Formation and evolution of adiabatic shear bands in zirconium alloy impacted by split Hopkinson pressure bar

The formation and evolution of the adiabatic shear bands in the zirconium alloy impacted by split Hopkinson pressure bar were investigated by means of the experimental design. The different strain levels in the zirconium alloy subjected to high strain rate loading were first designed by two times impact at almost same strain rate. Only deformed bands were formed in the zirconium alloy impacted once, and two types of adiabatic shear bands, namely deformed bands and transformed bands, were distinguished in the zirconium alloy impacted twice. Microstructural observation shows that the deformed bands showed the severe strain localization, and the transformed bands composed the ultrafine and equiaxed grains. The formation of the ultrafine and equiaxed grains in the transformed bands could be attributed to the rotational dynamic recrystallization mechanism. Based on the characterization of the ASBs formed at different strain stages, the evolution process of the ASBs is proposed. The deformed bands are suggested as the initial stage of the transformed bands formation, and the transformed bands are considered as the further development of the deformed bands. The microhardness measurements show that the microhardness values in the transformed bands were higher than that of the deformed bands and original sample because of strain hardening and grain refining.