Mechanical behaviour of a silicon nitride particulate ceramic composite

Mechanical behaviour of a particulate ceramic composite (Si3N4 + SiC) was investigated. Its strength and fracture toughness on heating up to 1300 °C were determined as well as stress–strain curves plotted for this temperature range were analyzed. It is emphasized that this material is not only heterogeneous but also inelastic, and its deformation and fracture behaviour differ considerably from those of conventional ceramics. It was established that SENB fracture toughness measurements on notched specimens in flexure were quite reliable. Thus, there is no need in employing sophisticated standard test methods for this purpose. Fracture resistance estimates by the edge fracture (EF) method demonstrated that this material exhibited a lower barrier to the onset of fracture and a nonlinearly rising R-line, i.e., it displayed the ability to resist crack propagation (R-curve effect). The fracture resistance FR and initial fracture toughness KIi were also determined. This information is rather useful for analysis of its actual performance under mechanical loading. The model of a nozzle vane of the gas turbine was employed to illustrate that the EF method was appropriate for evaluating the uniformity of ceramic items by their fracture resistance.