Effect of strain-hardening rate on the grain-to-grain variability of local plastic strain in spin-formed fcc metals

Micro-indentation hardness was used to assess the local equivalent plastic strain distribution in four fcc metals subjected to identical splined mandrel flow forming processes. Both the maximum local equivalent plastic strain and the grain-to-grain variability in the equivalent plastic strain increased with increasing strain-hardening rate of the work piece material. The deformed microstructure of the formed work pieces indicated that considerably more grain-to-grain variability in the dislocation slip step and deformation twin densities exist in the material with a high strain-hardening rate. These findings are of considerable importance and should be considered when assessing the suitability of high strain forming processes for producing reliable, and homogeneous, parts from fcc metal alloys that display high strain hardening rates.