Oxidation of nano-multilayered CrAlBN thin films between 600 and 1000 °C in air

Thin CrAlBN films, whose composition were 41.5Cr-8.0Al-0.2B-50.3 N (at.%), were deposited on steel substrates in a cathodic arc plasma deposition system. They consisted of alternating crystalline Cr2N and AlBN nanolayers. The CrAlBN film oxidized faster than the CrAlSiN film. After oxidation at 900 °C for 50 h in air, a thin Cr2O3 layer, containing dissolved Al and Fe ions, formed via outward diffusion of Cr, Al, and Fe ions. After oxidation at 1000 °C for 50 h in air, bi-layered oxides formed, comprising an outer Cr2O3 layer containing dissolved Al and Fe ions, and an inner (Cr2O3,Al2O3,Fe3O4)-mixed layer. The outer oxide layer formed primarily by outward diffusion of Cr, Al, and Fe ions, while the inner mixed layer formed primarily by inward diffusion of O−2 ions.