The research demonstrated that laser powder bed fusion(LPBF)coupled with controlled annealing at 1200°C,could significantly increase the proportion of coincidence site lattice(CSL)grain boundary,thereby achieving...The research demonstrated that laser powder bed fusion(LPBF)coupled with controlled annealing at 1200°C,could significantly increase the proportion of coincidence site lattice(CSL)grain boundary,thereby achieving an outstanding synergy of enhanced strength and exceptional ductility.The plastic deformation behavior,strain hardening behavior,and fracture behavior of LPBF 316L steel annealing at 1200℃for 20 h were studied through quasi-in-situ tensile process.It was found that LPBF 316L steel formed a certain proportion of deformation twins during the tensile process,and the formation of twins changed the crystal orientation,thus promoting further slip and crystal deformation.The synergistic effect of slip and twin promoted higher plasticity.LPBF process coupled with controlled annealing at 1200°C for 20 h leads to a ultimate tensile strength of 613 MPa and total elongation of 73.8%.展开更多
西交大发现金属镁塑性变形新机制镁是最轻的金属结构材料,相比于传统金属,镁的塑性变形加工难、成本高,制约了其广泛应用。近日,西交大单智伟团队在金属镁塑性变形行为和内在机制领域取得新进展。该成果以Rejuvenation of plasticity vi...西交大发现金属镁塑性变形新机制镁是最轻的金属结构材料,相比于传统金属,镁的塑性变形加工难、成本高,制约了其广泛应用。近日,西交大单智伟团队在金属镁塑性变形行为和内在机制领域取得新进展。该成果以Rejuvenation of plasticity via deformation graining in magnesium为题发表在Nature Communications上。展开更多
High temperature plastic deformation behavior of non-orientated electrical steel was investigated by Gleeble 1500 thermo-mechanical simulator at strain rate of 0.01-10 s^-1 and high temperature of 500-1 200 ℃. The st...High temperature plastic deformation behavior of non-orientated electrical steel was investigated by Gleeble 1500 thermo-mechanical simulator at strain rate of 0.01-10 s^-1 and high temperature of 500-1 200 ℃. The stress level factor （a）, stress exponent （n）, structural factor （A） and activation energy （Q） of high temperature plastic deformation process of non-orientated electrical steel in different temperature ranges were calculated by the Arrhenius model. The results show that, with dynamic elevation of deformation temperature, phase transformation from α-Fe to γ-Fe takes place simultaneously during plastic deformation, dynamic recovery and dynamic recrystallization process, leading to an irregular change of the steady flow stress. For high temperature plastic deformation between 500 and 800 ℃, the calculated values of a, n, A, and Q are 0.039 0 MPa 1, 7.93, 1.9× 10^18 s^-1, and 334.8 kJ/mol, respectively, and for high temperature plastic deformation between 1 050 and 1 200 ℃, the calculated values of a, n, A, and Q are 0.125 8 MPa1, 5.29, 1.0 × 10^28 s^-1, and 769.9 kJ/mol, respectively.展开更多
True stress-true strain curve,microstructure and texture information were obtained to investigate the superplastic deformation behavior of 1420 Al-Li alloy sheets with initial elongated grains.From the true stress-tru...True stress-true strain curve,microstructure and texture information were obtained to investigate the superplastic deformation behavior of 1420 Al-Li alloy sheets with initial elongated grains.From the true stress-true curve,the stress increases with the increase of strain to 0.15,then dramatically decreases with the increase of strain to 0.80,and finally keeps almost a horizontal line.Meanwhile,initial elongated grains are gradually changed into equiaxed grains and the initial strong Brass {0 1 1} <2 1 1> and S {1 2 3} <6 3 4> orientations are turned into nearly random orientation with increasing strain.All these results suggest that dislocation activity is the dominant mechanism during the first stage,then dynamic recrystallization occurs,and grain rotation is expected as an accommodation for grain boundary sliding(GBS).At larger strains,grain boundary migration(GBM) becomes necessary to accommodate GBS.展开更多
To reduce defects caused by non-homogeneous metal flow in conventional extrusion,a die with guiding angle was designed to improve the metal flow behavior. The characteristic quantities such as the second invariant of ...To reduce defects caused by non-homogeneous metal flow in conventional extrusion,a die with guiding angle was designed to improve the metal flow behavior. The characteristic quantities such as the second invariant of the deviator stress J2 and Lode's coefficient μ were employed for the division of deformation area. The results show that when the metal is extruded with the guiding angle,no metal flow interface forms at the container's bottom,the dead zone completely disappears,the deformation types of the metal in the plastic deformation area change from three types to one type of tension,and the homogeneity of the deformation as well as metal flow are greatly improved. The non-homogeneous metal flow at the final stage of extrusion is improved,reducing the shrinkage hole at the axis end. The radial stress of the furthest point from the axis is transformed from tensile stress to compressive stress and the axial stress,and decreased from 70.8 to 34.8 MPa. Therefore,the surface cracks caused by additional stress are greatly reduced.展开更多
An objective of this work is to develop a validated computational model that can be used to estimate ratcheting accumulation behavior of granular soils due to high-cyclic loading. An accumulation model was proposed to...An objective of this work is to develop a validated computational model that can be used to estimate ratcheting accumulation behavior of granular soils due to high-cyclic loading. An accumulation model was proposed to describe only the envelope of the maximum plastic deformations generated during the cyclic loading process, which can calculate the accumulated deformation by means of relatively large load cycle increments. The concept of volumetric hardening was incorporated into the model and a so-called overstress formulation was employed to describe the evolution of the accumulated volumetric deformation as a state parameter. The model accounted for ratcheting shakedown and accumulation such as a pseudo-yield surface(a shakedown surface) associated with loading inside the current virgin yield surface which was implemented into the well-known modified Cam-clay model. Finally, the model was calibrated using data from the stress-controlled drained cyclic triaxial tests on homogeneous fine grained sands. It is seen that the model can successfully represent important features of the ratcheting accumulation of both volumetric and deviatoric deformation caused by repeated drained loading over a large number of cycles.展开更多
基金Project(52474418)supported by the National Natural Science Foundation of ChinaProject(YDZJSX2022A012)supported by the Central Guiding Local Science and Technology Development Foundation,China。
文摘The research demonstrated that laser powder bed fusion(LPBF)coupled with controlled annealing at 1200°C,could significantly increase the proportion of coincidence site lattice(CSL)grain boundary,thereby achieving an outstanding synergy of enhanced strength and exceptional ductility.The plastic deformation behavior,strain hardening behavior,and fracture behavior of LPBF 316L steel annealing at 1200℃for 20 h were studied through quasi-in-situ tensile process.It was found that LPBF 316L steel formed a certain proportion of deformation twins during the tensile process,and the formation of twins changed the crystal orientation,thus promoting further slip and crystal deformation.The synergistic effect of slip and twin promoted higher plasticity.LPBF process coupled with controlled annealing at 1200°C for 20 h leads to a ultimate tensile strength of 613 MPa and total elongation of 73.8%.
文摘西交大发现金属镁塑性变形新机制镁是最轻的金属结构材料,相比于传统金属,镁的塑性变形加工难、成本高,制约了其广泛应用。近日,西交大单智伟团队在金属镁塑性变形行为和内在机制领域取得新进展。该成果以Rejuvenation of plasticity via deformation graining in magnesium为题发表在Nature Communications上。
基金Project(2005038560) supported by the Postdoctoral Foundation of ChinaProject(05GK1002-2) supported by Key Program of Hunan Province
文摘High temperature plastic deformation behavior of non-orientated electrical steel was investigated by Gleeble 1500 thermo-mechanical simulator at strain rate of 0.01-10 s^-1 and high temperature of 500-1 200 ℃. The stress level factor （a）, stress exponent （n）, structural factor （A） and activation energy （Q） of high temperature plastic deformation process of non-orientated electrical steel in different temperature ranges were calculated by the Arrhenius model. The results show that, with dynamic elevation of deformation temperature, phase transformation from α-Fe to γ-Fe takes place simultaneously during plastic deformation, dynamic recovery and dynamic recrystallization process, leading to an irregular change of the steady flow stress. For high temperature plastic deformation between 500 and 800 ℃, the calculated values of a, n, A, and Q are 0.039 0 MPa 1, 7.93, 1.9× 10^18 s^-1, and 334.8 kJ/mol, respectively, and for high temperature plastic deformation between 1 050 and 1 200 ℃, the calculated values of a, n, A, and Q are 0.125 8 MPa1, 5.29, 1.0 × 10^28 s^-1, and 769.9 kJ/mol, respectively.
基金Project(2006DFA53250) supported by the International Science and Technology Cooperation Program of ChinaProject(2005CB623706) supported by the National Basic Research Program of China
文摘True stress-true strain curve,microstructure and texture information were obtained to investigate the superplastic deformation behavior of 1420 Al-Li alloy sheets with initial elongated grains.From the true stress-true curve,the stress increases with the increase of strain to 0.15,then dramatically decreases with the increase of strain to 0.80,and finally keeps almost a horizontal line.Meanwhile,initial elongated grains are gradually changed into equiaxed grains and the initial strong Brass {0 1 1} <2 1 1> and S {1 2 3} <6 3 4> orientations are turned into nearly random orientation with increasing strain.All these results suggest that dislocation activity is the dominant mechanism during the first stage,then dynamic recrystallization occurs,and grain rotation is expected as an accommodation for grain boundary sliding(GBS).At larger strains,grain boundary migration(GBM) becomes necessary to accommodate GBS.
基金Project(RC2010QN017008) supported by the Excellent Young Teachers Program of Harbin City, China
文摘To reduce defects caused by non-homogeneous metal flow in conventional extrusion,a die with guiding angle was designed to improve the metal flow behavior. The characteristic quantities such as the second invariant of the deviator stress J2 and Lode's coefficient μ were employed for the division of deformation area. The results show that when the metal is extruded with the guiding angle,no metal flow interface forms at the container's bottom,the dead zone completely disappears,the deformation types of the metal in the plastic deformation area change from three types to one type of tension,and the homogeneity of the deformation as well as metal flow are greatly improved. The non-homogeneous metal flow at the final stage of extrusion is improved,reducing the shrinkage hole at the axis end. The radial stress of the furthest point from the axis is transformed from tensile stress to compressive stress and the axial stress,and decreased from 70.8 to 34.8 MPa. Therefore,the surface cracks caused by additional stress are greatly reduced.
基金Projects(41302219,41302076)supported by the National Natural Science Foundation of China
文摘An objective of this work is to develop a validated computational model that can be used to estimate ratcheting accumulation behavior of granular soils due to high-cyclic loading. An accumulation model was proposed to describe only the envelope of the maximum plastic deformations generated during the cyclic loading process, which can calculate the accumulated deformation by means of relatively large load cycle increments. The concept of volumetric hardening was incorporated into the model and a so-called overstress formulation was employed to describe the evolution of the accumulated volumetric deformation as a state parameter. The model accounted for ratcheting shakedown and accumulation such as a pseudo-yield surface(a shakedown surface) associated with loading inside the current virgin yield surface which was implemented into the well-known modified Cam-clay model. Finally, the model was calibrated using data from the stress-controlled drained cyclic triaxial tests on homogeneous fine grained sands. It is seen that the model can successfully represent important features of the ratcheting accumulation of both volumetric and deviatoric deformation caused by repeated drained loading over a large number of cycles.
