INTERFACIAL FRACTURE ENERGY-MECHANICAL BEHAVIOR RELATIONSHIP IN AL2O3SIC AND AL2O3/TIN NANOCOMPOSITES/

Grain boundary-interface dihedral angles in Al2O3/SiC and Al2O3/TiN na nocomposites have been measured from TEM micrographs, and the ratio of the particle/matrix interfacial energy gamma(i) to the alumina grain boundary energy gamma(gb) has been calculated on the basis of an energ y balance condition. The average ratio, gamma(i)/gamma(gb), was found to be 1.21 for Al2O3/SiC and 0.80 for Al2O3/TiN. These results, togeth er with estimates of surface energies, have been used to estimate inte rfacial fracture energies. It-is found that the interfacial fracture e nergy between SiC and alumina is more than twice the alumina grain bou ndary fracture energy, i.e. SIC nanoparticles strengthen grain boundar ies. The dominant factor in this result is the greater surface energy of SiC compared with Al2O3 Despite the higher surface energy of TIN an d the lower gamma(i)/gamma(gb) ratio for Al2O3/TiN, it is found experi mentally that TiN particles weaken grain boundaries instead of strengt hening them. The detrimental factor is believed to be the formation of TiO2 at the, interfaces. The weakening is consistent with a lower int erfacial fracture energy. The present work indicates the importance of interfacial properties, which should not be ignored in modelling. Cop yright (C) 1997 Acta Metallurgica Inc.