Study of the high-temperature oxidation resistance mechanism of magnetron sputtered Hf7B23Si17C4N45 film

Abstract

The microstructure evolution and high temperature oxidation mechanism of a hard, amorphous, and optically transparent Hf7B23Si17C4N45 film was studied by x-ray diffraction and transmission electron microscopy. The Hf7B23Si17C4N45 films were deposited by reactive pulse dc magnetron sputtering and annealed in air at temperatures from 1100 to 1500 °C. All annealed films were found to have a two-layered structure composed of the original amorphous and homogeneous layer followed by a nanocomposite oxidized surface layer. The top nanocomposite layer consists of an amorphous SiOx-based matrix and a population of HfO2 nanoparticles with two distinct sublayers. The first sublayer is next to the original amorphous layer and has a dense population of small HfO2 nanoparticles (up to several nanometers) followed by a surface sublayer with coarsened and dispersed HfO2 nanoparticles (up to several tens nm). The HfO2 nanoparticles in the bottom sublayer form by a nucleation and growth process whereas the ones in the surface sublayer coarsen via Ostwald ripening. An estimate of the activation energy for oxygen diffusion through the oxidized layer produced a value around 3.43 eV attesting to the high oxidation resistance of the film. The oxidation resistance mechanism is attributed to the precipitation of HfO2 nanoparticles within a dense SiOx-based matrix and quartz SiO2 in front of the base layer interface that can act as a barrier to heat transfer and O diffusion.