Microhardness anisotropy of silicon carbide

The effect of crystallographic anisotropy on the room-temperature Knoop microhardness of silicon carbide has been studied on each of three major sections of alpha single crystals (namely: {0 0 0 1}, {1 ¯1 0 0} and {1 1 ¯2 0}), measurements being made at 10° angular intervals over a range sufficient to include all the non-equivalent indenter orientations on each crystal section. The results are presented graphically and compared with a number of possible anisotropies computed for different slip systems using a model based on the effective resolved shear stress (ERSS) model of Brookes et al. [1] with a modification suggested by Arnell [2]. The results are interpreted to show that plastic deformation appears to occur preferentially on the {1 ¯1 0 0}〈1 1 ¯2 0〉 and {0 0 0 1}〈1 1 ¯2 0〉 slip systems over different ranges of orientations of the indenter. Further, it has been possible to estimate the ratio of the critical resolved shear stresses of these systems, the {0 0 0 1} 〈1 1 ¯2 0〉 system having a CRSS between 1.2 and 2.1 times that of the {1 ¯1 0 0}〈1 1 ¯2 0〉 system. Computation has also been used to investigate the detailed effect of the form of Brookes' constraint factor and the reliability of hardness anisotropies predicted in this way. The possible roles of slip and other deformation mechanisms in governing the response of brittle solids subjected to indentation hardness tests are also discussed.