Size effects in LiF micron-scale single crystals of low dislocation density

This study examines the deformation response of 20, 5, and 1μm diameter samples fabricated by FIB-milling from bulk ultrapure LiF single crystals. The bulk crystals have a very low initial dislocation density as revealed by an etch-pit technique. Two types of 〈001〉 microsamples were compressed preferentially by single slip inside a nanoindentation system. Similar to previously studied FCC-derivative metals, LiF microsamples demonstrate dramatic strengthening achieving the engineering flow stress o ≈ 650 MPa in 1-μm samples. The stress-diameter dependence obeys a power law, σ∼D -m, where m ≈ 0.8. Stochastic variation of flow stress, fast intermittent deformation events ( avalanches ) and highly localized slip bands after avalanches - all characteristic of size effects in metals, are also observed in LiF. Possible dislocation mechanisms of the observed size effects are discussed. © 2007 Materials Research Society

Microstructurally based cross-slip mechanisms and their effects on dislocation microstructure evolution in fcc crystals

Three newly identified cross-slip mechanisms from atomistic simulations of fcc crystals, namely surface, bulk and intersection cross-slip types, were hierarchically informed into discrete dislocation dynamics simulations. The influence of each cross-slip type on the evolution of the dislocation microstructure in face-centered cubic microcrystals having different crystal sizes and initial dislocation densities was investigated. Dislocation pattern formation, surface slip localization and initial strain hardening were observed, in agreement with experimental observations, and possible explanations are given in the light of these simulations. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved