Research on Deformation Behavior by Contact Stress and Microstructure of Silicon Carbide

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Four kinds of silicon nitride ceramics with different grain sizes and different amounts of the boundary phase were prepared, and the polished surface of the samples was indented with a round diamond indenter. The morphology of the surface deformation, cracks and the structure under the indented surface were investigated. After indentation, a round impression was formed on the surface and the swelling was found around the impression. The diameter and the maximum depth of the impression were larger in the samples with a large grain size and a large amount of the boundary phase. Two types of cracks were observed, namely a radial crack and a Hertzian crack. The radial crack propagated from the impression above the indentation load of 147 N, and its length was larger in the samples with a coarse grain size. The Hertzian crack was found inside the impression of the samples with a fine grain size. After etching in a NaOH melt a ring shape area was corroded away from the indented samples. The area of the corroded region depended on the grain size and the amount of the boundary phase. Load-depth curve during loading and unloading depended on the amount of the boundary phase.