Pre-treatment of substrates for improved adhesion of diamond-like carbon films on surgically implantable metals deposited by saddle field neutral beam source

The saddle field neutral beam process is one of the most promising coating processes used for the production of diamond-like carbon (DLC) films. The films are deposited from a beam of energetic, largely neutral molecules obtained from a source gas of acetylene. For surgical implant uses, the films are deposited on substrates of the principal orthopaedic metal alloys: 316L stainless steel, CoCr and Ti6Al4V. Of paramount importance in these applications is the adhesion of the films. It is known that numerous parameters have an influence on coating adhesion including stress in the film, contamination and chemical bonding between the film and the substrate, and the physical properties and roughness of the substrate. The adhesion of the films has been measured as a function of the duration of in situ etching by a neutral argon beam. The studies were performed on DLC films with thickness ∼0.35 μm. Adhesion was measured using the pull-off and Rockwell C tests. Optimal adhesion was obtained for a limited range of argon etch times; longer or shorter times showed reduced adhesion. The relationship between etching time, adhesion and film structure (sp3 content) was investigated. The effects of substrate temperature during etching and deposition on the adhesion and film structure were investigated.