PNNL

Abstract

The microstructural features of shear localization, generated by a high strain rate (~105 s-1) deformation, of a twinning-induced plasticity (TWIP) steel containing about 17.5 wt. % Mn were well characterized by means of transmission electron microscopy and electron back scatter diffraction. The high deformation rate was obtained by a ballistic impact penetration test on a TWIP steel sheet. In addition to the deformation twins observed as the domain microstructural characterization of high-strain-rate deformation outside shear bands, some shear bands consisting of complex microstructures were also evidenced in the highly-deformed area. Inside the shear band, there exist a large region of amorphous phase and a smooth transition zone containing nano-crystalline (NC) phase. The grain size decreased gradually in the transition zone, changing from coarse-scale (> 100 nm) next to the fully amorphous zone to fine-scale (