Enhancement of high-temperature oxidation resistance and thermal stability of hard and optically transparent Hf–B–Si–C–N films by Y or Ho addition

Abstract Hard and optically transparent amorphous Hf7B10Si32C2N44, Hf6B12Si29Y2C2N45 and Hf5B13Si25Ho3C2N48 films were prepared and examined for the oxidation resistance in air and thermal stability in inert gasses up to 1600 °C. A thermal evolution of their structure, hardness and optical properties was also studied. An addition of Y or Ho (2–3 at.%) into Hf–B–Si–C–N films leads to a stabilization of tetragonal HfO2 in a surface oxide layer upon oxidation. The thickness of this layer is the lowest for the Y addition. Upon annealing in He, no mass changes are detected up to 1315 °C and this temperature is shifted even to 1350 °C for the Hf6B12Si29Y2C2N45 film. The hardness of this film is enhanced from 22.2 GPa in the as-deposited state to 25.9 GPa after annealing to 1300 °C and the film retains its optical transparency up to 1400 °C. The crystallization of the amorphous structure occurs at around 1400 °C.