Cracking behavior and mechanism of the layered microstructure of Ti2AlNb-based alloy containing large stripped α2 and O phases

Abstract

Ti2AlNb-based alloys have complex phase compositions and are sensitive to temperature changes. This makes it easy to form a gradient microstructure, especially during the hot-working of large thin-walled workpieces, owing to local phase transition differences. This study prepared a layered microstructure in a Ti2AlNb-based alloy and investigated its cracking behavior and mechanism at room temperature, 750, and 930 °C. The layered microstructure comprised two layers, namely an outer large-stripped α2 + O phase and an inner B2 + acicular O phase. The layered microstructure at room temperature and 750 °C was brittle. During deformation, stripped α2 phases in the outer layer slipped with the basal <a> slip system and cracked. The cracks propagated along the phase interface of the stripped α2/O and the B2 phases, completely peeling the strip-precipitated phases from the matrix. B2 cleavage fracture occurred in the inner layer, and both the stripped and acicular O phases in the cleavage plane peeled. The layered microstructure at 930 °C was ductile and the α2 phase in the outer layer broke, but the B2 phase filled the gap produced by breakage and restricted crack initiation. The breaking of the α2 phase promoted the dynamic recrystallization of the B2 phase and further improved its plasticity, which blunted the crack tip and effectively restrained crack propagation.