J. Am. Ceram. Soc., 81 [4] 1004–12 (1998)

Crack Deflection and Propagation in Layered Silicon Nitride/Boron Nitride Ceramics

Desiderio Kovar,^*,†,‡ M. D. Thouless,^*,§ and John W. Halloran^*,†

Materials Science and Engineering Department and Mechanical Engineering and Applied Mechanics Department,

University of Michigan, Ann Arbor, Michigan 48109–2125

Crack deflection and the subsequent growth of delamination cracks can be a potent source of energy dissipation during the fracture of layered ceramics. In this study, multilayered ceramics that consist of silicon nitride (Si₃N₄) layers separated by boron nitride/silicon nitride (BN/Si₃N₄) interphases have been manufactured and tested. Flexural tests reveal that the crack path is dependent on the composition of the interphase between the Si₃N₄ layers. Experimental measurements of interfacial fracture resistance and frictional sliding resistance show that both quantities increase as the Si₃N₄ content in the interphase increases. However, contrary to existing theories, high energy absorption capacity has not been realized in materials that exhibit crack deflection but also have moderately high interfacial fracture resistance. Significant energy absorption has been measured only in materials with very low interfacial fracture resistance values. A method of predicting the critical value of the interfacial fracture resistance necessary to ensure a high energy-absorption capacity is presented.