Study on nanocrystalline dual phase Ni–Co alloy with high strength and excellent ductility

Abstract

In the present study, the room temperature mechanical properties of nanocrystalline Ni and Ni–75 wt-Co alloy, prepared by pulse electrodeposition, were contrasted. Both higher strength and higher ductility were obtained for the Ni–75Co alloy with a dual phase structure and an average grain size of 7·2 nm. By means of TEM observations of grain structures before and after tensile deformation for Ni and Ni–75Co samples, a link between the ductility and the variation of stress induced grain growth during tensile deformation was established. Observations of TEM showed stress induced grain growth during tensile deformation, subjected to very high stresses and large strains, is very insignificant for the Ni–75Co alloy in sharp contrast to the significant stress induced grain growth occurring in Ni. It was proposed that suppression of stress induced grain growth during tensile deformation can delay and even prohibit formation of shear banding plastic instability and thus enhances uniform strain leading to an enhanced ductility.