The microstructural evolution within the adiabatic shear band (ASB) of pure titanium subjected to high-rate loading was studied using a split Hopkinson pressure bar (SHPB) system. The results indicate that grain refinement within the ASB follows a twinning-assisted pathway involving grain subdivision and subsequent rotational dynamic recrystallization (RDR). Before stress collapse, intersecting networks of deformation twins, primarily 2 and 2, geometrically subdivide the coarse parent grains and generate numerous high-energy interfacial sites. During subsequent shear localization, these pre-existing twin boundaries are proposed to facilitate subgrain-boundary rotation and rapid recrystallization, leading to an ultrafast transition from twin-fragmented regions to an equiaxed ultrafine-grained structure at the ASB center. The concentrated deformation region was estimated to be ∼550 μm wide, whereas the highly localized ASB was only ∼23. 5 μm wide, and the average size of recrystallized grains at the band center was ∼0. 33 μm. This twinning-mediated pathway provides new insight into grain-refinement mechanisms in hexagonal close-packed (HCP) metals subjected to extreme dynamic loading. • ASBs in pure Ti arise via twinning-assisted rotational dynamic recrystallization. • Twinning subdivides grains before stress collapse, forming high-energy sites. • Twin boundaries catalyze shear localization, lowering barrier for grain rotation. • Twinning-mediated refinement leads to ultrafine grains during shear localization.
Yang et al. (Fri,) studied this question.
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