Strain-induced microstructure refinement in pure Al below 100 nm in size

Abstract

The obtainable minimum structural size and microstructural characteristics of pure Al processed by three different deformation techniques, i.e., cold rolling (CR), dynamic plastic deformation (DPD) and surface mechanical grinding treatment (SMGT), have been investigated by means of transmission electron microscope and orientation mapping. A systematic evaluation of the effects of deformation parameters on structural refinement was performed, mainly focusing on the microstructures at high strains. In contrast to the submicro-scale laminated structures from CR at ambient temperature, which are mainly composed of high angle grain boundaries, deformation at low temperature and high strain rate facilitates formation of high density low angle grain boundaries (LAGBs) in DPD and SMGT samples. With a combination of low temperature, high strain rate and large strain gradient, nanolaminated (NL) structures with a size of only ∼68 nm and a large fraction of LAGBs (∼65%) was fabricated by means of SMGT. NL Al exhibits a record high Vickers hardness of 780 MPa, which has its origin in the capability of accommodating high density dislocations in the form of LAGBs. This study provides an alternative approach to design nanostructures below the traditional refinement limit by generating more LAGBs.