Grain refinement and mechanical properties of nickel subjected to severe plastic deformation

The structure and mechanical properties of Ni subjected to severe plastic deformation have been investigated. By combining ECAP and cold rolling, Ni of grain size about 300 nm was obtained. The material displayed an ultimate tensile stress of more than 1000 MPa and considerable ductility. Annealing at 200degreesC decreased the strength by 15% but increased the ductility. The a transition from brittle fracture of coarse-grained Ni to quasi-tough one in fine grained Ni at room temperature was observed. It is proposed that the high strength and plasticity of the ultra fine grained nickel is related to a deformation mechanism involving grain boundary sliding and grain rotation. High strength Ni with good ductility may have prospective practical applications, particularly for micro-systems.