Microstructural effect on oxidation kinetics of NbSi2 at 1023 K

Poly- and single crystalline NbSi2 specimens with different microstructures were prepared by arc-melting, spark plasma sintering (SPS) and optical-heating floating zone melting for oxidation experiments at 1023 K. The effects of cracks, pores and grain boundary in the microstructure on the oxidation behavior of NbSi2 were investigated. For arc-melted poly-crystalline specimens containing micro-cracks, NbSi2 fully turned into powders after 3 h exposure at 1023 K, which is known as the “pesting” phenomenon. As a comparison, no pesting was found in the dense SPS poly-crystalline specimens and single crystals after 89 h. The oxide scale consists of Nb2O5 and SiO2. The oxidation kinetics of all specimens follows a linear law. The oxidation rate was higher in the poly-crystalline specimen in comparison to single crystalline. The mechanism of oxidation has been analysed using a kinetic model.