Anisotropy in room temperature microhardness and fracture of CaWo4 scheelite

Mechanical anisotropy of scheelite (CaWO4) has made it attractive as oxidation resistant fiber-coatings in high temperature ceramic composites. Microhardness and fracture anisotropy of natural single crystal scheelite were studied using Vickers and Knoop indentations. Indentations with loads from 10 to 200 g were applied on {0 0 1}, {1 0 0}, {1 1 0}, and {1 1 2} crystallographic planes with various orientations of the indenter diagonal around the plane normal. The indentations were characterized with optical microscopy and SEM for cleavage, the anisotropy of microhardness, and toughness. The observations are interpreted using the crystallographic structure of scheelite.