Microstructural and tribological characterization of DLC coatings deposited by plasma enhanced techniques on steel substrates

In this work, three plasma-enhanced techniques have been used to deposit Diamond-like Carbon coatings (DLCs), as follows: HiPIMS, PECVD, and PIID. The DLCs deposition was on nitrided and non-nitrided steel substrates. In the DLCs deposited by HiPIMS and by PECVD processes, an adhesion layer of Ti/TiN and Ti/TiN/TiC, respectively, was deposited using a W hot filament. In the PIID process, a SiCx interlayer was grown out of tetramethylsilane gas before DLC deposition. Subsequently, the DLCs coated systems were characterized by SEM/EDS, Raman Spectroscopy, instrumented hardness, adhesion, and tribological behavior. Raman characterization revealed that DLC deposited by PECVD presented the lowest ID/IG ratio, meaning the highest amount of sp3 bonding, consequently, was the hardest coating. Adhesion probed by a scratch test revealed that the DLC deposited by PECVD showed gross spallation, exposing the Ti/TiN/TiC adhesion layer. On the other hand, the DLCs deposited by HiPIMS and PIID showed wedging spallation, as the primary adhesive failure mode. The DLC that presented the best tribological behavior was the one deposited by PECVD due to its highest H/E ratio.