Abstract
Transmission electron microscopy is used to examine the nature of microcracking about small-scale indentations in two highly brittle solids, sapphire and carborundum. The observed crack geometry is discussed in terms of an earlier model of indentation fracture beneath a point force, in which both loading and unloading half-cycles contribute to the crack growth. The residual interfaces are generally found to exhibit moiré fringe contrast, and occasionally to contain dislocation networks. These observations are discussed in relation to spontaneous closure and healing mechanisms, and the associated “lattice mismatch” is estimated at about one part in a thousand. It is suggested that cleavage steps comprise the main source of obstruction to lattice restoration across the interfaces. Mechanical and thermal treatments of the indented specimens are found to influence the extent of the residual cracking. Some practical implications concerning the strength degradation of brittle solids are discussed.
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On study leave, from School of Physics, University of New South Wales, Kensington, N.S.W. 2033, Australia.
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Hockey, B.J., Lawn, B.R. Electron microscopy of microcracking about indentations in aluminium oxide and silicon carbide. J Mater Sci 10, 1275–1284 (1975). https://doi.org/10.1007/BF00540816
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DOI: https://doi.org/10.1007/BF00540816