Interfacial fracture energy-mechanical behaviour relationship in Al2O3/SiC and Al2O3/TiN nanocomposites

Grain boundary-interface dihedral angles in Al2O3/SiC and Al2O3/TiN nanocomposites 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 energy 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, together with estimates of surface energies, have been used to estimate interfacial fracture energies. It-is found that the interfacial fracture energy between SiC and alumina is more than twice the alumina grain boundary fracture energy, i.e. SIC nanoparticles strengthen grain boundaries. The dominant factor in this result is the greater surface energy of SiC compared with Al2O3 Despite the higher surface energy of TIN and the lower gamma(i)/gamma(gb) ratio for Al2O3/TiN, it is found experimentally that TiN particles weaken grain boundaries instead of strengthening them. The detrimental factor is believed to be the formation of TiO2 at the, interfaces. The weakening is consistent with a lower interfacial fracture energy. The present work indicates the importance of interfacial properties, which should not be ignored in modelling. Copyright (C) 1997 Acta Metallurgica Inc.