Hot deformation behavior, microstructural evolution and flow softening mechanism were investigated in Ti-46A1-8Nb alloy via isothermal compression approach. The true stress-strain curves exhibited typical work hardeni...Hot deformation behavior, microstructural evolution and flow softening mechanism were investigated in Ti-46A1-8Nb alloy via isothermal compression approach. The true stress-strain curves exhibited typical work hardening and flow softening, in which the dependence of the peak stress on temperature and strain rate was obtained by hyperbolic sine equation with Zener-Hollomon （Z） parameter, and the activation energy was calculated to be 446.9 kJ/mol. The microstructural analysis shows that the alternate dark and light deformed ribbons of Al-rich and Nb-rich regions appeared and were associated with local flow involving solute segregation. The Al segregation promoted flow softening mainly arising from the recrystaUization of V phase with low stacking fault energy. The coarse recrystallized 7 and several massive phase were observed at grain boundaries. While in the case of Nb segregation, t/B2 phase harmonized bending of lamellae, combined with the growth of recrystallized γ grains and α ＋ β ＋ γ→α＋ γ transition under conditions of temperature and stress, leading to the breakdown of α2/γ lamellar colony. During the hot compression process, gliding and dissociation of dislocations occurred in γ phase that acted as the main softening mechanism, leading to extensive γ twins and cross twins in α/γ lamellae and at grain boundaries. In general, homogeneous microstructure during the hot defor- mation process can be obtained in TiAl alloy with high Nb addition and low Al segregation. The deformation substructures intrinsically promote the formability of Ti--46Al-8Nb alloy.展开更多
A three-stage model is introduced to describe the tensile failure process of rock and concrete materials.Failure of the material is defined to contain three stages in the model,which include elastic deformation stage,...A three-stage model is introduced to describe the tensile failure process of rock and concrete materials.Failure of the material is defined to contain three stages in the model,which include elastic deformation stage,body damage stage and localization damage stage.The failure mode change from uniform body damage to localization damage is expressed.The heterogeneity of material is described with strain strength distribution.The fracture factor and intact factor,defined as the distribution function of strain strength,are used to express the fracture state in the failure process.And the distributive parameters can be determined through the experimental stress-strain curve.展开更多
基金supported by the National Key Research and Development Program of China(No.2016YFB0301201)the National Natural Science Foundation of China(Nos.51504060,51301140)the Fundamental Research Funds for the Central Universities(No.N160713001)
文摘Hot deformation behavior, microstructural evolution and flow softening mechanism were investigated in Ti-46A1-8Nb alloy via isothermal compression approach. The true stress-strain curves exhibited typical work hardening and flow softening, in which the dependence of the peak stress on temperature and strain rate was obtained by hyperbolic sine equation with Zener-Hollomon （Z） parameter, and the activation energy was calculated to be 446.9 kJ/mol. The microstructural analysis shows that the alternate dark and light deformed ribbons of Al-rich and Nb-rich regions appeared and were associated with local flow involving solute segregation. The Al segregation promoted flow softening mainly arising from the recrystaUization of V phase with low stacking fault energy. The coarse recrystallized 7 and several massive phase were observed at grain boundaries. While in the case of Nb segregation, t/B2 phase harmonized bending of lamellae, combined with the growth of recrystallized γ grains and α ＋ β ＋ γ→α＋ γ transition under conditions of temperature and stress, leading to the breakdown of α2/γ lamellar colony. During the hot compression process, gliding and dissociation of dislocations occurred in γ phase that acted as the main softening mechanism, leading to extensive γ twins and cross twins in α/γ lamellae and at grain boundaries. In general, homogeneous microstructure during the hot defor- mation process can be obtained in TiAl alloy with high Nb addition and low Al segregation. The deformation substructures intrinsically promote the formability of Ti--46Al-8Nb alloy.
基金Project supported by the National Program on Key Basic Research Project of China(973 Program,No.2015CB250903)CAS Strategic Priority Research Program(B)(No.XDB10030303)
文摘A three-stage model is introduced to describe the tensile failure process of rock and concrete materials.Failure of the material is defined to contain three stages in the model,which include elastic deformation stage,body damage stage and localization damage stage.The failure mode change from uniform body damage to localization damage is expressed.The heterogeneity of material is described with strain strength distribution.The fracture factor and intact factor,defined as the distribution function of strain strength,are used to express the fracture state in the failure process.And the distributive parameters can be determined through the experimental stress-strain curve.
