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 gamma/alpha(2) 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. (C) 2012 Elsevier Ltd. All rights reserved.