Different precipitation mechanism of B2 phase under three-way stress heat treatment

In this study, the classical Ti-44Al-8Nb-0.1B alloy is subjected to three-way stress heat treatment, and the evolution behavior of metastable α₂ phase with the increase of temperature or stress under the action of three-way stress is studied. It is found that with the increase of temperature or the increase of stress, the alloy always gradually transforms to the γ phase. In addition, two different B2 phases are found under different heat treatment conditions, and the precipitation mechanism of two different B2 phases is studied in detail. The B2 phase precipitated at 300 MPa/400 °C is directly transformed from the α₂ phase. Under the condition of 300 MPa/800 °C, the B2 phase is precipitated by α₂ phase and γ phase. The α₂ phase and γ phase first undergo compositional transformation and then structural transformation or both at the same time, resulting in the precipitation of B2 phase.