Oxidation and its effect on flexural strength of hot-pressed ZrB2-SiC composites with VC additives

Abstract

The oxidation and its effect on room-temperature flexural strength were investigated in the hot-pressed ZrB2-SiC composites with 3−7 wt% VC additives exposed to air within the temperature range of 1100−1300ºC, for up to 100 h. The parabolic weight gain versus oxidation time was measured for the period of 10−100 h. The apparent oxidation activation energy was determined to be 70−180 kJ/mol, dependent on the amount of VC. The oxidation products consisted of m-ZrO2, V2O5, and ZrSiO4 at 1100ºC, m-ZrO2, SiO2 (α- or β-cristobalite), ZrV2O7, and ZrSiO4 at 1200ºC and 1300ºC. Moreover, the room-temperature flexural strength of the postoxidized composites varied depending on the amount of VC as well as on oxidation temperature. The change in the strength of the postoxidized composites was associated with the formation of either outermost dense glassy scale or new defects in the oxide layer during the oxidation exposure.