A comparison of the wear and fatigue properties of plasma-assisted physical vapour deposition TiN, CrN and duplex coatings on Ti-6Al-4V

The study sets out to establish a comparison between duplex systems of plasma nitriding followed by plasma-assisted physical vapour deposition (PAPVD) of TiN deposited on Ti-6Al-4V, compared with PAPVD of TiN and CrN alone. The fatigue resistance has also been examined since conventional surface modifications can often impair fatigue resistance.

A rubber-wheel-type abrasion tester and pin-on-disc sliding wear tester were used to examine the wear resistance of the coatings and the load-bearing capacity of the substrate respectively. A Wohler-type rotating tester was used to study the fatigue properties.

Using smooth rotating-bending fatigue specimens tested in air at 5700 rev min-1 for 106 cycles or until failure it was found that TiN, CrN and the duplex coating did not impair fatigue resistance but actually improved the S-N curves and increased the endurance limit. From the wear results it was found that, although TiN and CrN do improve the wear resistance of Ti-6Al-4V significantly, it is the duplex coating that has much the greater load-bearing capacity on the titanium substrate and gives a significant improvement on PAPVD TiN or CrN coatings in sliding and abrasive wear conditions.