CHARACTERIZATION OF TI-6AL-4V MODIFIED BY NITROGEN PLASMA IMMERSION ION-IMPLANTATION

Ti-6Al-4V alloy is commonly used in biomedical or aerospace applicatio ns, due to its excellent combination of chemical and mechanical proper ties, such as bioinertness, corrosion resistance or high strength to w eight ratio. The use of surface treatments or coatings has widened the application possibilities of this alloy. The often observed poor trib ological performance can be overcome by the correct choice of surface: engineering methods. Ion implantation is a candidate among the differ ent available processes and excellent results have been obtained in bi omedical applications. However, when complex geometries are involved, it can be a difficult and less economically effective treatment. Plasm a immersion ion implantation (PIII) offers the possibility of performi ng three-dimensional ion beam treatments, reducing the need for manipu lation under vacuum to obtain a uniform treatment of geometrically com plex parts. In this work, PIII was used to implant nitrogen in the Ti- 6Al-4V alloy. The nitrogen plasma was generated with a 2.45 GHz microw ave excitation, and a pulsed bias voltage of 45 kV with pulse repetiti on rates of 50 and 400 Hz were applied. Nitrogen retained doses were e valuated by means crf Rutherford backscattering spectroscopy (RES). Pi n-on-disc wear and friction tests were performed on the implanted samp les. An ultra high molecular weight polyethylene pin was used as the c ounterface material to partially simulate the conditions encountered i n biomedical applications. A reasonable improvement in load bearing ca pacity with respect to the unimplanted alloy was observed after these tribological tests. However, no hardening could be measured after ion implantation. The worn surfaces were observed by scanning electron mic roscopy and optical profilometry after the tests and the type of wear mechanism was studied. The effect of the implantation was to increase the load at which breakthrough occurred on the protective surface laye r. (C) 1997 Elsevier Science S.A.