Effect of Mo on microstructure and high-temperature creep properties of a directionally solidified superalloy

The effects of Mo content (0, 0.75 wt.%, and 1.5 wt.%) on the microstructural evolution and high-temperature creep properties of a directionally solidified superalloy were investigated in this study. The results indicated that increasing Mo content significantly enhanced both the longitudinal creep life and the transverse stress rupture life of the alloy, which was closely correlated with microstructural evolution. Mo addition reduced the spacing of the γ/γ′ interfacial dislocation network and promoted γ′ rafting, thereby enhancing the longitudinal creep resistance, while the reduced eutectic fraction provided an additional benefit. The addition of Mo altered the dominant boride type at grain boundaries from M 3 B 2 to M 5 B 3 and promoted their transformation from continuous to dispersed distributions, which effectively reduced grain boundary stress concentration and suppressed crack propagation, leading to enhanced transverse stress rupture life. Overall, this study reveals that optimizing microstructure through Mo content regulation is an effective approach to enhancing the comprehensive high-temperature creep properties of directionally solidified superalloys, providing valuable insights for alloy composition design.