Microstructure control of Ti-45Al-8.5Nb-(W, B, Y) alloy during the solidification process

In this work, a two-step isothermal treatment (TIT) during the solidification process is proposed to eliminate micro-segregation and reduce the cracking tendency of Ti-45Al-8.5Nb-0.2W-0.213-0.02Y (at.%) alloy. The TIT consists of a short-term isothermal treatment in the single 0 phase region (1st IT) and a second isothermal treatment slightly above the beta + alpha transus temperature (2nd IT). The results show that solidification without the isothermal treatment (NIT) produces non -uniform microstructures due to Al -segregation, whereas microstructure homogeneity is improved after the 1st IT due to the elimination of the peritectic alpha phase. The TIT can yield fine and uniform lamellar structures without micro segregation, as well as reduced textures. Moreover, it is also found that the TIT can reduce the cracking tendency of TiAl alloys with high contents of Nb. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.