Effect of strain rate on the plastic strain gradient beneath the deformed surface of iron

Plastic strain gradients along the depth direction of a locally deformed surface of pure iron have been studied under different levels of strain and strain rates. Deformation at high strain rates was carried out by using a ball-dropping test, while deformation at low strain rates was performed by a ball-pressing test on a computer controlled servohydraulic machine. Evaluation of the local plastic strain was conducted by using the electron backscatter diffraction (EBSD) analysis. Experimental evidences indicate that high strains with high strain rates lead to large gradients of the plastic strain distribution profile and also a localized severe deformation near the surface. Furthermore, deformation at high strain rates is favourable to impose plastic deformation at the selected area near the surface.