Adhesion and friction-wear characterization of W-doped hydrogenated diamond-like carbon (a-C:H) coatings

The aerospace, automotive, and defense industries extensively use AISI 4130 alloy steel, a significant material type for most engineering applications in the industry, due to its crucial characteristics, such as high strength, durability, machinability, and corrosion resistance. In this study, enhancing the surface mechanical and tribological properties of the material with tungsten (W)-doped diamond-like carbon (DLC) coatings emerges as a prominent approach to improving performance. Amorphous hydrogenated diamond-like carbon (a-C:H) coating has outstanding mechanical and tribological properties. In this study, W-doped a-C:H-DLC coatings have been deposited on AISI 4130 using closed-field unbalanced magnetron sputtering. A L9 orthogonal array of the Taguchi method was utilized to optimize the variable coating parameters applied in the magnetron sputtering process. The microstructure and thickness of the W-doped a-C:H-DLC coatings were examined using scanning electron microscopy. Raman spectroscopy was used to characterize the structure of these DLC coatings. The hardness values of the coatings were determined using the Knoop microhardness test. The scratch test method was used to examine the adhesion properties of the coatings by determining their critical load values at which coating delamination occurred. The tribological behavior of uncoated AISI 4130 substrate and coating was determined with a pin-on-disc tribometer against an Al₂O₃ ball under dry sliding conditions. Delamination and gradual failures occurring in the wear test of the uncoated specimen increased the friction coefficient. On the contrary, the coating exhibits such superior tribological properties that the friction coefficient decreased due to the prevention of delamination and gradual failures to a certain extent. It was observed that the scratch-adhesion properties of the coated specimens significantly contributed to the improvement of tribological performance. These thin films are particularly valued for their ability to provide high wear resistance and low coefficients of friction, properties that are critical to industries that deal with harsh conditions, such as automotive and aerospace.