Micropillar compression of LiF [1 1 1] single crystals: Effect of size, ion irradiation and misorientation

The mechanical response under compression of LiF single crystal micropillars oriented in the [1 1 1] direction was studied. Micropillars of different diameter (in the range 1–5 μm) were obtained by etching the matrix in directionally-solidified NaCl–LiF and KCl–LiF eutectic compounds. Selected micropillars were exposed to high-energy Ga+ ions to ascertain the effect of ion irradiation on the mechanical response. Ion irradiation led to an increase of approximately 30% in the yield strength and the maximum compressive strength but no effect of the micropillar diameter on flow stress was found in either the as-grown or the ion irradiated pillars. The dominant deformation micromechanisms were analyzed by means of crystal plasticity finite element simulations of the compression test, which explained the strong effect of micropillar misorientation on the mechanical response. Finally, the lack of size effect on the flow stress was discussed to the light of previous studies in LiF and other materials which show high lattice resistance to dislocation motion.

► The micropillar compression of LiF [1 1 1] is studied. ► Plasticity occurs in the “hard” {1 0 0}〈0 1 1〉 slip system, impossible in bulk LiF at RT. ► No size effects are observed like in other systems with high Peierls stress. ► Ion irradiation leads to an increase of approximately 30% on yield strength. ► Small tilts activate the soft slip systems even if Schmid factor is almost zero.