TA32钛合金高温应力松弛行为及其对应的本构方程

Stress Relaxation Behavior and Corresponding Constitutive Relation of TA32 Titanium Alloy at High Temperature

摘要:

在不同温度（775℃，800℃，825℃）、不同初应力（150MPa、200MPa）和不同预应变（7.85%、15.7%）下进行TA32钛合金高温应力松弛实验，研究了工艺参数对应力松弛行为的影响。对实验后的试样进行微观组织观察，分析了温度对微观组织的影响。利用二次延迟函数对应力松弛曲线进行拟合，推导得到高温蠕变本构方程，进而将其应用于TA32钛合金应力松弛行为有限元模拟。结果表明：在应力松弛的前200s，应力松弛速率很快，其应力急剧下降，经过3600s后应力逐渐趋于平缓并最终达到松弛极限。应力松弛行为随着温度的升高而加快,但其松弛极限随之减小，初应力和预应变则对其影响不大。随着温度的升高晶粒发生了等轴化和长大现象，塑性增强。模拟结果和应力松弛的实验曲线有较高的吻合度，验证了此蠕变方程的可靠性。

Abstract:

Stress relaxation tests at different combinations of temperatures (775℃、800℃、825℃), initial stresses (150MPa、200MPa) and pre-strains (7.85%、15.7%) were performed for the titanium alloy TA32 to study the influences of the process parameters on its stress relaxation behavior. The microstructures of the specimen after the experiments at different temperatures were observed to investigate the temperature effects on the microstructure evolution. The stress relaxation curves were fitted with the quadratic delay function. And the creep constitutive equation at the high temperature was established and applied to define the stress relaxation behavior of TA32 titanium alloy in the finite element analysis. The experimental results show that the stress drops rapidly with high stress relaxation rate in the first 200 s of the stress relaxation. The stress tends to be stable and finally reaches the limit of stress relaxation after 3600s. The stress relaxation rate increases with the increasing temperature while the stress relaxation limit decreases. And the initial stress and pre-strain have little effect on the stress relaxation behavior. The equiaxed and grown grains can enhance the plasticity with the increase of temperature. The simulation results and experimental stress relaxation curves are in good correlation which validated the reliability of the creep constitutive equation.