Fracture toughness of zirconia-alumina composites

The dependence of fracture toughness on microstructure coarsening, induced by thermal treatment at 1600 degrees C, has been studied in zirconia-alumina composites with compositions 5%, 15% and 30% zirconia by volume. The fracture toughness has been evaluated using different methods based on producing small surface cracks by Vickers indenters, or on producing a large through the thickness crack. It is concluded that fracture toughness increases with the volume fraction of zirconia as well as with zirconia particle coarsening. This is explained by the effect of these microstructural parameters on the main operating toughening mechanism, which is found to be stress induced phase transformation. (C) 1999 Elsevier Science Ltd. All rights reserved.