Investigation into the wear behaviour of Tribaloy 400C during rotation as an unlubricated bearing at 600 °C

The wear behaviour of a cobalt-based superalloy, Tribaloy 400C, was studied during self-mating rotational sliding in a specially constructed bearing rig at 600 °C between 2 min and 12 h at a rotation speed of 3 ms−1. Stable wear protective oxide films often referred to as ‘glazes’ were formed with their coverage of the wear scar increasing with time. Six stages were identified in the formation of the wear protective oxide films: (i) transient oxidation to form a mixed oxide layer, (ii) preferential oxidation of the chromium to form a chromium oxide layer at the substrate interface, (iii) removal of this layer and compaction onto the surface, (iv) diffusion of mainly Co and Mo cations to the surface through the chromium oxide forming an oxidised layer above it, (v) slow breakdown and formation of the oxide films with further diffusion of mainly Co and Mo to the surface to form Co and Mo dominated layers on top a mixed Co, Cr, Si and Mo oxide film, and (vi) further breakdown and formation of the oxide film to form a uniform distribution of elements within the wear protective oxide film.