Observing the compositional ratios of the exposed metal surfaces, as well as their oxidation states reveals more information; the deconvoluted high-resolution scans are shown in Figure and Figure . ML (Ni) , with its surface mixture of copper and nickel, generally observes a reduction of nickel content over longer sliding times (Figure ). When tested at 5N load, the nickel content reduces from 13.8 at.% of the total surface at 100 revs to 6.2 at.% after 10,000 revs. Sliding at 25N shows a lower nickel content; from 7.5 to 4.0 at.% when analysed at the 100 and 20,000 rev scars, respectively. As a result, the Ni/Cu ratio on the exposed wear surfaces becomes copper-rich (or nickel-deficient) over longer sliding times.