Dresden 2014 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 13: Topical Session: Nanomechanics of nanostructured materials and systems III - Small scale plasticity

MM 13.3: Vortrag

Montag, 31. März 2014, 16:30–16:45, BAR 205

Size-dependent plasticity in KCl and LiF single crystals: Influence of orientation, temperature, pre-straining and doping — •Yu Zou and Ralph Spolenak — Laboratory for Nanometallurgy, Department of Materials, ETH Zurich, Zurich, Switzerland

Size dependence of plasticity is generally observed and intensively studied in metallic systems, but it is rarely investigated in ionic crystals. In this work, two typical ionic crystals with the rocksalt structure, KCl and LiF, were investigated using micro-compression technique. Single-crystalline KCl and LiF pillars with diameters ranging from four microns to two hundred nanometers were produced by focused ion beam milling. The pillars were compressed using a flat-punch tip in a nanoindenter, along [001]- and [111] orientations and at both room temperature and ~200 °C. Pre-strained [111] LiF and CaCl2 doped [001] KCl pillars were compressed as well. We found that, in contrast to KCl, the size-dependence in LiF pillars is more sensitive to the orientation and temperature change. [111] LiF exhibit smaller size dependence and displacement bursts than the other pillars measured. The results also show that the pre-straining strengthens [111] LiF pillars in micron-sized range but weakens them in submicron-sized range, resulting a reduced size-effect exponent. The doping in [001] KCl slightly increases strength levels and decreases the size dependence. Generally, in terms of size-effect phenomenon, [111] LiF is similar as body-centered-cubic metals, while [001]- and [111] KCl and [001] LiF are comparable with face-centered-cubic metals. The additivity of strengthening mechanisms is critically discussed.