Nanocrystalline $\alpha$-Al$_{2}$O$_{3}$ coatings obtained by reactive thermal anodic evaporation in arc discharge at low temperature

Al$_{2}$O$_{3}$ nanocrystalline coatings are obtained for the first time by anodic thermal evaporation of aluminum in an arc discharge in an oxygen–argon mixture at a temperature of 600$^\circ$C on stainless-steel substrates with a Cr$_{2}$O$_{3}$ sublayer. The effect of the surface state of the samples and ion energy on the phase composition, microstructure, and properties of the coating is assessed. The $\alpha$-Al$_{2}$O$_{3}$ phase is formed in the range of the bias potential of 25–200 V, with the growth of which the microcrystallite size decreases from 60 to 15 nm and the hardness of the coating increases from 8 to 20 GPa.