The deformation of micron-sized single-crystals was jumpy and stochastic, and this may pose potential formability and reliability problems if components for future micro-machines were to be made from small metal volumes. In this work, micron-sized bi-crystal pillars were fabricated by focussed ion-beam milling from grain-boundary regions in coarse-grained polycrystalline aluminium. Each bi-crystal pillar contained a grain boundary intersecting its top surface, and was subjected to compression using a flat-ended nano-indenter tip. Their deformation was found to have smaller strain bursts, fewer periods of strain hardening at elastic-like rates, as well as greater work-hardening rate and flow stress, than single-crystal pillars of similar sizes. Transmission electron microscopy revealed severe dislocation accumulation in the deformed bi-crystal pillars, whereas the residual dislocation density remained low in single-crystal micro-pillars of similar dimensions after deformation to comparable strains. The results suggest that a grain boundary inside a micro-specimen could trap dislocations inside the specimen, leading to a significant rise in the strain-hardening rate as well as to smoother deformation.

Deformation of Micron-Sized Aluminium Bi-Crystal Pillars. K.S.Ng, A.H.W.Ngan: Philosophical Magazine, 2009, 89[33], 3013-26