A review of issues in the fracture of interfacial ceramics and ceramic composites

This article reviews the fracture behavior of very fine grain ceramics and ceramics which contain fine grain inclusions. These are interfacial materials in the sense that interfaces make up a relatively large volume fraction of the total material, and may therefore significantly influence the properties. The theme is to examine established trends concerning fracture behavior and grain or inclusion size and then to evaluate the validity of extrapolating those trends to very small sizes. The first section examines possible toughening mechanisms in single phase ceramics with submicron grain sizes, including microcracking, crack tip plasticity due to grain boundary sliding and transformation toughening. There is little reason to expect that microcrack toughening or crack tip plasticity will occur in these very fine grain ceramics. The second section discusses the strength and fracture toughness of ceramics containing submicron inclusions of oxides or carbides. Possible reasons for enhancements in the fracture strength in these ‘nanocomposites’ are discussed.