中文摘要: 为了研究TiAl合金的热变形行为,掌握其热加工特性,采用Gleeble-1500试验机对TiAl合金在温度为1 050～1 200℃、应变速率为0. 001～1 s-1条件下的高温变形行为进行了研究,获得了上述变形条件范围内的流变行为数据,建立了适于TiAl合金的本构方程。结果表明:TiAl合金的流变行为对变形速率和温度敏感,在热压缩过程中TiAl合金的流动应力呈现出加工硬化和流变软化的特征。通过电子背散射衍射(EBSD)观测发现,软化机制主要是先在晶界位置发生动态再结晶,然后再结晶向晶内扩展。通过计算,TiAl合金的变形激活能为360 k J/mol。采用最小二乘法得出了TiAl合金的流动应力模型,基于此模型绘制的流变曲线与实验值吻合较好,误差小于±5%,能够对TiAl合金高温流变行为进行较为准确的预测。
Abstract:In order to study the hot deformation behavior and characteristics of TiAl alloy,the hot compressive experiments were conducted in the temperature range from 1 050 ℃ to 1 200 ℃ and at strain rate range from 0. 001 s-1 to 1 s-1 on Gleeble-1500 hot simulator. The flow stress data was acquired by experiments,and the constitutive relationship was established for TiAl alloy. The results show that the flow behavior of TiAl alloy is sensitive to deformation temperature and strain rate. TiAl alloy flow stress demonstrates significant work hardening and softening characteristics in hot compression. The main mechanism of softening occured dynamic recrystallization on the grain boundary first and then extended into the grain by the EBSD observation. Deformation activation energy is 360 kJ/mol by calculation. The flow stress model is obtained by least square method. The flow stress curve based on this model agrees well with the experimental data,the deviation between them is less than ± 5%,and can predict the flow stress precisely.