Tribological characteristics of SiC ceramics sintered with a small amount of yttria

Abstract

Mechanical and tribological properties of hot-pressed SiC ceramics sintered with a small amount of yttria (0.2 or 3wt%) additive were studied. The friction and wear properties of the SiC ceramics were estimated under unlubricated sliding conditions against commercially available WC balls at 5-N, 10-N or 20- N load and 0.1m/s linear speed using a ball-on-disk tribometer. SiC ceramics prepared with 3wt% yttria (3Y–SiC) consisted of equiaxed grains, whereas SiC ceramics sintered with 0.2wt% yttria (0.2Y–SiC) showed bimodal grain structure with some elongated grains. With increase in yttria content from 0.2 to 3wt%, hardness decreased from 27.7 to 26.1GPa, flexural strength decreased from 580 to 542MPa, and fracture toughness increased from 4.0 to 4.3MPam1/2. The coefficient of friction varied from 0.4 to 0.5 and specific wear rate from 1.8×10−6 to 6.7×10−6mm3/Nm with change in yttria content or sliding load. The specific wear rate of the 3Y–SiC was approximately double than that obtained for the 0.2Y–SiC at 20N load. Worn surface analysis indicated mechanical fracture as a dominant mechanism of material removal of SiC ceramics under the selected sliding conditions. The friction and wear results are related to the microstructure and mechanical properties of the sintered SiC ceramics.