Oxygen thermochemical treatment combined with DLC coating for enhanced loadbearing capacity of Ti-6AI-4V

In the present investigation, a novel duplex treatment of Ti-6Al-4V combining oxygen diffusion (OD) treatment with a carbon rich coating has been developed. A diamondlike carbon (DLC) coating containing a small amount of titanium was deposited on to OD treated Ti- 6Al-4V using an unbalanced magnetron sputtering system. A graded intermediate layer of Ti/TiN/TiCN/TiC between the OD treated zone and the DLC coating was applied to facilitate good bonding. The loadbearing capacities of the duplex treated, as well as solely DLC coated, Ti-6Al-4V specimens were evaluated, both statically and dynamically using a friction monitored scratch tester, a ball on disc tribometer, and an indentation tester. It was found that both the static and dynamic loadbearing capacities were significantly increased by a factor of 2-5 to 5 following the twofold treatment. Based on further fractographic examinations by high resolution SEM and finite element analysis, the excellent performance of the duplex system is discussed in terms of plastic deformation of the substrate, interface maximum shear stress, and coating/substrate interfacial integrity.