Failure of metal-ceramic composites with spherical inclusions

In this work the development of cavities in spherical metal inclusions with in a metal-ceramic composite and the subsequent influence upon the strength of the composite is investigated. A model experiment is undertaken whereby 100 mum diameter spherical aluminium inclusions are placed within an Al2O3 -Al interpenetrating network composite. The samples are then fractured at t emperatures ranging from room temperature to just below the melting tempera ture of aluminium. It is found that fracture originates from the aluminium inclusions and that there is clear evidence of cavitation in the ductile in clusions which also shows that these cavities formed as a result of high tr iaxial stress during cooling as a part of the fabrication process. This obs ervation is supported by a numerical model of the stress formation and cavi ty growth process within an inclusion during cooling. The model also provid es information on the effect of initial cavity size and location, Compariso ns of experimental fracture strength and toughness data indicate that the o bserved high strength of these composites is explained by crack growth resi stance due to ductile ligament bridging. (C) 2001 Published by Elsevier Sci ence Ltd on behalf of Acta Materialia Inc.