Synergistic effect of B2 phase and O phase in hot-rolled Ti2AlNb alloy and its influences on mechanical properties

Abstract

The Ti2AlNb alloy, solution-treated at 1070 °C, underwent hot rolling at 960 °C with different thickness reductions to investigate the synergistic effects of the O phase and B2 phase and their impact on its properties. The results reveal that after solution treatment, the Ti2AlNb alloy consists of nearly spherical O, lath O, and B2 matrix at 30% and 50% thickness reductions during hot rolling. However, at a 70% thickness reduction, the alloy exhibits spherical O, worm-like O, and a continuously distributed B2 phase. The α2 phase formed during solution treatment decomposes during hot rolling. As the thickness reduction increases from 30% to 70%, the O phase content initially rises and then declines, accompanied by an increase in the average dimension of the O phase from 0.25 ± 0.16 μm to 0.36 ± 0.18 μm. Additionally, the B2 phase in the alloy undergoes dynamic recrystallization (DRX) during hot rolling, coinciding with the growth and spheroidization of the O phase. With an increase in the thickness reduction during hot rolling, the elongation of the alloy increases from 5.9% at 30% reduction to 12.47% at 70% reduction. Meanwhile, the ultimate tensile strength reaches its peak value of 1092.2 MPa at 30% reduction, decreases to 936 MPa at 50%, and then increases to 970 MPa at 70%. The tensile strength of the alloy improves due to the interaction and accumulation of dislocations at the phase interface. The continuous distribution of the B2 matrix, dislocation movement, rotation of the O phase, DRX of the B2 phase, and interface slip all contribute to enhanced ductility. Furthermore, the fracture behavior of the Ti2AlNb alloys under various hot rolling conditions was elucidated.