Surface characteristics underpinning fretting wear performance of heavily loaded duplex chameleon/PEO coatings on Al

Abstract Duplex coatings comprising MoS2/Sb2O3/graphite layer burnished on top of plasma electrolytically oxidised AA6082 alloy enhanced fretting wear resistance against alumina and steel whilst reducing friction from ∼0.6…0.9 to ∼0.08…0.1 in dry nitrogen and humid air. Transitions to stick-slip (∼3 μm), partial slip (5-10 μm) and gross slip (>10 μm) showed an order of magnitude improvements over single-layer PEO coatings. In the latter mode, high initial contact pressures (∼1.1 GPa) with steel counterpart under oxidising atmosphere increased friction due to generation of Fe/Al/Cr oxides/hydroxides in the contact region, leading micro-cracking in PEO coating followed by fatigue damage of aluminium substrate. Reducing contact pressure