Pressureless sintering and microstructural development of B sub 4 C-TiB sub 2 composites

Densities >95% of theoretical were achieved by pressureless sintering of B{sub 4}C-TiB{sub 2} composites (with up to 50 wt% TiB{sub 2}) at 2,150{degree} to 2,175{degree}C using 1 wt% Fe as a sintering aid. Iron levels between 0 and 5 wt% were examined; densities >97% of theoretical were obtained with 1 wt% Fe for a B{sub 4}C-10 wt% TiB{sub 2} composite. Excessive grain growth was observed when excess liquid was present (i.e., high Fe additions), resulting in decreased flexural strength. The effects of the additives on the sintering behavior and microstructural alterations were examined. Microstructural investigations were conducted using optical and electron microscopy. Microstructures consisted of fine-grained B{sub 4}C and intergranular TiB{sub 2} (both phases generally {approx}5 {mu}m in diameter). Transmission electron microscopy revealed that the iron-rich grain-boundary phase(s) existed, both at B{sub 4}C/B{sub 4}C interfaces and at B{sub 4}C/TiB{sub 2} interfaces.