FRACTURE-MECHANICS AND DEFORMATION PROCESSES IN NATURAL QUARTZ - A COMBINED VICKERS INDENTATION, SEM, AND TEM STUDY

Conventional Vickers microhardness testing can be used to determine mode I fracture toughness, K//I//c, as well as hardness, H. This analysis is unreliable because it neglects residual stresses, which depend on the modulus to hardness ratio (E/H). A recent analysis incorporating this effect gives results compatible with published bend-test determinations. An extensive SEM study to determine three-dimensional indent-fracture morphology reveals a region of high backscattered electron contrast immediately adjacent to the indenter contact. TEM analysis shows this is an intensely deformed region with very high fracture density and evidence of partial melting. A submicrometer-scale blocky structure, perhaps resulting from cataclasis, occurs between fractures. The analysis shows that 'plastic' deformation associated with indentation in quartz is controlled largely by fracturing, although the absence of voids suggests some crystal-plastic accommodation process may also operate.