SINTERING AND CHARACTERIZATION OF AL2O3-B4C COMPOSITES

The effect of B4C on the densification, microstructure and mechanical properties of pressureless sintered Al2O3-B4C composites have been studied. Sintering was performed without sintering additives with varying B4C content from 0-40 vol%. Up to 20 vol% B4C, more than 97% theoretical density was always obtained when sintered at 1850-degrees-C for 60 min. On increasing the sintering time from 30-120 min, there was no change in density. The result of X-ray diffraction analysis showed that no reaction occurred between Al2O3 and B4C. The grain growth of Al2O3 was inhibited by B4C particles pinned at the grain boundary and the grain-boundary drag effect. The critical amount of B4C to drag the grain boundary migration effectively was believed to occur at 10 vol% B4C sintered at 1850-degrees-C for 60 min. The maximum three-point flexural strength was found to be 550 MPa for the specimen containing 20 vol% B4C, and the maximum microhardness was 2100 kg mm-2 for 30 vol% B4C specimen.