Protective coatings on medical implants by reactive diffusion

Abstract

Wear resistant and corrosion resistant surfaces are important for medical implants. Wear resistance is especially important for articulating surfaces in load bearing applications such as total hip and total knee replacements. Metal-on- polyethylene bearings result in relative large volumetric wear, ceramics such as alumina have an excellent wear resistance but are brittle, metal-on-metal bearings have good wear resistance, but release nanometric debris and ions that may cause allergy or have toxic effects. Hard ceramic coatings on metal substrates may be a good solution: low wear and low ion release and ductile metal alloy interior—no danger of brittle fracture and easy shaping. Ti alloys such as for example Ti–6Al–4 have the best combination of mechanical properties and biocompatibility, but have very poor wear resistance, Co–Cr–Mo have good wear resistance, but may cause allergy. TiN hard coatings deposited on Ti alloys by PVD have relatively poor adhesion to the substrate as a result limited durability.