TRIBOLOGICAL BEHAVIOR OF SIC-WHISKER/AL2O3 COMPOSITES AGAINST CARBURIZED 8620 STEEL IN LUBRICATED SLIDING

Mineral oil lubricated sliding tests of SiC-whisker (SiC(w))/Al2O3 composites and monolithic alumina against carburized 8620 steel were conducted on a cylinder-on-cylinder machine. The wear rate of the composites was one or two orders of magnitude less than that of pure alumina. Hot-pressed 25 wt% SiC(w)/Al2O3 composite had a lower wear rate than sintered and HIPed 7.5 wt% SiC/Al2O3 composite under the same conditions. The weight loss of the steel mating ring against the 25 wt% SiC(w) composite was a factor of four lower than against the 7.5 wt% SiC(w) composite, but the former was a factor of 50 to 60 less than that against pure alumina. The composites showed lower friction coefficients than alumina during the run-in stage. The friction coefficients decreased with initial wear. The steady-state friction coefficient decreased with increasing load up to 500 N for hot-pressed 25 wt% SiC(w)/Al2O3 composite. Further, SEM observation showed much less microfracture in composites than in alumina. EDAX analysis revealed less Fe transfer from the steel ring to the composites than to pure alumina. Wear by microfracture and by adhesion in composites was suggested to be suppressed by SiC whiskers. This in turn reduced wear of the steel because of the generation of fewer hard particles.