Mechanical behavior and shear banding of electropulsing-assisted micro-scale shear-compression in Ti-6Al-4V alloy

Abstract

Various electrically-assisted forming (EAF) technologies have been developed as a promising and new metal forming process, but few studies pay attention to the effect of electropulsing on shear deformation behavior and shear banding evolution. Here the electropulsing-assisted micro-scale shear-compression (EAMSC) experiments were conducted in Ti-6Al-4V alloy with lamellar and equiaxed microstructures under different current densities. Numerical simulation was used to investigate the field distributions during EAMSC. Scanning electron microscope (SEM) and transmission electron microscopy (TEM) were used to comparatively investigate the shear bands evolution and microcracks nucleation of two samples. The results show the electropulsing heating temperature was homogeneously distributed in the shear plane and formed a distinct gradient in the matrix. In lamellar microstructure, shear bands show a distribution of fork-shaped and the localised diffusive rotation occurs at grain boundary α (αGB) layer. The local fluctuations in stress/strain and temperature can contribute to the initiation of shear bands, and the microcracks nucleation will happen in the grain boundaries (GBs). While the formation of elongated dislocation cells, formation of elongated subgrains and break-up of elongated subgrains are the evolutionary process of shear bands for equiaxed microstructure, and the microvoids are nucleated at the breakpoint of subgrains with excessive elongation. In addition, the flow curves of EAMSC display obviously strain softening for lamellar microstructure, while hardening for equiaxed microstructure. It should be mainly attributed to that the equiaxed microstructure EAMSC caused the high dislocation pile-up and deformation twins (DTs). In contrast, the predominance of shear deformation during shear-compression deformation can cause the softening in lamellar microstructure.