| The focus of this research was to determine the deformation mechanisms during creep and cold-rolling of nanocrystalline nickel (average grain size: 40 nm) with a relatively wide grain size distribution. By varying the applied stress and temperature the creep deformation mechanisms were determined. While initial creep occurred by Coble creep, steady state creep was primarily controlled by dislocation movement, with Coble creep acting as a secondary mechanism. It is suggested that Coble creep occurs in the smaller grains, while dislocation creep operates in the larger grains. It is further proposed that dislocation movement becomes dominant when Coble creep diminishes as a result of the development of high frequencies of special grain boundaries.; It was found that the nanocrystalline nickel samples could be cold-rolled to a minimum strain of 680% without cracking. Considerable changes in crystallographic texture and, as a result, significant reductions in hardness were observed in the rolled material. |
