Effect of cooling rate on the grain refinement of TiAl-based alloys by rapid heat treatment

Abstract A novel approach was recently sought to refine the coarse, fully lamellar structure of cast TiAl alloys merely by rapid heat treatment. It is shown in this study that cooling rate is an important factor controlling the refining result of this approach. It is suggested that the grain size be refined first by massive transformation resulting from fast cooling, and then by precipitation of α laths with four different orientations in massive and feathery γ grains during subsequent cyclic heat treatment. Since the populations of massive and feathery γ grains are different under different cooling rates, they appear to influence the refining process. Namely, a high cooling rate favors formation of massive γ grains and abundant nucleation sites for the precipitation of α laths.