Microstructure optimization and improved tensile property in a high Nb-containing γ-TiAl alloy

The microstructure and the room-temperature tensile property of a γ-Ti–45Al–8.5Nb–(W, B, Y) alloy after different heat treatments have been investigated. The results show that the α2´ martensite plate and columnar α2 Widmanstatten microstructure with a small number of remnant B2 phase can be obtained for the γ-Ti–45Al–8.5Nb–(W, B, Y) alloy by water-quenching and air-cooling, respectively from the β phase field. The B2 phase with weak Nb enrichment retained from the β phase field can be removed easily after subsequent heat-treatment at 1340 oC for 3 h, which produces a fine lamellar α2 + γ microstructure in the alloy. The alloy subjected to a two-step heat-treatment (1450 oC followed by air-cooling/1340 oC followed by furnace-cooling) shows better tensile properties with an ultimate tensile strength of 826–850 MPa and a total elongation of 0.95–1.37% than the as-received alloy. The improved tensile properties can be attributed to microstructure refinement and reduction of remnant B2 phase located at lamellar colony boundaries in the γ-Ti–45Al–8.5Nb–(W, B, Y) alloy.