Deformation-induced α^″ and ω transition mechanisms and dislocation dynamics in the early stages of adiabatic shearing of a dual-phase titanium alloy

Adiabatic shear localization in its early stages poses a critical limitation for the application of dual-phase titanium alloys in high-impact environments. Despite its significance, the nanoscale features of adiabatic shear bands (ASB) remain poorly understood, necessitating further in-depth investigation. This study aims to elucidate the mechanistic contributions of deformation-induced α^″ and ω nano-structures, microstructural transitions, and quantitative dislocation dynamics to damage formation under shear instability, by analyzing thin foils from different ASB regions (transition to center zones) of A503 alloy subjected to 20 % strain. The analysis revealed elongated deformed and ultrafine grains in the transition region, while the center region featured lath-shaped grains, identified as {101¯2} extension nano-twins (ENTWs) and {101¯1}, {112¯1}, and {112¯4} contraction nano-twins (CNTWs). The ASB regions (transition to center zones) undergo substantial deformation-induced phase transformations, transitioning via pathways of β→α^″→α and β→SI_ω→α due to adiabatic heating. Besides, the rotational dynamic recrystallization (RDR) model effectively describes the dynamic recrystallization (DRX) in the ASB center. Thermodynamic and kinetic calculations reveal that, rather than reaching a peak temperature of 719 K (37%T_m), instantaneous grain refinement in the center requires an adiabatic temperature of 950 K (49%T_m), confirming that dynamic recovery (DRV) prevails over DRX. Micro-area X-ray diffraction identifies <a> and <c+a> slip dislocations as the main mechanism in dynamic plasticity at 1.7×10³s⁻¹ strain rate, with dislocation density of ∼(1.03±0.90)×10¹⁵m⁻². These findings provide critical insights into strain localization and offer a foundational framework for designing new class of titanium alloys resistant to ASB formation.