Strategic heat treatment for tailored room- and high-temperature properties in a high Nb–TiAl alloy

High Nb-TiAl alloys have attracted increasing attention in aerospace applications due to their superior high-temperature performance compared with conventional TiAl alloys. The combined addition of B and C can further enhance alloy properties; however, as-cast TiAl alloys typically contain numerous solidification-related defects, making heat treatment essential for microstructural optimization. In this study, two different heat-treatment schedules were applied to an as-cast Ti-45Al-8Nb-0.5B-0.6C alloy to investigate the effects of heat-treatment parameters on microstructure and mechanical properties. The results indicate that heat treatment significantly modifies both the microstructure and phase constitution. The as-cast alloy exhibits a coarse dendritic network structure consisting mainly of γ-TiAl, α 2 -Ti 3 Al, Ti 2 AlC, TiB 2 , and the B2 phase. After solution treatment in the same α single-phase region (1320 °C/0.5 h), low-temperature long-time aging (970 °C/6 h) produces a fine near-lamellar microstructure, whereas high-temperature short-time aging (1280 °C/10 min) results in a coarse fully lamellar structure. Mechanical testing reveals that both room- and high-temperature properties are improved after heat treatment. The low-temperature long-time aged alloy exhibits the best room-temperature tensile properties (388.3 MPa, 1.41%), while the high-temperature short-time aged alloy shows the optimal high-temperature compressive performance (1342.8 MPa, 12.5%). These findings establish the relationships between microstructure evolution and mechanical properties, providing critical insights into the heat treatment regulation of the room-temperature and high-temperature mechanical properties of high Nb-TiAl alloys.