Sintering and sliding wear studies of B4C-SiC composites

Abstract

Dense boron carbide (B4C) – silicon carbide (SiC) composites were obtained by spark plasma sintering technique at 1800°C with 3 wt% and 6 wt% aluminium oxide (Al2O3) additives. Addition of sintering additives results in formation of aluminium silicate (Al2SiO5) liquid phase which accelerates sintering kinetics and helps in obtaining high density ~ 99%. Microstructures reveal uniformly distributed SiC particles in B4C matrix. Increase in alumina from 3 wt% to 6 wt% results in decrease in hardness from 35.1 ± 0.8 to 33.7 ± 0.9 GPa, and increase in fracture toughness from 5.9 ± 0.4 to 6.5 ± 0.4 MPam0.5. Using a ball-on-disk tribo tester under dry unlubricated conditions at 5, 10 or 15 N load, influence of alumina content on friction and wear properties of B4C-SiC composites was investigated against SiC counterbody with a linear speed of 0.08 m/s for 60 min. The coefficient of friction (COF) increased from 0.25 to 0.65 with load, and the influence of alumina on frictional behaviour appeared to be negligible. With increase in load, wear volume of the composites increased from 7.5 × 10−2 mm3 to 16.1 × 10−2 mm3 for B4C-10 wt% SiC - 3 wt% Al2O3 and from 4.7 × 10−2 mm3 to 14.8 × 10−2 mm3 for B4C-10 wt% SiC - 6 wt% Al2O3 composites. Microcracking, abrasion and pull-outs contributed as major wear mechanisms of composites in selected wear conditions. The relation between wear behaviour and mechanical properties of sintered composites is discussed.