FRICTION AND WEAR OF BORIDE CERAMICS IN AIR AND WATER

The tribochemical response of hot-pressed boride ceramics, ZrB2, B4C, ZrB2 + B4C and ZrB2 + B4C + SiC, has been investigated in air and in d e-ionized water. In dry air, the coefficients of friction for all mate rials tested were about 0.9-0.95, while in humid air of relative humid ity (r.h.) 95% they ranged from 0.2-0.3, except for that of ZrB2, whic h was 0.4. Hertzian fractures were noted on the worn surfaces of monol ithic boride and ZrB2 + B4C composite, but not on those of SiC-toughen ed boride or SiC-toughened ZrB2 + B4C. In water, ZrB2 underwent very s evere tribochemical degradation, as suggested by the following reactio n: ZrB2 + 10H2O -->Zr(OH)4 + 2H3BO3 + 5H2, while B4C, ZrB2 + B4C and Z rB2 + B4C + SiC underwent less tribochemical degradation, and showed l ower specific wear rates than ZrB2 in water.