Effects of Cr content on the microstructure of the Cr/A-c coatings and resultant corrosion and electric conductivity

In this study, chromium/amorphous carbon (Cr/A-c) coatings with varying Cr doping concentrations were deposited using a magnetron sputtering system equipped with a high-frequency oscillating pulsed electric field. The effects of Cr content on the microstructure, electrical conductivity, and corrosion resistance of the Cr/A-c coatings were systematically investigated. The experimental results revealed that the surface morphology of the Cr/A-c coatings became progressively smoother, with a significant refinement of cluster particles, as the Cr target current increased. Microstructure analysis demonstrated that the coatings consisted of Cr nanocrystals and chromium carbides uniformly dispersed within an amorphous carbon matrix containing both C-sp² and C-sp³ hybridized carbon. With increasing Cr target current, the atomic percentage of Cr in the coatings showed a gradual rise, resulting in a higher density of Cr nanocrystals and chromium carbides. This microstructural evolution led to enhanced electrical conductivity and improved corrosion resistance of the coatings. Optimal performance was achieved at a Cr target current of 0.65 A, where the coating exhibited superior electrical and anti-corrosion properties. Specifically, the interfacial contact resistance (ICR) measured 2.4 mΩ⋅cm² and 1.9 mΩ⋅cm² under compressive pressure of 1.2 × 10⁶ Pa and 1.5 × 10⁶ Pa, respectively, while the corrosion current density reached an exceptionally low value of 1.2 × 10^-6 A/cm².