Surface enhancement by shallow carbon implantation for improved adhesion of diamond-like coatings

A surface layer of metal carbides provides an excellent interface to achieve a highly adherent diamond-like carbon (DLC) coating. A plasma immersion ion implantation based procedure is described which delivers a high retained dose of implanted carbon at the surface of aluminum alloys. This proposed implantation procedure employs a low target bias of only 10–12 kV, a pulse repetition rate of around 5 kHz, and a duty cycle of 25%. The resultant shallow implantation profile, followed by an argon sputter cleaning, is continued until a saturated carbon matrix is brought to the surface providing an excellent interface for subsequent growth of DLC. At a carbon retained dose above 10¹⁸ atoms/cm², the DLC adhesion exceeds the coating’s cohesion strength. Regardless of the silicon content in the aluminum, the coating produced by this method required tensile strengths typically exceeding 150 MPa to separate an epoxy coated stud from the coating in a standard pull test. Improved DLC adhesion was also observed on chromium and titanium. The reported tensile strength is believed to meet the majority of industrial applications. © 1999 American Vacuum Society.