Structure and frictional characteristics of Ti-6Al-4V plasma-based ion implanted with nitrogen then acetylene

The concentration depth profiles, structure and ball-on-disk frictional characteristics of Ti-6Al-4V plasma-based ion implanted with nitrogen (energy 60 keV) then acetylene (energy 10-30 keV) were investigated. The implanted samples (R = 0.05-2 x 10(11) Omega cm(-1) for the modified layers) included three zones: a top H-DLC zone, a C, N, Ti, O coexisting intermediate zone which had undergone chemical state changes indicating TiN, TiC, and Ti(C,N) second phases were formed, and the bottom zone of the substrate. The samples showed higher hardness especially at low plastic penetrations and higher wear resistance (lower coating brittleness) in the order of 10, 20, 30 and 10, 30, 20 keV implantation, respectively. A tribofilm transferred from disc to ball wear surface was found, lowering friction coefficient and reducing the ball wear, and this result possibly caused the ball weight increase after wear testing. With decreased load and increased speed, the function of the transfer film became more important, and tribological properties were improved (stable friction coefficient 0.15-0.25). When counterbody AISI 52100 was changed to Ti-6Al-4V modified as the disc, initial friction and wear life decreased, and wear was changed from only disc to both disc and ball abrasive dominated. The as-implanted samples demonstrated greatly improved tribological properties compared with unimplanted ones, showing a possible optimal implantation energy. (C) 1999 Elsevier Science S.A. All rights reserved.