Micro-abrasion wear testing of triode plasma diffusion and duplex treated Ti-6Al-4V alloy

Abstract

In this paper micro-abrasion wear testing is used to evaluate the wear resistance of triode plasma

diffusion-treated, single-layered TiN-, CrAlN-, and WC/C-coated and duplex-diffusion and coated

Ti–6Al–4V under uniform three-body rolling abrasion. Nanoindentation, Knoop microhardness, mechan- ical surface profilometry, optical microscopy, scanning electron microscopy and atomic force microscopy,

were used to characterise the surfaces under investigation. Optimum testing conditions for rolling abra- sion were established by varying the test parameters and resultant severity of contact. Very low normal

loads and high volume fractions of particles in the abrasive slurry are necessary to obtain predictable and

reproducible results. Relatively coarse SiC abrasive particles, having a mean diameter of around 3 m,

appear more suitable for micro-abrasion testing of the samples investigated, compared to finer Al2O3

particles. Problems associated with the measurement of the scar volume and subsequent calculation of

the wear rate for hard coatings deposited on relatively soft metals like titanium are identified, and suit- able testing and measurement techniques are suggested. Three-dimensional wear scar maps generated

by mechanical stylus profilometry were used to measure the wear volumes. Under the test conditions

used, wear coefficients can be determined from perforating and non-perforating tests, although perforat- ing tests provide more consistent results. Triode plasma diffusion treatments, plasma-assisted (PA) PVD

TiN and PAPVD CrAlN can reduce the specific wear rate of Ti–6Al–4V, while PACVD-based WC/C coatings

do not provide suitable protection against abrasive wear. The combination of triode plasma oxynitriding

diffusion treatments and PVD coatings to create duplex treatments can also lead to further reductions

in the coating wear coefficient when compared to non-duplex coatings deposited on non-pretreated

substrates.