Interferometric and hardness studies of the surfaces of crystals

Abstract

Part I of the thesis commences with a general picture of the various concepts of hardness and the relationship of indentation hardness to other physical properties. Types of measurement of hardness are reviewed with special reference to static indentation tests. The optical techniques and the apparatus made and used are described, including the interferometric techniques employed. The following aspects of hardness of silicon carbide are studied: (1) The variation of hardness with load, the relation between 'recovered' and 'unrecovered' hardness and the surface distortions around the indentations. (2) The variation of hardness with direction: it is found that the [1120] and [0110] are respectively the directions of maximum and minimum hardness. An attempt is made to explain the results in terms of the shear stress on the slip plane. (3) Ring cracks formed by steady pressure made by a diamond ball: the distortions round the cracks and the profiles of sections are studied by multiple-beam interferometry and phase-contrast microscopy. Hertz's classical equation is applied to compare the results. The micro-slip lines observed on a rare trigonal pyramid face of a silicon carbide crystal due to diamond ball impacts are described. A description is given of the analysis of silicon carbide crystals by X-rays. Part II of the thesis gives a description of various types of micro-features observed on transparent crystals of silicon carbide. The features are studied by applying the techniques of multiple-beam interferometry and phase-contrast microscopy. The special point about these features is that they are depressions. An attempt is made to explain their existence on the basis of a theory postulated by Tolansky and the dislocation theory of evaporation of crystals by Cabrera and Levine. A description is given of spiral-like features observed at the edge of some silicon carbide crystals. An appendix to the thesis gives a brief account of interferometric studies made on sawn surfaces of diamond.