The fretting phenomenon was investigated experimentally in contacts between nitrided, coated and nitrided-coated Ti-6-4 rods against uncoated M50 rods generating a circular Hertzian contact. A fretting wear test rig was designed and developed to facilitate mounting of rod specimens of different coating thicknesses. Fretting wear tests were performed on low temperature and high temperature nitrided Ti-6-4 rods as well as on T-800 (CoCrMoSi) thermal spray coated Ti-6-4 and T-800 coated M50 rods. Finally, tests were carried out on Ti-6-4 rods nitrided at low and high temperatures and T-800 thermal spray coated on the top. The results obtained from fretting tests of each surface against uncoated M50 are studied and compared. Fretting wear volumes and surface profiles are presented for the contacts studied. The fretting wear resistance of each surface is quantified and compared with Archard’s wear equation. The role of amplitude of motion and number of cycles on the fretting wear of coatings is discussed. It was observed that increase in fretting wear resistance of uncoated Ti-6-4 rods by nitriding is greater than thermal spray coating. The fretting wear resistance was found to be higher for high temperature nitrided-coated rods than for low temperature nitrided-coated rods.

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