Densification of B4C whisker reinforced Al2O3 matrix composites

Al2O3-B4C whisker composites have been successfully densified by pressureless sintering. These whisker reinforcements avoid the health hazards of other, more well known reinforcements. Low oxygen partial pressures, below 10(-10) atmospheres, were determined to be suitable for the composite densification, and the maximum densities were achieved at 1800 degreesC for 60 minutes. The B4C whiskers were screen 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 yielded the highest density results. The maximum value of relative densities was 98%, 97%, 94% and 89% at 10, 20, 30 and 40 vol% B4C Whiskers, respectively. Addition of B4C 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(1/2) was achieved in the composites containing 10-20 vol% B4C whiskers.