Abstract
The depth profile of indentation cracks has been determined by removing thin layers from the specimen by serial sectioning, as well as from observation of fracture areas after breaking of the specimens. A considerably defective deformed area has been identified under the indent, depth of which ranges from 120 to 140 μm. The shape of the deformed area is of angular, pyramid-like type. At the interface of the deformed and non-deformed area, minor cracks have been observed. The length of these minor cracks is much shorter when compared with the length of the major ones, however, they are more numerous. The volumes of the indents and the deformed areas have been compared for all of the indents. It follows from the calculations that the volume of the indent represents on average 8 % of the volume of deformed area.

Key words
silicon nitride, deformation under indent, depth profile of cracks, serial sectioning, fracture area

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