In-situ characterization of the dislocation-structure evolution in Ni micro-pillars

The high strength of micro-crystals is determined in the early flow regime, where a transition from elastic to plastic flow is obscured if compared to stress strain data from bulk single crystals. In the present work we therefore focus on the evolution of dislocation structures in Ni micro-pillars during early deformation by employing in-situ Laue micro-diffraction. It will be shown that substantial changes in the lattice fine structure, such as multiple subgrain formation and significant rotational gradients, can be resolved prior to the onset of large strain generation. The results reveal more pronounced effects for smaller sample dimensions and also suggest that most of the evolving dislocation structure is formed prior to the occurrence of large strain bursts. A clear increase in dislocation density as a function of strain is observed, which we discuss in the context of size-dependent strain hardening and exhaustion hardening. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.