Minimum necessary strain to induce tangled dislocation to form cell and grain boundaries in a 6N–Al

Abstract

Severe plastic deformation (SPD) techniques are known to promote exceptional material properties by inducing significant modifications in the metallic material microstructure. In particular, severe plastic deformation (SPD) techniques are known to effectively refine the initial grain structure of f.c.c. and b.c.c. crystals to sub-micrometre levels. Pure metals are mostly appropriate to study the early stages of the microstructure modifications induced by SPD. This is chiefly due to the possibility to isolate the material strengthening due to dislocations from other possible microstructure features. To this purpose, a high-purity 6N-aluminum (99.9999% purity) was here used to study the minimum necessary strain to form crystal boundaries (that is, cell and grain boundaries). Cell and grain boundaries are formed from previously introduced tangled dislocations (TD), which constitute the microstructure modification features at the early stages of plastic deformation. In this study, the 6N–Al was subjected to high-pressure torsion (HPT) by which the minimum necessary strain, εeq, to form cell boundaries was identified. It was thus find that, TD started to evolve to cell boundaries at εeq = 0.05. This finding was validated by a second SPD technique, such as accumulative roll bonding (ARB). A microstructure strengthening model was applied and validated by nanoindentation measurements.