Adiabatic shear instability mechanisms in BCC TiHfZrTaNb high entropy alloy: insights from microscale experiments and simulations

Refractory high-entropy alloys (RHEAs) hold great promise for impact engineering due to their superior dynamic mechanical properties. However, the limited understanding of the adiabatic shear instability mechanism in these alloys restricts their effective design and application for enhanced impact performance. This study provides a comprehensive investigation into the mechanical responses of near-equiatomic TiZrHfNbTa RHEA across a wide range of temperature and strain rate. Upon impact compression to substantial strains, adiabatic shear bands (ASBs) emerge as the predominant failure mode. Utilizing an in situ high-speed “force-heat-deformation” synchronous testing system based on the split Hopkinson pressure bar, we have meticulously characterized the initiation and propagation of ASBs. Our work clearly elucidates the pronounced adiabatic temperature rise associated with localized shear deformation. Moreover, through quasi- in situ microstructural evolution analysis, we have delineated the microscopic evolution wherein local deformation sites expand and interconnect along the most deformable grains, ultimately leading to the formation of through-shear zones. Additionally, we have uncovered the micro-mechanism by which dynamic recrystallization (DRX) within these shear zones induces plastic instability. To quantitatively decouple the specific contributions of thermal softening and dynamic recrystallization softening to dynamic instability, we have developed a crystal plasticity mechanical constitutive model to accurately capture the mechanical responses of the RHEA by incorporating the influence of dynamic recrystallization evolution. Our findings highlight the crucial role of DRX softening in driving local shear instability in the RHEA. By combining full-process microcharacterization with mesoscale crystal plasticity finite element simulations, this work offers a precise analysis of the formation mechanism underlying the dynamic instability in BCC RHEA. This research is expected to provide a robust theoretical foundation for the future design of advanced metallic materials with enhanced impact performance.