Superior high-temperature oxidation resistance of magnetron sputtered Hf-B-Si-C-N film

A hard and optically transparent amorphous Hf7B23Si17C4N45 film with a contamination level less than 4 at%, prepared by reactive pulsed dc magnetron sputtering, was subjected to systematic investigation of high-temperature oxidation behavior in air up to 1700 °C. We focus on thermogravimetric analysis of the film in air and on the evolution of the film structure, microstructure and elemental composition with an annealing temperature ranging from 1100 °C to 1700 °C. The film exhibits a superior oxidation resistance up to 1600 °C due to a formation of a nanocomposite protective oxide layer on the surface above 1000 °C. The layer consists of monoclinic and tetragonal (or orthorhombic) HfO2 nanocrystallites surrounded by a SiO2-based amorphous matrix, most probably containing boron. The HfO2 nanocrystallites exhibit a gradient in size with a dense population of small (a couple of nm) crystallites next to the interface and larger but dispersed crystallites close to the surface.