Effect of prior cooling rate on the grain size of fully-lamellar TiAl-base alloy developed by tempering/quenching

The near-gamma titanium aluminides are attractive for aerospace and automobile applications, because of their low density, good high-temperature strength and acceptable oxidation resistance. Investment casting appears to be the lowest cost alternative for the manufacture of near-net-shape TiAl components; but, the unavoidable remnant of coarse ingot grains in the final product deteriorates the advance of cast alloy. Recently, the authors found that the fine lamellar structure can be developed in cast TiAl-base alloy by a quenching/tempering process. By recrystallization of the quenched massive γ structure at temperature above the α transus, a fine fully-lamellar structure with a grain size of 150 microm can be obtained. For the engineering application of this process, it must be considered that, in some TiAl-base alloys, microcracks might be introduced during water quenching, and for thick-wall TiAl components, the cooling-rate in center region is lower than that in the surface. In this context, this paper aims to study the effect of prior cooling rate on the tempered lamellar grain size in a cast Ti48Al2W0.5Si alloy