Influence of small amount of sintering additives on unlubricated sliding wear properties of SiC ceramics

Fully densified SiC ceramics were developed from commercially available β-SiC powders using small amount (3 wt%) of AlN–Sc2O3 or AlN–Y2O3 additives by hot pressing at 2050 °C for 6 h in nitrogen atmosphere, and their wear properties were investigated by subjecting to self-mated sliding at different loads (1, 6 and 13 N) under unlubricated conditions. SiC ceramics prepared with 3 wt% AlN–Y2O3 additives consisted of mostly large equi-axed grains with amorphous grain boundary phase of ∼1.2 nm thickness, whereas SiC ceramics sintered with 3 wt% AlN–Sc2O3 additives showed duplex microstructure of elongated and fine equi-axed grains with clean grain boundary. As the load was increased, the steady state coefficient of friction reduced from ∼0.6 to ∼0.2, and wear rate increased from 10−6 to 10−5 mm3/N·m. It was observed that the friction did not depend on the additive composition, while less wear was observed for the SiC ceramics sintered with 3 wt% AlN–Sc2O3 additives consisting of clean grain boundary. The material loss was increased with the increased amount of sintering additive to 10 wt%. The worn surface morphology revealed that the material was primarily removed via surface grooving and microcracking at 1 N load, while tribochemical wear dominated at 6 and 13 N loads.