic-organic nanocomposites, which corresponds to a 5-fold enhancement compared to that of the Zn0.925Co0.075O matrix. This work demonstrates the effectiveness of nanojunctions and provides a rational route to high performance thermoelectrics in a bulk material.
Organic-inorganic nanojunction can results in a selective scattering of charge carrier depending on their energy, which leads to a simultaneous increase in Seebeck coefficient S and power factor PF when the Fermi levels of the constituent materials are aligned appropriately. In this work, the nanojunction was successfully employed at the organic-inorganic semiconductor interface of polyparaphenylene (PPP) and Zn1-xCoxO nanoparticles through sol-gel method. The resulting Zn0.925Co0.075O/9 wt% PPP hybrids exhibited a high power factor due to the largest electrical conductivity and higher Seebeck coefficient. Moreover, organic-inorganic nano-interface effectively reduces the thermal conductivity by interface scattering of phonons. All these effects finally lead to a thermoelectric figure of merit, ZT up to 0.22 in these inorganic-organic nanocomposites, which corresponds to a 5-fold enhancement compared to that of the Zn0.925Co0.075O matrix. This work demonstrates the effectiveness of nanojunctions and provides a rational route to high performance thermoelectrics in a bulk material.
2018, 47(2):457-462.
Abstract:
The combined effect of ultrasonic vibration (UT) and applied pressure (P) on the microstructure and mechanical properties of the as-cast Al-5.0Cu-0.6Mn-0.6Fe alloy was investigated by using optical microscope (OM), scanning electron microscope (SEM) coupled with energy dispersive X-ray (EDX), image analysis as well as tensile test. The results showed that the P+UT processing has an siginificant effect on the morphology and size of α-Al, Fe-rich intermetallics, and Al2Cu, which promotes the morphology of α-Al transformation from dendritic to globular structure and significantly reduces the size of α-Fe, Al6(FeMn), and Al2Cu phase. The P+UT processing is helpful to reduce the degree of bimodal structure which usually occurrence under applied pressure and reduce the segregation along the grain boundary. The best as-cast tensile properties produced by the P+UT processing were ultimate tensile strength (UTS): 268 MPa, yield strength (YS): 192 MPa, and elongation: 17.1%, which were 64%, 59%, and 307% higher than those of the non-treated alloy, respectively.
The combined effect of ultrasonic vibration (UT) and applied pressure (P) on the microstructure and mechanical properties of the as-cast Al-5.0Cu-0.6Mn-0.6Fe alloy was investigated by using optical microscope (OM), scanning electron microscope (SEM) coupled with energy dispersive X-ray (EDX), image analysis as well as tensile test. The results showed that the P+UT processing has an siginificant effect on the morphology and size of α-Al, Fe-rich intermetallics, and Al2Cu, which promotes the morphology of α-Al transformation from dendritic to globular structure and significantly reduces the size of α-Fe, Al6(FeMn), and Al2Cu phase. The P+UT processing is helpful to reduce the degree of bimodal structure which usually occurrence under applied pressure and reduce the segregation along the grain boundary. The best as-cast tensile properties produced by the P+UT processing were ultimate tensile strength (UTS): 268 MPa, yield strength (YS): 192 MPa, and elongation: 17.1%, which were 64%, 59%, and 307% higher than those of the non-treated alloy, respectively.
2018, 47(2):463-468.
Abstract:
The FeWB based cermets were produced by the reaction boronizing sintering at different temperature and with different holding time. The influences of temperature and holding time on the phase transformation, microstructure of cermets as well as the reaction mechanism were investigated by X-ray diffraction meter (XRD), scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS). The results showed that the hard phase FeWB was produced in the compact at the stage of solid phase sintering by the reaction W + Fe2B = FeWB +Fe and W + FeB = FeWB. Besides, the FeWB phase exhibited an equiaxed morphology. The distinctly rapid densification occurred at the temperature ranging from 800°C to 1150°C while the FeWB phase transformed to Fe7W6 phase, which resulted in the further improvement of the density when the temperature exceeded 1300°C. With an increase of temperature, the cermets prepared by liquid phase sintering exhibited a relatively homogenous microstructure, accompanied by in situ growth of thick FeWB grains. In order to obtain a higher density, the experimental results showed that the sintering temperature of preparing FeWB based cermets should be controlled between 1150°C and 1250°C. Moreover, it was necessary to appropriately increase the content of iron and ferro-boron.
The FeWB based cermets were produced by the reaction boronizing sintering at different temperature and with different holding time. The influences of temperature and holding time on the phase transformation, microstructure of cermets as well as the reaction mechanism were investigated by X-ray diffraction meter (XRD), scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS). The results showed that the hard phase FeWB was produced in the compact at the stage of solid phase sintering by the reaction W + Fe2B = FeWB +Fe and W + FeB = FeWB. Besides, the FeWB phase exhibited an equiaxed morphology. The distinctly rapid densification occurred at the temperature ranging from 800°C to 1150°C while the FeWB phase transformed to Fe7W6 phase, which resulted in the further improvement of the density when the temperature exceeded 1300°C. With an increase of temperature, the cermets prepared by liquid phase sintering exhibited a relatively homogenous microstructure, accompanied by in situ growth of thick FeWB grains. In order to obtain a higher density, the experimental results showed that the sintering temperature of preparing FeWB based cermets should be controlled between 1150°C and 1250°C. Moreover, it was necessary to appropriately increase the content of iron and ferro-boron.
2018, 47(2):469-473.
Abstract:
The effect of Y2O3 on the microstructure and properties of the Fe-Al-Si-B cladding by plasma transferred Arc was investigated. Fe-Al-Si-B in situ composite coating was prepared with plasma arc cladding on Q235 steel substrate. Moreover, rare earth oxide Y2O3 powder was added to the cladding powder in order to improve the microstructure and properties of the coating. The microstructure, phase constituent, microhardness and wear property of the coating were examined by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), micro hardness tester, friction and wear tester. The result indicated that the addition of Y2O3 can purify the grain boundaries and homogenize the inclusions, thus the shape and distribution of the inclusions were improved significantly. Furthermore, A dense, uniform, defect-free and significantly refined coating was then formed. When the content of Y2O3 reached 0.9%, the hardness of the coating reached 510HV, and the optimum wear resistance was obtained.
The effect of Y2O3 on the microstructure and properties of the Fe-Al-Si-B cladding by plasma transferred Arc was investigated. Fe-Al-Si-B in situ composite coating was prepared with plasma arc cladding on Q235 steel substrate. Moreover, rare earth oxide Y2O3 powder was added to the cladding powder in order to improve the microstructure and properties of the coating. The microstructure, phase constituent, microhardness and wear property of the coating were examined by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), micro hardness tester, friction and wear tester. The result indicated that the addition of Y2O3 can purify the grain boundaries and homogenize the inclusions, thus the shape and distribution of the inclusions were improved significantly. Furthermore, A dense, uniform, defect-free and significantly refined coating was then formed. When the content of Y2O3 reached 0.9%, the hardness of the coating reached 510HV, and the optimum wear resistance was obtained.
2018, 47(2):474-478.
Abstract:
Vacuum brazing of porous stainless steel tube and 316L stainless steel has been successfully performed using BNi-7 brazing paste as a filler metal. Ni-Cr solid solution and Ni-P intermetallics were the main phases in the brazing seam. And the interface microstructure of the joint was observed by means of SEM and EDS. The experimental results showed that the highest tensile strength of 245 MPa was acquired from the joint brazed at 980℃ for15min. Longer processing time or higher processing temperature than these conditions did not further improve the joint strength. This is ascribed to the interdiffusion between molten liquid of the filler and solid base metal due to concentration gradients.
Vacuum brazing of porous stainless steel tube and 316L stainless steel has been successfully performed using BNi-7 brazing paste as a filler metal. Ni-Cr solid solution and Ni-P intermetallics were the main phases in the brazing seam. And the interface microstructure of the joint was observed by means of SEM and EDS. The experimental results showed that the highest tensile strength of 245 MPa was acquired from the joint brazed at 980℃ for15min. Longer processing time or higher processing temperature than these conditions did not further improve the joint strength. This is ascribed to the interdiffusion between molten liquid of the filler and solid base metal due to concentration gradients.
2018, 47(2):479-484.
Abstract:
In this paper, two Cu-based bulk metallic glasses, Cu59Zr36Ti5 and Cu61Zr34Ti5, has been studied by nanoindentation in three different ways. Load rate control mode, load control mode, and cycles load control mode nanoindentation were employed. Young’s modulus of the specimen shows loading rate dependence when the loading rate is no more than 5mN/s. The Young’s modulus of both Cu59Zr36Ti5 and Cu61Zr34Ti5 decreases with holding load and loading rate. But neither loading rate nor holding load has significant influence on hardness. Cyclic loading leads to slight hardening for Cu59Zr36Ti5, while Cu61Zr34Ti5 doesn’t show such results. What’s more, Cu61Zr34Ti5 exhibits obvious higher hardness and modulus than Cu59Zr36Ti5 does.
In this paper, two Cu-based bulk metallic glasses, Cu59Zr36Ti5 and Cu61Zr34Ti5, has been studied by nanoindentation in three different ways. Load rate control mode, load control mode, and cycles load control mode nanoindentation were employed. Young’s modulus of the specimen shows loading rate dependence when the loading rate is no more than 5mN/s. The Young’s modulus of both Cu59Zr36Ti5 and Cu61Zr34Ti5 decreases with holding load and loading rate. But neither loading rate nor holding load has significant influence on hardness. Cyclic loading leads to slight hardening for Cu59Zr36Ti5, while Cu61Zr34Ti5 doesn’t show such results. What’s more, Cu61Zr34Ti5 exhibits obvious higher hardness and modulus than Cu59Zr36Ti5 does.
2018, 47(2):485-490.
Abstract:
The hot deformation behavior of Mo-Nb single crystals has been characterized through strain-stress curves and processing map in the temperature range of 1100-1300℃ and strain rates range of 0.001-10 s-1. The results indicate that the flow stress was affected significantly by deformation temperature and strain rate during the hot deformation of Mo-Nb single crystals. Base on the processing map, the optimum condition for hot deformation of Mo-Nb single crystals is the region of high temperatures (>1190℃) and high strain rates (>3.16s-1). Through observation of microstructure of deformed specimens at different deforming conditions, lots of orthogonal cracks, which result from the movement of dislocations along with the glide planes, were observed in specimens deformed at 1100℃/0.01s-1 and 1150℃/10s-1. Less cracks can be observed in specimens deformed at 1250℃/0.01s-1, and few cracks were found in specimens deformed at 1300℃/10s-1. The XRD result shows that the specimen deformed at 1300℃/10s-1 still retains single crystal structure, indicating that the specimen was not undergone instability of flow during hot deformation at the deformation condition of 1300℃/10s-1, which are in good agreement with the results of Mo-Nb single crystals predicted from processing map.
The hot deformation behavior of Mo-Nb single crystals has been characterized through strain-stress curves and processing map in the temperature range of 1100-1300℃ and strain rates range of 0.001-10 s-1. The results indicate that the flow stress was affected significantly by deformation temperature and strain rate during the hot deformation of Mo-Nb single crystals. Base on the processing map, the optimum condition for hot deformation of Mo-Nb single crystals is the region of high temperatures (>1190℃) and high strain rates (>3.16s-1). Through observation of microstructure of deformed specimens at different deforming conditions, lots of orthogonal cracks, which result from the movement of dislocations along with the glide planes, were observed in specimens deformed at 1100℃/0.01s-1 and 1150℃/10s-1. Less cracks can be observed in specimens deformed at 1250℃/0.01s-1, and few cracks were found in specimens deformed at 1300℃/10s-1. The XRD result shows that the specimen deformed at 1300℃/10s-1 still retains single crystal structure, indicating that the specimen was not undergone instability of flow during hot deformation at the deformation condition of 1300℃/10s-1, which are in good agreement with the results of Mo-Nb single crystals predicted from processing map.
2018, 47(2):491-495.
Abstract:
In this letter, we perform the experimental studies on La1-xCexMnO3 to investigate transport properties and field-induced transport mechanisms in electronic doped perovskite films. La1-xCexMnO3films exhibit significant metal-insulator transition, which can be modulated by the doping ratio of Ce. Resistance-temperature curves indicate that the magnetic domains and electron-electron scattering mainly contribute to the transport mechanism in the low temperature region, while the hopping conduction of small polaron becomes the dominating factor at the high temperatures. Laser irradiation was found to induce the shift of metal-insulator transition temperature towards the lower temperature region due to the coexistence of ferromagnetic (FM) metallic phase and paramagnetic (PM) insulating phase in La1-xCexMnO3 films. The higher laser intensity gives rise to more significant change in resistance. Furthermore, magnetoresistance effect can be affected by different doping ratios of Ce in La1-xCexMnO3 films Because of the MIT transition. Our findings are expected to drive the development and application for the new energy transducer devices.
In this letter, we perform the experimental studies on La1-xCexMnO3 to investigate transport properties and field-induced transport mechanisms in electronic doped perovskite films. La1-xCexMnO3films exhibit significant metal-insulator transition, which can be modulated by the doping ratio of Ce. Resistance-temperature curves indicate that the magnetic domains and electron-electron scattering mainly contribute to the transport mechanism in the low temperature region, while the hopping conduction of small polaron becomes the dominating factor at the high temperatures. Laser irradiation was found to induce the shift of metal-insulator transition temperature towards the lower temperature region due to the coexistence of ferromagnetic (FM) metallic phase and paramagnetic (PM) insulating phase in La1-xCexMnO3 films. The higher laser intensity gives rise to more significant change in resistance. Furthermore, magnetoresistance effect can be affected by different doping ratios of Ce in La1-xCexMnO3 films Because of the MIT transition. Our findings are expected to drive the development and application for the new energy transducer devices.
2018, 47(2):496-502.
Abstract:
In order to model the creep aging process of Al-Zn-Mg-Cu aluminum alloy using common temperature-related two-stage aging, a constitutive framework is proposed considering the creep strain and yield strength. The material parameters involved in the model were estimated using a simple fitting method from the experimental data. With a simple expression, this model was capable of handling stress relaxation, hardening response, and variable aging temperature in the creep aging process. It could also be implemented using finite element analysis software to simulate the creep strain, yield strength, and springback of the component. The modeling results were consistent with the creep strain curves measured under different applied stresses. The numerical simulations were compared with the applied experimental data and excellent consistency was observed between them.
In order to model the creep aging process of Al-Zn-Mg-Cu aluminum alloy using common temperature-related two-stage aging, a constitutive framework is proposed considering the creep strain and yield strength. The material parameters involved in the model were estimated using a simple fitting method from the experimental data. With a simple expression, this model was capable of handling stress relaxation, hardening response, and variable aging temperature in the creep aging process. It could also be implemented using finite element analysis software to simulate the creep strain, yield strength, and springback of the component. The modeling results were consistent with the creep strain curves measured under different applied stresses. The numerical simulations were compared with the applied experimental data and excellent consistency was observed between them.
2018, 47(2):503-508.
Abstract:
Aluminum foam-filled corrugated sandwich panels were fabricated by filling closed cell aluminum foam into the spaces of empty corrugated cores, and its out-of-plane compressive behaviors were investigated experimentally which showing significant coupling enhancement effects. The peak stress per unit mass and specific energy absorption (SEA) of the foam-filled panels could be as large as 6.3 and 14.8 times compared to that of the corresponding empty one. Compared to aluminum foam which have excellent energy absorption performances, SEA already have advantages with increasment of 50%. Peak compressive strength of corrugated panels varies with relative density were predicted theorically, and showing that the buckling model of the corrugated core web changed from low order to high order due to foam filling. The high order have shorter wavelength compared to the lower one and requires much larger compressive load to occur, therefore, a significant coupling enhancement effect was caused.
Aluminum foam-filled corrugated sandwich panels were fabricated by filling closed cell aluminum foam into the spaces of empty corrugated cores, and its out-of-plane compressive behaviors were investigated experimentally which showing significant coupling enhancement effects. The peak stress per unit mass and specific energy absorption (SEA) of the foam-filled panels could be as large as 6.3 and 14.8 times compared to that of the corresponding empty one. Compared to aluminum foam which have excellent energy absorption performances, SEA already have advantages with increasment of 50%. Peak compressive strength of corrugated panels varies with relative density were predicted theorically, and showing that the buckling model of the corrugated core web changed from low order to high order due to foam filling. The high order have shorter wavelength compared to the lower one and requires much larger compressive load to occur, therefore, a significant coupling enhancement effect was caused.
2018, 47(2):509-514.
Abstract:
In this paper, the composition of the Ti-Cu-Ni-Zr bulk metallic glasses(BMGs) was designed based on “binary eutectic mixture” method. The Ti-Cu-Ni-Zr alloy rods were prepared with the different diameters by a method of water-cooled copper mold casting. The thermodynamic parameters were tested and the microstructure were investigated by differential scanning calorimeter(DSC), X-ray diffraction(XRD), universal testing machine and scanning electron microscope(SEM). The experimental results show that the Ti-Cu-Ni-Zr BMGs have the high glass forming ability, and the critical diameter can reach 4 mm. The glass forming ability of Ti-Cu-Ni-Zr BMGs are approximately equal, and charactering the thermodynamic parameters of glass formation ability, such as supercooled liquid region DTx, g parameter, reduced glass transition temperature Trg, are also approximately equal, respectively. Based on the disscussion of mechanical properties, the results show that the Ti32.3Cu47.6Ni7.9Zr12.2 and Ti31.6Cu48.2Ni7.7Zr12.5 BMGs have the plastic of 0.7% and 0.2%; however, the fracture mechanism of Ti30Cu49.5Ni7.2Zr13.3 and Ti28.55Cu50.7Ni6.75Zr14 BMGs are the similar brittle fracture. For the Ti-Cu-Ni-Zr BMGs, the greater the plastic deformation is, the more the number of the shear bands are, the greater the depth are, and vice versa. In addition, for the plastic materials, when the amplitude of the serrated flow is the larger, the depth of the surface shear bands is more larger; and vice versa. For the approximate brittle materials, the serrated flow corresponds to the initiation of the second shear band; and for the completely brittle materials, the phenomenon of serrated flow is not found in the stress-strain curves, however, the shear bands were not found on the surface of the sample.
In this paper, the composition of the Ti-Cu-Ni-Zr bulk metallic glasses(BMGs) was designed based on “binary eutectic mixture” method. The Ti-Cu-Ni-Zr alloy rods were prepared with the different diameters by a method of water-cooled copper mold casting. The thermodynamic parameters were tested and the microstructure were investigated by differential scanning calorimeter(DSC), X-ray diffraction(XRD), universal testing machine and scanning electron microscope(SEM). The experimental results show that the Ti-Cu-Ni-Zr BMGs have the high glass forming ability, and the critical diameter can reach 4 mm. The glass forming ability of Ti-Cu-Ni-Zr BMGs are approximately equal, and charactering the thermodynamic parameters of glass formation ability, such as supercooled liquid region DTx, g parameter, reduced glass transition temperature Trg, are also approximately equal, respectively. Based on the disscussion of mechanical properties, the results show that the Ti32.3Cu47.6Ni7.9Zr12.2 and Ti31.6Cu48.2Ni7.7Zr12.5 BMGs have the plastic of 0.7% and 0.2%; however, the fracture mechanism of Ti30Cu49.5Ni7.2Zr13.3 and Ti28.55Cu50.7Ni6.75Zr14 BMGs are the similar brittle fracture. For the Ti-Cu-Ni-Zr BMGs, the greater the plastic deformation is, the more the number of the shear bands are, the greater the depth are, and vice versa. In addition, for the plastic materials, when the amplitude of the serrated flow is the larger, the depth of the surface shear bands is more larger; and vice versa. For the approximate brittle materials, the serrated flow corresponds to the initiation of the second shear band; and for the completely brittle materials, the phenomenon of serrated flow is not found in the stress-strain curves, however, the shear bands were not found on the surface of the sample.
2018, 47(2):515-520.
Abstract:
Palladium is widely used in hydrogen isotope technology owing to its obvious isotope effect, the systematic research of protium-deuterium seperation factor of sponge palladium was conducted by quadrupole mass spectrometer. The impact of temperatre (-25 ℃~155 ℃), protium-deuterium relative abundance (5%~90%), hydrogen-palladium ratio in the solid phase (0.05~0.7) on protium-deuterium seperation factor of sponge palladium was analyzed by experimental method. Combining the calculation of that in the a phase, the results show that protium-deuterium seperation factor of sponge palladium decreases with temperature, and increases with deuterium relative abundance. Protium-deuterium seperation factor increases with hydrogen-palladium ratio in the a+β and β phase, but such effect was not observed in the α phase.
Palladium is widely used in hydrogen isotope technology owing to its obvious isotope effect, the systematic research of protium-deuterium seperation factor of sponge palladium was conducted by quadrupole mass spectrometer. The impact of temperatre (-25 ℃~155 ℃), protium-deuterium relative abundance (5%~90%), hydrogen-palladium ratio in the solid phase (0.05~0.7) on protium-deuterium seperation factor of sponge palladium was analyzed by experimental method. Combining the calculation of that in the a phase, the results show that protium-deuterium seperation factor of sponge palladium decreases with temperature, and increases with deuterium relative abundance. Protium-deuterium seperation factor increases with hydrogen-palladium ratio in the a+β and β phase, but such effect was not observed in the α phase.
2018, 47(2):521-529.
Abstract:
The influence of Si content on the formation process and properties of PEO ceramic coating on the surface of Al Si alloy was studied. SEM, XRD and EDS were used to analyze the microstructure and phase of the ceramic layer, and the heat insulation performance and the hardness of the were tested by using the thermal insulation temperature measuring device and the 500MVDTM digital display. The results showed that in the early plasma electrolytic oxidation, silicon atom and a second phase Al3CuNi will hinder micro-arc discharge, inhibiting the formation of an aluminum oxide film, reducing the density of the film; with the matrix increased silicon content, primary silicon and eutectic silicon content increases in Al-xSi alloy, the phenomenon that silicon particles stacked appears, the more difficult plasma discharge, the growth rate of the coating is reduced, the content of silicon dioxide and silicon impurities in the ceramic layer will be increased, heat temperature also will increase, hardness decrease .
The influence of Si content on the formation process and properties of PEO ceramic coating on the surface of Al Si alloy was studied. SEM, XRD and EDS were used to analyze the microstructure and phase of the ceramic layer, and the heat insulation performance and the hardness of the were tested by using the thermal insulation temperature measuring device and the 500MVDTM digital display. The results showed that in the early plasma electrolytic oxidation, silicon atom and a second phase Al3CuNi will hinder micro-arc discharge, inhibiting the formation of an aluminum oxide film, reducing the density of the film; with the matrix increased silicon content, primary silicon and eutectic silicon content increases in Al-xSi alloy, the phenomenon that silicon particles stacked appears, the more difficult plasma discharge, the growth rate of the coating is reduced, the content of silicon dioxide and silicon impurities in the ceramic layer will be increased, heat temperature also will increase, hardness decrease .
2018, 47(2):530-537.
Abstract:
The differential scanning calorimetry (DSC) experiments with different heating/cooling rates in the range of 5~40℃/min were performed on a directionally solidified (DS) Ni-base superalloy DZ22. The equilibrium transformation temperatures (zero-heating/cooling rate) of the alloy were obtained by linear extrapolating the different heating/cooling rates or averaging specific peak temperatures of both heating and cooling DSC curves. The DSC experiments with 10℃/min heating/cooling rate were carried out on samples cut from different position of DS testing bar. The results indicated that the heating/cooling rate and sampling position both had obvious effect on the values of phase transformation temperatures of DSC curves. (1) The heating and cooling rate had effect on the DSC results, including the phase transformation temperatures of liquidus, MC carbides, solidus, eutectic (γ+γ′) and secondary γ′. As the heating and cooling rate increased, the peak of transformation temperature on the heating DSC curve shifted to high temperature direction, whereas the cooling curve tended to deviate to lower temperature. The peak height increase accompanied by the heating/cooling rate increase. However, the average values of heating and cooling curves corresponding to the phase transformation temperature points are consistent. The equilibrium transformation temperatures of alloy acquired by linear extrapolating the different heating/cooling rates will result in some differences for the result, whereas to average specific peak temperature of both heating and cooling DSC curves is an effective method to determine the equilibrium phase transformation temperatures of superalloys. The influence of different heating and cooling rate on the phase transformation temperature results in DSC test has reference significance for the control of the actual process parameters in the process of heat treatment and solidification cooling of superalloy. (2) The sampling position had obvious effect on the eutectic (γ+γ′) dissolve and solidus temperatures of heating DSC curve in relative low temperature range, there is a 17℃ and 20℃ gap respectively for eutectic and solidus temperatures between samples cut from the top and bottom part of the same directionally solidified test bar due to the micro-segregation and microstructure difference. However, this difference is absent in liquidus and MC carbides dissolve temperatures in high temperature range. Upon cooling, the sampling position has minor effect on phase transformation temperature of DSC curve because the similar microstructure of the different sampling parts of the alloy formed in the following solidification cooling process after heating to a full liquid state and phase transformation temperature tends to be consistent. For a superalloy with the same composition, the DSC test results are only meaningful as the microstructure of the sample is similar. In General, the heating/cooling rate and sampling position had obvious effect on the phase transformation temperatures of DSC curves and these influence factors should be considered for selecting the process parameters of Ni-base superalloys.
The differential scanning calorimetry (DSC) experiments with different heating/cooling rates in the range of 5~40℃/min were performed on a directionally solidified (DS) Ni-base superalloy DZ22. The equilibrium transformation temperatures (zero-heating/cooling rate) of the alloy were obtained by linear extrapolating the different heating/cooling rates or averaging specific peak temperatures of both heating and cooling DSC curves. The DSC experiments with 10℃/min heating/cooling rate were carried out on samples cut from different position of DS testing bar. The results indicated that the heating/cooling rate and sampling position both had obvious effect on the values of phase transformation temperatures of DSC curves. (1) The heating and cooling rate had effect on the DSC results, including the phase transformation temperatures of liquidus, MC carbides, solidus, eutectic (γ+γ′) and secondary γ′. As the heating and cooling rate increased, the peak of transformation temperature on the heating DSC curve shifted to high temperature direction, whereas the cooling curve tended to deviate to lower temperature. The peak height increase accompanied by the heating/cooling rate increase. However, the average values of heating and cooling curves corresponding to the phase transformation temperature points are consistent. The equilibrium transformation temperatures of alloy acquired by linear extrapolating the different heating/cooling rates will result in some differences for the result, whereas to average specific peak temperature of both heating and cooling DSC curves is an effective method to determine the equilibrium phase transformation temperatures of superalloys. The influence of different heating and cooling rate on the phase transformation temperature results in DSC test has reference significance for the control of the actual process parameters in the process of heat treatment and solidification cooling of superalloy. (2) The sampling position had obvious effect on the eutectic (γ+γ′) dissolve and solidus temperatures of heating DSC curve in relative low temperature range, there is a 17℃ and 20℃ gap respectively for eutectic and solidus temperatures between samples cut from the top and bottom part of the same directionally solidified test bar due to the micro-segregation and microstructure difference. However, this difference is absent in liquidus and MC carbides dissolve temperatures in high temperature range. Upon cooling, the sampling position has minor effect on phase transformation temperature of DSC curve because the similar microstructure of the different sampling parts of the alloy formed in the following solidification cooling process after heating to a full liquid state and phase transformation temperature tends to be consistent. For a superalloy with the same composition, the DSC test results are only meaningful as the microstructure of the sample is similar. In General, the heating/cooling rate and sampling position had obvious effect on the phase transformation temperatures of DSC curves and these influence factors should be considered for selecting the process parameters of Ni-base superalloys.
2018, 47(2):538-545.
Abstract:
According to the demand of remanufacturing engine crankshaft, use the automatic high velocity arc spraying system based on the six degree freedom robot, employed the self-design FeNiCrAl wire and ‘circular’, ‘Z’ spraying path for remanufacturing the worn failure crankshaft. Compared with the conventional 3Cr13 coating performance, the residual stress of FeNiCrAl coating was the agreement of the results with the new crankshaft, the bend fatigue performance of spraying FeNiCrAl coated crankshaft conducted accordance with the national standard QC-T637-2000 (test bending moment was 2305.38 N.m, load factor was 1.2, the fatigue life was exceeded 1×107) meet the demand of national standard. The results show that the bend fatigue of FeNiCrAl coated crankshaft was higher than that sprayed by 3Cr13. The remanufacture benefit show that the weights exhaust of FeNiCrAl spraying cored wire was not less than 3% to that product a new crankshaft. The cost of remanufactured a single crankshaft was fell by 90% compared with products a new one. The remanufacturing process saves time about 18% compared to the manufacture a new one. Therefore, the energy saving and environmental protection of the technology is obvious, and the application prospect is broad.
According to the demand of remanufacturing engine crankshaft, use the automatic high velocity arc spraying system based on the six degree freedom robot, employed the self-design FeNiCrAl wire and ‘circular’, ‘Z’ spraying path for remanufacturing the worn failure crankshaft. Compared with the conventional 3Cr13 coating performance, the residual stress of FeNiCrAl coating was the agreement of the results with the new crankshaft, the bend fatigue performance of spraying FeNiCrAl coated crankshaft conducted accordance with the national standard QC-T637-2000 (test bending moment was 2305.38 N.m, load factor was 1.2, the fatigue life was exceeded 1×107) meet the demand of national standard. The results show that the bend fatigue of FeNiCrAl coated crankshaft was higher than that sprayed by 3Cr13. The remanufacture benefit show that the weights exhaust of FeNiCrAl spraying cored wire was not less than 3% to that product a new crankshaft. The cost of remanufactured a single crankshaft was fell by 90% compared with products a new one. The remanufacturing process saves time about 18% compared to the manufacture a new one. Therefore, the energy saving and environmental protection of the technology is obvious, and the application prospect is broad.
2018, 47(2):546-552.
Abstract:
An experimental set-up was designed for measuring the self-field losses of Bi2223/Ag HTS tapes using a transport current method. Ti/Mn(0.8-x)SnxIr0.2O2 ternary oxide electrode materials were obtained by Pechini sol-gel method. The organizational structure and electrochemical performance of Ti/Mn(0.8-x)SnxIr0.2O2 electrodeswas investigated by Scanning electron microscope (SEM), X ray diffraction (XRD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results showed that: SnO2 has a great influence on the organization structure of coating. With the content of SnO2 increasing, affirmative structure of Mn3O4 phase in Ti/Mn (0.8-x) SnxIr0.2O2 electrodes oxide coating is gradually reduced, but affirmative structure of SnO2 phase increased. Compared with the Mn-Ir-based binary oxides, the addition of SnO2 can significantly improve the current response of electrodes in the range of 0~0.5V and enhance activity of manganese oxide, but suppress activity of iridium oxide. Impedance analysis indicated that the charge transfer resistance,the relaxation time constant and the capacity of different frequency response of electrode materials were changed after addition of SnO2. In contrast, the Ti/Ir0.2Mn0.6Sn0.2O2 electrode with better capacitance response and higher activity in the low frequency range (≤ 1Hz), demonstrates the highest specific capacitance.
An experimental set-up was designed for measuring the self-field losses of Bi2223/Ag HTS tapes using a transport current method. Ti/Mn(0.8-x)SnxIr0.2O2 ternary oxide electrode materials were obtained by Pechini sol-gel method. The organizational structure and electrochemical performance of Ti/Mn(0.8-x)SnxIr0.2O2 electrodeswas investigated by Scanning electron microscope (SEM), X ray diffraction (XRD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results showed that: SnO2 has a great influence on the organization structure of coating. With the content of SnO2 increasing, affirmative structure of Mn3O4 phase in Ti/Mn (0.8-x) SnxIr0.2O2 electrodes oxide coating is gradually reduced, but affirmative structure of SnO2 phase increased. Compared with the Mn-Ir-based binary oxides, the addition of SnO2 can significantly improve the current response of electrodes in the range of 0~0.5V and enhance activity of manganese oxide, but suppress activity of iridium oxide. Impedance analysis indicated that the charge transfer resistance,the relaxation time constant and the capacity of different frequency response of electrode materials were changed after addition of SnO2. In contrast, the Ti/Ir0.2Mn0.6Sn0.2O2 electrode with better capacitance response and higher activity in the low frequency range (≤ 1Hz), demonstrates the highest specific capacitance.
2018, 47(2):553-559.
Abstract:
2195 Al-Li alloy is identified as an ideal structural material for aerospace field, but limited research on its hot deformation behavior has been found in open publication. In this study, isothermal plane strain compression test was conducted on Gleeble-3500 thermal mechanical simulator, experimental temperature range from 400 ℃ to 500 ℃ and strain rate various from 0.01 s-1 to 10 s-1. The results show that flow stress decreases with increasing temperature and decreasing strain rate. Constitutive model based on the hyperbolic-sine equation was established to describe relationship between flow stress and deformation temperature, strain rate. The apparent activation energy of plane strain compression was estimated to be 217 KJ / mol. To evaluate the hot workability of this alloy, the processing maps at strains of 0.5 and 0.7 were constructed on the basis of dynamic material model and Prasad’s instability criterion. Optimum parameters were obtained in the temperature of 475~500 ℃, strain rate of 0.01 s-1 for plane strain compression.
2195 Al-Li alloy is identified as an ideal structural material for aerospace field, but limited research on its hot deformation behavior has been found in open publication. In this study, isothermal plane strain compression test was conducted on Gleeble-3500 thermal mechanical simulator, experimental temperature range from 400 ℃ to 500 ℃ and strain rate various from 0.01 s-1 to 10 s-1. The results show that flow stress decreases with increasing temperature and decreasing strain rate. Constitutive model based on the hyperbolic-sine equation was established to describe relationship between flow stress and deformation temperature, strain rate. The apparent activation energy of plane strain compression was estimated to be 217 KJ / mol. To evaluate the hot workability of this alloy, the processing maps at strains of 0.5 and 0.7 were constructed on the basis of dynamic material model and Prasad’s instability criterion. Optimum parameters were obtained in the temperature of 475~500 ℃, strain rate of 0.01 s-1 for plane strain compression.
2018, 47(2):560-566.
Abstract:
microstructure differences between the polysynthetically twinned crystal and the directional lamellar structure prepared by conventional casting for TiAl based alloy were analyzed, in order to detail discuss their influence on the microstructural degradation during creep loading. And micro-alloying methods were proposed to decrease the adverse effect. The microstructural differences mainly included colony boundary, Al segregation and excess α2 phase. Additionally, equiaxed gamma grain precipitation and lamellar coarsening during hot isostatic pressing were also other differences. These differences had adverse influence on the microstructure degradation of directional lamellar structure prepared by conventional casting during creep loading. Al segregation and excess α2 phase promoted the microstructural degradation for as-cast sample, and the equiaxed gamma grain precipitated during hot isostatic pressing aggravated the microstructural degradation. They caused significant reduction of creep rupture life. The effect of the former was less than that of the latter. The colony boundary had a little adverse effect on the microstructural degradation. Additionally, the methods that minor addition of Zr,Si,C improved the creep rupture properties by inhibiting microstructural degradation were also discussed.
microstructure differences between the polysynthetically twinned crystal and the directional lamellar structure prepared by conventional casting for TiAl based alloy were analyzed, in order to detail discuss their influence on the microstructural degradation during creep loading. And micro-alloying methods were proposed to decrease the adverse effect. The microstructural differences mainly included colony boundary, Al segregation and excess α2 phase. Additionally, equiaxed gamma grain precipitation and lamellar coarsening during hot isostatic pressing were also other differences. These differences had adverse influence on the microstructure degradation of directional lamellar structure prepared by conventional casting during creep loading. Al segregation and excess α2 phase promoted the microstructural degradation for as-cast sample, and the equiaxed gamma grain precipitated during hot isostatic pressing aggravated the microstructural degradation. They caused significant reduction of creep rupture life. The effect of the former was less than that of the latter. The colony boundary had a little adverse effect on the microstructural degradation. Additionally, the methods that minor addition of Zr,Si,C improved the creep rupture properties by inhibiting microstructural degradation were also discussed.
2018, 47(2):567-573.
Abstract:
TC4 titanium alloy honeycomb sandwich panel is manufactured by high-temperature brazing. In this paper, the mechanical performance parameters and failure modes of honeycomb sandwich panel are experimentally investigated via flatwise compression and three-point bending test subject to different temperatures. It is found by the test that flatwise compression elasticity modulus and strength of the honeycomb sandwich panel at 440℃ decrease to 35.2% and 61.7% of that at room temperature, respectively, indicating that higher temperature may result in lower compression elasticity modulus and strength. It is also found that the test temperature has no effect on the failure mode. On the other hand, it is noted in the three-point bending test that the failure mode changes, the flexural strength decreases, and that the maximum deflection increases with the increasing test temperature. It is also found that the bending performance of specimens in the L-direction is better than the W-direction. In addition, the face sheet of the bending specimen is ductile fracture, and the brazing zone is brittle fracture at room temperature as revealed by the experiment, while the brazing joints of surface/core debonding failure specimen is cleavage fracture a high temperature of 300℃.
TC4 titanium alloy honeycomb sandwich panel is manufactured by high-temperature brazing. In this paper, the mechanical performance parameters and failure modes of honeycomb sandwich panel are experimentally investigated via flatwise compression and three-point bending test subject to different temperatures. It is found by the test that flatwise compression elasticity modulus and strength of the honeycomb sandwich panel at 440℃ decrease to 35.2% and 61.7% of that at room temperature, respectively, indicating that higher temperature may result in lower compression elasticity modulus and strength. It is also found that the test temperature has no effect on the failure mode. On the other hand, it is noted in the three-point bending test that the failure mode changes, the flexural strength decreases, and that the maximum deflection increases with the increasing test temperature. It is also found that the bending performance of specimens in the L-direction is better than the W-direction. In addition, the face sheet of the bending specimen is ductile fracture, and the brazing zone is brittle fracture at room temperature as revealed by the experiment, while the brazing joints of surface/core debonding failure specimen is cleavage fracture a high temperature of 300℃.
2018, 47(2):574-580.
Abstract:
Electropulsing was introduced into the cutting process of the high-frequency quenched GCr15 bearing steel. Experiment results indicate that the main cutting force, axial roughness on machined surface, surface microhardness and tool wear show a significant decreasing tendency under the effect of electropulsing. For high-frequency quenched GCr15 bearing steel, the electroplasticity effect and Joule heating effect can accelerate the movement of dislocations, then the material tempered in a lower temperature and shorter time, the plastic deformation ability and the cutting properties of GCr15 bearing steel have a remarkable improvement.
Electropulsing was introduced into the cutting process of the high-frequency quenched GCr15 bearing steel. Experiment results indicate that the main cutting force, axial roughness on machined surface, surface microhardness and tool wear show a significant decreasing tendency under the effect of electropulsing. For high-frequency quenched GCr15 bearing steel, the electroplasticity effect and Joule heating effect can accelerate the movement of dislocations, then the material tempered in a lower temperature and shorter time, the plastic deformation ability and the cutting properties of GCr15 bearing steel have a remarkable improvement.
2018, 47(2):581-587.
Abstract:
Abstract: In order to study the effect of Zr on the microstructure and properties of Cu-Cr in situ composites, Cu-15Cr and Cu-15Cr-0.24Zr alloys were prepared by vacuum medium frequency induction melting technique. The effects of Zr on microstructure of Cu-15Cr as-cast alloy and microstructure after annealing at different temperatures was studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The tensile deformation test of the two kinds of test alloys was carried out, and the thermal stability of the alloy under the final deformation was studied. The experimental results show that the addition of Zr results in the formation of flaky CuZr intermetallics in the as-cast microstructure of the alloy, which inhibit the formation of eutectic Cr phase and make the eutectic Cr content much lower than that of Cu-15Cr alloy. The size of dendritic Cr is refined as well. The test results also show that the addition of Zr significantly improves the thermal stability of the alloy and increases its tensile strength by 100 MPa after annealed at 550 °C for 1 h. Through the calculation of Gibbs free energy (ΔGmix) in the solidification process of the test alloy, it is proved that the addition of Zr reduces the liquid phase separation temperature and decreases the dynamic nucleation driving force of the Cu-15Cr alloy in the process of solidification, which inhibits the formation of eutectic Cr and is consistent with the experimental results of the as-cast microstructure.
Abstract: In order to study the effect of Zr on the microstructure and properties of Cu-Cr in situ composites, Cu-15Cr and Cu-15Cr-0.24Zr alloys were prepared by vacuum medium frequency induction melting technique. The effects of Zr on microstructure of Cu-15Cr as-cast alloy and microstructure after annealing at different temperatures was studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The tensile deformation test of the two kinds of test alloys was carried out, and the thermal stability of the alloy under the final deformation was studied. The experimental results show that the addition of Zr results in the formation of flaky CuZr intermetallics in the as-cast microstructure of the alloy, which inhibit the formation of eutectic Cr phase and make the eutectic Cr content much lower than that of Cu-15Cr alloy. The size of dendritic Cr is refined as well. The test results also show that the addition of Zr significantly improves the thermal stability of the alloy and increases its tensile strength by 100 MPa after annealed at 550 °C for 1 h. Through the calculation of Gibbs free energy (ΔGmix) in the solidification process of the test alloy, it is proved that the addition of Zr reduces the liquid phase separation temperature and decreases the dynamic nucleation driving force of the Cu-15Cr alloy in the process of solidification, which inhibits the formation of eutectic Cr and is consistent with the experimental results of the as-cast microstructure.
2018, 47(2):588-593.
Abstract:
Abstract: Cr3C2-NiCr/NiAl coating was prepared by plasma spraying technique on the CuCo2Be alloy. The high temperature dry sliding friction and wear characteristics of Cr3C2-NiCr/NiAl coating and CuCo2Be was investigated in detail at UMT-2 tribometer by using Al2O3 ceramic ball as dual material, and it explored the temperature friction and wear behavior of the Cr3C2-NiCr/NiAl coating at different temperatures by three dimensional profile instrument，SEM， EDS, and XRD et.The results showed that the coating had obvious layered and nickel-aluminum compounds were angular,and the phase formation of the coating appeared amorphous. The study results about the friction and wear showed：500℃ through observing the wear volume morphology，it would find the wear of coating was significantly less than CuCo2Be before sprayed, so study conclusions showed Cr3C2-NiCr/NiAl coating have better high temperature wear resistance；At room temperature,the friction and wear mechanism of the composite coating was mainly abrasive wear, and wear less, and with the increase of temperature,the wear mechanism of the coating was mainly oxidation wear and adhesive wear.
Abstract: Cr3C2-NiCr/NiAl coating was prepared by plasma spraying technique on the CuCo2Be alloy. The high temperature dry sliding friction and wear characteristics of Cr3C2-NiCr/NiAl coating and CuCo2Be was investigated in detail at UMT-2 tribometer by using Al2O3 ceramic ball as dual material, and it explored the temperature friction and wear behavior of the Cr3C2-NiCr/NiAl coating at different temperatures by three dimensional profile instrument，SEM， EDS, and XRD et.The results showed that the coating had obvious layered and nickel-aluminum compounds were angular,and the phase formation of the coating appeared amorphous. The study results about the friction and wear showed：500℃ through observing the wear volume morphology，it would find the wear of coating was significantly less than CuCo2Be before sprayed, so study conclusions showed Cr3C2-NiCr/NiAl coating have better high temperature wear resistance；At room temperature,the friction and wear mechanism of the composite coating was mainly abrasive wear, and wear less, and with the increase of temperature,the wear mechanism of the coating was mainly oxidation wear and adhesive wear.
2018, 47(2):594-599.
Abstract:
In this paper,Fe3O4@SiO2particles were prepared by chemical co-precipitation method. Oil sodium was added when Fe3O4nuclear growing. Then, TEOS was added to prepare Fe3O4@SiO2 composite nanoparticles and magnetic microspheres. The properties of theFe3O4, Fe3O4@SiO2 composite nanoparticles and Fe3O4@SiO2 composite microspheres were tested by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). The magnetic properties were studied by vibrating sample magnetometer (VSM). The result shows that the maximum saturation magnetization of Fe3O4@SiO2 microspheres (34.85emu/g) was lower than that of the Fe3O4 powder (79.55emu/g), but obviously higher thanFe3O4@SiO2 nanoparticles, but the residual magnetism and coercivity force of microspheres were obviously enhanced.
In this paper,Fe3O4@SiO2particles were prepared by chemical co-precipitation method. Oil sodium was added when Fe3O4nuclear growing. Then, TEOS was added to prepare Fe3O4@SiO2 composite nanoparticles and magnetic microspheres. The properties of theFe3O4, Fe3O4@SiO2 composite nanoparticles and Fe3O4@SiO2 composite microspheres were tested by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). The magnetic properties were studied by vibrating sample magnetometer (VSM). The result shows that the maximum saturation magnetization of Fe3O4@SiO2 microspheres (34.85emu/g) was lower than that of the Fe3O4 powder (79.55emu/g), but obviously higher thanFe3O4@SiO2 nanoparticles, but the residual magnetism and coercivity force of microspheres were obviously enhanced.
2018, 47(2):600-605.
Abstract:
The pure MnO and Mn2O3 doped MnO catalysts for oxygen reduction were synthesized by reducing maganese oxide under ammonia and hydrogen atmosphere seperately. X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy tests ascertained the synthesis of the two kinds of catalysts. The cyclic voltammetry, tafel, linear scanning voltammetry and current-time chronoamperometric tests proved that the potential of peak current of oxygen redcution located in the rage of -0.5 to -0.1V. The doping of Mn2O3 enhanced the peak potential of oxygen reduction. Both the rotate disc electrode and rotate ring disc electrode tests confirmed that the ORR were major happened through 4-electron reaction style under the catalysis of Mn2O3 doped MnO, thus, through 2-electron style onder the catalysis of pure MnO. It is approved that the doping of Mn2O3 improved the catalysis of MnO. The coexistence of ions with different valents can promote the promote the catalytic activity.
The pure MnO and Mn2O3 doped MnO catalysts for oxygen reduction were synthesized by reducing maganese oxide under ammonia and hydrogen atmosphere seperately. X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy tests ascertained the synthesis of the two kinds of catalysts. The cyclic voltammetry, tafel, linear scanning voltammetry and current-time chronoamperometric tests proved that the potential of peak current of oxygen redcution located in the rage of -0.5 to -0.1V. The doping of Mn2O3 enhanced the peak potential of oxygen reduction. Both the rotate disc electrode and rotate ring disc electrode tests confirmed that the ORR were major happened through 4-electron reaction style under the catalysis of Mn2O3 doped MnO, thus, through 2-electron style onder the catalysis of pure MnO. It is approved that the doping of Mn2O3 improved the catalysis of MnO. The coexistence of ions with different valents can promote the promote the catalytic activity.
2018, 47(2):606-611.
Abstract:
In this paper, carbonyl iron powder and DISPER-Y220 are used as raw material and dispersant, respectively. The viscosity of slurry is detected as 0.55 Pa ? s and the slurry has good flowability slurry to be a printing ink. The ferromagnetic soft magnetic workpieces are prepared by direct inkjet printing process with the nozzle size of 0.5mm, 0.8mm and 1.0mm respectively, and then the samples printed have been through degreasing and sintering. The results showed that the viscosity of the slurry is lowest when the dosage of dispersant is1wt% and the viscosity of the slurry is increased with the solids content and shear rate increased .The slurry is shear thinning over the shear rate .The sintered body printed with the nozzle size of 0.8mm has a lowest surface roughness of 0.8μm. After sintered at 1300 ℃ for 2h ,the sintered body printed with the nozzle size of 0.5mm has a relative density of 96.3%, the saturation magnetization (BS ) and the maximum magnetic permeability (μmax ) reaching to 1.53T and 2630, respectively.
In this paper, carbonyl iron powder and DISPER-Y220 are used as raw material and dispersant, respectively. The viscosity of slurry is detected as 0.55 Pa ? s and the slurry has good flowability slurry to be a printing ink. The ferromagnetic soft magnetic workpieces are prepared by direct inkjet printing process with the nozzle size of 0.5mm, 0.8mm and 1.0mm respectively, and then the samples printed have been through degreasing and sintering. The results showed that the viscosity of the slurry is lowest when the dosage of dispersant is1wt% and the viscosity of the slurry is increased with the solids content and shear rate increased .The slurry is shear thinning over the shear rate .The sintered body printed with the nozzle size of 0.8mm has a lowest surface roughness of 0.8μm. After sintered at 1300 ℃ for 2h ,the sintered body printed with the nozzle size of 0.5mm has a relative density of 96.3%, the saturation magnetization (BS ) and the maximum magnetic permeability (μmax ) reaching to 1.53T and 2630, respectively.
2018, 47(2):612-617.
Abstract:
In the paper, the condition of steady gaseous detonation and detonation product composition were analyzed theoretically. Nano carbon material and carbon coated iron nano particles were prepared by gaseous detonation method with oxygen and benzene, oxygen and benzene dissolved ferrocene, respectively. Characterized by X-ray diffraction and transmission electron microscope, it can be found that carbon nano materials are spherical or quasi-spherical, particle size ranges in 10~30nm, and dispersity is poor. The cluster area is mainly amorphous carbon, while a few of onion-like fullerenes in dispersing region. The molar ratio of free carbon and iron has an influence on morphology and structure of carbon coated iron nanoparticles. When the molar ratio value ranges in 10~28, carbon coated iron nanoparticles can be prepared, which are spherical, with a clear core-shell structure and good dispersion; when the value greater than 50, carbon coated iron morphology is changed and part of carbon with a sheet structure.
In the paper, the condition of steady gaseous detonation and detonation product composition were analyzed theoretically. Nano carbon material and carbon coated iron nano particles were prepared by gaseous detonation method with oxygen and benzene, oxygen and benzene dissolved ferrocene, respectively. Characterized by X-ray diffraction and transmission electron microscope, it can be found that carbon nano materials are spherical or quasi-spherical, particle size ranges in 10~30nm, and dispersity is poor. The cluster area is mainly amorphous carbon, while a few of onion-like fullerenes in dispersing region. The molar ratio of free carbon and iron has an influence on morphology and structure of carbon coated iron nanoparticles. When the molar ratio value ranges in 10~28, carbon coated iron nanoparticles can be prepared, which are spherical, with a clear core-shell structure and good dispersion; when the value greater than 50, carbon coated iron morphology is changed and part of carbon with a sheet structure.
2018, 47(2):618-623.
Abstract:
Thermal oxidation process was performed on TC4 alloy for 10 h at the temperature of 700 °C. The static and dynamic mechanical behaviors of the thermal oxidized TC4 were investigated by quasi-static compression, nanoindentation and split Hopkinson pressure bar impact tests. Moreover, the micro-morphology of the oxide layer after impact tests was analyzed by scanning electron microscope (SEM). The results indicate that after thermal oxidation the static mechanical properties of TC4 is improved and its strain rate hardening effect is enhanced. Under a relatively low strain rate, the oxide layer could increase the plastic deformation ability of TC4. At a large strain rate, however, the oxidation layer reduces its plastic deformation ability. Through fitting of the impact test data and constitutive model correction, the Johnson-Cook (J-C) constitutive equation of the thermal oxidized TC4 is obtained. Compared to experimental results, the correction and experimental curves have a good agreement in the plastic deformation region.
Thermal oxidation process was performed on TC4 alloy for 10 h at the temperature of 700 °C. The static and dynamic mechanical behaviors of the thermal oxidized TC4 were investigated by quasi-static compression, nanoindentation and split Hopkinson pressure bar impact tests. Moreover, the micro-morphology of the oxide layer after impact tests was analyzed by scanning electron microscope (SEM). The results indicate that after thermal oxidation the static mechanical properties of TC4 is improved and its strain rate hardening effect is enhanced. Under a relatively low strain rate, the oxide layer could increase the plastic deformation ability of TC4. At a large strain rate, however, the oxidation layer reduces its plastic deformation ability. Through fitting of the impact test data and constitutive model correction, the Johnson-Cook (J-C) constitutive equation of the thermal oxidized TC4 is obtained. Compared to experimental results, the correction and experimental curves have a good agreement in the plastic deformation region.
2018, 47(2):624-629.
Abstract:
In order to improve the laser welding quality of TC4 titanium alloy, an technology named ultrasonic processing across different phases based on laser welding was introduced to assist laser welding, and the effects of ultrasonic vibration field on the macromorphologies, microstructures and microhardness of the laser welding joints were studied by changing the ultrasonic vibration power. The results show that under the effect of the ultrasonic vibration field, with the increase of ultrasonic vibration power, there are clumped concave appear on the welding surface, and the surface roughness of the welding joints is lower, meanwhile, the acicular α′-martensite content is more intense, orientation and arrangement are more cluttered, besides, the acicular α′-martensite average length is shorter because of ultrasonic vibration and radiation pressure. The microhardness of welding joints increases, but the microhardness of heat affected zone and the base metal area remain unchanged with the increase of ultrasonic vibration power.
In order to improve the laser welding quality of TC4 titanium alloy, an technology named ultrasonic processing across different phases based on laser welding was introduced to assist laser welding, and the effects of ultrasonic vibration field on the macromorphologies, microstructures and microhardness of the laser welding joints were studied by changing the ultrasonic vibration power. The results show that under the effect of the ultrasonic vibration field, with the increase of ultrasonic vibration power, there are clumped concave appear on the welding surface, and the surface roughness of the welding joints is lower, meanwhile, the acicular α′-martensite content is more intense, orientation and arrangement are more cluttered, besides, the acicular α′-martensite average length is shorter because of ultrasonic vibration and radiation pressure. The microhardness of welding joints increases, but the microhardness of heat affected zone and the base metal area remain unchanged with the increase of ultrasonic vibration power.
2018, 47(2):630-635.
Abstract:
Silane coupling agent modified silica sol was prepared with ethyl silicate (TEOS), 3-Methacryloxypropyltrimethoxysilane (silane coupling agent KH570) and vinyl trimethoxy silane (silane coupling agent A171) as main raw material, and then modified silica sol film on zirconium hydride was made by dip-coating method. FTIR analysis showed that coupling agent could participate in copolymerization reaction of the sol effectively. TEM analysis showed that it’s advantageous to refine colloidal particle size, improve and maintain the affinity between them as KH570 and A171 were added one by one into the sol. SEM analysis showed that dried crack-free sol film could be prepared on zirconium hydride substrate using KH570 and A171 modified silica sol. Micro cracks exist on the sintered sol film but without apparent flaking. Elements distribute evenly on the surface of the sol film in which residual carbon exists after sintering. Thermal hydrogen release experiment in vacuum demonstrated the preparation of sintered sol film on zirconium hydride could resistant hydrogen permeation. In CO2 atmosphere under 600℃, oxygen diffusion could also be hindered by the sintered silica sol film, which shows oxidation resistance for zirconium hydride substrate.
Silane coupling agent modified silica sol was prepared with ethyl silicate (TEOS), 3-Methacryloxypropyltrimethoxysilane (silane coupling agent KH570) and vinyl trimethoxy silane (silane coupling agent A171) as main raw material, and then modified silica sol film on zirconium hydride was made by dip-coating method. FTIR analysis showed that coupling agent could participate in copolymerization reaction of the sol effectively. TEM analysis showed that it’s advantageous to refine colloidal particle size, improve and maintain the affinity between them as KH570 and A171 were added one by one into the sol. SEM analysis showed that dried crack-free sol film could be prepared on zirconium hydride substrate using KH570 and A171 modified silica sol. Micro cracks exist on the sintered sol film but without apparent flaking. Elements distribute evenly on the surface of the sol film in which residual carbon exists after sintering. Thermal hydrogen release experiment in vacuum demonstrated the preparation of sintered sol film on zirconium hydride could resistant hydrogen permeation. In CO2 atmosphere under 600℃, oxygen diffusion could also be hindered by the sintered silica sol film, which shows oxidation resistance for zirconium hydride substrate.
37 Ni-Ti-O Nanotube Arrays Supported Nano-Ni(OH)2 Electrode for Electrocatalytic Oxidation of Methanol
2018, 47(2):636-641.
Abstract:
Ni-Ti-O nanotube arrays (NTOs) were fabricated by the anodized Ni-Ti alloy and then annealed under hydrogen atmosphere at 500oC for 2hours. The Ni(OH)2/NTOs electrodes were prepared by a convenient impregnating method. The FESEM, XPS and CV will be used to characterize the microstructure, surface electronic states and catalytic performance of Ni(OH)2/NTOs. The effect of the process factors such as impregnation time and concentration of Ni2+ on catalytic activity were investigated. The results show that with prolonging impregnation time and increasing concentration of Ni2+, the catalsty partical size gradually increase and the peak current denstiny firstly increase and then decrese. When the Ni-Ti-O NTs is impregnated in 0.2M NiCl2?6H2O ethanol solution and 0.2M NH4OH ethanol solution 12h in sequence at 25oC,the resulting sample has the best catalytic performance and its peak current density is 38.41 mA?cm-2. Meanwhile, the peak current density of Ni(OH)2/NTOs remain 75% of original value after a consecutive sweep for 1000 times, indicating the excellent lcyclic stability. The Ni(OH)2/NTOs should a promising electrocatalytic electrode for direct methanol fuel cells.
Ni-Ti-O nanotube arrays (NTOs) were fabricated by the anodized Ni-Ti alloy and then annealed under hydrogen atmosphere at 500oC for 2hours. The Ni(OH)2/NTOs electrodes were prepared by a convenient impregnating method. The FESEM, XPS and CV will be used to characterize the microstructure, surface electronic states and catalytic performance of Ni(OH)2/NTOs. The effect of the process factors such as impregnation time and concentration of Ni2+ on catalytic activity were investigated. The results show that with prolonging impregnation time and increasing concentration of Ni2+, the catalsty partical size gradually increase and the peak current denstiny firstly increase and then decrese. When the Ni-Ti-O NTs is impregnated in 0.2M NiCl2?6H2O ethanol solution and 0.2M NH4OH ethanol solution 12h in sequence at 25oC,the resulting sample has the best catalytic performance and its peak current density is 38.41 mA?cm-2. Meanwhile, the peak current density of Ni(OH)2/NTOs remain 75% of original value after a consecutive sweep for 1000 times, indicating the excellent lcyclic stability. The Ni(OH)2/NTOs should a promising electrocatalytic electrode for direct methanol fuel cells.
2018, 47(2):642-646.
Abstract:
The solidus, liquidus and volume of residual liquid were achieved by study the solidification behavior of a sub-eutectiod U-Nb alloy. It is found under metallographic observation that their microstructure reveals as the dentritic crystal connected each other and residual liquid separated by solid phase during terminal solidification. Thus, serious micro-porosity form easily in oisolated residual liquid area for the filling channels plugging and residual liquid unable to fill the pore, and the amount of porosity in casting is about 1.6% derived from theoretical calculation. The chemical analysis results showed that segregation coefficients of niobium at intermediate and terminal solidifaction are 0.16 and 0.11 respectively, which indicated that Nb is a strong negative segregation element and it severely cluster in the dendritic area.
The solidus, liquidus and volume of residual liquid were achieved by study the solidification behavior of a sub-eutectiod U-Nb alloy. It is found under metallographic observation that their microstructure reveals as the dentritic crystal connected each other and residual liquid separated by solid phase during terminal solidification. Thus, serious micro-porosity form easily in oisolated residual liquid area for the filling channels plugging and residual liquid unable to fill the pore, and the amount of porosity in casting is about 1.6% derived from theoretical calculation. The chemical analysis results showed that segregation coefficients of niobium at intermediate and terminal solidifaction are 0.16 and 0.11 respectively, which indicated that Nb is a strong negative segregation element and it severely cluster in the dendritic area.
liuhao
,
Chen Guangchao
,
Du Lingzhong
,
Lan Hao
,
Huang Chuanbing
,
Wang Binli
,
Zhang Huiying
,
Zhang Weigang
2018, 47(2):647-651.
Abstract:
Aimed at the problem of friction and wear of titanium alloy blade in aero-engine compressor, in this paper, we use a technology of composite electroplating combining with the surface activation of the titanium alloy processing, a Ni-cBN composite coating on Ti-6Al-4V(TC4) substrate was successfully prepared with improved bonding strength. The friction and wear properties of the coating with the Ni-based abradable seal coating were studied with high temperature friction and wear test,and the results were compared with the TC4 rub with Ni-based abradable seal coating coating. The experimental results were characterized by scanning electron microscopy (SEM), X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS). The results shown that a well bonded composite coating on the TC4 substrate was obtained after surface activation treatment of titanium alloy matrix. The deposited Ni-cBN composite coating exhibits a very strong grinding ability and low friction coefficient, which provids protection to the titanium alloy tips.
Aimed at the problem of friction and wear of titanium alloy blade in aero-engine compressor, in this paper, we use a technology of composite electroplating combining with the surface activation of the titanium alloy processing, a Ni-cBN composite coating on Ti-6Al-4V(TC4) substrate was successfully prepared with improved bonding strength. The friction and wear properties of the coating with the Ni-based abradable seal coating were studied with high temperature friction and wear test,and the results were compared with the TC4 rub with Ni-based abradable seal coating coating. The experimental results were characterized by scanning electron microscopy (SEM), X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS). The results shown that a well bonded composite coating on the TC4 substrate was obtained after surface activation treatment of titanium alloy matrix. The deposited Ni-cBN composite coating exhibits a very strong grinding ability and low friction coefficient, which provids protection to the titanium alloy tips.
2018, 47(2):652-656.
Abstract:
This paper investigated the damage behavior of AZ31 magnesium alloy plate by numerical simulation method by finite element software DEFORM, which is based on variable gauge rolling. The rolling temperature of magnesium plate is 350℃,the rolling speed is 20r/min and the lateral pre-deformation by vertical roll are 37.5%,75% and 112.5%, respectively. Then the specimens that have been pre-deformation are rolled by flat roll with multi cycles of small reduction or single cycle with a large deformation. The results showed that the variable gauge rolling process can significantly reduce edge damage of rolled magnesium plate. When vertical roll reduction is 75%, the variable gauge rolling process reach the best, and that the maximum edge damage factor is 0.35. Variable gauge rolling process seems to more suitable for large reduction rolling. The maximum damage factor is only 0.126 when vertical reduction is 75% and flat reduction is 49% were combined to produce magnesium plate. The value of vertical roll reduction was related to the initial thickness of magnesium plate.
This paper investigated the damage behavior of AZ31 magnesium alloy plate by numerical simulation method by finite element software DEFORM, which is based on variable gauge rolling. The rolling temperature of magnesium plate is 350℃,the rolling speed is 20r/min and the lateral pre-deformation by vertical roll are 37.5%,75% and 112.5%, respectively. Then the specimens that have been pre-deformation are rolled by flat roll with multi cycles of small reduction or single cycle with a large deformation. The results showed that the variable gauge rolling process can significantly reduce edge damage of rolled magnesium plate. When vertical roll reduction is 75%, the variable gauge rolling process reach the best, and that the maximum edge damage factor is 0.35. Variable gauge rolling process seems to more suitable for large reduction rolling. The maximum damage factor is only 0.126 when vertical reduction is 75% and flat reduction is 49% were combined to produce magnesium plate. The value of vertical roll reduction was related to the initial thickness of magnesium plate.
2018, 47(2):657-661.
Abstract:
The deformation behavior of near-β Ti-5553 alloy under the impact of light gas gun has been studied by optical microscopy (OM) combined with quantitative metallographic analysis, transmission electron microscope (TEM) and X-Ray Diffraction (XRD). The experimental results demonstrated that Ti-5553 alloy deform via dislocation slipping，deformation twinning and stress-induced martensite (SIM) phase transformation. Meanwhile, the amount of SIM is influenced by the velocity of flyer plates by which Ti-5553 alloy was impacted. The amount of SIM increased obviously as the impact velocity increased. Particularly, when the velocity increased from 380m/s to 560m/s, the length of the SIM wire per unit area (LA) increased from 39.18mm/mm2 to 52.65 mm/mm2.
The deformation behavior of near-β Ti-5553 alloy under the impact of light gas gun has been studied by optical microscopy (OM) combined with quantitative metallographic analysis, transmission electron microscope (TEM) and X-Ray Diffraction (XRD). The experimental results demonstrated that Ti-5553 alloy deform via dislocation slipping，deformation twinning and stress-induced martensite (SIM) phase transformation. Meanwhile, the amount of SIM is influenced by the velocity of flyer plates by which Ti-5553 alloy was impacted. The amount of SIM increased obviously as the impact velocity increased. Particularly, when the velocity increased from 380m/s to 560m/s, the length of the SIM wire per unit area (LA) increased from 39.18mm/mm2 to 52.65 mm/mm2.
2018, 47(2):662-666.
Abstract:
Two kinds of BCC and BCC-Z Titanium alloy porous structures were manufactured by selective laser melting, and its feasibility of forming complex porous structures was verified. Then, static compression tests were carried out and the results show that the products always fracture around 45 °. The stress strain curve shows that the tensile strength of the porous structures is greatly reduced, and the peak stress is decreased with the increase of the ratio of length diameter and porosity. In addition, in the case of similar ratios of length diameter and porosity, the ability to bear loads of BCC-Z is significantly higher than that of BCC. Finally, the stress distribution of BCC parts in the process of compression was analyzed by finite element simulation. In view of the stress concentration at the nodes of the unit, the method of node reinforcement was put forward. And the elastic modulus and the yield strength of the porous products are predicted, which fits the experiment results.
Two kinds of BCC and BCC-Z Titanium alloy porous structures were manufactured by selective laser melting, and its feasibility of forming complex porous structures was verified. Then, static compression tests were carried out and the results show that the products always fracture around 45 °. The stress strain curve shows that the tensile strength of the porous structures is greatly reduced, and the peak stress is decreased with the increase of the ratio of length diameter and porosity. In addition, in the case of similar ratios of length diameter and porosity, the ability to bear loads of BCC-Z is significantly higher than that of BCC. Finally, the stress distribution of BCC parts in the process of compression was analyzed by finite element simulation. In view of the stress concentration at the nodes of the unit, the method of node reinforcement was put forward. And the elastic modulus and the yield strength of the porous products are predicted, which fits the experiment results.
2018, 47(2):667-671.
Abstract:
In this paper, the pool boiling heat transfer performances of copper fiber porous materials which were composited with four different fiber diameters (i.e 30μm, 50μm, 100μm and 160μm) and copper plane plate were investigated under the atmospheric pressure. The experiment results show that the heat transfer performances of the copper fiber porous materials with the porosity of 90%, 80% and 75% are much better than that of the Cu plane plate when the superheat is below 20oC. The heat transfer performance of the copper fiber porous materials is enhanced as decreasing the fiber diameter when the porosity of copper fiber felt was 90%. When the fiber diameter is 160μm, the heat transfer performance is enhanced as decreasing porosity of copper fiber felt. There are many factors which can affect the pool boiling heat transfer, such as the number of active evaporation core, the resistance of bubble overflow and the fiber capillary attraction, and so on. Then, there should be different optimal pore structures under different working conditions.
In this paper, the pool boiling heat transfer performances of copper fiber porous materials which were composited with four different fiber diameters (i.e 30μm, 50μm, 100μm and 160μm) and copper plane plate were investigated under the atmospheric pressure. The experiment results show that the heat transfer performances of the copper fiber porous materials with the porosity of 90%, 80% and 75% are much better than that of the Cu plane plate when the superheat is below 20oC. The heat transfer performance of the copper fiber porous materials is enhanced as decreasing the fiber diameter when the porosity of copper fiber felt was 90%. When the fiber diameter is 160μm, the heat transfer performance is enhanced as decreasing porosity of copper fiber felt. There are many factors which can affect the pool boiling heat transfer, such as the number of active evaporation core, the resistance of bubble overflow and the fiber capillary attraction, and so on. Then, there should be different optimal pore structures under different working conditions.
44 The effects of doping additives on the wettability and contact resistance of AgSnO2 contact material
2018, 47(2):672-676.
Abstract:
Wettability reflects the physical properties of AgSnO2 contact materials.Improving the wettability will directly affect the electrical contact performance of AgSnO2 contact materials.What’s more, doping with different additives can alter the wettability of the AgSnO2 contact material . In this paper, TiO2, La2O3, Bi2O3 three kinds of additives were chosen.Each additive was selected from seven different proportions, and the wettability of AgSnO2 contact material was measured.The results showed that the wetting angle of silver to oxide was different from the same time.What’s more,the influence of the same type of additives on the wettability of AgSnO2 contact material has a direct relationship with the addition content.In order to further verify,electrical properties of the contact materials for AgSnO2 and three kinds of additives were tested.The experimental results showed that the variation of contact resistance is basically consistent with the change of wettability.
Wettability reflects the physical properties of AgSnO2 contact materials.Improving the wettability will directly affect the electrical contact performance of AgSnO2 contact materials.What’s more, doping with different additives can alter the wettability of the AgSnO2 contact material . In this paper, TiO2, La2O3, Bi2O3 three kinds of additives were chosen.Each additive was selected from seven different proportions, and the wettability of AgSnO2 contact material was measured.The results showed that the wetting angle of silver to oxide was different from the same time.What’s more,the influence of the same type of additives on the wettability of AgSnO2 contact material has a direct relationship with the addition content.In order to further verify,electrical properties of the contact materials for AgSnO2 and three kinds of additives were tested.The experimental results showed that the variation of contact resistance is basically consistent with the change of wettability.
45 Microstructure and Mechanical Properties of Diffusion Bonded Joint of TC4 Alloy Using Zr Interlayer
2018, 47(2):677-681.
Abstract:
Reliable diffusion bonding of TC4 alloy was achieved using Zr interlayer. The interfacial microstructure was characterized by scanning electron microscopy(SEM), energy dispersive spectrum analysis(EDS) and X-ray diffraction(XRD). Effects of joining parameters on the microsturcture and mechanical propertie s of the joints were investigated. The results indicated that (Ti,Zr) diffusion layer with uniform components transition was formed at the interface of the joint, in which consisted of a large amount of lath-like α′-Ti(titanium martensite). With the increase of bonding temperature and holding time, the thickness of the diffusion layer increased, and the shear strength of the joint increased until the maximum shear strength was reached and then decreased. The maximum shear strength was 190MPa when the joint was bonded at 800℃ for 40min under 5MPa.
Reliable diffusion bonding of TC4 alloy was achieved using Zr interlayer. The interfacial microstructure was characterized by scanning electron microscopy(SEM), energy dispersive spectrum analysis(EDS) and X-ray diffraction(XRD). Effects of joining parameters on the microsturcture and mechanical propertie s of the joints were investigated. The results indicated that (Ti,Zr) diffusion layer with uniform components transition was formed at the interface of the joint, in which consisted of a large amount of lath-like α′-Ti(titanium martensite). With the increase of bonding temperature and holding time, the thickness of the diffusion layer increased, and the shear strength of the joint increased until the maximum shear strength was reached and then decreased. The maximum shear strength was 190MPa when the joint was bonded at 800℃ for 40min under 5MPa.
2018, 47(2):682-686.
Abstract:
Titanium billet surface high temperature oxidation resistant coatings were prepared with Al powder as mainly raw material and Sn powder, SiO2 powder, styrene acrylic emulsion, polyvinyl alcohol, sodium carboxymethyl cellulose as burdening. Subsequently, the coating is sprayed onto the surface of titanium billet, and placed in constant temperature conditions of 1050 ℃ for 8 h, and then in comparison with the surface topography of the flakes with coating or not. The microstructure of the exposed surface and spraying surface analyzed by optical microscope, the coating microstructure and elements diffusion analyzed by field emission scanning electron microscopy and energy spectrum analysis instrument, the interface phase structure analyzed by X- ray diffraction. The results show that titanium billet surface with high temperature oxidation resistant coatings can effectively reduce the thermal processing of titanium billet spalling, the effect of the coating thickness on the thickness of Ti-Al diffusion layer is not significant, the Al2O3-TiAl layers and TiAl3-Ti multilayers co-formed the coating layer, moreover, the excellent coating thickness is about 50 μm .
Titanium billet surface high temperature oxidation resistant coatings were prepared with Al powder as mainly raw material and Sn powder, SiO2 powder, styrene acrylic emulsion, polyvinyl alcohol, sodium carboxymethyl cellulose as burdening. Subsequently, the coating is sprayed onto the surface of titanium billet, and placed in constant temperature conditions of 1050 ℃ for 8 h, and then in comparison with the surface topography of the flakes with coating or not. The microstructure of the exposed surface and spraying surface analyzed by optical microscope, the coating microstructure and elements diffusion analyzed by field emission scanning electron microscopy and energy spectrum analysis instrument, the interface phase structure analyzed by X- ray diffraction. The results show that titanium billet surface with high temperature oxidation resistant coatings can effectively reduce the thermal processing of titanium billet spalling, the effect of the coating thickness on the thickness of Ti-Al diffusion layer is not significant, the Al2O3-TiAl layers and TiAl3-Ti multilayers co-formed the coating layer, moreover, the excellent coating thickness is about 50 μm .
2018, 47(2):687-691.
Abstract:
For further reduction of oxygen, nitrogen and sulphur contents in master alloy GH3625, two vacuum induction remelting experiments (high vacuum without calcium and high vacuum with addition calcium) were carried out. Alloy composition and purity were investigated. The results show that: under high vacuum induction remelting burning loss and enrichment of alloying elements are all in the range of standard composition; deoxidation is excellent under high vacuum induction remelting, O content is reduced from 17ppm to 10ppm by C-O reaction; but removal of nitrogen and sulphur is not obvious; High vacuum induction remelting with addition Ca using Al2O3 Ca-O and Ca-Al2O3 (the inner wall of crucible) reaction is helpful to deep deoxidation, Ca-S reaction makes S content is greatly reduced, reducing nitrogen content is limited, it is far higher than N solubility in alloy GH3625. In Al2O3 crucible, adopting high vacuum melting technology and proper calcium addition amounts, oxygen, nitrogen and sulphur content could be reduced to 6ppm,60ppm and 9ppm respectively.
For further reduction of oxygen, nitrogen and sulphur contents in master alloy GH3625, two vacuum induction remelting experiments (high vacuum without calcium and high vacuum with addition calcium) were carried out. Alloy composition and purity were investigated. The results show that: under high vacuum induction remelting burning loss and enrichment of alloying elements are all in the range of standard composition; deoxidation is excellent under high vacuum induction remelting, O content is reduced from 17ppm to 10ppm by C-O reaction; but removal of nitrogen and sulphur is not obvious; High vacuum induction remelting with addition Ca using Al2O3 Ca-O and Ca-Al2O3 (the inner wall of crucible) reaction is helpful to deep deoxidation, Ca-S reaction makes S content is greatly reduced, reducing nitrogen content is limited, it is far higher than N solubility in alloy GH3625. In Al2O3 crucible, adopting high vacuum melting technology and proper calcium addition amounts, oxygen, nitrogen and sulphur content could be reduced to 6ppm,60ppm and 9ppm respectively.
2018, 47(2):692-696.
Abstract:
Three complexants, maleic acid, sodium citrate and sodium salicylate, were used to modify the activated carbon, using the activated carbon without modification for comparison. And the effects of the complexants on the performance of Pd/C catalysts used for the disproportionation of rosin were analyzed by FTIR，XRD, XPS, and TEM. The results show that the chelating agents deposited on activated carbon have a strong bonding ability with Pd cation, which is beneficial to form a smaller Pd particle, enhancing the utilization ratio of Pd. So the activity of Pd/C catalyst prepared with the modified activated carbon was significantly higher than that of untreated activated carbon.
Three complexants, maleic acid, sodium citrate and sodium salicylate, were used to modify the activated carbon, using the activated carbon without modification for comparison. And the effects of the complexants on the performance of Pd/C catalysts used for the disproportionation of rosin were analyzed by FTIR，XRD, XPS, and TEM. The results show that the chelating agents deposited on activated carbon have a strong bonding ability with Pd cation, which is beneficial to form a smaller Pd particle, enhancing the utilization ratio of Pd. So the activity of Pd/C catalyst prepared with the modified activated carbon was significantly higher than that of untreated activated carbon.
2018, 47(2):697-700.
Abstract:
Using metal fibrous to prepare sound absorption materials, the pore inner this material presented gradient arrangement. The gradient pore structure can be carved up two kinds, porosity gradient structure (PGS) and fiber diameter gradient structure (FGS). In this paper, the sound absorption characteristics of two kinds of these structures were studied. The results indicate that when the thickness higher than 6mm, the porosity of the PGS according to from high to low, can be enhanced the sound absorption performance in the whole frequency range at 50Hz to 6400Hz. But this law is just opposite to the thinner PGS when thickness is about 3mm. The characteristic of the FGS is when the thin fiber ahead the structure (3mm), the sound absorption performance is very well for the thicker structure in whole frequency, and when the thick fiber ahead the structure (≥20mm), the sound absorption performance is very well for the thinner structure in whole frequency. When the thickness at the range from 3mm to 20mm, there is a point of intersection between the sound absorption and frequency curves of the FGS with two kinds of arrange way.
Using metal fibrous to prepare sound absorption materials, the pore inner this material presented gradient arrangement. The gradient pore structure can be carved up two kinds, porosity gradient structure (PGS) and fiber diameter gradient structure (FGS). In this paper, the sound absorption characteristics of two kinds of these structures were studied. The results indicate that when the thickness higher than 6mm, the porosity of the PGS according to from high to low, can be enhanced the sound absorption performance in the whole frequency range at 50Hz to 6400Hz. But this law is just opposite to the thinner PGS when thickness is about 3mm. The characteristic of the FGS is when the thin fiber ahead the structure (3mm), the sound absorption performance is very well for the thicker structure in whole frequency, and when the thick fiber ahead the structure (≥20mm), the sound absorption performance is very well for the thinner structure in whole frequency. When the thickness at the range from 3mm to 20mm, there is a point of intersection between the sound absorption and frequency curves of the FGS with two kinds of arrange way.
Xiong bin
,
Li Xue
,
zheng jibo
,
Li Xining
,
Lu gonghao
,
Wang Zhenmin
,
Ju dongying
,
Makino Akihiro
2018, 47(2):701-704.
Abstract:
Using micro alloy technology, Fe68.4-xCo7.6Si7B10P5C2Crx (x=0, 1, 2, 3) bulk amorphous alloys were prepared. The ribbon and rod samples were prepared by single-roller melt spinning and copper mold casting, respectively. The thermodynamic properties and forming ability of the bulk amorphous alloys were characterized by using XRD, DSC and DTA. Further, the corrosion behaviors of the amorphous alloys were tested in H2SO4 solution by using potentiodynamic polarization method. The experimental results showed that the forming ability of the amorphous alloys increased with the addition of Cr element. Moreover, in the 1N H2SO4 solution, a protective layer rich in Cr elements formed on the surfacr of the alloy because of the addition of Cr element, which can effectively prevent the further corrosion of the material. Therefore, the corrosion resistance was improved significantly
Using micro alloy technology, Fe68.4-xCo7.6Si7B10P5C2Crx (x=0, 1, 2, 3) bulk amorphous alloys were prepared. The ribbon and rod samples were prepared by single-roller melt spinning and copper mold casting, respectively. The thermodynamic properties and forming ability of the bulk amorphous alloys were characterized by using XRD, DSC and DTA. Further, the corrosion behaviors of the amorphous alloys were tested in H2SO4 solution by using potentiodynamic polarization method. The experimental results showed that the forming ability of the amorphous alloys increased with the addition of Cr element. Moreover, in the 1N H2SO4 solution, a protective layer rich in Cr elements formed on the surfacr of the alloy because of the addition of Cr element, which can effectively prevent the further corrosion of the material. Therefore, the corrosion resistance was improved significantly
2018, 47(2):705-710.
Abstract:
Metastable ω phase in near-β titanium alloys is helpful for the precipitation of fine α precipitates, which can affect mechanical properties of these alloys. Therefore, researchers have studied the formation conditions, classification, transformation mechanism and diffraction patterns of the ω phase since it has been found. This article summarized the recent research results about embryonic ω, composition of ω and effects on α phase, which were researched by high resolution transmission electron microscopy and three-dimensional atom probe. On this basis, this paper expounds the current research difficulties and possible development direction.
Metastable ω phase in near-β titanium alloys is helpful for the precipitation of fine α precipitates, which can affect mechanical properties of these alloys. Therefore, researchers have studied the formation conditions, classification, transformation mechanism and diffraction patterns of the ω phase since it has been found. This article summarized the recent research results about embryonic ω, composition of ω and effects on α phase, which were researched by high resolution transmission electron microscopy and three-dimensional atom probe. On this basis, this paper expounds the current research difficulties and possible development direction.
2018, 47(2):711-716.
Abstract:
:The characteristics of iridium and the possible mechanisms of the brittle fracture of pure iridium in room temperature are generally discussed and it also describes the problems exited in the application of pure iridium in ultra-high temperature.The research ideas as well asas-obtained research results on the diversification of iridium alloys athome and abroad are systematically reviewed in this paper. Finally the future development propectsof iridium alloys used in the ultra-high temperature are presentedand it also point out the research directionsin the future.
:The characteristics of iridium and the possible mechanisms of the brittle fracture of pure iridium in room temperature are generally discussed and it also describes the problems exited in the application of pure iridium in ultra-high temperature.The research ideas as well asas-obtained research results on the diversification of iridium alloys athome and abroad are systematically reviewed in this paper. Finally the future development propectsof iridium alloys used in the ultra-high temperature are presentedand it also point out the research directionsin the future.
