EFFECTS OF PLASMA IMMERSION ION-IMPLANTATION OF OXYGEN ON MECHANICAL-PROPERTIES AND MICROSTRUCTURE OF TI6AL4V

Plasma immersion ion implantation (PIII) is a surface treatment with i ncreasing interest, as it offers the possibility of performing three-d imensional ion beam treatments, reducing the need for manipulation und er vacuum to obtain a uniform treatment in geometrically complex parts . In this work the PIII process has been used to perform surface treat ment on Ti6Al4V alloy. This Ti alloy is commonly used in aerospace and biomedical applications, due to its good combination of mechanical an d chemical properties, such as strength to weight ratio, corrosion res istance or bioinertness. However, due to its poor tribological propert ies, the use of surface treatments to improve wear resistance or decre ase friction coefficient is often recommended. PIII has been used to i mplant the surface of Ti6Al4V alloy with oxygen ions. The oxygen plasm a was generated by electron cyclotron resonance microwave excitation, working at two different pressures. At the lower pressure plasma densi ty was increased by means of an external ring magnet. High voltage pul ses of -40 kV, at of 400 and 600 Hz pulse repetition rates, were appli ed. Elastic recoil detection (ERD) analysis showed retained doses in t he range of 3 x 10(17) to 1 x 10(18) O atoms cm(-2), with oxygen conce ntration values ca 65% in the near surface region. Surface mechanical properties such as hardness, wear and friction have been evaluated. Mi croindentation tests showed an increase of up to 100% in the surface h ardness of the ion implanted samples compared to the non implanted mat erial. Dry pin-on-disk tests with spherical ended UHMWPE pins showed a very significant increase in wear resistance in oxygen implanted Ti6A l4V samples. Scanning electron microscopy and optical profilometry sho wed an important roughening of the Ti alloy surface after PIII treatme nt under selected conditions. (C) 1998 Elsevier Science S.A.