Modified diamond-like carbon (Cr-DLC) coating applied by PACVD-CAPVD hybrid method: Characterization and evaluation of tribological and corrosion behavior

The objective of this study is to apply a thin diamond-like carbon (DLC) coating modified with Cr onto a St37 (S235JR) carbon steel substrate. This was accomplished using a combination of plasma-assisted chemical vapor deposition and cathodic arc physical vapor deposition (PACVD-CAPVD). An intermediate Cr-CrN layer was first added to the substrate by CAPVD to enhance coating bonding. Next, DLC coating was applied using PACVD with various Cr contents and target cathodic currents of 80, 100, and 120 A. The coatings were analyzed using Raman spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Furthermore, mechanical properties, tribological behavior, and electrochemical behavior were evaluated using a nanoindentation tester, pin-on-disk tribometer, and potentiodynamic polarization, respectively. Raman spectroscopy revealed an increase in the fraction of sp3 bonds in the DLC coatings as the cathodic current increased. The G and D peaks of the DLC coatings also showed this trend. Wear resistance and elasticity modulus were improved with an increase in Cr content, while hardness and adhesion strength decreased. The DLC coating debonded and metallic bonding became dominant at higher Cr concentrations, which may account for these trends. The DLC coating with Cr had a lower friction coefficient during wear testing. However, friction coefficient increased significantly when the cathodic current exceeded 100A and when there was a higher Cr concentration. As for the polarization test, increasing the cathodic current to 100A and the Cr content to 35 at.% lowered the corrosion current density from 1.19 to 0.53 μA/cm2 and increased the polarization resistance from 33.93 to 76.66 kΩ.