A COMPARISON OF THE WEAR AND FATIGUE PROPERTIES OF PLASMA-ASSISTED PHYSICAL VAPOR-DEPOSITION TIN, CRN AND DUPLEX COATINGS ON TI-6A1-4V

The study sets out to establish a comparison between duplex systems of plasma nitriding followed by plasma-assisted physical vapour depositi on (PAPVD) of TiN deposited on Ti-6Al-4V, compared with PAPVD of TiN a nd CrN alone. The fatigue resistance has also been examined since conv entional 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 rotatin g-bending fatigue specimens tested in air at 5700 rev min-1 for 10(6) cycles or until failure it was found that TiN, CrN and the duplex coat ing did not impair fatigue resistance but actually improved the S-N cu rves and increased the endurance limit. From the wear results it was f ound that, although TiN and CrN do improve the wear resistance of Ti-6 Al-4V significantly, it is the duplex coating that has much the greate r load-bearing capacity on the titanium substrate and gives a signific ant improvement on PAPVD TiN or CrN coatings in sliding and abrasive w ear conditions.