Analysis of the wear scars of ML (Cu) (5N) testing further identifies key chemical changes (Table ). Both the copper and carbon content continues to be high, however, there is a small decline in carbon content with longer sliding times, dropping from approx. 28% to 23% over the 10,000 rev lifetime In contrast to ML (Ni) , the wear tracks on ML (Cu) have a higher oxygen content. The content increases from ~6 at.% after 100 revs to over 16 at.% by the end of the test (at 10,000 revs).