Characterization and tribological evaluation of duplex treatment by depositing carbon nitride films on plasma nitrided Ti-6Al-4V

Carbon nitride (CNX) films (with N/C ratio of 0.5) were deposited on both u ntreated and plasma nitrided Ti-6Al-4V substrates by D.C. magnetron sputter ing using a graphite target in nitrogen plasma. TEM and XPS analysis reveal ed the formation of both amorphous CNX structure and crystalline beta-C3N4 phases in the deposited coatings. Nano-indentation tests showed that the fi lm hardness was about 18.36 GPa. Both the scratch tests and indentation tes ts showed that compared with CNX film deposited directly on Ti-6Al-4V, the load bearing capacity of CNX film deposited on plasma nitrided Ti-6Al-4V wa s improved dramatically. Ball-on-disk wear tests under both dry sliding and lubricated conditions (with simulated body fluids) were performed to evalu ate the friction and wear characteristics of the deposited coatings. Result s showed that under both dry and lubricated conditions, the duplex treated system (i.e., with CNX film deposited on plasma nitrided Ti-6Al-4V substrat e) was more effective in maintaining a favorable low and stable coefficient of friction and improving wear resistance than both individual plasma nitr iding and CNX films on Ti-6Al-4V substrate. Under dry sliding conditions, t he generated wear debris of spalled films were accumulated on the wear trac k, mechanically alloyed and graphitized, thus significantly reducing the co efficient of friction and preventing wear of the substrate. However, under lubricated conditions, due to the flowing of the fluids, the lubricating we ar debris was taken away by the fluids, and therefore, the direct contact o f two original surfaces resulted in high coefficient of friction and extens ive abrasive wear of the substrate for CNX films deposited on Ti-6Al-4V sub strate. Also when there was some small-area spallation of CNX films, the fl uids could seep into the interface between the film and substrate, thus deg rading the interfacial adhesion and resulting in a large area spallation. ( C) 2000 Kluwer Academic Publishers.