Improved adhesion of diamondlike coatings using shallow carbon implantation
- PDF / 59,580 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 23 Downloads / 230 Views
A surface layer of metal carbides provides an excellent interface to achieve a highly adherent diamondlike carbon (DLC) coating. A plasma immersion ion implantation (PIII)-based procedure is described, which delivers a high retained dose of implanted carbon at the surface of aluminum alloys. A shallow implantation profile, followed by argon sputter cleaning and continued until a saturated carbon matrix is brought to the surface, provides 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 140 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 substantially exceed performance of DLC coatings produced by any other method. A process for forming an adherent diamondlike carbon coating (DLC) on an aluminum alloy has been reported previously.1 The process consists of an argonplasma sputter-cleaning step, a methane implant using plasma immersion ion implantation (PIII), an argon-plasma sputter-cleaning to remove an amorphous carbon film and other contaminants from the surface of the carbon implanted target, and finally DLC deposition. The last step utilizes acetylene plasma, and is also run in the PIII mode. The resultant adhesion using previous techniques was in the range of 30–75 MPa for DLC deposited on highly eutectic aluminum A390 alloy (Si content, approximately 18%).2,3 When bombarded with carbon atoms, A390 produces a subsurface layer of silicon and aluminum carbides. Our unpublished experiments also proved that similar adhesion can be achieved when carbon implantation is performed (prior to diamondlike coating) on substrates like magnesium, magnesium alloys, titanium, chromium, and various types of steel. In some cases, however, even better adhesion of the coating to the substrate might be necessary due to the expected high working loads of the application. In this paper we describe our effort to better understand the proper surface treatment leading to even more improved adhesion of the DLC to the substrate material. Early experiments using PIII carbon implantation into the substrate were limited to the formation of moderate concentrations of surface carbides [the retained dose was in the range of (2 to 3) × 1017 atoms/cm2]. However, one may hypothesize, that only a near-surface layer of carbides needs to be present for good DLC adherence. Con590
http://journals.cambridge.org
J. Mater. Res., Vol. 15, No. 3, Mar 2000 Downloaded: 12 Mar 2015
sequently, the shallowest implantation profile featuring the highest “surface retained dose density” at any given implantation energy is desired and can be achieved when the sputter yield equals the implantation rate. In other words, for this specific application, the implantation profile should have it
Data Loading...
