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

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 α_s (secondary α) phase. Meanwhile, the applied stress also induces the presence of twinning in the α_s phase, leading to the relaxation of the elastic energy in the α_s. 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.