Cryogenic rolling induced microstructural evolution, mechanical behaviour, and phase stability in Ti-6Al-4V and CP-Ti alloys

Abstract

Titanium and its alloys are well known for their high specific strength, corrosion resistance and biocompatibility. Due to its remarkable combination of properties, it is widely used in aerospace, chemical, biomedical and naval applications. Cryo-rolling in the presence of liquid nitrogen enhanced microstructural characteristics and resulted in superior strength. This study systematically investigates the effect of cryo-rolling on the microstructural evolution and mechanical properties of two commercially used titanium alloys, the dual-phase Ti-6Al-4V (α+β alloy) and commercially pure titanium (CP-Ti) Grade 2 (α-phase). The research aims to understand the role of initial microstructures influence the cryo-rolling process and the resulting structure-property relationships. Both alloys were prepared in mill-annealed and heattreated conditions, then rolled in liquid nitrogen to various thickness reductions. The low temperature rolling technique suppresses thermally activated recovery. The study examines the characteristic changes in grain size and dislocation density with increasing strain and relates these to variations in yield strength (YS), ultimate tensile strength (UTS), and percentage elongation. Advanced characterization techniques such as scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to examine surface features, grain orientations, boundary mapping, nanoscale defects and face-centred cubic (FCC) phases to understand the deformation mechanisms and structural effects. Microscopic observations, complemented by uniaxial tensile tests, provided a comprehensive understanding of processing and mechanical behaviour. Results indicate that cryo-rolling refines grains, increases dislocation densities, and promotes sub-grain formation in both alloys. In Ti-6Al-4V, suppressed dynamic recovery at low temperatures preserves dislocati