This study examines the size-dependent deformation response of pure LiF single crystals using microcompression testing. Microcrystals with an 〈001〉 orientation and sample diameter D ranging from 1 to 20 m were fabricated by focused ion beam (FIB)-milling from bulk crystals having a low initial dislocation density. Both as-grown and ␥-irradiated crystals were examined to characterize the effect of an increased point defect density on the size-affected plastic flow response. Similar to previously studied face-centered cubic (FCC)-derivative metals, both types of LiF microcrystals exhibit typical size-dependent plastic flow behavior: a dramatic size-dependent and statistically varying flow stress, atypically high strain hardening rates at small plastic strains, and fast intermittent strain bursts. The size-dependent strengthening obeys a power law, ∼ D −m , where m ≈ 0.8, and this rapid hardening results in engineering flow stresses of 650 MPa in 1-m samples. The findings are evaluated against possible dislocation mechanisms that could be responsible for the observed size effects.

The first experimental statistical study is reported of intermittent plastic deformation of LiF microscopic samples having low initial dislocation densities, in both as-grown and gamma-irradiated conditions. The investigations used the microcompression testing method. Data sets were evaluated independently for the loading and flow deformation stages for each material. Investigations selectively examined evolution of the strainburst response in both the spatial and temporal domains. A revised analysis technique provided advances in quantitative evaluations of the statistical experimental data relative to previous studies. Platen displacement event cumulative probability distributions exhibited both Gaussian regimes at small displacements and power law regimes for event displacement, duration and average velocity at larger sizes. However, the observed event size scaling exponents did not follow the expectation from mean-field theory, revealing scaling exponents in the range 1.8-2.9. Additionally, extraordinarily large displacement events were observed that exceeded the sizes of those found in previous studies by at least 10 times. Quantitative clarification of the power-law exponent values and their dependence on deforming sample conditions demands both further experimental studies with larger numbers of samples and a wider range of sample conditions. Such studies would benefit from better matching of the time scales of dislocation processes and observation and, still further improvements to the data analysis methods.

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Experimental investigations of plastic flow have demonstrated temporal intermittency as deformation proceeds in a series of intermittent bursts with scale-free size distribution. In the present investigation, a corresponding spatial intermittency is demonstrated for plastic flow of KCl single crystals. Deformation bursts lead to large surface steps with a height distribution that is consistent with the distribution of strain increments in deformation of micro-columns, and the energy distribution of acoustic emission bursts observed in deformation of macroscopic single crystal samples of a wide class of materials.