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

Tungsten disulfide (WS 2 ) 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 WS 2 -dispersed polyalphaolefin (PAO 6) lubrication using ball-on-disk experiments, post-test surface analysis, and nonequilibrium molecular dynamics (MD) simulations. The addition of WS 2 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 mm 3 (≈ 42.1% reduction). X-ray photoelectron spectroscopy of the worn surface displayed W 4 f and S 2 p signals, consistent with WS 2 -derived species remaining within the wear track after sliding. MD simulations provided a mechanism-level atomistic interpretation consistent with this macroscopic friction trend: the WS 2 -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 WS 2 than with Fe (− 101.42 vs. −244.51 eV). This weaker PAO–WS 2 coupling suggests that WS 2 -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 WS 2 -mediated case.