TENSILE CREEP OF ALUMINA-SILICON CARBIDE NANOCOMPOSITES

The tensile creep behavior of an (Al2O3-SiC) nanocomposite that contai ns 5 vol% of 0.15 mu m SiC particles is examined in air under constant -load conditions, For a stress level of 100 MPa and in the temperature range of 1200 degrees-1300 degrees C, the SiC reduces the creep rate of Al2O3 by 2-3 orders of magnitude, In contrast to Al2O3 the nanocomp osite exhibits no primary or secondary stages, with only tertiary cree p being observed. Microstructural examination reveals extensive cavita tion that is associated with SiC particles that are located at the Al2 O3 grain boundaries. Failure of the nanocomposite occurs via growth of subcritical cracks that are nucleated preferentially at the gauge cor ners. A modified test procedure enables creep lifetimes to be estimate d and compared with creep rupture data. Several possible roles of the SiC particles are considered, including (i) chemical alteration of the Al2O3 grain boundaries, (ii) retarded diffusion along the Al2O3-SiC i nterface, and (iii) inhibition of the accommodation process (either gr ain-boundary sliding or grain-boundary migration).