Analysis of deformation behaviors of ultrafine grained Cu-30%Zn with bimodal grain-size distribution

Abstract

Ultrafine grained (UFG) metals have remarkably high strength in comparison with that of coarse grained metals. However, the UFG metals often exhibit low tensile ductility. It has been reported that the UFG metals having bimodal grain-size distributions consisting of coarse grains and fine grains perform large elongation keeping high strength. However, the exact deformation mechanism of the bimodal UFG metals has not yet been clarified. Deformation behaviors of a bimodal UFG metal were studied in the present paper. A sheet of Cu-30%Zn was highly deformed by accumulative roll-bonding (ARB) process and then annealed. The annealed specimen showed a fully-recrystallized UFG structure with a bimodal grain size distribution. To clarify deformation behaviors of the bimodal metal, an identical region was observed by the electron backscattered diffraction (EBSD) method at various tensile strains. The grain average misorientation (GAM) increased with increasing the tensile strain. The increase in GAM of the coarse grains was larger than that of the fine grains, suggesting the difference in local deformation and strain-hardening behaviors between different grain sizes. The enhanced uniform elongation of the bimodal UFG specimen was considered to be associated with the difference in strain-hardening between the coarse grains and fine grains.