Volume 51,Issue 4,2022 Table of Contents
2022, 51(4):1145-1151.
DOI: 10.12442/j.issn.1002-185X.20210171
Abstract:
The evolution of deformation behavior and microtexture in one pass cold Pilgering process was investigated. Results show that during cold Pilgering, the {10
The evolution of deformation behavior and microtexture in one pass cold Pilgering process was investigated. Results show that during cold Pilgering, the {10
2 Preparation of Powder Metallurgy Titanium Alloy with Bimodal Structure of High Mechanical Properties
2022, 51(4):1152-1157.
DOI: 10.12442/j.issn.1002-185X.E20210030
Abstract:
Powder metallurgy (PM) Ti6Al4V alloy with a relative density of 99% was prepared by low temperature vacuum sintering using fine Ti6Al4V powder. To eliminate porosity and control the microstructure morphology, forging was performed. The results show that microstructure of as-forged samples is bimodal structure with long lath primary α and α+β lamellae. The as-forged samples show tensile properties with ultimate tensile strength (UTS) of 1176 MPa, yield strength (YS) of 1100 MPa, elongation (EL) of 18.2%, and good low-cycle fatigue life. The as-forged PM Ti6Al4V has good fatigue performance with more than 105 cycles under the stress of 700 MPa. In order to explore the reasons for good fatigue properties, in-situ observation tests were carried out. It is found that the long lath primary α structure can effectively prevent the crack propagation in the steady propagation stage and prolong the fatigue life. Besides, fully dense structure decreases the fatigue crack initiation. Thus, the bimodal structure shows excellently comprehensive mechanical properties.
Powder metallurgy (PM) Ti6Al4V alloy with a relative density of 99% was prepared by low temperature vacuum sintering using fine Ti6Al4V powder. To eliminate porosity and control the microstructure morphology, forging was performed. The results show that microstructure of as-forged samples is bimodal structure with long lath primary α and α+β lamellae. The as-forged samples show tensile properties with ultimate tensile strength (UTS) of 1176 MPa, yield strength (YS) of 1100 MPa, elongation (EL) of 18.2%, and good low-cycle fatigue life. The as-forged PM Ti6Al4V has good fatigue performance with more than 105 cycles under the stress of 700 MPa. In order to explore the reasons for good fatigue properties, in-situ observation tests were carried out. It is found that the long lath primary α structure can effectively prevent the crack propagation in the steady propagation stage and prolong the fatigue life. Besides, fully dense structure decreases the fatigue crack initiation. Thus, the bimodal structure shows excellently comprehensive mechanical properties.
2022, 51(4):1158-1163.
DOI: 10.12442/j.issn.1002-185X.20210074
Abstract:
After commercially pure titanium (CP-Ti) annealed sheet was cold-rolled to 9% reduction, electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) were employed to evaluate activated slip and twin in the samples. Meanwhile, the activation of slip systems in deformed grains and the interaction between grains were simulated by reaction stress (RS) model, in which the plastic deformation process in a grain was regarded as a combined consequence of external stress and statistically varied intergranular reaction stress. The results indicate that the reaction stress model is suitable to estimate the deformation behavior of polycrystalline titanium. The model predicts slip occurring in deformed titanium grains, which is confirmed by experimental data. The distribution of slip and twin in deformed grains is non-uniform, connecting to uneven in-grain strain distribution. This uneven in-grain strain can also be generated by deformation of adjacent grains with different crystal orientations. When the plastic deformation in a grain shows significant difference from that of its neighboring grain, additional local slips are triggered to decrease the strain inconsistency. The plastic strain is realized by mechanical twinning in some cases, which combines with the active slips to satisfy in-grain and intergranular strain consistency.
After commercially pure titanium (CP-Ti) annealed sheet was cold-rolled to 9% reduction, electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) were employed to evaluate activated slip and twin in the samples. Meanwhile, the activation of slip systems in deformed grains and the interaction between grains were simulated by reaction stress (RS) model, in which the plastic deformation process in a grain was regarded as a combined consequence of external stress and statistically varied intergranular reaction stress. The results indicate that the reaction stress model is suitable to estimate the deformation behavior of polycrystalline titanium. The model predicts slip occurring in deformed titanium grains, which is confirmed by experimental data. The distribution of slip and twin in deformed grains is non-uniform, connecting to uneven in-grain strain distribution. This uneven in-grain strain can also be generated by deformation of adjacent grains with different crystal orientations. When the plastic deformation in a grain shows significant difference from that of its neighboring grain, additional local slips are triggered to decrease the strain inconsistency. The plastic strain is realized by mechanical twinning in some cases, which combines with the active slips to satisfy in-grain and intergranular strain consistency.
4 Microstructure and Arc Erosion Behavior of AgSnO2TiB2 Contact Material Prepared by Different Methods
Liu Yanfeng
,
Wang Xianhui
,
He Xuan
,
Wan Mengyu
,
Su Yaning
,
Chi Xiaotong
,
Chen Tingting
,
Miao Yu
,
Wang Lizhao
2022, 51(4):1164-1171.
DOI: 10.12442/j.issn.1002-185X.E20210031
Abstract:
The AgSnO2TiB2 composite powders were synthesized by the ball milling, soluble starch template and filter paper template methods, and subsequently consolidated by spark plasma sintering (SPS). The physical properties and arc erosion behavior of Ag4wt%- SnO24wt%TiB2 contact materials were investigated. The results reveal that the spatial domain-limiting effects of the template can remarkably improve the dispersion of the reinforcements in the Ag matrix, and then electrical conductivity and hardness of Ag4wt%-SnO24wt%TiB2 contact materials are increased. As compared to the ball milling, the electrical conductivity of Ag4wt%SnO24wt%TiB2 composites fabricated by filter paper template and starch template method is increased by 12.18 and 9.60 times, while the microhardness is increased by 17.10% and 33.94%, respectively. The filter paper template is more beneficial for the uniform dispersion of SnO2 and TiB2, which can alleviate concentrated arc erosion and reduce splash, thereby exhibiting better arc erosion resistance.
The AgSnO2TiB2 composite powders were synthesized by the ball milling, soluble starch template and filter paper template methods, and subsequently consolidated by spark plasma sintering (SPS). The physical properties and arc erosion behavior of Ag4wt%- SnO24wt%TiB2 contact materials were investigated. The results reveal that the spatial domain-limiting effects of the template can remarkably improve the dispersion of the reinforcements in the Ag matrix, and then electrical conductivity and hardness of Ag4wt%-SnO24wt%TiB2 contact materials are increased. As compared to the ball milling, the electrical conductivity of Ag4wt%SnO24wt%TiB2 composites fabricated by filter paper template and starch template method is increased by 12.18 and 9.60 times, while the microhardness is increased by 17.10% and 33.94%, respectively. The filter paper template is more beneficial for the uniform dispersion of SnO2 and TiB2, which can alleviate concentrated arc erosion and reduce splash, thereby exhibiting better arc erosion resistance.
2022, 51(4):1172-1182.
DOI: 10.12442/j.issn.1002-185X.20210102
Abstract:
To study the impacting mechanism of variable polarity frequency (VPF) on the weld pool stability in variable polarity plasma arc welding (VPPAW), the thermal-mechanical coupling process of the keyhole weld pool was analyzed by a variable-polarity finite element model. The model was developed based on the computational fluid dynamics (CFD), which can realize the periodic variation of thermal and mechanical effects of variable polarity arc on the weld pool. Moreover, in order to more accurately express the heat and force distribution on the keyhole boundary along the keyhole depth, the secondary compression effect of the keyhole on heat flux and arc pressure was taken into account. The thermal-mechanical “oscillations intensity” on the keyhole boundary and the force balance of the molten bridge were compared at different VPFs. The results show that the “oscillation intensity” of the arc pressure, heat flux and the flow velocity on the keyhole boundary decreases with increasing the VPFs during the keyhole formation. In addition, the variation of the temperature field in the weld pool caused by different thermal-mechanical oscillations results in the change of surface tension and the force balance condition of the molten bridge is changed, which affects the keyhole weld pool stability. When the VPFs are more than 33 and less than 83 and the duty radio of current in EP phase is 1/5, the thermal-mechanical “oscillations intensity” on the keyhole boundary is weak, and the molten bridge can stay force balance in the critical state of being penetrated, so the weld pool can maintain stable. When the VPFs are less than 33, the “oscillations intensity” is strong and the force balance of the molten bridge is broken, and the weld tends to be cut. If the VPFs are more than 83, the weld pool is unstable due to the broken force balance of the molten bridge although the “oscillations intensity” is weak. Finally, the accuracy of the developed model was verified by the comparison of the fusion zone, the keyhole penetration time and keyhole dimensions on the backside of the weld.
To study the impacting mechanism of variable polarity frequency (VPF) on the weld pool stability in variable polarity plasma arc welding (VPPAW), the thermal-mechanical coupling process of the keyhole weld pool was analyzed by a variable-polarity finite element model. The model was developed based on the computational fluid dynamics (CFD), which can realize the periodic variation of thermal and mechanical effects of variable polarity arc on the weld pool. Moreover, in order to more accurately express the heat and force distribution on the keyhole boundary along the keyhole depth, the secondary compression effect of the keyhole on heat flux and arc pressure was taken into account. The thermal-mechanical “oscillations intensity” on the keyhole boundary and the force balance of the molten bridge were compared at different VPFs. The results show that the “oscillation intensity” of the arc pressure, heat flux and the flow velocity on the keyhole boundary decreases with increasing the VPFs during the keyhole formation. In addition, the variation of the temperature field in the weld pool caused by different thermal-mechanical oscillations results in the change of surface tension and the force balance condition of the molten bridge is changed, which affects the keyhole weld pool stability. When the VPFs are more than 33 and less than 83 and the duty radio of current in EP phase is 1/5, the thermal-mechanical “oscillations intensity” on the keyhole boundary is weak, and the molten bridge can stay force balance in the critical state of being penetrated, so the weld pool can maintain stable. When the VPFs are less than 33, the “oscillations intensity” is strong and the force balance of the molten bridge is broken, and the weld tends to be cut. If the VPFs are more than 83, the weld pool is unstable due to the broken force balance of the molten bridge although the “oscillations intensity” is weak. Finally, the accuracy of the developed model was verified by the comparison of the fusion zone, the keyhole penetration time and keyhole dimensions on the backside of the weld.
2022, 51(4):1183-1187.
DOI: 10.12442/j.issn.1002-185X.20210153
Abstract:
To reveal the dislocation evolution law of 7A85 aluminum alloy during the aging process, the influences of aging temperature and aging time on dislocation density was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the dislocation density is reduced rapidly from 3.59×1014 m-2 to 0.62×1014 m-2 (decreased by 82.7%) when the aging temperature increases from 80 °C to 160 °C. Similarly, the dislocation density is decreased by 41% with the extension of aging time, and it tends to a steady value after aging treatment for 12 h. Furthermore, the TEM micrographs indicate that dislocations tend to form a low-energy dislocation cell and gradually turn into subgrain. Finally, on the basis of the results of XRD and TEM, the dislocation densities of dislocation entanglement, dislocation cell and subgrain were quantified.
To reveal the dislocation evolution law of 7A85 aluminum alloy during the aging process, the influences of aging temperature and aging time on dislocation density was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the dislocation density is reduced rapidly from 3.59×1014 m-2 to 0.62×1014 m-2 (decreased by 82.7%) when the aging temperature increases from 80 °C to 160 °C. Similarly, the dislocation density is decreased by 41% with the extension of aging time, and it tends to a steady value after aging treatment for 12 h. Furthermore, the TEM micrographs indicate that dislocations tend to form a low-energy dislocation cell and gradually turn into subgrain. Finally, on the basis of the results of XRD and TEM, the dislocation densities of dislocation entanglement, dislocation cell and subgrain were quantified.
2022, 51(4):1188-1194.
DOI: 10.12442/j.issn.1002-185X.20210126
Abstract:
Three kinds of WC-17Co powders with different densities were selected as starting material, and a coating with 0.3 mm in thickness was prepared by high velocity oxygen fuel (HVOF) method. The porosity of the three coatings was analyzed by SEM, the Knoop hardness and Young's modulus of the coatings were measured by indentation method. At the same time, the residual stress of the WC-17Co coating prepared by powders with different densities was measured by layer-stripping method. Results show that the porosity level of the coatings increases with increasing WC-17Co powder density, while the Knoop hardness and Young's modulus of the coatings decrease with the increase of powder density. The residual stress existing in the WC-17Co coating appears as compressive stress, which increases with the increase of the coating depth, and then decreases rapidly near the coating-substrate interface. The maximum residual stresses of the coatings deposited with powder density of 11.52, 12.86 and 13.49 g·cm-3 are -798, -986 and -1120 MPa, respectively.
Three kinds of WC-17Co powders with different densities were selected as starting material, and a coating with 0.3 mm in thickness was prepared by high velocity oxygen fuel (HVOF) method. The porosity of the three coatings was analyzed by SEM, the Knoop hardness and Young's modulus of the coatings were measured by indentation method. At the same time, the residual stress of the WC-17Co coating prepared by powders with different densities was measured by layer-stripping method. Results show that the porosity level of the coatings increases with increasing WC-17Co powder density, while the Knoop hardness and Young's modulus of the coatings decrease with the increase of powder density. The residual stress existing in the WC-17Co coating appears as compressive stress, which increases with the increase of the coating depth, and then decreases rapidly near the coating-substrate interface. The maximum residual stresses of the coatings deposited with powder density of 11.52, 12.86 and 13.49 g·cm-3 are -798, -986 and -1120 MPa, respectively.
2022, 51(4):1195-1202.
DOI: 10.12442/j.issn.1002-185X.20210165
Abstract:
To improve the bonding strength of the chromium-doped diamond-like carbon (Cr-DLC ) films on the surface of the copper alloy, multilayer structure films of Cr/CrN/Cr-DLC with different thickness of Cr interlayer were designed and prepared on the copper alloy samples by magnetron sputtering and plasma enhanced chemical vapor deposition. The microstructure, residual stress, nanohardness, elastic modulus, bonding strength and impact toughness of the film were tested by high-resolution Raman spectrometer, film stress meter, nanoindenter, scratch tester and repetitive impact tester. The results show that the residual stress of Cr-DLC film on the surface of copper alloy decreases from -1.92 GPa to -0.47 GPa with increasing the thickness of Cr interlayer, reduced by 75.5%. When the thickness of Cr interlayer reaches 1.01 μm, the bonding strength between the Cr-DLC film and the substrate is the best, which is 69% and 67% higher than the first (Lc1) and the second (Lc2) critical loads of Cr-DLC film without Cr adhesive layer, respectively. After 20 000 times of repetitive impact tests, there is no elastic recovery in the impact depth for all Cr-DLC coated samples, and exfoliation of a certain area for the film is observed at the center of the impact pit. Among all samples, Cr-DLC coated sample with Cr interlayer of 1.01 μm in thickness has the smallest peeling area, and shows the best performance of repetitive impact resistance. Therefore, Cr interlayer with a certain thickness can significantly reduce the residual stress of the Cr-DLC film while improve the bonding strength and repetitive impact resistance.
To improve the bonding strength of the chromium-doped diamond-like carbon (Cr-DLC ) films on the surface of the copper alloy, multilayer structure films of Cr/CrN/Cr-DLC with different thickness of Cr interlayer were designed and prepared on the copper alloy samples by magnetron sputtering and plasma enhanced chemical vapor deposition. The microstructure, residual stress, nanohardness, elastic modulus, bonding strength and impact toughness of the film were tested by high-resolution Raman spectrometer, film stress meter, nanoindenter, scratch tester and repetitive impact tester. The results show that the residual stress of Cr-DLC film on the surface of copper alloy decreases from -1.92 GPa to -0.47 GPa with increasing the thickness of Cr interlayer, reduced by 75.5%. When the thickness of Cr interlayer reaches 1.01 μm, the bonding strength between the Cr-DLC film and the substrate is the best, which is 69% and 67% higher than the first (Lc1) and the second (Lc2) critical loads of Cr-DLC film without Cr adhesive layer, respectively. After 20 000 times of repetitive impact tests, there is no elastic recovery in the impact depth for all Cr-DLC coated samples, and exfoliation of a certain area for the film is observed at the center of the impact pit. Among all samples, Cr-DLC coated sample with Cr interlayer of 1.01 μm in thickness has the smallest peeling area, and shows the best performance of repetitive impact resistance. Therefore, Cr interlayer with a certain thickness can significantly reduce the residual stress of the Cr-DLC film while improve the bonding strength and repetitive impact resistance.
2022, 51(4):1203-1210.
DOI: 10.12442/j.issn.1002-185X.20210095
Abstract:
Effects of doping single Al, Zn, Cu, Ni, Li, and Zr atoms on interfacial bonding in the 3C-SiC/Mg system were studied using the first-principles method based on density functional theory. The Mulliken charge, overlapping population and density of states of representative Zn and Zr atoms were calculated and analyzed. Results show that the most stable stacking structure of the 3C-SiC/Mg interface model is that 5-layer Mg(0001) is stacked on the 10-layer 3C-SiC(111) surface. Among the six 3C-SiC/Mg model structures, the C-terminated center site model has the largest separation energy, the smallest interfacial spacing and the best interfacial wettability. After doping with Zn atom, Zn and Mg atoms are in the anti-bonding state, resulting in the decrease of the separation work of the 3C-SiC/Mg-Zn system. The decrease of the pseudo-energy gap in the density of states weakens the covalent bond in the 3C-SiC/Mg-Zn system, and this is not conducive to interfacial bonding in the 3C-SiC/Mg-Zn system. After doping with Al, Cu, Ni, Li, and Zr atoms, the separation work of the system increases, and Zr has the best effect on improving the interfacial wettability. After doping with Zr, the anti-bonding state of Mg and Si atoms disappears, and a strong Zr-C covalent bond is formed at the interface between the Zr atom and C atom. The delocalization of the density of states increases, and the bonding ability is enhanced, resulting in a maximum increase in the separation work of the 3C-SiC/Mg-Zr system.
Effects of doping single Al, Zn, Cu, Ni, Li, and Zr atoms on interfacial bonding in the 3C-SiC/Mg system were studied using the first-principles method based on density functional theory. The Mulliken charge, overlapping population and density of states of representative Zn and Zr atoms were calculated and analyzed. Results show that the most stable stacking structure of the 3C-SiC/Mg interface model is that 5-layer Mg(0001) is stacked on the 10-layer 3C-SiC(111) surface. Among the six 3C-SiC/Mg model structures, the C-terminated center site model has the largest separation energy, the smallest interfacial spacing and the best interfacial wettability. After doping with Zn atom, Zn and Mg atoms are in the anti-bonding state, resulting in the decrease of the separation work of the 3C-SiC/Mg-Zn system. The decrease of the pseudo-energy gap in the density of states weakens the covalent bond in the 3C-SiC/Mg-Zn system, and this is not conducive to interfacial bonding in the 3C-SiC/Mg-Zn system. After doping with Al, Cu, Ni, Li, and Zr atoms, the separation work of the system increases, and Zr has the best effect on improving the interfacial wettability. After doping with Zr, the anti-bonding state of Mg and Si atoms disappears, and a strong Zr-C covalent bond is formed at the interface between the Zr atom and C atom. The delocalization of the density of states increases, and the bonding ability is enhanced, resulting in a maximum increase in the separation work of the 3C-SiC/Mg-Zr system.
2022, 51(4):1211-1217.
DOI: 10.12442/j.issn.1002-185X.20210068
Abstract:
Planar flow casting (PFC) is an advanced technology to produce amorphous and nanocrystalline ribbons in electrical application. One of the major challenges of this technology is not only to have a rapid cooling rate to suppress the crystallization but also to achieve a high surface quality of ribbons. A new way to predict the fluid flow fields and heat transfer coefficient distribution of two types of single-roll cooling structures which are widely used in industrial production was proposed, i. e. 3-D time-independent steady simulation models. The flow velocity distribution of the two types of structures was calculated by software FLUENT, combined with energy and momentum equations. Additionally, the convective heat transfer coefficient distribution of the two structures was predicated. The results show that the velocity distribution of the roller with a water channel structure (WCS) is neither uniform nor periodic, and that of the roller with a water gap structure (WGS) is not uniform but periodic. The convective heat transfer coefficient distribution of the two kinds of rollers is not centrally symmetric, and the cooling feature of WGS roller is more regular. Three appropriate zones with symmetric distribution were predicated for a WGS roller, which was verified by the succeeding times of continuous production of ribbons. According to the thermal equilibrium principle, the heat transfer process of PFC technology was also described. These data suggest that uniform distribution of convective heat transfer coefficient can be one of the criterions to design the structure of cooling roller.
Planar flow casting (PFC) is an advanced technology to produce amorphous and nanocrystalline ribbons in electrical application. One of the major challenges of this technology is not only to have a rapid cooling rate to suppress the crystallization but also to achieve a high surface quality of ribbons. A new way to predict the fluid flow fields and heat transfer coefficient distribution of two types of single-roll cooling structures which are widely used in industrial production was proposed, i. e. 3-D time-independent steady simulation models. The flow velocity distribution of the two types of structures was calculated by software FLUENT, combined with energy and momentum equations. Additionally, the convective heat transfer coefficient distribution of the two structures was predicated. The results show that the velocity distribution of the roller with a water channel structure (WCS) is neither uniform nor periodic, and that of the roller with a water gap structure (WGS) is not uniform but periodic. The convective heat transfer coefficient distribution of the two kinds of rollers is not centrally symmetric, and the cooling feature of WGS roller is more regular. Three appropriate zones with symmetric distribution were predicated for a WGS roller, which was verified by the succeeding times of continuous production of ribbons. According to the thermal equilibrium principle, the heat transfer process of PFC technology was also described. These data suggest that uniform distribution of convective heat transfer coefficient can be one of the criterions to design the structure of cooling roller.
2022, 51(4):1218-1225.
DOI: 10.12442/j.issn.1002-185X.20210466
Abstract:
The finite element method (FEM) was used to simulate and to verify the axisymmetric nanoindentation response of a transversely isotropic piezoelectric ceramics by a conductive rigid flat indenter from half-space to thin film. The cylindrical, flat indenter without prescribed electric force was adopted to mechanically load the piezoelectric ceramics. The results show that the linear relationship between indentation load and indentation displacement is obtained. And the same relationship is obtained between electric potential and indentation displacement. In addition, resultant mechanoelectrical responses were analyzed. The simulation results indicate that the contact stress and electric field exhibit singularities round the edge of the indenter. Both stress and electric field singularities vary exponentially with respect to the thickness of the solids under the indenter. At the same time, the normal stress and electric potential distributions of the direct piezoelectric effects are given. Through the fitting formula of the normal stress, normal electric potential and tangential electric potential from the indentation interior to the contact edge under different indentation depths, the singular constants of electric field and stress field under different thickness of piezoelectric ceramics are proposed, and their variation rules are analyzed.
The finite element method (FEM) was used to simulate and to verify the axisymmetric nanoindentation response of a transversely isotropic piezoelectric ceramics by a conductive rigid flat indenter from half-space to thin film. The cylindrical, flat indenter without prescribed electric force was adopted to mechanically load the piezoelectric ceramics. The results show that the linear relationship between indentation load and indentation displacement is obtained. And the same relationship is obtained between electric potential and indentation displacement. In addition, resultant mechanoelectrical responses were analyzed. The simulation results indicate that the contact stress and electric field exhibit singularities round the edge of the indenter. Both stress and electric field singularities vary exponentially with respect to the thickness of the solids under the indenter. At the same time, the normal stress and electric potential distributions of the direct piezoelectric effects are given. Through the fitting formula of the normal stress, normal electric potential and tangential electric potential from the indentation interior to the contact edge under different indentation depths, the singular constants of electric field and stress field under different thickness of piezoelectric ceramics are proposed, and their variation rules are analyzed.
2022, 51(4):1226-1230.
DOI: 10.12442/j.issn.1002-185X.20210120
Abstract:
In order to solve the problem of fracture and large springback during the bending forming of Al-Li alloy, the bending forming process under the compound energy-field (CEF) of temperature and ultrasonic vibration was studied. It is expected to reduce the temperature required for bending forming of Al-Li alloy with the help of ultrasonic vibration energy-field while maintaining the forming quality. The research was carried out by combining with ultrasonic vibration energy of 1.0~1.6 kW under the temperature conditions of 80~200 °C. The effects of CEF on the bending force, springback, bending fillet radius and microstructure of 2195 Al-Li alloy sheets were analyzed. The results show that at a relatively low temperature for hot forming, the bending force can be reduced by combining with ultrasonic vibration energy-field. The springback and fracture are effectively inhibited, thus improving the high temperature softening effect and bending properties of 2195 Al-Li alloy.
In order to solve the problem of fracture and large springback during the bending forming of Al-Li alloy, the bending forming process under the compound energy-field (CEF) of temperature and ultrasonic vibration was studied. It is expected to reduce the temperature required for bending forming of Al-Li alloy with the help of ultrasonic vibration energy-field while maintaining the forming quality. The research was carried out by combining with ultrasonic vibration energy of 1.0~1.6 kW under the temperature conditions of 80~200 °C. The effects of CEF on the bending force, springback, bending fillet radius and microstructure of 2195 Al-Li alloy sheets were analyzed. The results show that at a relatively low temperature for hot forming, the bending force can be reduced by combining with ultrasonic vibration energy-field. The springback and fracture are effectively inhibited, thus improving the high temperature softening effect and bending properties of 2195 Al-Li alloy.
2022, 51(4):1231-1238.
DOI: 10.12442/j.issn.1002-185X.20210134
Abstract:
A series of SrO-modified Pd-Rh/Al2O3 catalysts were synthesized by co-impregnation technique, i.e., Sr precursor was introduced into the mixed salt solution of Pd and Rh prior to their impregnation on Al2O3 powders. The results reveal that owing to the diffusion barrier effect of SrO, the introduction of appropriate amount of SrO (1wt%~2wt%) can increase the dispersion of Pd and Rh, as well as improve the hydrothermal stability of the catalyst. After hydrothermal aging treatment, higher dispersion and more active oxidation state of Pd and Rh are maintained. Consequently, modified reduction capability and improved three-way catalytic performance can be obtained for the appropriate SrO-modified Pd-Rh/Al2O3 catalyst. However, when excessive amount of SrO is introduced, plenty of surface sites on Al2O3 support will be occupied, and new SrAl2O4 phase is generated, leading to adverse effect instead. To sum up, the catalyst modified by 2wt% SrO exhibits the best three-way catalytic performance, by which after hydrothermal aging treatment, the light-off temperatures of CO, HC and NO are 23, 15 and 27 °C lower than those by bare Pd-Rh/Al2O3 catalyst.
A series of SrO-modified Pd-Rh/Al2O3 catalysts were synthesized by co-impregnation technique, i.e., Sr precursor was introduced into the mixed salt solution of Pd and Rh prior to their impregnation on Al2O3 powders. The results reveal that owing to the diffusion barrier effect of SrO, the introduction of appropriate amount of SrO (1wt%~2wt%) can increase the dispersion of Pd and Rh, as well as improve the hydrothermal stability of the catalyst. After hydrothermal aging treatment, higher dispersion and more active oxidation state of Pd and Rh are maintained. Consequently, modified reduction capability and improved three-way catalytic performance can be obtained for the appropriate SrO-modified Pd-Rh/Al2O3 catalyst. However, when excessive amount of SrO is introduced, plenty of surface sites on Al2O3 support will be occupied, and new SrAl2O4 phase is generated, leading to adverse effect instead. To sum up, the catalyst modified by 2wt% SrO exhibits the best three-way catalytic performance, by which after hydrothermal aging treatment, the light-off temperatures of CO, HC and NO are 23, 15 and 27 °C lower than those by bare Pd-Rh/Al2O3 catalyst.
14 Microstructure and Magnetocaloric Effect of Spark Plasma Sintered LaFeSi Magnets with LaAl Addition
2022, 51(4):1239-1244.
DOI: 10.12442/j.issn.1002-185X.20210069
Abstract:
Using LaFe11.3Si1.7 and La0.77Al0.23 alloys as precursors, the bulk LaFeSi samples with excellent magnetocaloric performance were synthesized through the spark plasma sintering (SPS) technology. The results show that the La0.77Al0.23 compound with a low melting point is helpful in facilitating peritectic reaction, and NaZn13-type phase with high content can be achieved. A slight itinerant-electron-metamagnetic transition is observed. The increased thermal annealing time facilitates magnetic transition from the first order to the second order, which is ascribed to the excessive Al diffusion into the 1:13 phase. Under the thermal treatment condition of 1000 °C/6 h, the maximum entropy change (-ΔSM) max of 12.40 J?kg-1?K-1 can be obtained, and the highest refrigerating capacity, up to 318.40 J?kg-1, is achieved under thermal annealing condition of 1000 °C/10 h.
Using LaFe11.3Si1.7 and La0.77Al0.23 alloys as precursors, the bulk LaFeSi samples with excellent magnetocaloric performance were synthesized through the spark plasma sintering (SPS) technology. The results show that the La0.77Al0.23 compound with a low melting point is helpful in facilitating peritectic reaction, and NaZn13-type phase with high content can be achieved. A slight itinerant-electron-metamagnetic transition is observed. The increased thermal annealing time facilitates magnetic transition from the first order to the second order, which is ascribed to the excessive Al diffusion into the 1:13 phase. Under the thermal treatment condition of 1000 °C/6 h, the maximum entropy change (-ΔSM) max of 12.40 J?kg-1?K-1 can be obtained, and the highest refrigerating capacity, up to 318.40 J?kg-1, is achieved under thermal annealing condition of 1000 °C/10 h.
2022, 51(4):1245-1252.
DOI: 10.12442/j.issn.1002-185X.20210166
Abstract:
The thermal behavior of Al2O3/NH4HF2 mixtures with different mass ratios of NH4HF2:Al2O3 were analyzed by simultaneous thermogravimetry and differential thermal analysis (TG-DTA) and the critical temperature of DTA curve were determined. The morphologies and phases of the products obtained by direct thermal treatment before and after each critical temperature were further analyzed. The results show that the mass ratio has no influence on the critical reaction temperature and processes. The fluorination starts at room temperature with the formation of (NH4)3AlF6, which dominates at 162.3~162.8 °C and is completed around 180 °C. After further heat-treatment, (NH4)3AlF6 decomposes sequentially through a two-step decomposition reac-tion with the formation of NH4AlF4 at 249.8~250.1 °C and finally decomposes to β-AlF3 at 356.8~357.7 °C. The transformation of β-AlF3 to α-AlF3 occurs at 400~650 °C.
The thermal behavior of Al2O3/NH4HF2 mixtures with different mass ratios of NH4HF2:Al2O3 were analyzed by simultaneous thermogravimetry and differential thermal analysis (TG-DTA) and the critical temperature of DTA curve were determined. The morphologies and phases of the products obtained by direct thermal treatment before and after each critical temperature were further analyzed. The results show that the mass ratio has no influence on the critical reaction temperature and processes. The fluorination starts at room temperature with the formation of (NH4)3AlF6, which dominates at 162.3~162.8 °C and is completed around 180 °C. After further heat-treatment, (NH4)3AlF6 decomposes sequentially through a two-step decomposition reac-tion with the formation of NH4AlF4 at 249.8~250.1 °C and finally decomposes to β-AlF3 at 356.8~357.7 °C. The transformation of β-AlF3 to α-AlF3 occurs at 400~650 °C.
2022, 51(4):1253-1262.
DOI: 10.12442/j.issn.1002-185X.20210180
Abstract:
High-performance Nd-Fe-B magnets are widely needed in various fields. The purpose of studying Nd-Fe-B nanometer magnetic powder is that the coercivity of the powdered magnets is the largest at the single domain size. The preparation of nanoparticles by the chemical method can better control the microstructure and grain size. Moreover, metal salts as precursors and simplified process routes can significantly reduce costs and energy consumption. In this review, several popular chemical methods for synthesizing Nd-Fe-B nanoparticles were reported, including sol-gel, auto-combustion, microwave-assisted combustion, thermal decomposition, and mechanochemical method. The preparation process and reaction mechanism of these methods were discussed. Finally, the relationship between microstructure and magnetic properties of Nd-Fe-B nanoparticles prepared by different chemical methods was summarized and some future trends and perspectives in the magnetic research areas were submitted.
High-performance Nd-Fe-B magnets are widely needed in various fields. The purpose of studying Nd-Fe-B nanometer magnetic powder is that the coercivity of the powdered magnets is the largest at the single domain size. The preparation of nanoparticles by the chemical method can better control the microstructure and grain size. Moreover, metal salts as precursors and simplified process routes can significantly reduce costs and energy consumption. In this review, several popular chemical methods for synthesizing Nd-Fe-B nanoparticles were reported, including sol-gel, auto-combustion, microwave-assisted combustion, thermal decomposition, and mechanochemical method. The preparation process and reaction mechanism of these methods were discussed. Finally, the relationship between microstructure and magnetic properties of Nd-Fe-B nanoparticles prepared by different chemical methods was summarized and some future trends and perspectives in the magnetic research areas were submitted.
2022, 51(4):1263-1269.
DOI: 10.12442/j.issn.1002-185X.E20210003
Abstract:
Gasar, which is based on the gap of gas solubility between liquid and solid metals, is a revolutionary process for fabricating porous metal. Recently, the research on fabricating porous alloys with ordered pore structure, has been one of the most popular topics and technical issues concerning the application of Gasar porous metals. The main reasons for difficulties in controlling the ordered porous structure include the influence of the “mushy zone” at the front of the interface during the solidification of the alloy, and the fact that after alloying elements are added, the solid-liquid interface becomes unstable and the solidification mode changes. Preliminary researches mainly focused on reducing the influence of the above two factors on the directional growth of pores from the following two perspectives: preparation technology improvement and alloy composition design (micro-alloying). This study reviewed the research progress of Gasar porous alloys based on the development of preparation techniques (mould casting technique→continuous zone melting technique→continuous casting technique), summarized the main factors that affect pore structure of porous alloys, and analyzed the shortcomings and development trends of future research.
Gasar, which is based on the gap of gas solubility between liquid and solid metals, is a revolutionary process for fabricating porous metal. Recently, the research on fabricating porous alloys with ordered pore structure, has been one of the most popular topics and technical issues concerning the application of Gasar porous metals. The main reasons for difficulties in controlling the ordered porous structure include the influence of the “mushy zone” at the front of the interface during the solidification of the alloy, and the fact that after alloying elements are added, the solid-liquid interface becomes unstable and the solidification mode changes. Preliminary researches mainly focused on reducing the influence of the above two factors on the directional growth of pores from the following two perspectives: preparation technology improvement and alloy composition design (micro-alloying). This study reviewed the research progress of Gasar porous alloys based on the development of preparation techniques (mould casting technique→continuous zone melting technique→continuous casting technique), summarized the main factors that affect pore structure of porous alloys, and analyzed the shortcomings and development trends of future research.
2022, 51(4):1270-1282.
DOI: 10.12442/j.issn.1002-185X.20210840
Abstract:
SiC particle-reinforced aluminum matrix composites have high specific strength, high specific modulus, high wear resistance, and excellent corrosion resistance, which are one of the best materials for replacing traditional steel due to the lightweight design they offer in mechanical structures. They have broad application prospects in the automotive, machinery, aviation, and electronic packaging fields. Therefore, they have received much attention from scientific research workers in all fields. This research summarized the fabrication technology, properties, and reinforcement mechanisms of SiC particle-reinforced aluminum matrix composites, and discussed the technical difficulties and improvements in the preparation of these composites. Finally, the research and applications of SiC particle-reinforced aluminum composites were summarized.
SiC particle-reinforced aluminum matrix composites have high specific strength, high specific modulus, high wear resistance, and excellent corrosion resistance, which are one of the best materials for replacing traditional steel due to the lightweight design they offer in mechanical structures. They have broad application prospects in the automotive, machinery, aviation, and electronic packaging fields. Therefore, they have received much attention from scientific research workers in all fields. This research summarized the fabrication technology, properties, and reinforcement mechanisms of SiC particle-reinforced aluminum matrix composites, and discussed the technical difficulties and improvements in the preparation of these composites. Finally, the research and applications of SiC particle-reinforced aluminum composites were summarized.
2022, 51(4):1283-1292.
DOI: 10.12442/j.issn.1002-185X.20210270
Abstract:
In order to investigate the dynamic mechanical properties and deformation mechanism of 2195 Al-Li alloy as quenched. The high strain rate tensile experiments were carried out by the split Hopkinson tension bar equipment. Experimental strain rate ranges from 1000 s-1to 4500 s-1. The texture types and microstructure evolution of the alloy in different strain rates were analyzed by EBSD. The results show that strength and elongation of the alloy increase gradually with strain rate. The ultimate tensile strength and elongation reach 396 MPa and 63% respectively in 4200 s-1. Compared with quasi-static tensile test, the elongation is significantly improved. According to the analysis of EBSD results, with increase in strain rate, the proportion of small-angle grain boundaries and the average KAM increase at the same time. And the strength and volume fraction of Goss texture and S texture increase with the increase in strain rate. In high strain rate tension, not only the plastic deformation of soft-oriented grains is more sufficient, but also more coordinated deformation of hard-oriented grains can be initiated. Furthermore, the deformation mechanism in high strain rate tension is revealed
In order to investigate the dynamic mechanical properties and deformation mechanism of 2195 Al-Li alloy as quenched. The high strain rate tensile experiments were carried out by the split Hopkinson tension bar equipment. Experimental strain rate ranges from 1000 s-1to 4500 s-1. The texture types and microstructure evolution of the alloy in different strain rates were analyzed by EBSD. The results show that strength and elongation of the alloy increase gradually with strain rate. The ultimate tensile strength and elongation reach 396 MPa and 63% respectively in 4200 s-1. Compared with quasi-static tensile test, the elongation is significantly improved. According to the analysis of EBSD results, with increase in strain rate, the proportion of small-angle grain boundaries and the average KAM increase at the same time. And the strength and volume fraction of Goss texture and S texture increase with the increase in strain rate. In high strain rate tension, not only the plastic deformation of soft-oriented grains is more sufficient, but also more coordinated deformation of hard-oriented grains can be initiated. Furthermore, the deformation mechanism in high strain rate tension is revealed
20 Molecular dynamics simulation of compression of nanocrystalline magnesium under different conditions
2022, 51(4):1293-1303.
DOI: 10.12442/j.issn.1002-185X.20210271
Abstract:
To design and develop magnesium-based nanostructured alloys with excellent mechanical properties, a model of nanocrystalline magnesium with random grain orientation was constructed by the Voronoi geometry method. The compression simulation of nanocrystalline magnesium under different conditions was realized by molecular dynamics software. The simulation results were analysed by visualization software. The results show that with the increase of temperature, the grain size changes from refinement to fusion growth; the results show that the compression speed affects the time of grain refinement. With the increase of compression speed, the atoms in the grain still keep the original structure, only the atoms at the edge of the grain move, the grain refinement occurs later, the yield strength increases, the ultimate strain decreases, and the elastic modulus increases; the shift of atomic position in nano polycrystalline magnesium makes it easier to form FCC structure, resulting in Shockley incomplete dislocation, which is in positive proportion to the growth rule of FCC structure.
To design and develop magnesium-based nanostructured alloys with excellent mechanical properties, a model of nanocrystalline magnesium with random grain orientation was constructed by the Voronoi geometry method. The compression simulation of nanocrystalline magnesium under different conditions was realized by molecular dynamics software. The simulation results were analysed by visualization software. The results show that with the increase of temperature, the grain size changes from refinement to fusion growth; the results show that the compression speed affects the time of grain refinement. With the increase of compression speed, the atoms in the grain still keep the original structure, only the atoms at the edge of the grain move, the grain refinement occurs later, the yield strength increases, the ultimate strain decreases, and the elastic modulus increases; the shift of atomic position in nano polycrystalline magnesium makes it easier to form FCC structure, resulting in Shockley incomplete dislocation, which is in positive proportion to the growth rule of FCC structure.
2022, 51(4):1304-1311.
DOI: 10.12442/j.issn.1002-185X.20210276
Abstract:
Stress corrosion cracking (SCC) as a potential failure mechanism endangers structural integrity of the nickel-base 690 alloy components and welds that are widely used in the high temperature and high pressure water environment in pressurized water reactors (PWRs). Due to the complexity of the interweaving influences, the existing parameterized prediction models developed for SCC are limited for engineering assessment by rather lower accuracy. In this study, a Knowledge-Based Random Forest (KBRF) model was developed for predicting the SCC growth rate of the nicked-base 690 alloy through combining random forest machine learning algorithm (RF) with domain knowledge-based MRP-386 parameterized model. It was found that the robustness and accuracy of the KBRF model were significantly improved, in comparison with the MRP-386 parameterized model and the RF machine learning model by introducing domain knowledge into the machine learning modeling. The results demonstrate potential engineering application of the presented model on SCC growth rate prediction of nicked-base 690 alloy components and welds in PWRs.
Stress corrosion cracking (SCC) as a potential failure mechanism endangers structural integrity of the nickel-base 690 alloy components and welds that are widely used in the high temperature and high pressure water environment in pressurized water reactors (PWRs). Due to the complexity of the interweaving influences, the existing parameterized prediction models developed for SCC are limited for engineering assessment by rather lower accuracy. In this study, a Knowledge-Based Random Forest (KBRF) model was developed for predicting the SCC growth rate of the nicked-base 690 alloy through combining random forest machine learning algorithm (RF) with domain knowledge-based MRP-386 parameterized model. It was found that the robustness and accuracy of the KBRF model were significantly improved, in comparison with the MRP-386 parameterized model and the RF machine learning model by introducing domain knowledge into the machine learning modeling. The results demonstrate potential engineering application of the presented model on SCC growth rate prediction of nicked-base 690 alloy components and welds in PWRs.
2022, 51(4):1312-1317.
DOI: 10.12442/j.issn.1002-185X.20210294
Abstract:
As one of the most important fuel candidates in fast reactor, MOX fuel is critical in the advanced fuel cycle. Thermal conductivity of MOX fuel is a key parameter in its service life, which will affect the safety of fast reactor. The empirical formula of themal conductivity variation was usually obstained by fitting the experimental data. However, few investigations have been conducted on a theoretical basis to analyze the thermal conductivity of MOX fuel with different Pu content and oxygen-to-metal ratio (O/M). In this paper, the effect of various point defects on the thermal conductivity of MOX fuel was investigated by analyzing the influence factors of thermal conductivity for MOX samples with different Pu content and O/M in light of the classical phonon conduction theory. The results show that the phonon conduction models can be used to predict the thermal conductivity of MOX fuels with different compositions. The oxygen vacancies induced by lower O/M in MOX fuel predominate in deterimining the thermal conductivity, rather than the substituted ions point defects with small mass and radius difference. This work is beneficial to the prediction of thermal conductivity and material design of MOX fuels with different compositions.
As one of the most important fuel candidates in fast reactor, MOX fuel is critical in the advanced fuel cycle. Thermal conductivity of MOX fuel is a key parameter in its service life, which will affect the safety of fast reactor. The empirical formula of themal conductivity variation was usually obstained by fitting the experimental data. However, few investigations have been conducted on a theoretical basis to analyze the thermal conductivity of MOX fuel with different Pu content and oxygen-to-metal ratio (O/M). In this paper, the effect of various point defects on the thermal conductivity of MOX fuel was investigated by analyzing the influence factors of thermal conductivity for MOX samples with different Pu content and O/M in light of the classical phonon conduction theory. The results show that the phonon conduction models can be used to predict the thermal conductivity of MOX fuels with different compositions. The oxygen vacancies induced by lower O/M in MOX fuel predominate in deterimining the thermal conductivity, rather than the substituted ions point defects with small mass and radius difference. This work is beneficial to the prediction of thermal conductivity and material design of MOX fuels with different compositions.
2022, 51(4):1318-1324.
DOI: 10.12442/j.issn.1002-185X.20210352
Abstract:
Based on the first-principles calculation method, the effects of Si alloying on the stability and fracture toughness of the C15 NbCr2 Laves phase were studied by calculating the enthalpy of formation, binding energy, atomic free volume and electronic structure. The site occupation energy indicates that Si tends to occupy the Cr site. The calculation of formation enthalpy and binding energy showed that the formation ability and stability of the Nb8Cr16-xSix (X= 0 ~ 5 ) phase were enhanced with the addition of Si content and maintained a linear correlation with Si content. The atomic free volume calculation shows that the atomic free volume of the Nb8Cr16-xSix phase is higher than that of the NbCr2 matrix phase, and the atomic free volume reaches the maximum when the content of Si is 8.33 at% (Nb8Cr14Si2), that is, the fracture toughness is the best. The electronic structure calculation shows that Si alloying makes the DOS curve shift to the right and the Fermi level approaches to the pseudo-energy gap, which stabilizes the NbCr2 matrix phase. Meanwhile, all the bonding peaks decrease and widen, which weakens the bonding strength of Nb-Cr atoms and makes the shear deformation easy to carry out, thus improving the toughness.
Based on the first-principles calculation method, the effects of Si alloying on the stability and fracture toughness of the C15 NbCr2 Laves phase were studied by calculating the enthalpy of formation, binding energy, atomic free volume and electronic structure. The site occupation energy indicates that Si tends to occupy the Cr site. The calculation of formation enthalpy and binding energy showed that the formation ability and stability of the Nb8Cr16-xSix (X= 0 ~ 5 ) phase were enhanced with the addition of Si content and maintained a linear correlation with Si content. The atomic free volume calculation shows that the atomic free volume of the Nb8Cr16-xSix phase is higher than that of the NbCr2 matrix phase, and the atomic free volume reaches the maximum when the content of Si is 8.33 at% (Nb8Cr14Si2), that is, the fracture toughness is the best. The electronic structure calculation shows that Si alloying makes the DOS curve shift to the right and the Fermi level approaches to the pseudo-energy gap, which stabilizes the NbCr2 matrix phase. Meanwhile, all the bonding peaks decrease and widen, which weakens the bonding strength of Nb-Cr atoms and makes the shear deformation easy to carry out, thus improving the toughness.
2022, 51(4):1325-1331.
DOI: 10.12442/j.issn.1002-185X.20210640
Abstract:
Hafnium oxide (HfO2) thin films were deposited on a silicon substrate using atomic layer deposition (ALD), and microwave annealing (MWA) was performed for different time. X-ray diffraction (XRD), Raman spectroscopy (Raman), atomic force microscopy (AFM), ultraviolet-visible spectroscopy (UV-Vis), ellipsometer (SE) and impedance analyzer were used to characterize the film performances. The effects of different microwave annealing time on the structure, optical and electrical properties of the film were studied in detail. The results show that the as-deposited HfO2 film was amorphous, when the microwave annealing time is increased from 5min to 20min, the crystallinity of the HfO2 film increases and the surface roughness decreases; but the dielectric constant decreases. In addition, the refractive index of the HfO2 film hardly changes with the increasing of the microwave annealing time.
Hafnium oxide (HfO2) thin films were deposited on a silicon substrate using atomic layer deposition (ALD), and microwave annealing (MWA) was performed for different time. X-ray diffraction (XRD), Raman spectroscopy (Raman), atomic force microscopy (AFM), ultraviolet-visible spectroscopy (UV-Vis), ellipsometer (SE) and impedance analyzer were used to characterize the film performances. The effects of different microwave annealing time on the structure, optical and electrical properties of the film were studied in detail. The results show that the as-deposited HfO2 film was amorphous, when the microwave annealing time is increased from 5min to 20min, the crystallinity of the HfO2 film increases and the surface roughness decreases; but the dielectric constant decreases. In addition, the refractive index of the HfO2 film hardly changes with the increasing of the microwave annealing time.
2022, 51(4):1332-1340.
DOI: 10.12442/j.issn.1002-185X.20210770
Abstract:
The high temperature oxidation behavior of BT25Y titanium alloy was studied at 600 ℃, 700 ℃and 800 ℃. The thermodynamics and kinetics of the alloy oxidation were calculated by the method of continuous oxidation weight gain, the oxidation rate constant and the oxidation activity. The phase composition, surface and cross-section morphologies and elemental distribution of the oxide scale were respectively investigated by XRD, SEM and EDS. The results showed that BT25Y titanium alloy exhibited good oxidation resistance at 600 ℃and 700 ℃, and their oxidation kinetics curves followed the parabolic law. The continuous oxide scale composed of fine TiO2 and Al2O3 particles can effectively prevent oxygen from infiltrating into the matrix and then remarkably reduce the oxidation rate. At 800 ℃, the oxidation behavior of the BT25Y titanium alloy was catastrophic, and its oxidation kinetics approximately followed the linear law. The oxide layer was alternately composed of Al2O3 layer and TiO2 layer, and the oxidation film was loose and porous, which cannot effectively prevent the diffusion of oxygen into the matrix.
The high temperature oxidation behavior of BT25Y titanium alloy was studied at 600 ℃, 700 ℃and 800 ℃. The thermodynamics and kinetics of the alloy oxidation were calculated by the method of continuous oxidation weight gain, the oxidation rate constant and the oxidation activity. The phase composition, surface and cross-section morphologies and elemental distribution of the oxide scale were respectively investigated by XRD, SEM and EDS. The results showed that BT25Y titanium alloy exhibited good oxidation resistance at 600 ℃and 700 ℃, and their oxidation kinetics curves followed the parabolic law. The continuous oxide scale composed of fine TiO2 and Al2O3 particles can effectively prevent oxygen from infiltrating into the matrix and then remarkably reduce the oxidation rate. At 800 ℃, the oxidation behavior of the BT25Y titanium alloy was catastrophic, and its oxidation kinetics approximately followed the linear law. The oxide layer was alternately composed of Al2O3 layer and TiO2 layer, and the oxidation film was loose and porous, which cannot effectively prevent the diffusion of oxygen into the matrix.
2022, 51(4):1341-1347.
DOI: 10.12442/j.issn.1002-185X.20210264
Abstract:
Mo2C possesses the electronic structure and catalytic properties similar to that of Pt-like noble metals, thus been suggested to be an encouraging non-noble metal electrocatalysts substitute to the noble metals. However, pure Mo2C has poor conductivity and slow hydrogen release kinetics. In order to improve the electrocatalytic hydrogen evolution performance of Mo2C, this work employed a low-temperature molten salt method to prepare several self-supporting Mo2C electrocatalysts on carbon fiber paper (CFP). The effects of molybdenum sources (Mo, MoO3), nickel sources (Ni, Ni(NO3)2) and carbon black on the phase, microstructure/morphology and electrocatalytic performance of the synthesized product were investigated. The results show that the introduction of carbon black and Ni can promote the refinement of Mo2C grains and the formation of wrinkled structure on its surface, thus providing more active sites. When using MoO3 as molybdenum source, Ni(NO3)2 makes the morphology of Mo2C transforming from granular to flower-like, which greatly increases its specific surface area, and also promotes the electron transfer efficiency in the synthesized Ni(NO3)2-Mo2CCBO@CFP composite electrode. This composite electrode shows the best HER activity, with the smallestη10 of 117 mV and the lowest Tafel slop of 73.8 mV dec-1.
Mo2C possesses the electronic structure and catalytic properties similar to that of Pt-like noble metals, thus been suggested to be an encouraging non-noble metal electrocatalysts substitute to the noble metals. However, pure Mo2C has poor conductivity and slow hydrogen release kinetics. In order to improve the electrocatalytic hydrogen evolution performance of Mo2C, this work employed a low-temperature molten salt method to prepare several self-supporting Mo2C electrocatalysts on carbon fiber paper (CFP). The effects of molybdenum sources (Mo, MoO3), nickel sources (Ni, Ni(NO3)2) and carbon black on the phase, microstructure/morphology and electrocatalytic performance of the synthesized product were investigated. The results show that the introduction of carbon black and Ni can promote the refinement of Mo2C grains and the formation of wrinkled structure on its surface, thus providing more active sites. When using MoO3 as molybdenum source, Ni(NO3)2 makes the morphology of Mo2C transforming from granular to flower-like, which greatly increases its specific surface area, and also promotes the electron transfer efficiency in the synthesized Ni(NO3)2-Mo2CCBO@CFP composite electrode. This composite electrode shows the best HER activity, with the smallestη10 of 117 mV and the lowest Tafel slop of 73.8 mV dec-1.
2022, 51(4):1348-1355.
DOI: 10.12442/j.issn.1002-185X.20210274
Abstract:
A stray grain with the regular shape was found in the transition zone between the airfoil and the platform of some single crystal blades, which are prepared by the Bridgman method. The stray grain is band like and its length direction is parallel or perpendicular to the growth direction of dendrite in the airfoil and the platform. The metallographic method (OM), the electron probe microanalysis (EPMA), and electron backscatter diffraction (EBSD) are used to analyze the microstructure, composition and crystallographic relationship of the stray grain and its surrounding area, respectively. ProCAST is used to simulate the distribution of temperature field and undercooling of platform during solidification. The defect includes many columnar grains, whose composition is not significantly different from the airfoil or platform. However, there exit grain boundary angles between columnar grains and surrounding matrix. The results of temperature distribution show that the undercooling of the transition zone of airfoil and platform is smaller than that of the platform edge. Thus, the solidification speed of the alloy liquid is lower, and the transition zone is the final solidification area. Based on these results, the formation mechanism of defect in the transition zone is proposed, which provides a theoretical basis for eliminating the defects.
A stray grain with the regular shape was found in the transition zone between the airfoil and the platform of some single crystal blades, which are prepared by the Bridgman method. The stray grain is band like and its length direction is parallel or perpendicular to the growth direction of dendrite in the airfoil and the platform. The metallographic method (OM), the electron probe microanalysis (EPMA), and electron backscatter diffraction (EBSD) are used to analyze the microstructure, composition and crystallographic relationship of the stray grain and its surrounding area, respectively. ProCAST is used to simulate the distribution of temperature field and undercooling of platform during solidification. The defect includes many columnar grains, whose composition is not significantly different from the airfoil or platform. However, there exit grain boundary angles between columnar grains and surrounding matrix. The results of temperature distribution show that the undercooling of the transition zone of airfoil and platform is smaller than that of the platform edge. Thus, the solidification speed of the alloy liquid is lower, and the transition zone is the final solidification area. Based on these results, the formation mechanism of defect in the transition zone is proposed, which provides a theoretical basis for eliminating the defects.
2022, 51(4):1356-1362.
DOI: 10.12442/j.issn.1002-185X.20210287
Abstract:
The design and preparation of antifriction coating on the surface of aluminum alloy is one of the key technologies to improve the friction properties of aluminum alloy components. In this study, nano-MoS2 was synthesized in situ on the surface of 6063 aluminum alloy by one-step micro-arc oxidation method to prepare MoS2/Al2O3 composite ceramic coating with antifriction effect. The effect of sulfur concentration on the composition, morphology and friction properties of the coating was discussed. The friction reducing mechanism of the coating was analyzed. The results show that the self-lubricating composite ceramic coating containing MoS2 was successfully prepared on the surface of 6063 aluminum alloy by micro-arc oxidation. The friction coefficient of the coating decreases first and then increases with the increase of the sulfur concentration. When the sulfur concentration in the electrolyte is 15g/L, the friction coefficient of the coating is 0.15, which is reduced by 76% compared with the conventional micro-arc oxidation coating. The MoS2 in the coating is distributed on the surface and inside of the coating. Under the action of contact and extrusion with the friction pair, a uniformly distributed MoS2 lubricating film is formed, showing good antifriction performance.
The design and preparation of antifriction coating on the surface of aluminum alloy is one of the key technologies to improve the friction properties of aluminum alloy components. In this study, nano-MoS2 was synthesized in situ on the surface of 6063 aluminum alloy by one-step micro-arc oxidation method to prepare MoS2/Al2O3 composite ceramic coating with antifriction effect. The effect of sulfur concentration on the composition, morphology and friction properties of the coating was discussed. The friction reducing mechanism of the coating was analyzed. The results show that the self-lubricating composite ceramic coating containing MoS2 was successfully prepared on the surface of 6063 aluminum alloy by micro-arc oxidation. The friction coefficient of the coating decreases first and then increases with the increase of the sulfur concentration. When the sulfur concentration in the electrolyte is 15g/L, the friction coefficient of the coating is 0.15, which is reduced by 76% compared with the conventional micro-arc oxidation coating. The MoS2 in the coating is distributed on the surface and inside of the coating. Under the action of contact and extrusion with the friction pair, a uniformly distributed MoS2 lubricating film is formed, showing good antifriction performance.
2022, 51(4):1363-1370.
DOI: 10.12442/j.issn.1002-185X.20210289
Abstract:
Wrinkling is one of the main defects that affect the part’s quality and dimensional precision during plastic forming process of sheet metal. However, the influence of thickness and microstructure of sheet on wrinkling behavior is not clear. Taking ultra-thin GH4169 superalloy strip with different thicknesses (0.2mm~0.25mm) and grain sizes (7.12~88.39μm) as the research object, Yoshida Buckling Test are carried out. Then, the load-displacement curves of experimental and simulation results are compared so that the effectiveness of the numerical simulation is verified. By combining the theory of energy method with finite element numerical simulation, wrinkling limit curves of GH4169 strip with different thicknesses and grain sizes are established. The results show that with the reduction of the number of grains in the strip thickness direction, the the absolute slope of the wrinkling limit curves of GH4169 strip decreases, which is more prone to wrinkle. With the decrease of the grain number in the thickness direction, the anisotropy among different grains is enhanced, and the deformation coordination ability of the material is weakened. As a consequence, the wrinkle resistance ability is weakened and the wrinkling of superalloy strip shows size dependence.
Wrinkling is one of the main defects that affect the part’s quality and dimensional precision during plastic forming process of sheet metal. However, the influence of thickness and microstructure of sheet on wrinkling behavior is not clear. Taking ultra-thin GH4169 superalloy strip with different thicknesses (0.2mm~0.25mm) and grain sizes (7.12~88.39μm) as the research object, Yoshida Buckling Test are carried out. Then, the load-displacement curves of experimental and simulation results are compared so that the effectiveness of the numerical simulation is verified. By combining the theory of energy method with finite element numerical simulation, wrinkling limit curves of GH4169 strip with different thicknesses and grain sizes are established. The results show that with the reduction of the number of grains in the strip thickness direction, the the absolute slope of the wrinkling limit curves of GH4169 strip decreases, which is more prone to wrinkle. With the decrease of the grain number in the thickness direction, the anisotropy among different grains is enhanced, and the deformation coordination ability of the material is weakened. As a consequence, the wrinkle resistance ability is weakened and the wrinkling of superalloy strip shows size dependence.
2022, 51(4):1371-1377.
DOI: 10.12442/j.issn.1002-185X.20210290
Abstract:
The deformation behavior of W-Cu material during high-pressure torsion (HPT) was simulated by ABAQUS software. The distributions of stress and equivalent strain, as well as the influence of applied pressure and deformation temperature on the strain accumulation of interface layer were analyzed. The simulation results show that shear deformation is mainly occurred on copper, but has little influence on tungsten, and the strain accumulation of interface layer is the largest. The increase of deformation temperature varying from 300 ℃ to 500 ℃ and applied pressure varying from 1 GPa to 3 GPa have positive effect on the strain accumulation of interface layer, but the higher temperature and applied pressure may lead to the extrusion of copper and the failure of HPT die. At the same time, the W-Cu gradient material with noble bonding interface was obtained through 5 turns of HPT processing under 300 ℃ and 1 GPa, and the diffusion distance of tungsten and copper at the bonding interface is 1.74 μm and 2.59 μm, respectively. The experimental results show that with the increase of torsion radius, the microstructures of W and Cu were significantly refined to 32.6 μm and 0.28 μm, respectively. Also, a transition layer of Cu with grain size of about 4.8 μm can be found at the interface. The microhardness of copper increases from 79 Hv to 131 Hv, and that of tungsten at the interface increases from 347 Hv to 424 Hv, which indicates that grain refinement and defect accumulation under large deformation condition are beneficial to interface bonding and performance improvement.
The deformation behavior of W-Cu material during high-pressure torsion (HPT) was simulated by ABAQUS software. The distributions of stress and equivalent strain, as well as the influence of applied pressure and deformation temperature on the strain accumulation of interface layer were analyzed. The simulation results show that shear deformation is mainly occurred on copper, but has little influence on tungsten, and the strain accumulation of interface layer is the largest. The increase of deformation temperature varying from 300 ℃ to 500 ℃ and applied pressure varying from 1 GPa to 3 GPa have positive effect on the strain accumulation of interface layer, but the higher temperature and applied pressure may lead to the extrusion of copper and the failure of HPT die. At the same time, the W-Cu gradient material with noble bonding interface was obtained through 5 turns of HPT processing under 300 ℃ and 1 GPa, and the diffusion distance of tungsten and copper at the bonding interface is 1.74 μm and 2.59 μm, respectively. The experimental results show that with the increase of torsion radius, the microstructures of W and Cu were significantly refined to 32.6 μm and 0.28 μm, respectively. Also, a transition layer of Cu with grain size of about 4.8 μm can be found at the interface. The microhardness of copper increases from 79 Hv to 131 Hv, and that of tungsten at the interface increases from 347 Hv to 424 Hv, which indicates that grain refinement and defect accumulation under large deformation condition are beneficial to interface bonding and performance improvement.
2022, 51(4):1378-1384.
DOI: 10.12442/j.issn.1002-185X.20210292
Abstract:
The ultra-high strength Al-Zn-Mg-Cu alloy with strength of 800MPa has a promising application prospect in the aviation industry, and also a great effect on the structural lightweight, however, its application is limited at present due to its poor corrosion resistance. In this paper, the corrosion resistance of ultra-high strength Al-Zn-Mg-Cu alloy was controlled by controlling the quenching temperature of the colling water (quenching temperature for short). The microstructure, tensile mechanical properties, intergranular corrosion properties and exfoliation corrosion properties of the alloy after ageing were compared. It is found that increasing the quenching temperature promoted the formation of the intragranular and intergranular precipitates, and also promoted the intermittent distribution of the aged precipitation and the content of Cu in intergranular precipitations. The tensile strength at room temperature decreased by only 1.4%, but the intergranular corrosion depth decreased by about 50%. The exfoliation corrosion decreases from ED grade to PA-EA grade when the quenching temperature increased to 80 ℃, but decreased when exceeds 80 ℃. The analysis belives that when the proper quenching temperature is between 60 ℃ and 80 ℃, in which the precipitations increase the grain boundary potential and block the corrosion propagation channel. At the same time, the number and size of precipitations can be controlled, which didn’t cause significantly reducing of the mechanical properties.
The ultra-high strength Al-Zn-Mg-Cu alloy with strength of 800MPa has a promising application prospect in the aviation industry, and also a great effect on the structural lightweight, however, its application is limited at present due to its poor corrosion resistance. In this paper, the corrosion resistance of ultra-high strength Al-Zn-Mg-Cu alloy was controlled by controlling the quenching temperature of the colling water (quenching temperature for short). The microstructure, tensile mechanical properties, intergranular corrosion properties and exfoliation corrosion properties of the alloy after ageing were compared. It is found that increasing the quenching temperature promoted the formation of the intragranular and intergranular precipitates, and also promoted the intermittent distribution of the aged precipitation and the content of Cu in intergranular precipitations. The tensile strength at room temperature decreased by only 1.4%, but the intergranular corrosion depth decreased by about 50%. The exfoliation corrosion decreases from ED grade to PA-EA grade when the quenching temperature increased to 80 ℃, but decreased when exceeds 80 ℃. The analysis belives that when the proper quenching temperature is between 60 ℃ and 80 ℃, in which the precipitations increase the grain boundary potential and block the corrosion propagation channel. At the same time, the number and size of precipitations can be controlled, which didn’t cause significantly reducing of the mechanical properties.
2022, 51(4):1385-1390.
DOI: 10.12442/j.issn.1002-185X.20210293
Abstract:
Boron carbide ceramic has been known to possess ultrahigh hardness and good thermal conductivity. However, these properties greatly depend on the phase composition of boron carbide, that is, the B/C ratio. As the combined B/C ratio in boron carbide deviates from the stoichiometry of B4C, all these properties decrease dramatically. In some standards and industrial applications, the ratio of total boron and total carbon which may be easy to control has been concerned, rather than the combined B/C ratio. Few investigations have been conducted on the control of the boron-rich phases and other impurities in B4C ceramics. In this paper, the phase compositions of several commercial boron cabide powders were confirmed through the detailed analysis of their X-ray diffraction patterns, from which the diffraction peaks of the boron-rich phases were separated and calibrated from the overlapping peaks. The final phase compositions of hot pressed boron carbide ceramics and the transformation of boron-rich phases to B4C under different sintering temperatures were then investigated. The results show that the commercial boron carbide powder is usually a mixture of B4C and boron-rich phases such as B6.5C as well as other impurities. The results of X-ray diffraction and Raman spectroscopy show that the boron-rich phases react with free carbon to form B4C as the sintering temperature increases. A boron carbide ceramic with pure B4C phase was prepared using a commercial boron carbide powder by hot pressing at 2100oC and 40MPa for 60min.
Boron carbide ceramic has been known to possess ultrahigh hardness and good thermal conductivity. However, these properties greatly depend on the phase composition of boron carbide, that is, the B/C ratio. As the combined B/C ratio in boron carbide deviates from the stoichiometry of B4C, all these properties decrease dramatically. In some standards and industrial applications, the ratio of total boron and total carbon which may be easy to control has been concerned, rather than the combined B/C ratio. Few investigations have been conducted on the control of the boron-rich phases and other impurities in B4C ceramics. In this paper, the phase compositions of several commercial boron cabide powders were confirmed through the detailed analysis of their X-ray diffraction patterns, from which the diffraction peaks of the boron-rich phases were separated and calibrated from the overlapping peaks. The final phase compositions of hot pressed boron carbide ceramics and the transformation of boron-rich phases to B4C under different sintering temperatures were then investigated. The results show that the commercial boron carbide powder is usually a mixture of B4C and boron-rich phases such as B6.5C as well as other impurities. The results of X-ray diffraction and Raman spectroscopy show that the boron-rich phases react with free carbon to form B4C as the sintering temperature increases. A boron carbide ceramic with pure B4C phase was prepared using a commercial boron carbide powder by hot pressing at 2100oC and 40MPa for 60min.
Liang Yanyuan
,
Qiu Haipeng
,
Ma Xin
,
Wang Ling
,
Liu Shanhua
,
Chen Mingwei
,
Xie Weijie
,
Wang Xiaomeng
2022, 51(4):1391-1396.
DOI: 10.12442/j.issn.1002-185X.20210295
Abstract:
The reinforcement and matrix of the oxide/oxide ceramic matrix composite material are both made of oxide, and there is no oxidation problem. It is an ideal material for long-life and high-reliability components. It can be used for a long time in the high temperature environmentr ,ranging 1000~1300℃ . In this paper, unidirectional fiber wet prepreg was prepared by configuring alumina powder slurry on a winding wet prepreg machine, and then the prepreg was laid. Alumina fiber reinforced alumina ceramic matrix composite material was obtained by layer molding and high temperature heat treatment, and the properties of the composite material were characterized at the same time. The results show that the solid content of the alumina powder slurry is 50 vol%, the ratio of water to glycerol in the slurry solvent is 3:1, the fiber"s wire speed is 6m/min, and the parallel progress of the drum is 0.5mm. prepreg with no gaps, no fiber overlap, and with smooth surface was abtained. The tensile strength of the composite material prepared by hot pressing of the prepreg layer is as high as 208.2MPa, and the bending strength is 386.7MPa. Compared with the slurry coating process of two-dimensional fiber cloth, the mechanical properties are greatly improved, and the prepreg process has the advantages of easy storage, simple operation, and suitability for industrial production.
The reinforcement and matrix of the oxide/oxide ceramic matrix composite material are both made of oxide, and there is no oxidation problem. It is an ideal material for long-life and high-reliability components. It can be used for a long time in the high temperature environmentr ,ranging 1000~1300℃ . In this paper, unidirectional fiber wet prepreg was prepared by configuring alumina powder slurry on a winding wet prepreg machine, and then the prepreg was laid. Alumina fiber reinforced alumina ceramic matrix composite material was obtained by layer molding and high temperature heat treatment, and the properties of the composite material were characterized at the same time. The results show that the solid content of the alumina powder slurry is 50 vol%, the ratio of water to glycerol in the slurry solvent is 3:1, the fiber"s wire speed is 6m/min, and the parallel progress of the drum is 0.5mm. prepreg with no gaps, no fiber overlap, and with smooth surface was abtained. The tensile strength of the composite material prepared by hot pressing of the prepreg layer is as high as 208.2MPa, and the bending strength is 386.7MPa. Compared with the slurry coating process of two-dimensional fiber cloth, the mechanical properties are greatly improved, and the prepreg process has the advantages of easy storage, simple operation, and suitability for industrial production.
Wu Hongfei
,
Wang Weirong
,
Wang Guowei
,
Sun Chaoming
,
Zhang Wenkang
,
Shen Xianfeng
,
Chen Jinming
2022, 51(4):1397-1405.
DOI: 10.12442/j.issn.1002-185X.20210300
Abstract:
The metal lattice structures manufactured by selective laser melting (SLM) has a wide range of engineering applications in aerospace and other fields due to its advantages such as large freedom of structural design, lightweight, shock absorption and so on. However, the research on its mechanical properties is still insufficient. In this study, Body-centered cubic (BCC) and Diamond (Dia) lattice structures with different directions were designed, and AlSi10Mg lattice structures were manufactured by SLM. Compressing tests were carried out on the formed samples, combined with finite element analysis (FEA), the anisotropy effects of lattice structures on the compression and energy absorption efficiency were studied. The results show that BCC and Dia lattice structures have obvious anisotropy. In the case of roughly the same relative density, from 0° to 45°, the yield strength increases obviously with the increase of the angle. The anisotropy of the BCC lattice structure has a more obvious effect on the compressive yield strength, and the yield strength of the Dia lattice structure is significantly higher than the BCC lattice structure. The specific energy absorption (SEA) of the lattice structure in different directions is obviously different. From 0° to 45°, as the angle increases, the specific energy absorption increases significantly. The specific energy absorption of the Dia lattice structure is significantly higher than the BCC lattice structure. The crash load efficiency (CLE) of the lattice structure in different directions is obviously different. The BCC lattice structure reaches a maximum of 1.07 in the 0° direction and gradually decreases with the increase of lattice structure angle. The crash load efficiency of the Dia lattice structure increases with the increase of lattice structure angle and reaches the maximum of 1.01 in the 45° direction.
The metal lattice structures manufactured by selective laser melting (SLM) has a wide range of engineering applications in aerospace and other fields due to its advantages such as large freedom of structural design, lightweight, shock absorption and so on. However, the research on its mechanical properties is still insufficient. In this study, Body-centered cubic (BCC) and Diamond (Dia) lattice structures with different directions were designed, and AlSi10Mg lattice structures were manufactured by SLM. Compressing tests were carried out on the formed samples, combined with finite element analysis (FEA), the anisotropy effects of lattice structures on the compression and energy absorption efficiency were studied. The results show that BCC and Dia lattice structures have obvious anisotropy. In the case of roughly the same relative density, from 0° to 45°, the yield strength increases obviously with the increase of the angle. The anisotropy of the BCC lattice structure has a more obvious effect on the compressive yield strength, and the yield strength of the Dia lattice structure is significantly higher than the BCC lattice structure. The specific energy absorption (SEA) of the lattice structure in different directions is obviously different. From 0° to 45°, as the angle increases, the specific energy absorption increases significantly. The specific energy absorption of the Dia lattice structure is significantly higher than the BCC lattice structure. The crash load efficiency (CLE) of the lattice structure in different directions is obviously different. The BCC lattice structure reaches a maximum of 1.07 in the 0° direction and gradually decreases with the increase of lattice structure angle. The crash load efficiency of the Dia lattice structure increases with the increase of lattice structure angle and reaches the maximum of 1.01 in the 45° direction.
2022, 51(4):1406-1412.
DOI: 10.12442/j.issn.1002-185X.20210302
Abstract:
The microstructure, texture and phase transformation of hot rolled 316L stainless steel at different cooling rates were studied by high temperature laser confocal microscopy, nano-indentation and EBSD. The results showed that the second phase in hot rolled 316L plate had long strip shape with the hardness of 13.48 GPa. Its internal phase structure was complex, which was composed of austenite, ferrite and σ (sigma) phase. In-situ observation showed that the temperature reached 1065.4 ℃ at 457.01s, the ferrite and sigma phase in the second phase transformed to austenite. After 10 minutes of short homogenization, however, the austenite grains transformed from the second phase were still rich in Cr and Mo elements. After cooling, the austenite therefore transformed to ferrite / sigma phase and had similar long strip shape. The initial deformation texture weakened and transformed into random texture at different cooling rates. The homogenization degree and the percentage of austenite increased with the reducing of cooling rate. The austenite grains transformed from the second phase all transformed into ferrite at 500 ℃ / min, a small amount of sigma phase appeared at 100 ℃ / min, and mostly transform into sigma phase at 12 ℃ / min.
The microstructure, texture and phase transformation of hot rolled 316L stainless steel at different cooling rates were studied by high temperature laser confocal microscopy, nano-indentation and EBSD. The results showed that the second phase in hot rolled 316L plate had long strip shape with the hardness of 13.48 GPa. Its internal phase structure was complex, which was composed of austenite, ferrite and σ (sigma) phase. In-situ observation showed that the temperature reached 1065.4 ℃ at 457.01s, the ferrite and sigma phase in the second phase transformed to austenite. After 10 minutes of short homogenization, however, the austenite grains transformed from the second phase were still rich in Cr and Mo elements. After cooling, the austenite therefore transformed to ferrite / sigma phase and had similar long strip shape. The initial deformation texture weakened and transformed into random texture at different cooling rates. The homogenization degree and the percentage of austenite increased with the reducing of cooling rate. The austenite grains transformed from the second phase all transformed into ferrite at 500 ℃ / min, a small amount of sigma phase appeared at 100 ℃ / min, and mostly transform into sigma phase at 12 ℃ / min.
2022, 51(4):1413-1419.
DOI: 10.12442/j.issn.1002-185X.20210306
Abstract:
: Themicrostructure and texture of Mg-8.07Al-0.53Zn-1.36Nd magnesium alloy were characterized by SEM、EBSD and EDS.The results show that the heat-treated alloy is mainly composed of α-Mg matrix, β-Mg17Al12 precipitates and Nd-containing compounds. The bimodal grain structure ofβ-Mg17Al12 precipitates zones andfree zonein the alloy after heat treatment below 400℃. A large number of nanoscale granular β-Mg17Al12 precipitates mainly along the deformation zone and twin interface are precipitated first,andthen the static recrystallization of α-Mg matrix formed. With the increasing of annealing temperature, the amount of β-Mg17Al12 decreases, and the size and amount of rare earth phaseshaven’tbeen changed significantly. The static recrystallization occurs preferentially in the precipitates-free zones ofβ-Mg17Al12 precipitates in bimodal grain structure, which indicates that the precipitation particles can delay the static recrystallization. Theβ-Mg17Al12 precipitates in the alloy after heat treatment at 400℃ are dissolved and the amount is reduced significantly.The magnesium matrix recrystallized completely and the recrystallized grains grew up significantly. EBSD results show that the texture of the experimental alloy after heat treatment is mainly weakbasal texture, accompanied by part of the non-basal texture. In the alloy after heat treatment below 400℃, a large number of β-Mg17Al12 precipitates play an important role in weakening basal texture. With the increasing of heat treatment temperature, the dislocation density in the alloy decreases, and the main texture components change from {0001}< 10-10 > deformation texture to {0001}< 11-20 > recrystallization texture.
: Themicrostructure and texture of Mg-8.07Al-0.53Zn-1.36Nd magnesium alloy were characterized by SEM、EBSD and EDS.The results show that the heat-treated alloy is mainly composed of α-Mg matrix, β-Mg17Al12 precipitates and Nd-containing compounds. The bimodal grain structure ofβ-Mg17Al12 precipitates zones andfree zonein the alloy after heat treatment below 400℃. A large number of nanoscale granular β-Mg17Al12 precipitates mainly along the deformation zone and twin interface are precipitated first,andthen the static recrystallization of α-Mg matrix formed. With the increasing of annealing temperature, the amount of β-Mg17Al12 decreases, and the size and amount of rare earth phaseshaven’tbeen changed significantly. The static recrystallization occurs preferentially in the precipitates-free zones ofβ-Mg17Al12 precipitates in bimodal grain structure, which indicates that the precipitation particles can delay the static recrystallization. Theβ-Mg17Al12 precipitates in the alloy after heat treatment at 400℃ are dissolved and the amount is reduced significantly.The magnesium matrix recrystallized completely and the recrystallized grains grew up significantly. EBSD results show that the texture of the experimental alloy after heat treatment is mainly weakbasal texture, accompanied by part of the non-basal texture. In the alloy after heat treatment below 400℃, a large number of β-Mg17Al12 precipitates play an important role in weakening basal texture. With the increasing of heat treatment temperature, the dislocation density in the alloy decreases, and the main texture components change from {0001}< 10-10 > deformation texture to {0001}< 11-20 > recrystallization texture.
2022, 51(4):1420-1426.
DOI: 10.12442/j.issn.1002-185X.20210307
Abstract:
The Cu-added Ni60/Cu directional structure composite coating was prepared by flame spraying+ induction remelting + forced cooling composite technology. The effect of Cu content on the microstructure, phase evolution, microhardness and friction and wear properties of Ni60/Cu oriented structure coating was systematically studied. The results showed that the Cu element diffuse continuously into the grain during the formation of the directional structure coating, resulting in a continuously decrease in the hardness of the coating as the Cu content increase. The content of Cu has an important influence on the microstructure of the coating, when the Cu content is 15%, the directional structure of the coating shows a growth characteristic perpendicular to the interface, and the microstructure is fine and regular. The coating is mainly abrasive wear, which shows the lowest friction coefficient and the lowest wear rate, and gives full play to the friction reducing effect caused by Cu element when the Cu content is 15%. However, the excessive addition of Cu makes the wear resistance of the coating worse.
The Cu-added Ni60/Cu directional structure composite coating was prepared by flame spraying+ induction remelting + forced cooling composite technology. The effect of Cu content on the microstructure, phase evolution, microhardness and friction and wear properties of Ni60/Cu oriented structure coating was systematically studied. The results showed that the Cu element diffuse continuously into the grain during the formation of the directional structure coating, resulting in a continuously decrease in the hardness of the coating as the Cu content increase. The content of Cu has an important influence on the microstructure of the coating, when the Cu content is 15%, the directional structure of the coating shows a growth characteristic perpendicular to the interface, and the microstructure is fine and regular. The coating is mainly abrasive wear, which shows the lowest friction coefficient and the lowest wear rate, and gives full play to the friction reducing effect caused by Cu element when the Cu content is 15%. However, the excessive addition of Cu makes the wear resistance of the coating worse.
Xiao Lei
,
Cui Jinyan
,
Wang Chong
,
Ma Xiangdong
,
Xiong Jiangying
,
Long Anping
,
Yang Jinlong
,
Guo Jianzheng
2022, 51(4):1427-1435.
DOI: 10.12442/j.issn.1002-185X.20210315
Abstract:
A novel third generation Ni-based PM (Powder Metallurgy) superalloy WZ-A3 has been evaluated for its hot compression behavior. Gleeble simulation tests on the extruded WZ-A3 samples over the temperature range of 1040~1130 ℃ and strain rate range of 0.01~0.0025 s-1 have been conducted. The samples compressed at different conditions were analyzed for grain size and microstructure evolution. The results indicate that under the compression conditions of temperatures from 1070 ℃ to 1100 ℃, and strain rate from 0.01 s-1 to 0.005 s-1, a uniform fine grain structure around 4.5 μm can be obtained. No abnormal grain growth and necklace grains were observed throughout. To validate compression property of the extruded WZ-A3 alloy, Hot die forging was conducted successfully to make two prototype forgings of the size of 190 mm in diameter and 97 mm in height.
A novel third generation Ni-based PM (Powder Metallurgy) superalloy WZ-A3 has been evaluated for its hot compression behavior. Gleeble simulation tests on the extruded WZ-A3 samples over the temperature range of 1040~1130 ℃ and strain rate range of 0.01~0.0025 s-1 have been conducted. The samples compressed at different conditions were analyzed for grain size and microstructure evolution. The results indicate that under the compression conditions of temperatures from 1070 ℃ to 1100 ℃, and strain rate from 0.01 s-1 to 0.005 s-1, a uniform fine grain structure around 4.5 μm can be obtained. No abnormal grain growth and necklace grains were observed throughout. To validate compression property of the extruded WZ-A3 alloy, Hot die forging was conducted successfully to make two prototype forgings of the size of 190 mm in diameter and 97 mm in height.
39 Microstructural characteristics and mechanical properties of TC11 titanium alloy friction stir welds
2022, 51(4):1436-1441.
DOI: 10.12442/j.issn.1002-185X.20210323
Abstract:
Friction stir welding of TC11 titanium alloy was carried out under different rotational speeds, the microstructures and mechanical properties of the welded joints were analyzed, and the relationships among processing parameters, microstructures and properties of the joints were established. The SZ produced the fully β transformed microstructure, which contained grain boundary α phase, intragranular lamellar α+β phases and acicular α′ phase. The double strengthening was caused by the fine α phase and α+β phases as well as the presence of α′ phase, which led to the highest hardness value in the SZ. The retained original α phase and β transformed microstructure were found in the HAZ and TMAZ, while the TMAZ showed the streamlined deformation characteristics. The proportion of β transformed microstructure in these zones was higher when closer to the SZ, and thus the strengthening effect was enhanced. The size of α phase and α+β phases increased and the content of α′ phase decreased with the rotational speed ascending, which resulted in the reduction of hardness value in the SZ. Similar to the law reflected from the hardness test, all the joints fractured in BM after tensile test, the tensile strengths of the SZs under different rotational speeds were significantly higher than BM, and they decreased with the ascent of rotational speed. Besides, the fine α phase and α+β phases caused the higher elongations of SZs compared with the BM, meaning that the SZ had the good plasticity. With the rotational speed ascending, the elongations of SZs decreased owing to the increase of the size of α phase and α+β phases.
Friction stir welding of TC11 titanium alloy was carried out under different rotational speeds, the microstructures and mechanical properties of the welded joints were analyzed, and the relationships among processing parameters, microstructures and properties of the joints were established. The SZ produced the fully β transformed microstructure, which contained grain boundary α phase, intragranular lamellar α+β phases and acicular α′ phase. The double strengthening was caused by the fine α phase and α+β phases as well as the presence of α′ phase, which led to the highest hardness value in the SZ. The retained original α phase and β transformed microstructure were found in the HAZ and TMAZ, while the TMAZ showed the streamlined deformation characteristics. The proportion of β transformed microstructure in these zones was higher when closer to the SZ, and thus the strengthening effect was enhanced. The size of α phase and α+β phases increased and the content of α′ phase decreased with the rotational speed ascending, which resulted in the reduction of hardness value in the SZ. Similar to the law reflected from the hardness test, all the joints fractured in BM after tensile test, the tensile strengths of the SZs under different rotational speeds were significantly higher than BM, and they decreased with the ascent of rotational speed. Besides, the fine α phase and α+β phases caused the higher elongations of SZs compared with the BM, meaning that the SZ had the good plasticity. With the rotational speed ascending, the elongations of SZs decreased owing to the increase of the size of α phase and α+β phases.
2022, 51(4):1442-1447.
DOI: 10.12442/j.issn.1002-185X.20210330
Abstract:
M-phase vanadium dioxide(VO2(M)) is a kind of intelligent heat-insulating window material with special phase change characteristics at around 68℃.However, the phase change stability of VO2(M) is still poor and its ability to modulate sunlight it is not high enough, which severely limits its industrial application in smart thermal insulation windows.This article mainly uses vanadium pentoxide as the vanadium source,oxalic acid as the reducing agent,urea as the precipitant,titanium sulfate as the dopant, and the hydrothermal reduction method to prepare powder M-phase titanium(Ti) doped VO2,referred to as Ti-VO2(M) powder.Through X-ray diffractometer(XRD),field emission scanning electron microscope(SEM),ultraviolet-visible-near infrared spectrophotometer(UV-Vis-NIR),differential scanning calorimeter(DSC) and X-ray energy spectrometer(EDS) analyze the element/phase composition and structure,crystal form,sunlight reflectance/transmittance and phase transition temperature of the synthesized powder,and optimize the Ti4+ doping amount.The study found that when the Ti4+ doping amount is controlled at 3%,the overall performance of the prepared Ti-VO2(M) powder is the best,which provides important data and technical support for the further application of intelligent thermal insulation plexiglass.
M-phase vanadium dioxide(VO2(M)) is a kind of intelligent heat-insulating window material with special phase change characteristics at around 68℃.However, the phase change stability of VO2(M) is still poor and its ability to modulate sunlight it is not high enough, which severely limits its industrial application in smart thermal insulation windows.This article mainly uses vanadium pentoxide as the vanadium source,oxalic acid as the reducing agent,urea as the precipitant,titanium sulfate as the dopant, and the hydrothermal reduction method to prepare powder M-phase titanium(Ti) doped VO2,referred to as Ti-VO2(M) powder.Through X-ray diffractometer(XRD),field emission scanning electron microscope(SEM),ultraviolet-visible-near infrared spectrophotometer(UV-Vis-NIR),differential scanning calorimeter(DSC) and X-ray energy spectrometer(EDS) analyze the element/phase composition and structure,crystal form,sunlight reflectance/transmittance and phase transition temperature of the synthesized powder,and optimize the Ti4+ doping amount.The study found that when the Ti4+ doping amount is controlled at 3%,the overall performance of the prepared Ti-VO2(M) powder is the best,which provides important data and technical support for the further application of intelligent thermal insulation plexiglass.
2022, 51(4):1448-1454.
DOI: 10.12442/j.issn.1002-185X.20210333
Abstract:
WO3 thin films were deposited on ITO/PET substrates by DC magnetron reactive sputtering at different glancing angles. The surface and cross-section morphology as well as chemical composition of WO3 thin film were characterized by field emission scanning electron microscope (FE-SEM) and energy dispersive spectrometer (EDS); Electrochemical and optical performances were measured by electrochemical workstation and ultraviolet spectrophotometer. The results show that the film surface forms a mountain-like morphology as the glancing angle 60, and the cross-section presents slant nano-columnar structure, which is benefit to the migration of ions and electrons. As the glancing angle =80, WO3 thin film has the fastest ion diffusion rate and the largest light modulation amplitude. The colorization efficiency reaches to 27.05cm2/C. Furthermore, the film also shows fast response and good cycle stability.
WO3 thin films were deposited on ITO/PET substrates by DC magnetron reactive sputtering at different glancing angles. The surface and cross-section morphology as well as chemical composition of WO3 thin film were characterized by field emission scanning electron microscope (FE-SEM) and energy dispersive spectrometer (EDS); Electrochemical and optical performances were measured by electrochemical workstation and ultraviolet spectrophotometer. The results show that the film surface forms a mountain-like morphology as the glancing angle 60, and the cross-section presents slant nano-columnar structure, which is benefit to the migration of ions and electrons. As the glancing angle =80, WO3 thin film has the fastest ion diffusion rate and the largest light modulation amplitude. The colorization efficiency reaches to 27.05cm2/C. Furthermore, the film also shows fast response and good cycle stability.
Hong Min
,
Wang Shanlin
,
Sun WenJun
,
Lin Bo
,
Wu Ming
,
Zhang Hong
,
He Jie
,
Hua YongPing
,
Wu ChengJun
2022, 51(4):1455-1461.
DOI: 10.12442/j.issn.1002-185X.20210334
Abstract:
30CrMnSiNi2A steel has become an important material for manufacturing aircraft landing gear and flaps due to its excellent mass-strength ratio. The welding speed of electron beam welding has a great influence on the microstructure and mechanical properties of 30CrMnSiNi2A steel in engineering applications. The microstructure of the joint transforms from the small equiaxed tempered sorbite and martensite mixed structure in the heat-affected zone to dendritic lath martensite grains in the weld area. The microhardness gradually increases from the base metal to the center of the weld. The microhardness of the weld area can reach up to 690HV0.2, which is about twice that of the base metal; the tensile strength is up to 842MPa, reaching 96.9% of the base metal strength. In addition, as the welding speed increases, the grain size decreases and the microhardness increases. However, the decrease in the number of HAGB and cementite is not good for the strength of the joint, so that the tensile strength of the joint decreases with the increase of the welding speed. The fracture mode of the lower joint is brittle fracture.
30CrMnSiNi2A steel has become an important material for manufacturing aircraft landing gear and flaps due to its excellent mass-strength ratio. The welding speed of electron beam welding has a great influence on the microstructure and mechanical properties of 30CrMnSiNi2A steel in engineering applications. The microstructure of the joint transforms from the small equiaxed tempered sorbite and martensite mixed structure in the heat-affected zone to dendritic lath martensite grains in the weld area. The microhardness gradually increases from the base metal to the center of the weld. The microhardness of the weld area can reach up to 690HV0.2, which is about twice that of the base metal; the tensile strength is up to 842MPa, reaching 96.9% of the base metal strength. In addition, as the welding speed increases, the grain size decreases and the microhardness increases. However, the decrease in the number of HAGB and cementite is not good for the strength of the joint, so that the tensile strength of the joint decreases with the increase of the welding speed. The fracture mode of the lower joint is brittle fracture.
2022, 51(4):1462-1469.
DOI: 10.12442/j.issn.1002-185X.20210335
Abstract:
This paper studies the characteristics of the microstructure of industrial electrolytic nickel deposits changing with deposition time. XRD, SEM, EBSD and other analysis methods were used to study the preferred orientation, microstructure and characteristic grain boundary distribution of electrolytic nickel plate with the production time were studied. The results show that the crystals on the surface of the electrodeposited nickel plate mainly grow in the direction perpendicular to the (200) plane, the cross-section shows the (111) and (200) double preferred orientations, and the crystal growth method is lateral growth. The surface and the cross-section show different microstructure, the surface morphology changes from a pyramid shape to a cell shape,and the growth mechanism changes from spiral dislocation-driven growth to atom aggregation and accumulation,the cross-sectional morphology of the nickel plate is always a lamellar structure at each stage. The cross-section of the deposited layer is mainly high-angle grain boundaries and a large number of Σ3 twin grain boundaries. In the stable growth process, the proportion of large-angle grain boundaries gradually decreases as the deposition progresses, neverthless the relative frequency of Σ3 grain boundaries gradually increases, but they will all be affected by changes in the environment of the electrolytic cell. In the cross-section along the growth direction, the electrolytic nickel plate mainly shous the fiber texture of <001> direction, and a large number of Σ3 twin boundaries affect the orientation of the deposited layer.
This paper studies the characteristics of the microstructure of industrial electrolytic nickel deposits changing with deposition time. XRD, SEM, EBSD and other analysis methods were used to study the preferred orientation, microstructure and characteristic grain boundary distribution of electrolytic nickel plate with the production time were studied. The results show that the crystals on the surface of the electrodeposited nickel plate mainly grow in the direction perpendicular to the (200) plane, the cross-section shows the (111) and (200) double preferred orientations, and the crystal growth method is lateral growth. The surface and the cross-section show different microstructure, the surface morphology changes from a pyramid shape to a cell shape,and the growth mechanism changes from spiral dislocation-driven growth to atom aggregation and accumulation,the cross-sectional morphology of the nickel plate is always a lamellar structure at each stage. The cross-section of the deposited layer is mainly high-angle grain boundaries and a large number of Σ3 twin grain boundaries. In the stable growth process, the proportion of large-angle grain boundaries gradually decreases as the deposition progresses, neverthless the relative frequency of Σ3 grain boundaries gradually increases, but they will all be affected by changes in the environment of the electrolytic cell. In the cross-section along the growth direction, the electrolytic nickel plate mainly shous the fiber texture of <001> direction, and a large number of Σ3 twin boundaries affect the orientation of the deposited layer.
2022, 51(4):1470-1477.
DOI: 10.12442/j.issn.1002-185X.20210340
Abstract:
At present, the Kroll method is still the only industrialized method for the production of metal titanium, and the newly developed electrolysis method and metal thermal reduction method are both in the research stage. In this paper, the reduction mechanism of the primary reduction stage and the law of the amount of magnesium are studied for the titanium powder prepared by the multi-stage reduction process. Through analysis and result verification, increasing the amount of magnesium can promote the kinetics of the reaction, which is conducive to the improvement of the reduction of TiO2 and inhibits the residual magnesium impurities. Magnesium is mostly wrapped in fluid form on the surface of titanium dioxide particles for mass transfer formation during the primary reduction process Multiphase microspheres and titanium oxide are sintered under high temperature to form the product morphology of the pore network structure. On the basis of considering the utilization of magnesium and the quality of the actual deep reduction product, the stoichiometric ratio is determined by experiments as the best ingredient ratio. The oxygen content of the primary reduction product of this ratio can reach 16.04wt.%, the specific surface area and the median particle size are 1.76m2/g and 34.39μm, respectively, and the O and Mg content of the prepared titanium powder are 0.274wt.% and 0.010wt.%, respectively.
At present, the Kroll method is still the only industrialized method for the production of metal titanium, and the newly developed electrolysis method and metal thermal reduction method are both in the research stage. In this paper, the reduction mechanism of the primary reduction stage and the law of the amount of magnesium are studied for the titanium powder prepared by the multi-stage reduction process. Through analysis and result verification, increasing the amount of magnesium can promote the kinetics of the reaction, which is conducive to the improvement of the reduction of TiO2 and inhibits the residual magnesium impurities. Magnesium is mostly wrapped in fluid form on the surface of titanium dioxide particles for mass transfer formation during the primary reduction process Multiphase microspheres and titanium oxide are sintered under high temperature to form the product morphology of the pore network structure. On the basis of considering the utilization of magnesium and the quality of the actual deep reduction product, the stoichiometric ratio is determined by experiments as the best ingredient ratio. The oxygen content of the primary reduction product of this ratio can reach 16.04wt.%, the specific surface area and the median particle size are 1.76m2/g and 34.39μm, respectively, and the O and Mg content of the prepared titanium powder are 0.274wt.% and 0.010wt.%, respectively.
2022, 51(4):1478-1487.
DOI: 10.12442/j.issn.1002-185X.20210345
Abstract:
A new third-generation nickel-based powder superalloy WZ-A3 was designed through a thermodynamic software. It was prepared by hot isostatic pressing (HIP) + hot extrusion (HEX) + isothermal forging (IF) + heat treatment (HT) processes. The influence of the process conditions on the microstructure of the alloy was studied. The high temperature tensile, creep and fatigue performance of the alloy after supersolvus heat treatment were also explored. The results show that the average grain size of the HIPed alloy is ASTM 8~9, while coarse γ" phase exists on the grain boundary and finer γ" particles presents within grain. After extrusion + forging, the grain size reduces to ASTM 13~14, the γ" particle within the grain is refined, but the number density of large γ" phase increases significantly. After supersolvus heat treatment, the large γ" particles are absent and the average size of the γ" particle is refined to 200nm. Corresponding tensile strength and yield strength of the supersolvus heat-treated alloy at 700℃ are 1360MPa and 1029MPa, respectively, and the elongation and percentage reduction of area after fracture are 23.5% and 17%, respectively. Under the condition of 800℃/330MPa, the time required for the creep strain to reach 0.2% is 229 hours, and the fatigue life at 700°C with a strain of 0~0.8% is 24,500 cycles. The creep and fatigue performance of the alloy are equivalent to typical third-generation nickel-based powder superalloys such as LSHR and ME3. This self-developed alloy has a tensile strength of nearly 50 MPa higher at 700°C and an elongation rate of 3 times compared with the supersolvus heat-treated LSHR alloy, but the yield strength is slightly lower.
A new third-generation nickel-based powder superalloy WZ-A3 was designed through a thermodynamic software. It was prepared by hot isostatic pressing (HIP) + hot extrusion (HEX) + isothermal forging (IF) + heat treatment (HT) processes. The influence of the process conditions on the microstructure of the alloy was studied. The high temperature tensile, creep and fatigue performance of the alloy after supersolvus heat treatment were also explored. The results show that the average grain size of the HIPed alloy is ASTM 8~9, while coarse γ" phase exists on the grain boundary and finer γ" particles presents within grain. After extrusion + forging, the grain size reduces to ASTM 13~14, the γ" particle within the grain is refined, but the number density of large γ" phase increases significantly. After supersolvus heat treatment, the large γ" particles are absent and the average size of the γ" particle is refined to 200nm. Corresponding tensile strength and yield strength of the supersolvus heat-treated alloy at 700℃ are 1360MPa and 1029MPa, respectively, and the elongation and percentage reduction of area after fracture are 23.5% and 17%, respectively. Under the condition of 800℃/330MPa, the time required for the creep strain to reach 0.2% is 229 hours, and the fatigue life at 700°C with a strain of 0~0.8% is 24,500 cycles. The creep and fatigue performance of the alloy are equivalent to typical third-generation nickel-based powder superalloys such as LSHR and ME3. This self-developed alloy has a tensile strength of nearly 50 MPa higher at 700°C and an elongation rate of 3 times compared with the supersolvus heat-treated LSHR alloy, but the yield strength is slightly lower.
2022, 51(4):1488-1496.
DOI: 10.12442/j.issn.1002-185X.20210348
Abstract:
The EuVO4-V2O5 composite nanowire with plum blossom structure is prepared by hydrothermal method, cation-exchange and calci-nation method. The EuVO4-V2O5 nanowire electrode materials are calcined at 300 and 500 oC, respectively. The results show that as the temperature continued to increase, the nanoparticles on the surface of the EuVO4-V2O5 nanowires has a certain agglomeration. When the temperature increased to 500 oC, the nanowires melted. Among them, the EuVO4-V2O5 composite nanowire prepared by calcination at 300 oC has the best electrochemical performance, and the charge-discharge specific capacity remains 376 mAh g-1 after 50 cycles with a current density of 30 mA g-1, showing good cycle stability, and this article developed a new synthetic route of rare earth vanadate.
The EuVO4-V2O5 composite nanowire with plum blossom structure is prepared by hydrothermal method, cation-exchange and calci-nation method. The EuVO4-V2O5 nanowire electrode materials are calcined at 300 and 500 oC, respectively. The results show that as the temperature continued to increase, the nanoparticles on the surface of the EuVO4-V2O5 nanowires has a certain agglomeration. When the temperature increased to 500 oC, the nanowires melted. Among them, the EuVO4-V2O5 composite nanowire prepared by calcination at 300 oC has the best electrochemical performance, and the charge-discharge specific capacity remains 376 mAh g-1 after 50 cycles with a current density of 30 mA g-1, showing good cycle stability, and this article developed a new synthetic route of rare earth vanadate.
2022, 51(4):1497-1513.
DOI: 10.12442/j.issn.1002-185X.20210418
Abstract:
In recent years, in order to meet the market requirements for bulk metallic glasses (BMGs) with large size and complex geometry, the advanced additive manufacturing technologies (AM) with smart characters (e.g., high flexible forming, excellent performance, less machining and high dimensional accuracy) were successfully applied to different kinds of BMGs. According to reported investigations on BMGs fabricated by AM in the past decades, the present work briefly introduces the progress on bulk metallic glasses and the advanced additive manufacturing of metals, and then systematically elaborate the forming mechanisms and properties of BMGs fabricated by AM. Subsequently, the bottleneck of the additive manufacturing of BMGs was discussed comprehensively. Finally, it is suggested that mastering the relationship of the AM processing, microstructure and properties to achieve the AMed BMGs with high quality and high performance are one of the most important development directions of BMGs fabricated by AM in the future
In recent years, in order to meet the market requirements for bulk metallic glasses (BMGs) with large size and complex geometry, the advanced additive manufacturing technologies (AM) with smart characters (e.g., high flexible forming, excellent performance, less machining and high dimensional accuracy) were successfully applied to different kinds of BMGs. According to reported investigations on BMGs fabricated by AM in the past decades, the present work briefly introduces the progress on bulk metallic glasses and the advanced additive manufacturing of metals, and then systematically elaborate the forming mechanisms and properties of BMGs fabricated by AM. Subsequently, the bottleneck of the additive manufacturing of BMGs was discussed comprehensively. Finally, it is suggested that mastering the relationship of the AM processing, microstructure and properties to achieve the AMed BMGs with high quality and high performance are one of the most important development directions of BMGs fabricated by AM in the future
2022, 51(4):1514-1524.
DOI: 10.12442/j.issn.1002-185X.20210447
Abstract:
Based on laser cladding technology of titanium alloy surface, the research progress of functional coatings with good wear resistance, corrosion resistance, high temperature oxidation resistance and biological activity is reviewed. And analyzes the law of material selection and strengthening mechanism of cladding layer. The advantages and necessity of laser cladding biomimetic coupling unit and multifunctional coating are discussed. Aiming at the causes of major defects such as cracks and pores in the cladding layer, improvement measures such as preheating the substrate, post-treatment, adjusting process parameters and preparing gradient coatings are proposed. Meanwhile, the future application and development trend of laser cladding technology on titanium alloy surface are prospected in order to promote the innovation and development of this surface coating technology and provide new ideas for the preparation of high quality, high efficiency and low cost new cladding coating.
Based on laser cladding technology of titanium alloy surface, the research progress of functional coatings with good wear resistance, corrosion resistance, high temperature oxidation resistance and biological activity is reviewed. And analyzes the law of material selection and strengthening mechanism of cladding layer. The advantages and necessity of laser cladding biomimetic coupling unit and multifunctional coating are discussed. Aiming at the causes of major defects such as cracks and pores in the cladding layer, improvement measures such as preheating the substrate, post-treatment, adjusting process parameters and preparing gradient coatings are proposed. Meanwhile, the future application and development trend of laser cladding technology on titanium alloy surface are prospected in order to promote the innovation and development of this surface coating technology and provide new ideas for the preparation of high quality, high efficiency and low cost new cladding coating.
2022, 51(4):1525-1530.
DOI: 10.12442/j.issn.1002-185X.20210783
Abstract:
Electric-explosive spraying is a new method of surface modification. It uses high voltage to pulse discharge the sprayed material, and the instantaneous high current heats it and explodes, producing high-temperature particles that are sprayed onto the surface of the substrate along with the shock wave to form a coating. In this paper, a new process of preparing high entropy alloy coating by electric explosion method is proposed. The feasibility of this method to prepare high-entropy alloy coatings was studied by XRD, SEM, EDS, and current and voltage waveforms. The results show that FeCoCrNiAlx (x=0, 0.5, 1.0) alloy coatings have formed simple solid solutions of FCC, BCC and FCC+BCC structures, and the phase structure of the coating gradually changes from FCC phase to BCC phase with the increase of Al content. The surface of the coating is smooth and dense, without obvious cracks, and the elements are evenly distributed on the surface of the coating, and no obvious element segregation is found. The energy deposition under the initial charging voltage of 11kV is 285.770 J, and the average deposition efficiency reaches 48.8%. With the increase of Al content, the microhardness of the coating gradually increases. When x=1.0, the average microhardness reaches the maximum value of 531.8HV, which is about twice the microhardness of the substrate. It can be seen that the high entropy alloy coating is successfully prepared by electric-explosive method.
Electric-explosive spraying is a new method of surface modification. It uses high voltage to pulse discharge the sprayed material, and the instantaneous high current heats it and explodes, producing high-temperature particles that are sprayed onto the surface of the substrate along with the shock wave to form a coating. In this paper, a new process of preparing high entropy alloy coating by electric explosion method is proposed. The feasibility of this method to prepare high-entropy alloy coatings was studied by XRD, SEM, EDS, and current and voltage waveforms. The results show that FeCoCrNiAlx (x=0, 0.5, 1.0) alloy coatings have formed simple solid solutions of FCC, BCC and FCC+BCC structures, and the phase structure of the coating gradually changes from FCC phase to BCC phase with the increase of Al content. The surface of the coating is smooth and dense, without obvious cracks, and the elements are evenly distributed on the surface of the coating, and no obvious element segregation is found. The energy deposition under the initial charging voltage of 11kV is 285.770 J, and the average deposition efficiency reaches 48.8%. With the increase of Al content, the microhardness of the coating gradually increases. When x=1.0, the average microhardness reaches the maximum value of 531.8HV, which is about twice the microhardness of the substrate. It can be seen that the high entropy alloy coating is successfully prepared by electric-explosive method.
2022, 51(4):1531-1536.
DOI: 10.12442/j.issn.1002-185X.20210350
Abstract:
In this experiment, thermal physical simulation experiments were carried out on 5vol.%TiCp/near-α titanium matrix composites to investigate the precipitation behavior of silicides and the deformation mechanism of β phase during β phase region. After deformation, microstructure is mainly composed of lamellar α phase and broken TiCp at room temperature. The existence of (Ti,Zr)6Si3 silicides in the microstructure was confirmed by transmission electron microscopy (TEM)，with the grain size of 350-600nm. The numeber of silicides increases with the increasing temperature or decreasing strain rate. In addition, the parent β grains were reconstructed by α phase at room temperature. TiCp was distributed along the β grain boundary, which promoted the dynamic recrystallization of β phase by providing nucleation sites and hindering dislocation movement. The high-density dislocations induced and promoted the precipitation of silicides caused by accumulation of strain and TiCp during hot deformation.
In this experiment, thermal physical simulation experiments were carried out on 5vol.%TiCp/near-α titanium matrix composites to investigate the precipitation behavior of silicides and the deformation mechanism of β phase during β phase region. After deformation, microstructure is mainly composed of lamellar α phase and broken TiCp at room temperature. The existence of (Ti,Zr)6Si3 silicides in the microstructure was confirmed by transmission electron microscopy (TEM)，with the grain size of 350-600nm. The numeber of silicides increases with the increasing temperature or decreasing strain rate. In addition, the parent β grains were reconstructed by α phase at room temperature. TiCp was distributed along the β grain boundary, which promoted the dynamic recrystallization of β phase by providing nucleation sites and hindering dislocation movement. The high-density dislocations induced and promoted the precipitation of silicides caused by accumulation of strain and TiCp during hot deformation.
