Phase transition in directionally solidified TiAl-based alloys containing Nb and Mo

To improve the oxidation resistance of TiA-based alloys, beta stabilizer elements such as Nb,Mo were commonly added. However, degradation of the mechanical properties might occur by two factors: B2 phase remained at room temperature due to the -phase solidification, and the micr- segregation brought by pesitectic reaction. In the present work, microstructure formation in TiA-based alloys containing Nb and Mo were investigated in directional solidification experiments at velocities ranging from 20μm/s-500μm/s. High temperature quenching were used to determine the solidification path and the associated microsegregation. The effect of alloy composition and growth velocity on solidification path has been studied. it was found that both addition of Mo to Ti46Al6Nb0. 2B alloys or increasing growth rates would shift the solidification path from pestectic solidification to the β-phase solidification. At the growth rate of 500μm/s in Ti46Al6Nb2Mo0. 2B alloys, a typical α-phase solidification microstructure was observed.