Adiabatic shear instability in a titanium alloy: Extreme deformation-induced phase transformation, nanotwinning, and grain refinement

Increasingly harsh service conditions place higher requirements for the high strain-rate performance of titanium alloys. Adiabatic shear band (ASB), a phenomenon prone to dynamic loading, is often accom-panied by catastrophic damage. Yet, it is unclear how the internal nanostructures are related to shear instability. Here we report detailed microstructural evolution in the ASB of a titanium alloy via in-depth focused ion beam (FIB), transmission Kikuchi diffraction (TKD), and high-resolution transmission electron microscope (HRTEM) analyses, with the deformation instability phenomenon discussed from the energy perspective. The ASB interior undergoes multifaceted changes, namely deformation-induced beta-to-alpha transformation and deformation-induced martensitic transformation to form substantially refined and heterogeneous structures. Meanwhile, two types of extremely fine twins are identified to occur within both nano-sized martensite and alpha phase. The critical plastic work representing the onset of adiabatic shear instability and dynamic equilibrium is observed to be constant for a specific structure in the same deformation mode. The energy analysis could be extended to other materials subjected to high strain-rate dynamic deformation. (c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.