(selection of sliding tracks in Figure , the full survey shown in Figure ). In the short sliding tests (up to 1,600 revs), a bichromatic appearance is present (which can be enhanced by applying a false-colour filter on the acquired images; Figure ). In the early stages of sliding the bi-colouration is distinct, but blends with longer sliding time until a (generally) monochromatic colour is observed at 3,200 revs and remains until the test ends at 10,000 revs. EDS mapping indicates the nature of this two-phase appearance, as it identifies nickel phases within a copper matrix in the early stages of sliding (Figure ). After 100 revs sliding the nickel phases are distinct and can be identified in the EDS maps. However, with increasing sliding, the nickel phase becomes more diffuse, suggesting a mechanically-driven forming process is occurring on the surface of the coating. Quantification of the EDS maps shows that the nickel content is reducing with longer sliding times, revealing a copper-rich surface over this period (Table ). This suggests that the nickel is ejected from the surface of the coating over prolonged sliding.