Evolution of Metastable α 2 Phase in a Quenched High‐Nb‐Containing TiAl Alloy at 800 °C

Fast cooling from high temperatures is a common way in heat treatments and hot processing, which could introduce excess metastable α 2 phase in the microstructure. Herein, the evolution of the metastable α 2 phase in a water‐quenched Ti–45Al–8.5Nb–(W, B, Y) alloy from different single‐phase regions is experimentally studied. After water quenching from the β single‐phase region, Widmanstätten α 2 , as well as residual β o , γ grains form from β phase and thin γ laths in α 2 phase are observed. However, the water‐quenched microstructure from the α single‐phase region consists of equiaxed α 2 grains, residual β o , and massive γ phase. When annealing the quenched samples at 800 °C, similar microstructural evolutions are found in both samples quenched from different temperatures. 1) α 2 phase transform into α 2 /γ nanolamellar structure immediately. 2) Recrystallization and discontinuous coarsening occur at the colony boundaries. 3) The nanometer‐scale γ/γ T lamellae transformed from α 2 grains are also unstable, which merge into thicker γ lamellae, and the interfaces of coarsened γ lamellae become curvy and blurry.