The hardness (H) and rate sensitivity (m) of nanocrystalline NiFe alloys were studied by nano-indentation testing. It was found that H increased, and m decreased after rolling in the alloys. It was interesting that the decrease in m by rolling was totally contrary to the conventional coarse-grained alloys. The dislocation density was remarkably enhanced by rolling deformation, which leads to the hardening behaviour of the samples. The dislocation absorbed at the grain boundary and/or sub-grain boundary  and grain growth by rolling were responsible for the reduced m of the rolled alloys.

Rolling Deformation Induced Reduction of Rate Sensitivity and Enhancement of Hardness in Nanocrystalline NiFe Alloys. Z.H.Cao, P.Y.Li, Z.H.Jiang, X.K.Meng: Journal of Physics D, 2011, 44[29], 295403