High temperature mechanical behavior of nanocrystalline Ni

The high temperature deformation behavior was studied in nanocrystalline (nc)-Ni with an initial grain size of ~60 nm. Conventional tensile stress-strain behavior of nc-Ni was studied as a function of temperature and strain rate. The strength of nc-Ni was found to decrease and ductility was found to increase with increasing temperature. The YS was found to reduce from ~703 MPa at RT to 184 MPa at 300 °C. The effect of temperature and strain rate on the work-hardening capacity of nc-Ni was found to be pronounced. The strain range during which work hardening take place was found to be higher for low strain rates and work hardening rate was found to decrease above 200 °C due to substantial grain growth. Detailed experimental studies were also performed to delineate the influence of thermally activated process and dynamic grain growth on strain rate sensitivity (m) in nc-Ni. The m was found to be strongly dependent on grain growth during high temperature deformation of nc-Ni. Fracture morphology of the nc-Ni showed dimple fracture with dimple diameter and depth were significantly larger than the average grain size (~60 nm) in nc-Ni.