In the present work, the relationship curve of the coefficient of friction (COF) with varying loads of different morphology WS2 lubricating additives in the friction process at various sliding speeds was studied. On this basis, wear marks and elements on the wear surfaces after friction were analyzed, and then the anti-wear and mechanism effects of WS2 of different forms in the lubrication process were discussed. Meanwhile, the Stribeck curve was used to study the lubrication state of the lubricating oil in the friction process. It was revealed that the COF of lubricating oil containing lamellar WS2 decreased by 29.35% at optimum condition and the minimum COF was concentrated at around 100 N. The COF of lubricating oil containing spherical WS2 decreased by 30.24% and the minimum coefficient was concentrated at 120 N. The extreme pressure property of spherical WS2 was better than that of lamellar WS2, and the wear resistance of spherical WS2 was more stable when the load was over 80 N. The different morphology of WS2 additives can play anti-wear and anti-friction roles within a wide range of sliding speeds.

Purpose This study aims to prevent the sharp decline in the load-carrying capacity of lubricating oil film under harsh conditions of abrupt changes in friction interface temperature, which is a major challenge in lubrication technology. Design/methodology/approach In this paper, we synthesized a series of silver pyrazole methylpyridine complexes containing a high metal concentration and minimal supporting organic ligands (complex 1 [Ag(LMe)]2(BF4)2, complex 2 [Ag(Li-Pr)n](BF4)n and complex 3 [Ag(LMe)(NO3)]2). The thermal decompose behavior of as-prepared silver complex was investigated by thermogravimetric analysis and X-ray photoelectron spectrometry (XPS). Four-ball friction testers were used to evaluate the friction and wear properties of lubricating oil in the temperature ranges associated with the operation of modern heavy machinery. Findings The complex decomposed silver particles at high-temperature, which could fill the pits on the friction surface, change the wear form of the friction pair and reduce the roughness of the friction surface. Reduction in both friction coefficients and wear scar diameters was obtained by adding silver complexes in oil. The lubricating oil, with the additive content of 1.5 Wt.%, has the best tribological performance, moreover, the lubricating performance of the silver complexes in oil were correlated with their concentration and thermal decomposed temperatures, respectively. Originality/value As a result, a series of silver pyrazole methylpyridine complexes as oil additives can support friction and wear reduction under abrupt high-temperature conditions are intended to be a controllable backup lubricant additive.