Wear of fluorapatite single crystals: IV. Influence of sliding direction on frictional behavior and surface failure.

Preliminary studies of the wear of fluorapatite single crystals subjected to sliding neglected the possible influence of crystallographic direction on the frictional behavior and surface failure of the basal plane.1-3 In these studies, possible anisotropic effects were considered to contribute to the experimental error in the analysis of the data. Buckley4 has observed that friction coefficients (with limited plowing components) for a number of metals in sliding contact with other metals were lowest on the preferred slip or glide plane in the preferred slip direction. The anisotropy of surface failure has been discussed to a limited extent by Steijn5 for sapphire and by Bowden. Brookes, and Hanwell6 and Bowden and Brookes7 for magnesium oxide single crystals. The purpose of this study was to evaluate