An ultra-refining microstructure in rapidly solidified Ti–45Al-8.5Nb-(W, B, Y) alloy after an isothermal heat treatment

In the present work, the microstructure evolution of a rapidly solidified TiAl alloy with the nominal composition of Ti–45Al-8.5Nb-0.2W-0.2B-0.02Y (atom %) prepared by melt spinning method was investigated. An ultra-fine and homogenized microstructure containing metastable supersaturated α₂ phase with a grain size of 3–10 μm was obtained by rapid solidification. α phase became the primary phase during rapid solidification and the solidification path was discussed using phase selection hierarchy map calculated by CALPHAD method. After one-step heat treatment (aging at 800 °C), the metastable α₂ grain decomposed to α₂/γ nano-lamellar structure quickly and then greatly refined via recrystallization, which might be attribute to a large elastic strain and high interfacial energy stored in lamellar structure. The resulting microstructure is constituted by ultra-fine equiaxed γ grains, B2 grains and very small globular Y₂O₃ precipitates. This study can provide some reference information on the microstructure after rapid solidification and the microstructural thermostability.