Stress Relaxation Stability of (Nb, W) Coalloying TiAl-Based Alloys at Different Temperatures of 500–800 °C and Different Initial Stresses of 300–600 MPa

In order to explore the feasibility of (Nb, W) coalloying TiAl-based alloy and high Nb–TiAl-based alloy as high-temperature fasteners, Ti–44Al–4Nb–1W–0.1B alloy, and Ti–44Al–8Nb–0.1B alloy are chosen as the experimental material. The stress relaxation stability of two alloys is judged by stress–time curves under different stress and temperature. The results show that at 500, 600, 700 °C, and initial stress 300 MPa, the stress of two alloys first quickly increases and then maintains stability. However, at 800 °C and different initial stresses of 300, 450, and 600 MPa, the stress of two alloys first quickly decreases, and then slowly decreases. At 600 MPa, the stress of two alloys both drops to zero quickly. The factors increasing stress are work-hardening and solid-solution strengthening. The factors decreasing stress are dynamic recrystallization, B2 phase coordination, and phase transition. It is found that the Schmidt factor of the B2 phase is higher, thus producing a good stress–strain coordination effect. It is also found that the volume fraction of dynamic recrystallization is small under all these conditions, approximately less than 3.3%.