Porosity and Oxide Layer Dependence of Thermal Shock Behavior of Porous Silicon Nitride Ceramics

A water-quenching technique has been adopted to evaluate thermal shock fracture and fatigue behaviors of porous Si₃N₄ ceramics in an air atmosphere. The high-porosity Si₃N₄ ceramics exhibit a higher strength retention and a better resistance to thermal shock fatigue because of its role of the pores as crack arresters. A dense and coherent surface oxide layer leads to a significant benefit in residual strength during thermal fatigue, however, an increased fatigue number to 30th cycle cannot cause a further influence although a thicker oxide layer presents, which is attributed to holes defect and disappearance of part intergranular phase.