A Two-Step Heat Treatment to Eliminate the Micro-Segregation of Ti–45Al–8.5Nb–0.2W–0.2B–0.02Y Alloy

Micro-segregation in high Nb-containing TiAl alloys usually causes the inhomogeneous of microstructure and the initiation of microcracks. In this paper, a novel two-step heat treatment (HT) approach is proposed based on the phase transformation sequence to remove the micro-segregation. In the first step, Ti–45Al–8.5Nb–0.2W–0.2B–0.02Y alloy is annealed in 1470 °C for 30 min to eliminate the solidification segregation and reduce the stability of β phase. The alloy is then cooled to 1340 °C, slightly above the α + β transus (T_{α + β}) for about 60 min in order to remove the β-segregation. Results show that the homogeneity of the lamellar colony is improved after the two-step HT.