Objects of titanium or titanium alloys having the surface converted to a hard and wear-resistant nitride layer with good adhesion, which is distributed uniformly and also provides internal capillaries. The objects are produced by being treated in a vacuum furnace with an atmosphere of pure nitrogen gas at a temperature of 650.degree.-1000.degree. C. and at a pressure below atmospheric pressure. The thickness of the nitride layer can be controlled by controlling the treatment time and temperature.
For titanium and titanium alloys in tribological applications under bound lubrication conditions, there are employed epoxy coatings adhered to the surface of the titanium or titanium alloy by a titanium oxide primer layer. The anti-wear properties of the epoxy coating can be improved by incorporation of an anti-wear filler such as diamond powder. These coatings improve the friction coefficient and anti-wear properties of the titanium and titanium alloys.
The present invention relates to ion nitriding of pure titanium or titanium-containing alloys at low pressure by intensifying the glow discharge. Plasma intensification was produced by thermionic emission in conjunction with a triode glow discharge system. Effective ion nitriding can be achieved by employing the present invention at relatively low temperatures (480.degree. C.) and with significantly enhanced compound layer growth kinetics compared to the conventional nitriding techniques. Processed Ti and Ti-6Al-4V developed a surface layer of TiN followed by a Ti.sub.2 N layer and an interstitial nitrogen diffusion zone. Processed specimens showed a three fold increase in surface hardness. Surface roughness was found to be a function of the degree of plasma intensification. Processing of Ti-6Al-4V resulted in a higher wear, corrosion and wear-corrosion resistance. The present invention indicates that ion nitriding with intensified glow discharge has a great potential as a surface modification method for Ti and Ti alloys. Materials nitriding by the present invention having the properties defined above are suitable for use as orthopaedic implant devices as well as other applications of titanium and titanium alloys requiring resistance to wear and corrosion.
A prosthesis is provided having at least a smooth non-articulating load bearing surface disposed adjacent a bone. The prosthesis includes a substrate formed from a metallic alloy. At least the regions of the substrate defining the load bearing surface are coated with a biologically inert abrasion resistant material harder than the substrate for preventing leaching of ions from the substrate into adjacent body tissue and for preventing wear. The coating may be titanium nitride or zirconium or other such material exhibiting biological inertness and acceptable hardness. The coating preferably defines a thickness of 8-10 microns.
