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

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.

Key words:TA32 titanium alloy; stress relaxation; constitutive equation