Microstructural refinement of boron-containing Beta-solidifying Gamma-titanium aluminide alloys through heat treatments in the Beta phase field

Abstract

The addition of B effectively supports the generation of fine and homogeneous microstructures in as-cast β-solidifying γ-based titanium aluminide alloys. The microstructural refinement in such alloys can be attributed to the borides acting as nucleation sites for new α grains during the solid-state β → α transformation (Hecht U, Witusiewicz V, Drevermann A, Zollinger J, Intermetallics 2008; 16: 969–978). In the current work it is shown that the cooling rate plays a crucial role in determining whether borides serve as nucleation sites for grain refinement. Surprisingly, if the cooling rate is too high then grain refinement by borides is hampered. The positive effect of borides can be used to obtain grain refinement in these materials by a simple heat treatment, even if the microstructure has been extensively coarsened through prior heat treatment.