Effect of rare earth y (0.3 at%) on as-cast microstructure of Ti-45Al-5M 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 microstructure 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 element distribute inner 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 beta phase through the enrichment of Y earlier than the solidification. And the latter more contributed to the refinement of microstructure.