COLD-PLASMA FOR SURFACE-TREATMENT OF TITANIUM-ALLOYS

Because of their poor tribological properties, titanium alloys have a restricted field of applications. Modifying their surface properties i s thus a real concern. The introduction of nitrogen on the surface imp roves significantly the tribological behaviour of these materials. Nit rogen ion implantation is a technique largely used in titanium alloy s urface treatment. Industrial applications of this process are numerous (biomedical, aeronautics,...) but the limitations of this technique ( essentially treatment depth) prevent its use in certain cases. The inc rease in treatment temperature can overcome these limitations. Thus, t he analysis of the properties obtained after treatment at various temp eratures (20 degrees C to 1000 degrees C) enables us to find the best compromise between metallurgic, geometrical properties (surface condit ion, deformation) and friction properties. This compromise enables us to solve a majority of tribological problems of titanium alloys. TITAN IUM AND ITS ALLOYS are materials which are more and more frequently us ed in mechanical applications. Their low density combined with their v ery advantageous mechanical characteristics (such as resistance to fat igue), make them the first choice of material in many areas (aeronauti cs, automobile precision mechanics, biomedical applications, for examp le), especially in chlorinated environments. However, their mediocre t ribological properties often lead to their rejection as friction surfa ces. Treating the surface of these materials with nitrogen can give th em excellent tribological properties. It is necessary, though, to choo se the most suitable surface treatment in accordance with the stresses and frictional pairs encountered, in order to avoid deterioration of the mass properties of the pieces. We present here an industrial techn ique for adding nitrogen to the surface of titanium alloys, ion implan tation together with a development of this process towards a surface h eat treatment effect.