Abstract: A medical device, such as an orthopedic or prosthetic joint, has a protective coating bonded to the substrate material of the device. Suitable substrate materials may include pure metals and metal alloys, ceramics, polymers and composites of the above. The protective coating includes a thin layer of tetrahedral bonded Carbon (ta-C). The coating also optionally includes an interface layer to facilitate the initial bonding and retention of the ta-C layer, such as by acting as an adhesion promoter, fluid barrier layer, or coefficient of thermal expansion mismatch reducing layer, or combination thereof. The interface layer may include various tightly adherent metals and metal nitrides, such as Cr, Ti, Nb, Ta and carbides, nitrides and carbonitrides thereof. The ta-C layer has a concentration of sp3 bonded carbon which varies through its thickness. Many concentration profiles of sp3 carbon bonds through the thickness are possible.