Adherence of diamondlike carbon coatings on total joint substrate materials

This paper reports the results of preliminary assessment of the relative adherence of diamondlike carbon coatings on typical metal, ceramic, and polymeric total joint prosthesis materials. Coatings were applied, using an ion assisted method, from a hydrocarbon precursor. The latter was generated in vacuum and allowed to condense on the workpiece surface while simultaneously being subjected to 20-50 keV nitrogen ion bombardment. Such ion energies lead to disruption of CH bonds, with most of the hydrogen escaping in gaseous form; this leaves behind a principally carbonaceous amorphous residue, i.e. DLC. A cobalt-chrome alloy, an alumina, stainless steel, and a high density polyethylene (HDPE) were coated with DLC under varying surface preparation, and ion deposition conditions. Adhesion was measured qualitatively by means of scratch hardness testing. The smoothness of the DLC coating on glass was examined by atomic force microscopy. Differences in adhesive strength and damage mechanisms are discussed in terms of coating conditions, and implications for performance under realistic total joint loads of 6 to 10 MPa are considered.