Microstructural, mechanical, and corrosion properties of Cr1-xNbx and (Cr1-xNbx)Ny coatings for harsh-environment applications

• (Cr 1-x Nb x )N y coatings were deposited by DC magnetron sputtering without external heating and substrate bias. • Increasing Nb content (0.19 ≤ x ≤ 0.55) led to the formation of X-ray amorphous microstructure. • Nitrogen addition transformed amorphous films into nanocrystalline coatings with ∼66 % higher hardness. • Nb and N co-alloying significantly improved corrosion resistance by maintaining passivity >1 V vs Ag/AgCl. • Tailoring microstructure, hardness, and corrosion resistance was achieved by Nb and N incorporation in Cr. Chromium-based coatings are of interest for applications in harsh environments due to their high hardness and excellent resistance to corrosion. However, coatings deposited by magnetron sputtering often exhibit columnar microstructure which can compromise their performance by promoting porosity and reducing mechanical integrity. In this work, we present an approach to overcome this limitation by alloying Cr with Nb and N, forming (Cr 1-x Nb x )N y films. Increasing Nb content in Cr 1-x Nb x films (0.19 ≤ x ≤ 0.55) led to an X-ray amorphous microstructure, confirmed by X-ray diffractometry and high-resolution transmission electron microscopy, while hardness remains ∼8 to 11 GPa regardless of Nb content. Adding N to Nb-containing films (0.19 < x < 0.55) produced a nanocrystalline, denser microstructure with reduced column width, resulting in a ∼66 % higher hardness (∼15 GPa) than the metallic films. Electrochemical measurements show enhanced passivity of Nb-containing coatings above 1 V vs. Ag/AgCl, attributed to the suppression of soluble Cr 6+ species. X-ray photoelectron spectroscopy results indicate that Nb 2 O 5 could oxidize soluble species in the electrolyte forming NbO 2 on the surface. These findings show how Nb and N additions can tailor the microstructure, mechanical properties, and corrosion resistance of (Cr 1-x Nb x )N y films.