Effect of rare earth Y(0.3 at%) on as-cast microstructure of Ti-45Al-5Nb alloy

As-cast microstructures of the Ti-45Al-5Nb (at%) and Ti-45Al-5Nb-0.3Y (at%) alloys were investigated. Results show that as-cast micro structure is changed and equiaxed grains are remarkably refined due to the addition of Y. Most Y element accumulates along the grain boundaries with the discontinuous networks and a small amount of Y elements distribute in the grains with the fine particles. A new phase is produced as YAl₂ compound. The mechanisms of grain refinement are analyzed, and indicate that Y could promote nucleation of TiAl alloy and greatly suppress the growth of the primary β phase through the enrichment of Y earlier than the solidification. And the latter more contributed to the refinement of microstructure.