Corrosion Resistance and Structure of Cr−O−N Coatings Formed in Vacuum Arc Plasma Fluxes With PIIID

Abstract

Cr−O−N-based vacuum arc coatings are very promising for the wear and corrosion protection of various steel parts. The aim of the work was to determine the effect of frequency and amplitude of the pulsed bias voltage (U_B) on the elemental and phase composition, mechanical, and corrosion properties of Cr−O−N coatings. They have an amorphous structure with embedded nanosized solid solution crystallites based on CrN with a cubic structure and Cr₂O₃ with a rhombohedral structure. The increase in the bias voltage results in a reduction in the grain size of the Cr₂O₃ and CrN phases by about four times to about 5 nm, as well as a change in the CrN phase content in the coating. The lattice parameter increases slightly for the Cr₂O₃ phase but decreases for the CrN phase. The increase in the pulse frequency results in an increase in the CrN phase content in the coating and the lattice constant of both phases and a slight decrease in the crystallite size. The hardness of Cr−O−N coatings slightly increased with the U_B from 26 ± 1 GPa (DC) to 28 ± 1 GPa (−300 V, pulsed), and the elastic modulus ranges from 290 to 310 GPa. The greatest changes were observed in corrosion resistance. With an increase in the bias voltage and pulse frequency, the corrosion current of Cr−O−N coatings on steel in 3% NaCl solution decreased by three orders of magnitude compared to coatings deposited at DC voltage and by five orders of magnitude compared to the base steel. Therefore, the use of a pulsed bias voltage with a frequency of at least 10 kHz and an amplitude of 700 V can significantly increase the corrosion resistance of Cr−O−N coatings on steel substrates.