Effect of Si 3 N 4 addition on oxidation resistance of ZrB 2 -SiC composites

Abstract

The oxidation behavior of ZrB 2 -20 vol % SiC and ZrB 2 -20 vol % SiC-5 vol % Si 3 N 4 composites prepared by hot-pressing and subjected to isothermal exposure at 1200 or 1300 °C for durations of 24 or 100 h in air, as well as cyclic exposure at 1300 °C for 24 h, have been investigated. The oxidation resistance of the ZrB 2 -20 vol % SiC composite has been found to improve by around 20%-25% with addition of 5 vol % Si 3 N 4 during isothermal or cyclic exposures at 1200 or 1300 °C. This improvement in oxidation resistance has been attributed to the formation of higher amounts of SiO 2 and Si 2 N 2 O, as well as a greater amount of continuity in the oxide scale, because these phases assist in closing the pores and lower the severity of cracking by exhibiting self-healing type behavior. For both the composites, the mass changes are found to be higher during cyclic exposure at 1300 °C by about 2 times compared to that under isothermal conditions.