Nanopowder processing of ultrafine Si3N4 with improved wear resistance.

The processing, microstructure, and material properties of monolithic Si₃N₄ were investigated by using two amorphous Si₃N₄ nanopowders doped with (1) 6 wt% Y₂O₃ and (2) 6 wt% Y₂O₃ + 8 wt% Al₂O₃. The orthorhombic Si₂N₂O-based phase was found in the two as-sintered bulks. Carbothermal reduction treatment (CRT) was thus applied at 1400 °C for 10 h with 3 wt% and 6 wt% carbon black added to the precursor powders of the Si-Y-O-N and Si-Y-Al-O-N systems, respectively, resulting in an increased nitrogen-to-oxygen (N:O) ratio and elimination of Si₂N₂O within the sintered bulks. The possible mechanisms of nucleation and grain growth of Si₃N₄ are discussed during CRT and the sintering process. The best wear resistance was achieved in ultrafine Si₃N₄ doped with Y₂O₃, which has good hardness, indentation toughness and a protective tribo-film. [ABSTRACT FROM AUTHOR]