Response of the solidification microstructure of a high Nb containing TiAl alloy to an isothermal high-temperature heat treatment

Vacuum induction melting device combined with temperature control system was employed to investigate the effect of isothermal heat treatment (IHT) during solidification process on the microstructure evolution of a high Nb containing TiAl alloy. The microstructures of the alloy in as-cast condition and after IHT were studied. The results show that the as-cast microstructures exhibit a significant microstructural inhomogeneity with fine grains in dendrite core and coarse grains in interdendritic region. A new treatment approach by means of a short-term IHT within the β phase field during solidification process is proposed to obtain a uniform and refined microstructure. Compared with the as-cast alloy, IHT can reduce the tendency for crack. This phenomenon is attributed to the improvement of microstructural homogeneity by the elimination of peritectic α phase and the microstructure refinement by β → α transformation.