Pressureless sintering and elastic constants of Al2O3-SiC 'nanocomposites'

A study is presented of how to obtain very near theoretical densities (greater than or equal to 99.6%) in Al2O3-SiC 'nanocomposites' by pressureless sintering. Several factors are considered in order to achieve the optimal densification. The most important factors are: good dispersion of SiC particles in the matrix, cold-isostatic pressing of green samples and use of a relatively coarse-sized bedding powder (which allows efficient effusion of carbon monoxide from the sample), correct choice of sintering temperature (which depends on the size of alumina particles), and the use of a nitrogen atmosphere curing sintering. The elastic constants of the nanocomposites produced depend on the degree of densification. About 2% reduction from theoretical density leads to about a 6% reduction of the Young's modulus. The experimentally obtained moduli are correlated with three models that relate porosity to Young's modulus. (C) 1997 Elsevier Science Limited All rights reserved.