Dislocation motion and strengthening mechanism of Ti-Al-Mo-Si alloy with multiple interlaced phases

The Mo and Si elements were introduced into the Ti₅₀Al₅₀ alloy to form Ti₅Si₃ phase and ordered structure of (βTi) (B2 phase) in the TiAl (γ) matrix. The microstructure of Ti₅₀Al₄₂Mo₄Si₄ alloy was regulated by electromagnetic levitation. As the undercooling increased, the microstructure was gradually refined, the volume fraction of single γ phase decreased while that of γ/B2 structure increased until it totally replaced single γ phase. The correlation between microstructure evolution and tensile properties of alloy was analyzed via electron channeling contrast imaging (ECCI) and transmission electron microscope (TEM). The dislocations and slip traces in the master alloy were mainly distributed in the single γ phase, and the coarse Ti₅Si₃ phases were prone to cause stress concentration. The refined Ti₅Si₃ and B2 reinforcing phases of the highly undercooled alloy effectively hindered the dislocation motion of γ matrix. The distribution of von Mises stress and true strain calculated by crystal plasticity finite element simulation proved that refined structure resisted the stress concentration and crack propagation. The fine-grain strengthening and the second-phase strengthening synergistically enhanced the strength of alloy.