Increased adhesion of diamond-like carbon–Si coatings and its tribological properties

A pre-activation process on substrate surface has remarkably improved the poor adhesion strength of diamond-like carbon (DLC)–Si coatings on steels which is the largest obstacle in achieving a widespread application of the coatings onto machine components. The activation process consists of preliminary nitriding followed by ion etching under the selected condition. Very fine protrusions formed by the processes provide large adhesion strength to the coatings that were made continuously within the same DC-plasma-assisted chemical vapor deposition (PACVD). No intermediate layers are necessary. The critical load of DLC–Si coatings thus treated reached over 50 N in the scratch tests. The coatings with the critical load over 50 N showed much improved rolling fatigue life. The DLC–Si coating with over 50 N critical load endured a rotationa1 stress of 108 cycles at a contact pressure of 3.4 GPa, whereas the DLC–Si coatings with 10 N spalled at 106 cycles.