Effect of intergranular phase chemistry on the sliding-wear resistance of pressureless liquid-phase-sintered α-SiC

The effect was investigated of the intergranular phase chemistry on the sliding-wear resistance of pressureless liquid-phase-sintered (PLPS) α-SiC densified with 10 vol.% 5Al2O3 + 3RE2O3 (RE = La, Nd, or Yb) additives. It was found that the sliding-wear behaviour of these ceramics is similar to what is observed in other polycrystalline ceramics: initial mild, plasticity-controlled wear followed by severe, fracture-controlled wear, with a well-defined wear transition. Most importantly, the sliding-wear resistance of PLPS SiC is found to increase with decreasing size of the RE3+ cation in the rare-earth oxide additive, with a lower susceptibility to mild and severe wear and a delayed transition to severe wear. Underlying this effect is likely the hardening of the intergranular phase resulting from the increase in the field strength of the RE3+–O2− bonds as the size of the RE3+ cation decreases. Tailoring the intergranular phase chemistry via the selection of RE2O3 sintering additives with cations as small as possible thus emerges as a potentially interesting approach to improving the sliding-wear resistance of PLPS SiC ceramics.