PROCESSING AND MECHANICAL-PROPERTIES OF BORON-CARBIDE SINTERED WITH TIC

The suitability of TiC as a sintering aid for boron carbine is investi gated. The in situ reaction of TiC with boron carbide generates elemen tal carbon and TiB2 which both aid the sintering process and permit pr essureless sintering at temperatures between 2150 and 2200 degrees C. Relative densities of as-sintered materials exceed 93% of theoretical, but can be increased to nearly full density by subsequent hot isostat ic pressing. The grain size of both B4C and TiB2 increases with sinter ing temperature and decreases with the amount of sintering aid The pre sence of TiB2 causes a slight increase in Young's modulus and a small decrease of hardness as compared to single phase B4C materials. The fl exural strength of B4C-TiC is found to decline with increasing fractur e toughness. This behavior is related to crack length dependent toughn ess, particularly to the slope and steady scare value of the R-curve. The dependence of R-curve properties on the grain size of the B4C matr ix is discussed. (C) 1998 Elsevier Science Limited. All rights reserve d.