ANALYSIS OF CHEMICAL VALENCE OF THE ELEMENTS OF THE OXIDIZED SURFACE-LAYER OF A THERMALLY SPRAYED NI-CR COATING UNDER FRETTING

The XPS technique was used to determine the valence of the elements in the oxidized surface layer of Ni-Cr coated axles under fretting. Oxid es of Fe3+ and Cr3+ exist in the surface, and oxides of Fe2+, Fe3+ and Cr3+ are in the subsurface at a depth of 10 nm from the surface. The oxide films of Fe2O3-C2O3 and FeO-C2O3 play an important role in resis ting fretting of the axles: avoiding metal-to-metal contact between th e wheel hub and the axle; decreasing the friction coefficient; reducin g adhesive wear and preventing axles from fretting fatigue fracture. H owever, fretting causes particles of oxide, and this hard oxide accele rates fretting wear. (C) 1998 Elsevier Science S.A.