Impact wear resistance of plasma diffusion treated and duplex treated/PVD-coated Ti-6Al-4V alloy

In this paper dynamic ball-on-plate impact wear testing is utilised to evaluate the intrinsic fatigue strength of the surface of triode plasma diffusion treated, single-layered TiN-, CrAlN-, and WC/C-coated and duplex diffusion treated/PVD-coated Ti-6Al-4V. The test is used to assess the resistance of surfaces to dynamic, high-cycle loading caused by the repeated impact of a cemented carbide ball. The subsequent observation and comparison of the wear craters produced (and their measured volumes) was used to identify which diffusion treatment (or treatment/coating combination) provided the most marked reduction in contact-induced deformation and overall improvement in wear behaviour. A combination of nanoindentation, Knoop hardness microindentation, scratch adhesion, stylus profilometry, optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and atomic force microscopy test and evaluation methods, was used to characterise the surfaces under investigation. Experimental results revealed that triode plasma diffusion treatments can provide exceptional improvements in the impact fatigue resistance, particularly when the diffusion process has been designed to maximise the resultant hardened case depth. Also, amongst the three coatings tested, PVD CrAlN was found to be the most suitable for applications involving such dynamic impact loading. Finally, the results presented show that an appropriate sequential triode plasma oxidation and nitriding diffusion pretreatment, in combination with a hard and tough PVD ceramic coating, can provide a significant reduction in surface impact wear when compared to either plasma diffusion treatments alone, or PVD ceramic coatings deposited on non-pretreated Ti-alloy substrates.