Nanoindentation investigation of micro-fracture wear mechanisms in polycrystalline alumina

The initiation of surface damage under point loading has been investigated in polycrystalline alumina materials using low load continuous depth-sensing indentation equipment (nanoindentation). Pure alumina and liquid phase sintered materials containing 10% by weight of magnesium or calcium monosilicate have been examined and data obtained from plots of displacement as a function of load assessed in relation to erosive wear rates. In the pure alumina material, discontinuities ("pop-ins") in the load-displacement trace appear to be associated with the induction of radial cracking around a plastic impression. The pop-ins provide information on the indentation load at which fracture was initiated, and an estimate of the energy associated with crack formation. SEM imaging of the indentations before and after etching allowed crack paths to be related to microstructural features