Evaluating the effects of plasma diffusion processing and duplex diffusion/PVD-coating on the fatigue performance of Ti-6Al-4V alloy

Abstract

The effect of triode-plasma enhanced low-pressure oxygen and/or nitrogen diffusion treatments, either

as a single process or in conjunction with plasma-assisted physical vapour deposition (PAPVD) on Ti–

6Al–4V has been studied under rotating-bending fatigue testing. Following the diffusion treatment, sam- ples exhibit a hardened case, more than 30 lm deep. Semi-logarithmic S–N plots are used to demonstrate

and compare the significant changes in fatigue resistance obtained from each process. Fractography and

residual stress measurements show that, compared to annealed samples, the fatigue strength of the dif- fusion-treated samples was superior; although the result changed depending on the processing param- eters and microstructure of the substrate material. Also, unsupported and mechanically uncompliant

ceramic coatings, such as TiN, promote the initiation of multiple crack sites, which lead to premature fail- ure of the Ti-alloy substrate and a consequent reduction in endurance limit.