The Effect of Pressure Stress on the Evolution of B2(ω) Phase in High Nb Containing TiAl Alloy

The thermal stability of the B2(ω) phase in high Nb containing TiAl alloy has attracted intense attention in recent years. This study focuses on the phase transformation between B2 and ω phases under the influence of thermal pressure stress in the Ti–45Al–8.5Nb–(W, B, Y) alloy. A large number of ω phases with the volume fraction of 42.3% exist within the B2 region in as-cast alloys. The as-cast samples were subjected to thermo-compressive loading at 850 and 900 °C under the stresses of 300 and 500 MPa. Results show that the transformation of B2 → ω occurs at 850 °C, which can be promoted under a pressure stress. Further, the ω particles dissolved into the B2 matrix at 900 °C, and this transformation is suppressed by the role of thermal pressure. The mechanisms of the phase transformations mentioned above were discussed.