Abstract:The effects of heat treatments on typical microstructures of directionally solidified (DS) Ti-45Al-8Nb-(W, B, Y) (molar fraction, %) alloys prepared by the Bridgeman method were studied. Two typical DS microstructures including full lamellae with cellular growth morphology and massive structure with dendritic growth morphology were examined. The results show that the heat treatment of 1250 °C for 24 h + 900 °C for 30 min+air cooling can efficiently eliminate the B2 phase in the DS alloys and change the massive structure of the rapid DS alloy into lamellar microstructure. Columnar lamellar colonies with widths of 150−200 μm and 50−100 μm respectively were observed in intercellular and dendritic arm regions. The heat treatment of 1 400 °C for 12 h+900 °C for 30 min+air cooling could simultaneously remove the B2 phase, massive structure and solidification segregations from the DS alloys, however, it caused severe growth of grains.

Key words: TiAl alloy; directional solidification; heat treatment; microstructure; segregation