Deformation mode and plastic flow in ultra fine grained metals

Mechanical behavior of ultra fine grained (UFG) metals fabricated by severe plastic deformation (SPD) is considered in the paper. The mechanisms of a crystallographic glide during a continuous micro flow and shear band (SB) localization/fragment rotation during a discontinuous micro flow are analyzed by simple models. It is shown that localized flow and the transition to localization are sensitive to deformation mode and conditions of processing or subsequent loading. Experimental data on texture evolution and tensile properties of ultra fine and fine grained aluminum alloy Al-0.5Cu as well as dynamic recrystallization of high purity aluminum Al5N5 are presented for pure shear and simple shear deformation modes. These results comply with theoretical models. Tensile tests of ultra fine grained structures reveal two stages of localization, into a sample neck and inside a planar material layer. In contrast to ordinary materials, the second stage modifies tensile loading and leads to different fracture mechanisms.