Adhesion properties of diamond-like coated orthopaedic biomaterials

Abstract

This study details an experimental analysis to investigate the most suitable orthopaedic alloy for diamond-like carbon deposition using a saddle field neutral beam deposition process. The paper specifically identifies the adhesion strength properties of diamond-like coatings and its dependence on process parameters for application to orthopaedic steels and polymer substrates. Sub-micron thickness films were deposited directly on stainless steel, cobalt chrome alloy, titanium alloy and ultra high mol. wt. polyethylene substrates. It was found from Rockwell and pull-off adhesion tests that superior adhesion is acquired for stainless steel substrates followed by cobalt chrome and titanium alloys. Adhesion strength was also shown to be inversely related to increases in deposition pressure and to increase with time up to a threshold. The maximum adhesion strength of coatings deposited on the polymer substrates was 60% of the value for stainless steel. Surface roughness was also inversely related to adhesion strength for the substrates examined. It is demonstrated that stainless steel offers a superior substrate material for the application of diamond-like thin-films where wear mechanisms and mechanical constraints are operational such as in orthopaedic articulating joint replacements.