Pressureless sintering of BC whisker reinforced AlO matrix composites

AlO-BC whisker composites have been successfully densified by pressureless sintering. Low oxygen partial pressures, below 10 atmospheres, were determined to be suitable for the composite densification, and the maximum densities were achieved at 1800 °C for 60 minutes. The BC whiskers were screened classified into five size fractions and the effect of size and size distribution on the densification were studied. The small whiskers with a narrow size distribution (-325+400 mesh) yielded the highest density results. The maximum value of relative densities was 98%, 97%, 94% and 89% at 10, 20, 30 and 40 vol% BC whiskers, respectively. Addition of BC between 5 and 15 vol% proved to be a sintering aid to the alumina densification via mechanisms other than being a grain growth inhibitor. An increased fracture toughness up to 6.2 MPa·m was achieved in the composites containing 10-20 vol% BC whiskers.