Phase transformation-induced microstructural inhomogeneity in adiabatic shear bands of a metastable beta-titanium alloy

The growing demands for industrial applications with enhanced high strain-rate performance necessitates a deeper understanding of material behavior under dynamic loading. Adiabatic shear band (ASB) formation is a primary instability in materials subjected to high strain-rate dynamic loading. Understanding the microstructural evolution within ASBs is crucial for elucidating the mechanisms of adiabatic shear instability. In this study, advanced characterization techniques and lattice strain calculations were employed to identify the intricate atomic-level deformation mechanisms in the adiabatic shear region of a metastable β titanium alloy. This investigation revealed a phase transformation sequence of β to α'' and subsequently to α, which resulted in a heterogeneous multi-phase microstructure. Additionally, nano-twinning was observed in both α''-martensite and the HCP-α phase, significantly promoting grain refinement. Inhomogeneous strain distributions at twin and phase boundaries facilitated the initiation of micro-void and micro-cracks during dynamic deformation, ultimately resulting in adiabatic shear failure. ‌The limited temperature rise within the ASB, supported by kinetic calculations, suggested that grain refinement occurred predominantly through dislocation migration-governed dynamic recovery mechanism. By systematically correlating the microstructural evolution with the mechanical response of the alloy, the findings provide a theoretical foundation for developing high-performance materials with improved resistance to adiabatic shear failure under high-speed dynamic loading. • Reveal high-speed deformation mechanisms governing adiabatic shear band formation. • Observe nano-twins in both α"-martensite and α phase, promoting grain refinement. • Identify β→α"→α phase transition, yielding a heterogeneous multi-phase structure. • Analyze the role of microstructural heterogeneity in triggering shear instability.