Accelerated stress relaxation with simultaneously enhanced strength of titanium alloy by phase transformation and stress-induced twinning

Abstract

Stress relaxation with synchronous aging for titanium alloys was proposed to reduce the stress relaxation limit and enhance the mechanical strength simultaneously. Stress relaxation tests at 600 °C of solution treated sample and aged sample were performed to study the interplay between microstructure evolution and stress relaxation. Kohlrausch-Williams-Watts equation was employed to analyze the relaxation kinetics. Results show that the applied stress promotes the rapid precipitation and growth of the αs (secondary α) phase. Meanwhile, the applied stress also induces the presence of twinning in the αs phase, leading to the relaxation of the elastic energy in the αs. In return, both phase transformation and stress-induced twinning reduce the stress relaxation limit by 56 %. Moreover, the tensile strength of Ti-6.5Al-2Zr-1Mo-1 V alloy at room and service temperature was improved by 3.4 % and 9.2 %, respectively.