Comparison of directional solidification of γ-TiAl alloys in conventional Al₂O₃ and novel Y₂O₃-coated Al₂O₃ crucibles

The effects of novel Y₂O₃-coated Al₂O₃ (Y₂O₃/Al₂O₃) crucibles on the microstructure and composition of directionally solidified TiAl alloys were investigated and compared with those of single layered Al₂O₃ and Y₂O₃ crucibles, based on which the corresponding alloy-crucible interaction mechanisms were discussed. The DS alloys exhibited a fully lamellar γ/α₂ structure interspersed with some Al₂O₃ or Y₂O₃ particles. Differently from that in the case of using Al₂O₃ crucibles, no interfacial interaction layer was found in the ingots prepared using Y₂O₃/Al₂O₃ crucibles. Dissolution and erosion were the main mechanisms responsible for the alloy-crucible interactions which increased with the heating temperature and interaction time. Nevertheless, the interaction extents when using Y₂O₃/Al₂O₃ crucibles were much lower than using Al₂O₃ crucibles, making the former promising candidate crucibles for the high quality DS of highly reactive TiAl alloys.