Influence of oxygen content on structure, thermal stability, oxidation resistance, and corrosion resistance of arc evaporated (Cr, Al)N coatings

(CrxAl1-x)(OyN1-y)(epsilon) coatings with different oxygen fractions were prepared by cathodic arc evaporation through variation of injected oxygen flux, and elaborated concerning structure, mechanical properties, thermal stability, oxidation resistance, and electrochemical properties. A moderate addition of O into (Cr, Al)N coatings generates a (Cr, Al)(O, N) solid solution with a face-centered cubic structure, whereas an additional corundum-structured (Cr, Al)(2)O-3 solid solution is formed with superfluous oxygen introduced. The addition of O effectively improves the thermal stability by retarding the formation of w-AlN as well as the dissociation of the Cr-N bond, allowing the oxynitride coatings to maintain higher hardness after annealing. Notably, a small fraction of O-addition (e.g. 8 or 21 at.% in non-metal sublattice) enhances significantly the resistance against oxidation to above 1100 degrees C by facilitating the formation of a protective Al-rich oxide scale. Further incorporation of O gives rise to a development of oxide scale with unity elemental distribution and hence results in inferior oxidation resistance. Nevertheless, the O-rich oxynitride coatings provide better protection against electrochemical corrosion while the N-rich coatings exhibit higher corrosion current as well as lower polarization resistance compared to the CrAlN coating.

Automated summary

(CrxAl1-x)(OyN1-y)(epsilon) coatings with different oxygen fractions were prepared and their structure, properties, and application characteristics were investigated. A moderate addition of oxygen improved thermal stability and oxidation resistance, while excessive oxygen reduced the oxidation resistance. Additionally, the oxynitride coatings provided better protection against electrochemical corrosion.