EFFECTS OF LIQUID-PHASES ON INTRINSIC INTERFACIAL SLIDING OF ALKALI-HALIDE CRYSTALS

The effects of liquids on intrinsic interfacial sliding have been studied in NaCl crystals. The primary liquids examined in the study were water, methanol, and mixtures thereof. Sliding experiments were performed using a simple specimen geometry in which shear and normal compressive forces were exerted on a planar interface. The geometry consisted of two single crystals joined at a boundary whose normal was inclined at an angle, theta, to an axis along which a compressive load, P, was applied. The specimens were found to deform in two distinct ways: (1) by sliding along the interface, and (2) by indenting into one another in a direction normal to the interface. The introduction of liquids into the interface through channel-like defects was found to increase both the rate of sliding and indentation, with the increases being much greater for liquids with higher water content. It was found that the overall rate of displacement along the axis of the specimen was for the most part independent of P but increased in roughly a linear fashion with theta. A model for the process is developed in which displacement is produced primarily by interfacial sliding, with the liquid acting to promote the rate by undercutting the boundary and reducing the effective area of contact. The area of contact is determined using concepts borrowed from friction theory which lead to the observed P and theta-dependencies of the displacement rate.