Effects of adsorption on the indentation deformation of non-metallic solids

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Abstract
Marked changes in indentation microhardness have been observed in a wide range of non-metallic materials due to the presence of adsorbed water and other polar species. Opposite polar faces of crystals with non-centrosymmetric structures, including II–VI, III–V and IV–IV compounds, exhibit large differences in microhardness and anomalous indentation creep behaviour. Such differences are shown to be due to differential effects of water adsorption on the opposite polar faces rather than being an intrinsic polar mechanical property of the crystal. The usefulness of microhardness measurements for absolute determinations of crystallographic polarity of non-centrosymmetric crystals is discussed. Effects of environment on the extent of edge dislocation motion away from the indentation are examined. Possible mechanisms to explain the adsorption-induced changes in microhardness and related mechanical properties of non-metallic solids are critically discussed.