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

A novel approach was recently sought to refine the coarse, fully lamellar s tructure of cast TiAl alloys merely by rapid heat treatment. It is shown in this study that cooling rate is an important factor controlling the refini ng result of this approach. It is suggested that the grain size be refined first by massive transformation resulting from fast cooling, and then by pr ecipitation of alpha laths with four different orientations in massive and feathery gamma grains during subsequent cyclic heat treatment. Since the po pulations of massive and feathery gamma grains are different under differen t cooling rates, they appear to influence the refining process. Namely, a h igh cooling rate favors formation of massive gamma grains and abundant nucl eation sites for the precipitation of alpha laths. (C) 2000 Elsevier Scienc e B.V. All rights reserved.