Friction and wear mechanisms in MoS2/Sb2O3/Au nanocomposite coatings

Fundamental phenomena governing the tribological mechanisms in sputter deposited amorphous MoS2/Sb2O3/Au nanocomposite coatings are reported. In dry environments the nanocomposite has the same low friction coefficient as pure MoS2 (∼0.007). However, unlike pure MoS2 coatings, which wear through in air (50% relative humidity), the composite coatings showed minimal wear, with wear factors of ∼1.2-1.4 x 10-7 mm3 Nm-1 in both dry nitrogen and air. The coatings exhibited non-Amontonian friction behavior, with the friction coefficient decreasing with increasing Hertzian contact stress. Cross-sectional transmission electron microscopy of wear surfaces revealed that frictional contact resulted in an amorphous to crystalline transformation in MoS2 with 2H-basal (0 0 0 2) planes aligned parallel to the direction of sliding. In air the wear surface and subsurface regions exhibited islands of Au. The mating transfer films were also comprised of (0 0 0 2)-oriented basal planes of MoS2, resulting in predominantly self-mated 'basal on basal' interfacial sliding and, thus, low friction and wear.