Frictional behaviour of oxygen diffusion hardened titanium in dry sliding against Co–28Cr–5W–4Fe–3Ni–1Si cobalt alloy

The results of conformal pin-on-disc tribological tests of a hard layer of the solid solution of oxygen in α-titanium sliding against a Co–28Cr–5W–4Fe–3Ni–1Si cobalt alloy counterspecimen are presented. The α-Ti(O) layer was diffusely produced over 2–8 h of oxidising in the superficial zone of a technical quality titanium specimen. iction and wear responses of the system were recorded and the wear mechanisms were studied. Investigations of the material structure and chemical constitution in micro-areas of the titanium specimen, cobalt alloy counterspecimen and wear debris formed in dry sliding were performed with a Philips XL20 microscope equipped with an EDAX analyser. Crushing of the α-Ti(O) layer, lowering of the wear rate after comminution of the hard α-Ti(O) layer, local tack spots and fine powder wear particles, mostly Ti oxides, were detected at the beginning of each test. Gradual brittle fracture and decay by pulverising of the α-Ti(O) particles embedded in both mating surfaces, which occurred during the test, led to the increase of the wear rate of the couple and domination of microcutting and tack spots spalling after their partial oxidation. Finally, after the disappearance of the α-Ti(O) loose particles, adhesive junctions, metal transfer and smearing become leading wear mechanisms.