# Corrosion Resistance of Amorphous Carbon Coatings Doped with Nitrogen and Hydrogen in 3.5% NaCl Solution and Mine Waters

## TL;DR

This study examines how adding nitrogen and hydrogen affects the corrosion resistance of carbon coatings on steel in harsh environments like mine waters and salt solutions.

## Contribution

The study identifies an optimal gas ratio (N2:CH4:H2 3:4:2) that enhances corrosion resistance through improved coating-substrate adhesion.

## Key findings

- Coatings with N2:CH4:H2 ratio 3:4:2 showed the best corrosion resistance in both 3.5% NaCl and mine waters.
- Improved adhesion between coating and substrate correlates with better corrosion resistance parameters.
- Doping elements altered surface damage morphology and electrochemical properties like corrosion current density.

## Abstract

To evaluate the effect of nitrogen and hydrogen on the corrosion resistance of diamond-like carbon (DLC) coatings, potentiodynamic tests were carried out on DLC coatings deposited under various reactive atmosphere compositions on martensitically hardened 34CrAlNi steel. In order to replicate actual operating conditions of steel components, the tests were conducted both in a reference 3.5% NaCl solution and in natural mine waters, which are in direct contact with mining gearbox mechanisms. Although it is generally assumed that the addition of other elements tends to deteriorate the corrosion resistance of amorphous carbon coatings, such doping simultaneously improves adhesion to metallic substrates, and enhanced adhesion in turn contributes to improved corrosion resistance. Variation in the proportions of the doping elements altered the damage morphology on the sample surface, as well as the corrosion current density, corrosion potential, and polarization resistance. Improvements in corrosion resistance parameters correlated with the quality of the coating–substrate adhesion, evaluated in accordance with the VDI3918 standard. The most favorable properties were obtained for coatings deposited under a gas composition of N2:CH4:H2 with a ratio of 3:4:2.