Ultrafine-grained nickel refined by dislocation activities at intermediate strain rate impact: deformation microstructure and mechanical properties

Abstract

This article presents an application of the impact-induced deformation in effective grain refinement in polycrystalline nickel. Ultrafine-grained microstructure was processed by means of Dynamic Plastic Deformation at room temperature using a falling impactor with a max- imum impact velocity of 10 m s -1 . The commercially pure (98.4 wt%) starting material was characterised by a coarse- grained (*25 lm) microstructure. Electron backscattering diffraction and transmission electron microscopy studies showed that the initial equiaxed grains evolved into a laminar structure of submicron size narrow domains delineated by high-angle grain boundaries. The texture after deformation exhibits preferential orientations includ- ing a strong h220i fibre texture. The mechanical behaviour under quasi-static compression at room temperature and at a strain rate of 2 9 10 -3 s -1 was investigated in directions parallel and perpendicular to the impact axis. Stress-strain responses showed an increased yield strength (440-520 MPa) compared with the initial state (90 MPa). The strain- hardening behaviour was found to strongly depend on the orientation of the compression axis.