晶界对近片层TiAl高温动态力学行为的数值模拟

Numerical simulation of dynamic mechanical behavior of near lamellar TiAl at elevated temperature with influence of grain boundary

基于晶体塑性理论,给出了同时考虑位错滑移、形变孪晶和晶界变形的近片层组织TiAl本构模型;在此基础上,建立基于Voronoi算法的近层片TiAl三维多晶有限元模型,并在晶粒交界处引入壳单元来描述晶界;利用上述有限元模型,对不同温度(室温、500和700℃)和不同拉伸应变率(10-3、320、800和1 350 s-1)下近层片TiAl的塑性力学行为进行数值模拟。结果显示:模拟得到的应力塑性应变曲线与试验结果吻合较好,能够反映近层片TiAl在不同温度和应变率下的材料响应;由于晶界的存在,晶粒内的应力分布会发生明显改变,晶界附近产生一定的应力集中。此外,晶界对孪晶存在一定的阻碍作用,使得晶界附近实体单元的孪晶体积分数要略低于多晶整体的平均孪晶体积分数。

Based on the rate dependent crystal plasticity theory,a constitutive relationship of near lamellar TiAl was presented to account for the influence of dislocation slip,twinning evolution and grain boundary movement.With the help of the Voronois arithmetic,a three-dimensional polycrystalline finite element framework,in which the shell elements were used to describe the grain boundaries,was constructed for the implementation of the proposed constitutive model.Numerical simulations of the plastic mechanical behavior of near lamellar TiAl under temperatures of room temperature,500 ℃,700 ℃ and tensile strain rates of 10-3 s-1,320 s-1,800 s-1 and 1 350 s-1 were conducted,subsequently.The results drawn from the simulations agree well with the experimental data.The influence of grain boundary on the mechanical behavior of the near lamellar TiAl was also investigated.The results show that the stress distribution within a grain is significantly changed by the grain boundary,and certain stress concentration appears near the grain boundary.In addition,the calculated results also show that the grain boundary can obstruct the twinning evolution,leading to the volume ratio of deformation twinning around the grain boundaries smaller than that of the whole model.