Size effects resulting from local strain hardening; microstructural evaluation of Fe-3% Si and Cu deformed in tension and deep drawing using orientation gradient mapping (OGM)

Abstract

Abstract Mesoscale strain hardening phenomena and the effect on the macroscale behavior (yield under tension, earing in deep drawing) are investigated in Fe-3 % Si and Cu. Fe-3 % Si shows a smooth upper and lower yield point depending on grain size and sheet thickness which can be attributed to a lack of mobile dislocations. A free surface effect (reduced strain hardening of near-surface regions) is found for sheets of 300 μm and 960 μm thickness, but limited to small and medium strains. By means of the new orientation gradient mapping, which is correlated with local strain hardening, the local deformation microstructure is investigated in incremental tensile tests and incremental deep drawing for Fe-3 % Si and Cu. The orientation gradient distribution significantly depends on the material. Based on these results phenomenological descriptions of the microstructure at the mesoscale are proposed. From orientation gradient mapping, geometrically necessary and statistical orientation gradients are evaluated which agree well with results of transmission electron microscopy investigations of geometrically necessary boundaries and incidental dislocation boundaries. A constitutive equation correlating orientation gradient mapping and local dislocation density is proposed.