Effect of Er₂O₃ and Y₂O₃ on microstructure and mechanical properties of Ti₂AlNb alloy

Rare earth oxides can significantly refine the microstructure of the cast alloys and improve their mechanical properties. In this study, Er₂O₃ and Y₂O₃ particles were chosen to add into the Ti₂AlNb-based alloy with vacuum non-consumable arc melting method. For the Er₂O₃ particles, it has obvious dissolution and re-precipitation characteristics during melting. While for the Y₂O₃ particles, they are more stable, and aggregated and grew up during melting. These two kinds of Er₂O₃ or Y₂O₃ both have obvious refinement effects on the B2 grains due to their heterogeneous nucleation. Specially, adding Er₂O₃ particles can promote the decomposition of the B2 and α₂ phases and the increases of the O-phase content. But adding the Y₂O₃ particles can inhibits the B2 decomposition and just only promotes the α₂ decomposition into the O-phase. Additionally, the TAC-Er₂O₃ ingot shows the worst mechanical properties at room-temperature due to its large size and grain boundary segregation of the Er₂O₃ reinforcements. Conversely, the TAC-Y₂O₃ alloy exhibits excellent strength and ductility whatever at room- and high- temperatures owing to its fine grain strengthening and effective strengthening of the second precipitated Y₂O₃ phases.