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

Abstract

A metastable β 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 ω phase is followed by precipitation of the α phase during linear heating. In contrast, in the HPT-deformed material the nucleation of the α phase is shifted to lower temperatures, resulting in the coexistence of all three β, ω, and α phases at ~550 °C. Moreover, in HPT-deformed samples, the growth of α 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 °C remains ultra-fine grained with equiaxed grains of α phase.