Effects of minor B, Y and cooling rate on the micro-structure refinement of Ti-47Al-2Cr-2Nb alloy

Effects of minor B and Y as well as cooling rate on compound refinement of microstructure of Ti47Al-2Cr-2Nb alloy were investigated. The results show that in the condition of smelting with the watercooled copper crucible vacuum induction skull furnace and investment casting with Y₂O₃ shell mold, grain size of Ti-47Al-2Cr-2Nb castings is greatly refined with B addition, where coarse columnar grain is converted into fine equaixed one, however, refining effects on lamellar spacing are absent. B and Y compound refinement can not only further effectively refine grain size, but also significantly refine the lamellar spacing. Macro-structure of Ti-47Al-2Cr-2Nb-0. 8B-0. 3Y alloy castings exhibits equiaxed grain with different thickness from 2 mm to 20 mm, meanwhile, with increasing in thickness of the castings, equiaxed grain size is gradually coarsened. It is beneficial for obtaining fine lamellar structure with proper decrease of pre-heating temperature of mold shell.