Oxidation resistance and strength retention of ZrB2–SiC ceramics

Oxidation behavior and effect of oxidation on the room-temperature flexural strength were investigated for ZrB2–10 vol% SiC (ZB10S) and ZrB2–30 vol% SiC (ZB30S) in air at 1500 °C with times ranging from 0.5 h to 10 h. The oxide scale of both ZB10S and ZB30S was composed of an outer glassy layer and an inner extended SiC-depleted layer. The changes in weight gain, glass layer thickness, and extended SiC-depleted layer thickness with oxidation were measured. Analysis suggested that the extended SiC-depleted layer was most indicative for evaluating the oxidation resistance. Compared to the ZB10S, the improved oxidation resistance in ZB30S was attributed to the viscosity increase of glassy layer and the lower number of ZrO2 inclusions in the glassy layer. Because of the healing of surface flaws by the glassy layer, the strength increased significantly by ∼110% for ZB10S and by ∼130% for ZB30S after oxidation for 0.5 h.