Tribological properties of two kinds of rare earth complexes as lubricant additives for laser cladding coatings

Purpose ‐ The purpose of this paper is to test two kinds of rare earth complexes of Lanthanum Dialkyldithiophosphate (LaDDP) and Lanthanum Dialkylphosphate (LaDP) as lubricant additives in liquid paraffin for the untreated 60Si2Mn steel and laser-cladding Ni35A coating on 60Si2Mn steel sliding pairs which are a potential substitute for Zinc Dialkldithiophosphate (ZnDDP). Design/methodology/approach ‐ Tribological properties were evaluated by an Optimol-SRV oscillating friction and wear test. The morphologies of the worn surfaces were observed by a scanning electron microscope (SEM), and the chemical states of several typical elements on the worn surfaces were examined by means of X-ray photoelectron spectroscopy (XPS). Findings ‐ Treated laser cladding coatings of steel can improve its hardness and strength and the coated steel possess higher load-carrying capacity than that of 60Si2Mn; The rare earth complexes of LaDDP and LaDP possess good oil-solubility, friction-reducing and wear resistance properties. Those rare earth complexes as additives in liquid paraffin during the friction process can form a protective film containing rare earth oxide, sulfate and sulfur-containing compound during the friction process. Research limitations/implications ‐ The paper presents two kinds of potentially useful, environmentally-friendly and highly efficient substitutes for the ZnDDP additives in lubricants. Practical implications ‐ Owing to their good friction-reducing and wear resistance properties, LaDDP and LaDP are two optimum and promising industry lubrication additives. Originality/value ‐ This work is a new application of rare earth complex as lubricant additive in liquid paraffin, which provides a new direction for designing friction pairs and lubricant additive. The tribology experiments have been carried out through the variation of experiment conditions.