In-situ investigation of phase transformations in ultra-fine grained Ti15Mo alloy

A metastable beta solution treated Ti15Mo alloy was deformed by high pressure torsion (HPT) resulting in a severely deformed microstructure with high density of lattice defects. In order to gain insight into the kinetics of phase transformations, both non-deformed and HPT-deformed materials were studied in-situ during linear heating; phase evolution was investigated using high energy synchrotron X-ray diffraction (HEXRD) complemented by the measurement of electrical resistance. It was shown that in the non-deformed material the dissolution of the omega phase is followed by precipitation of the alpha phase during linear heating. In contrast, in the HPT-deformed material the nucleation of the alpha phase is shifted to lower temperatures, resulting in the coexistence of all three beta, omega, and alpha phases at similar to 550 degrees C. Moreover, in HPT-deformed samples, the growth of a particles is accelerated due to high density of dislocations and grain boundaries. Post-mortem observations of selected samples revealed that the microstructure of the HPT-deformed material after heating up to 650 degrees C remains ultra-fine grained with equiaxed grains of a phase. (C) 2021 Published by Elsevier B.V.