In contrast, in the early phases of sliding, ML (Cu) surfaces appeared bright and copper coloured (as shown by the optical images of the 100 rev wear track), but became darkened over further sliding passes, eventually appearing dark at 10,000 revs (Figure -d and Figure ). Several metallic particulates were found embedded within the coatings with successive sliding (see Figure , Figure ); EDS mapping of these particulates reveals that among the bulk copper surface, an increasing content of iron, nickel, chromium and molybdenum is observed (Table ). The presence of these elements is thought to arise from the wear and subsequent deposition of the 316SS counterface ball onto the sliding track. The EDS map in the 1,600 rev scar reveals larger particulates of the counterface embedded into the coating (Figure ), but smaller debris can also be found in most wear tracks after 800 revs. It is worth noting that only trace amounts of these elements are found in any of the ML (Ni) sliding tracks (Table ), suggesting that the counterface does not exhibit wear in that system.