The Mutual Transformation Behavior of α₂ and γ Phases under Low-Temperature Stress in Ti-47Al-8Nb-0.1B Alloy

This study shows the microstructure evolution behavior of Ti-47Al-8Nb-0.1B alloy under low-temperature stress heat treatment. Through in-depth research, the behavior of mutual transformation between α2 and γ phases is found. In addition, the existence of novel duplex microstructure is found under the conditions of 1300 °C/30 min and subsequent 600 °C/30 min and 700 °C/30 min. That is, irregular α2 phase and needle-like α2 phase are precipitated from the γ phase. The reason for this transformation is closely related to the large orientation difference between adjacent γ grains and the large cooling rate. In addition, the transformation of α2 phase to γ lamellar structure is found under both stress-free and stress conditions. The newly generated γ lamellar structure shows discontinuous growth state under stress-free conditions, but shows continuous growth state under stress conditions. The reason for this phenomenon is closely related to the diffusion rate of Al element. Stress can accelerate the diffusion of Al element and provide more energy to accelerate the nucleation and growth of γ lamellar structure.