The characteristics and mechanisms of creep brittle-ductile transition in TiAl alloys

This article presents the performance and mechanisms of brittle-ductile transition during creep in Ti-46Al-8Nb alloys. Experimental results show that the brittle-ductile transition temperature (BDTT) was determined to be 760–780 °C in Ti-46Al-8Nb alloy, and the creep lifetime and creep strain obviously changed at BDTT. Major dislocation slip systems of α2 lamellae are activated above BDTT, which promote the plastic deformation of α2/γ lamellae and contribute to overall creep strain. The thermal activation is very active that dislocations can overcome obstacle under a small effective stress during creep above BDTT, and the deformation depends on dislocation slip assisted by the thermal activation during creep below BDTT. The apparent activation energy is 402 kJ/mol during creep above BDTT, as the creep is controlled by dislocation climb. The liner relationship between 1/T and ln(ε) breaks down during creep below BDTT, as the interface sliding mechanism being dominant in this regime. There is a significant change in apparent activation energy value at BDTT. Moreover, the BDTT of Ti-46Al-8Nb alloy is 60 °C higher than binary Ti-44Al alloy.