Based on rate dependent crystal plasticity theory,the single crystal constitutive equation of TiAl was developed to incorporate the effect of slip and twinning at different temperatures and strain rates.A polycrystalline model consisting of grains with random orientations was constructed to simulate the elastoplastic mechanical behavior of NG TiAl at temperatures ranging from room temperature to 840 ℃ and strain rates of 0.001,320,800 and 1 350/s.The conclusions drawn from the simulations agree well with the experimental results.Besides,the influence of twining on the plastic deformation was investigated.The calculated result shows that deformation twin is one of the major mechanisms of plastic deformation.The twin volume fraction under dynamic loading is higher than that under quasi-static loading,which increase the ductility of NG TiAl under dynamic loading.However,temperature has little influence on the evolution of deformation twin.%基于率相关的晶体塑性理论,发展了更为合理的同时考虑位错滑移和形变孪晶作用、并计及温度影响的TiAl单晶本构模型.在此基础上,建立了能够反映晶粒随机取向的多晶有限元模型,对不同温度(室温～840℃)不同拉伸应变率(0.001～1 350/s)下NGTiAl的弹塑性力学行为进行了模拟.结果显示,模拟得到的应力应变曲线与试验结果基本一致,能够比较好地模拟NG TiAl在不同温度和应变率下的材料响应.还考察了形变孪晶对塑性变形的影响,结果表明孪晶为NG TiAl重要的变形方式之一；动态条件下孪晶的体积分数增大,从而提高了NG TiAl的塑性变形；而温度对孪晶体积分数演化的影响不明显.
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