Microstructure and oxidation behavior of in situ formed TaSi2–Si3N4 nanocomposite coating grown on Ta substrate

TaSi2 coating reinforced with nanosized Si3N4 particles was formed on Ta substrate by in situ displacement reaction between Ta-nitrides (TaN and Ta2N) and silicon. Microstructure and oxidation behavior of this TaSi2–Si3N4 nanocomposite coating was investigated. Monolithic TaSi2 coating showed the typical columnar grain structure perpendicular to the Ta substrate. On the contrary, the nanocomposite coating consisted of the equiaxed or short-rod-shaped TaSi2 grains and the Si3N4 particles having oblate-spheroidal shape. Nanosized Si3N4 particles were located mostly at the grain boundaries of TaSi2. The average size of TaSi2 grains and Si3N4 particles were about 100–190 nm and 38–56 nm, respectively. The volume percentage of Si3N4 particles ranged from 11.3 to 28.4% with respect to the nitrogen concentration in the Ta-nitride layers. No cracks were observed in the nanocomposite coating, indicating that its thermal expansion coefficient was close to that of Ta substrate. The isothermal and cyclic oxidation resistance of nanocomposite coating at temperatures between 1300 °C and 1400 °C was superior to that of monolithic TaSi2 coating.