Oxidation behaviour of Si3N4/Y2O3 system ceramics and effect of crack-healing treatment on oxidation

This paper describes the oxidation behaviour of Si3N4/Y2O3-based ceramics. We prepared three kinds of ceramics, which have excellent crack-healing abilities, in different composites – Si3N4/Y2O3, Si3N4/SiC/Y2O3, and Si3N4/Y2O3/Al2O3 – and investigated the effect of crack-healing treatment on their oxidation behaviour. The oxidation tests were carried out at 700–1200 °C for 500 h. Measurements of weight gain and bending strength and observations of the oxidized surfaces were carried out. in results obtained are as follows: (1) when Y2O3 was used as an additive, Si3N4 ceramics exhibited extensive oxidation at low temperatures (700–1000 °C). (2) Si3N4/Y2O3 ceramics with 3-wt% Al2O3 added as an additive showed no extensive oxidation. (3) Crack-healing, as a pre-oxidation treatment, is useful for increasing the oxidation–resistance of ceramics at 1000 °C and for increasing the strength.