Phase transitions and mechanical behavior of Ti-3wt.%Nb alloy after high pressure torsion and low-temperature annealing

Abstract

The influence of microstructure and phase transitions on tensile strength, plasticity and microhardness of a Ti-3wt.%Nb alloy subjected to high pressure torsion (HPT) followed by annealing is studied in this work. The initial state of the alloy was the α-solid solution with a small amount of the β-precipitates. The characterization of microstructure and phase transitions has been performed using scanning and transmission electron microscopy as well as X-ray diffraction. During HPT, the grain refinement took place and the α-phase partially transformed into ω-phase. The tensile test of the HPT-deformed sample showed an almost two-fold increase of ultimate strength in comparison with the initial state, as well as lower plasticity. During the short-term annealing of the deformed state up to 250 °C, the grain size slightly increased, the density of the crystal structure defects decreased and ω-phase transformed back to the α-phase. Such microstructural changes led to an important growth of plasticity and a slight decrease in ultimate strength of the HPT-deformed alloy.