Creep behaviour of Al2O3SiC nanocomposites

Compared with monolithic fine grained Al2O3, Al2O3 nanocomposites reinforce d with SiC nanoparticles display especially high modulus of rupture as well as reduced creep strain. Taking into account the fracture mode change, the morphology of ground surfaces showing plastic grooving, the low sensitivit y to wear and the low dependence of erosion rate with grain size, it can be reasonably assumed that the strength improvement is associated with an inc rease of the interface cohesion (due to bridging by SiC particles) rather t han with a grain size refinement involving substructure formation (as initi ally suggested by Niihara). In the present work, creep tests have been perf ormed and the results agree with such a reinforcement of the mechanical pro perties by SiC particle bridging Al2O3-Al2O3 grain boundaries. Indeed, part icles pinning the grain boundaries hinder grain boundary sliding resulting in a large improvement in creep resistance. In addition, SiC particles, whi le counteracting sliding, give rise to a recoverable viscoelastic contribut ion to creep. Because of the increased interface strength, the samples unde rgoing creep support stress levels, greater than the threshold value requir ed to activate dislocation motion. The high stress exponent value as well a s the presence of a high dislocation density in the strained materials sugg ests that a lattice mechanism controls the deformation process. Finally, a model is proposed which fits well with the experimental creep results. (C) 1999 Elsevier Science Ltd. All rights reserved.