Precipitation behaviors in a quenched high Nb-containing TiAl alloy during annealing

The precipitation of γ phase and heterogeneous nucleation of ωo phase within βo phase areas are common phenomena in TiAl alloys. However, detailed explanation on the corresponding phase transformation mechanisms is still lacking. In this study, the precipitation behaviors of γ and ωo phases in a quenched Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy are investigated. The results show that large γ grains form after quenching whereas small γ particles can directly nucleate within the remaining βo phase during annealing. Semi-coherent interfaces are observed between γ and βo phases and the average distance between dislocations is evaluated. The heterogeneous nucleation of ωo phase at the lamellar colony boundary is imaged by HRTEM. Edge-to-edge method is used to calculate the orientation relationship between γ and ωo phases. The γ phase grows up faster than ωo phase within the βo phase areas during annealing at 800 °C.