Indentation fracture of polycrystalline cubic ceramics

Abstract

The fracture properties of two polycrystalline cubic ceramics, MgO and Y2O3, are studied during and after indentation. Direct observation through transparent specimens of the indentation process (while simultaneously monitoring the indenter load and displacement) shows that radial cracks form almost immediately on loading in both materials. Lateral cracks form with the radials during loading in MgO, and during unloading in Y2O3. The indentation observations are used to interpret and model the variation of strength with indentation load of four MgO and two Y2O3 microstructures. Overall, the data suggest a significant effect of microstructure on the fracture properties of cubic ceramics, especially for MgO, in which an increase in toughness with crack length - a T-curve - was observed. Similar to non-cubic Al2O3 materials, the T-curve of the cubic MgO materials effective during long-crack tests is greater and exhibits less increase with crack extension than that applicable during strength tests.