Interfacial reconfiguration for low-shear sliding and wear suppression in WS₂-mediated boundary lubrication

Tungsten disulfide (WS₂) nanoparticles are widely considered as promising solid lubricant additives for boundary/mixed lubrication. However, the consistent mechanism linking macroscopic tribotests to atomistic behavior remains elusive. We investigated WS₂-dispersed polyalphaolefin (PAO 6) lubrication using ball-on-disk experiments, post-test surface analysis, and nonequilibrium molecular dynamics (MD) simulations. The addition of WS₂ markedly reduced and stabilized friction, with the average coefficient of friction (COF) decreasing from 0.146 to 0.055, and mitigated wear, with the measured wear volume decreasing from 0.019 to 0.011 mm³ (≈ 42.1% reduction). X-ray photoelectron spectroscopy of the worn surface displayed W 4f and S 2p signals, consistent with WS₂-derived species remaining within the wear track after sliding. MD simulations provided a mechanism-level atomistic interpretation consistent with this macroscopic friction trend: the WS₂-containing interface exhibited a lower interfacial shear response than the PAO-only interface (time-averaged COF: ≈10.9% reduction from 0.46 to 0.41), while interfacial energetics indicated weaker PAO coupling with WS₂ than with Fe (- 101.42 vs. -244.51 eV). This weaker PAO-WS₂ coupling suggests that WS₂-derived interfacial species may reduce effective PAO-Fe coupling and facilitate lower-shear interfacial accommodation, which is consistent with the experimentally observed friction stabilization and wear reduction. Representative MD configurations also displayed Fe atom detachment in the PAO-Fe model but not prominently in the WS₂-mediated case.