Effect of Aluminum Content on Interfacial Reaction of Directionally Solidified TiAl Alloys

High Nb-containing TiAl alloys with different aluminum content were prepared by vacuum induction casting technology, and then processed via directional solidification in a Y2O3-coated Al2O3 crucible. The effect of aluminum content on the metal and coating interface, chemical composition, and phases at the interfaces were evaluated. The variations of microhardness of the samples from surface to interior were presented. The results showed that there is no significant difference between the matrix structure of TiAl alloy with different aluminum content. Nevertheless, with increasing aluminum content in the melt, the thickness of the reaction layer decreased. Moreover, the elements diffusion distance and hardness also showed an apparent decrease with the increasing of aluminum content. Besides inherent phases in the melt, simultaneous precipitation of Al2O3 particles also occurred.