Comparative study on the oxidation behavior of Si2BC3N/Ta4HfC5 ceramics at 1000 °C and 1500 °C: Microstructural evolution and kinetics consideration

Abstract

The oxidation kinetics and oxide scale morphology of the Si2BC3N/Ta4HfC5 ceramics sintered by hot-pressing were explored at 1000 °C and 1500 °C in flowing air. Dense Si2BC3N/Ta4HfC5 ceramic sintered at 1900 °C with fine grain sizes shows the optimal oxidation resistance both at 1000 °C and 1500 °C. When oxidized at 1000 °C, the formation of a porous oxide layer of Ta2O5, Hf6Ta2O17 and HfO2 containing amorphous SiO2 are primarily responsible for the unsatisfying oxidation resistance of the composite. A highly oxidation resistance component like Si2BC3N can promote the oxidation resistance of Ta4HfC5 at 1500 °C, thanks to the formation of a dense and continuous tantalum-hafnium silicate glass. The oxidation kinetic curve at 1500 °C can be described by a parabolic law whilst the oxidation process is controlled by the diffusion rate of oxygen through the oxide layer; however, the oxidation reaction rate governs the oxidation progress at 1000 °C via a linear oxidation kinetics.