Positive Deviation from a Hall-Petch Relation in Nanocrystalline Aluminum

Abstract

The grain size dependence of yield stress has been investigated for nanocrystalline (nc) bulk aluminum produced by hot extrusion of ball-milled powders. The Hall-Petch slope is positively deviated as the grain size is reduced below 60 nm. For the specific grain size range from 60 nm down to 48 nm, structural analyses and estimation of deformation mechanism exhibit that perfect dislocation emission critically governs deformation of nc aluminum, since the inherent aluminum properties of high stacking fault energy and low twinability can not afford any other deformation modes.