Residual thermal stresses and calculation of the critical metal particle size for interfacial crack extension in metal-ceramic matrix composites

A combined experimental and theoretical study was carried out to analyze the effect of residual thermal stresses on the interfacial bonding in particulate metal-ceramic matrix composites, in particular, ductile phase toughened ceramics. The metal-ceramic microstructure studied is a two phase Ni/Al₂O₃ system produced by an in situ reduction processing technique. When a Ni particle exceeds the critical size, crack extension occurs along the particle/matrix interface upon cooling from the reduction temperature to room temperature. A closed form solution is derived for the case of thermal loading for the energy release rate and the phase angle for a crack along the interface of a cylindrical particle embedded in an infinite matrix. A theoretical estimate of the critical size for the nickel particle for crack extension is then computed based on the closed form solution and experimental data on the toughness of the Ni/Al₂O₃ interface.