Plastic deformation mechanism and interaction of B2, α2, and O phases in Ti-22Al-25Nb alloy at room temperature

In this work, quasi-in situ tensile unloading and electron backscatter diffraction (EBSD)-based slip trace analysis were applied to study the room-temperature deformation behaviour of Ti-22Al-25Nb alloys with three different microstructures and the plastic deformation mechanism of the B2, alpha(2), and O phases. In addition, the interaction model of the three phases was presented. The results showed obvious B2 slip deformation in the necking region of the B2 + alpha(2) microstructure and the B2 texture + alpha(2) samples. The cracks expanded along the regions with low grain boundary density, and the fracture mode was transgranular fracture. The B2 texture improved the harmony and uniformity of the slip deformation between different grains, obviously improving ductility. Owing to the obstruction of the O phase to the B2 phase slip, the B2 + O + alpha(2) sample generated an obvious deformation strengthening effect, had no necking phenomenon, and it was also transgranular fracture. The B2 phase slip deformation mode included single system, double system, tri-system, and cross slips. The B2 phase induced a small number of the alpha(2) phases to experience basal slip ((0001) [11-20]) and cracking. The O phase had two deformation modes: (001) plane slip and twin that had (021) as a twinning plane. Two of the 24 slip systems of the B2 phase {110} < 111 > and {112} < 111 > can induce an O phase (001) plane slip, 12 systems whose < 111 > slip direction formed a 54.7 degrees angle with the (001) plane can induce an O phase twin, and other 10 systems cannot induce O phase deformation.