Study on stress relaxation and creep behavior of TB18 titanium alloy during the aging process

To study the stress relaxation and creep mechanism of TB18 titanium alloy in the aging process, the stress relaxation and creep tests were carried out at temperatures of 400, 440, 480 and 520 °C with an initial load of 300 MPa, and the microstructures of the specimens were analyzed by using the techniques of OM, SEM, TEM and in-situ XRD in the various test states. The results show that the dynamic precipitation of the α phase during aging is the cause of the " abnormal " phenomena of a rapid decrease in the stress relaxation and a rapid increase in the creep curve. The slow increase in creep strain and slow relaxation of stress at the lower temperatures of 400 °C and 440 °C are due to the negative plastic strain caused by the lattice shrinkage of the β phase due to the redistribution of elements in the dynamic precipitation of the α phase. The significant increase in creep strain and rapid relaxation of stress in the high-temperature range of 480 °C and 520 °C are due to a significant increase in plastic strain due to accelerated diffusion creep driven by the β→α phase transition and dislocation climb creep/grain-boundary creep due to the migration of the α/β interface.