The effect of $B_4C$ on the densification, mocrostructure and mechanical properties of pressureless sintered $Al_2O_3-B_4C$ composites was studied.
Sintering was performed without sintering additives varying $B_4C$ content from 0 to 40vol.%. More than 95% of theoretical density was obtained up to 20vol.% of $B_4C$ when sintered at 1850℃ for 60min. With the increase of sintering time from 30 to 120min, no change of density results. It was found that the reaction of between $Al_2O_3$ and $B_4C$ did not bring to anything products, according to the results of XRD.
The grain growth of $Al_2O_3$ is inhibited by $B_4C$ particles pinning at the grain boundary, and is reduced with increasing $B_4C$ content because of grain boundary drag effect of $B_4C$ particles. The critical amount of $B_4C$ for effective dragging of grain boundary migration occurred at 10vol.% addition for $Al_2O_3-B_4C$ composites, pressureless sintered at 1850℃ for 60min.
The maximum 3-point bending strength was 550MPa for specimen contained 20vol.% $B_4C$, and the microhardness was 2100kg/㎟ for 30vol.% $B_4C$ specimen.
Fully dense $Al_2O_3-B_4C$ composites was obtained by hot pressed at 1700℃, 35MPa, 60min. Wear characteristics of $Al_2O_3-B_4C$ composites by hot pressed as a ceramic cutting tool was investigated. It was shown that the $Al_2O_3-B_4C$ tool exhibits good wear resistance since the $B_4C$ is resistant to mechanical wear due to high hardness.
