Microstructure Evolution and Phase Transformation of Ti-1.0 wt%Fe Alloy with an Equiaxed α + β Initial Microstructure during High-Pressure Torsion and Subsequent Annealing
Herein, the microstructure evolution and phase transformation during high-pressure torsion (HPT) and subsequent annealing of Ti-1.0 wt%Fe alloy with an equiaxed α + β initial microstructure are investigated. Both α and β grains in the initial microstructure fragment into smaller and elongated areas during HPT. X-ray diffraction (XRD) analysis reveals that the deformation-induced α to ω and β to ω phase transformations occur from the onset of HPT deformation. The β phase totally disappears after 1.5 rotations, whereas some α phase still remains even after 4 rotations. The nano-hardness of β grains is much larger than that of α grains in the initial microstructure, due to the nano-sized athermal ω precipitates inside the β grains. With an increase in the HPT rotation, the nano-hardness of prior α areas continuously increases, whereas that of the prior β areas gradually decreases. During the subsequent annealing of HPT-deformed sample, both ω to α and ω to β reverse-phase transformations occur, and the deformation-induced ω phase totally disappears at annealing temperatures above 400 °C. The recrystallization of α phase completes at an annealing temperature of 500 °C. At higher annealing temperatures, secondary α precipitates with ultrafine grain sizes start to appear inside the prior β areas.