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This research paper addresses the optimization of various control parameters by using the Taguchi method to assess the tribological properties of PAOs based nanolubricants. The concentration of COOH-functionalized multiwalled carbon nanotubes (MWCNTs), applied load, sliding velocity and kinematic viscosity of polyalphaolefins (PAOs) were selected as process parameters or control factor. The MWCNTs at a varying concentration (0.025-0.15 wt.%) were blended separately in PAOs to formulate the nanolubricants. The tribological experimentations were performed by Taguchi’ L18 mixed orthogonal array using “ball on disc” type tribometer. The analysis of variance (ANOVA) was adopted to estimate the most prominent factors influencing the tribological performance of nanolubricants. The statistical results showed that the applied load, followed by a concentration of MWCNTs conferred the most significant impact on the frictional characteristic. In contrast, the kinematic viscosity of PAOs, followed by concentration of MWCNTs has been observed the most significant influencing factors on the antiwear properties of nanolubricants. The probabilistic rationale for the advancement in friction and wear properties were assessed through various analytical tools.

In the present investigation, the COOH-functionalized multi-walled carbon nanotubes (MWCNTs) having an outer diameter of 20–30 nm and length 1−2 μm were dispersed in four different grades of polyalphaolefins (PAOs; i.e., PAO 4, PAO 6, PAO 40, and PAO 100) at various concentrations (0.025, 0.05, 0.075, 0.10, and 0.15 wt%) to evaluate friction, anti-wear, and extreme pressure properties. The tribological test was conducted as per ASTM standard using four-ball tester. The test results showed that with the addition of MWCNTs, the friction and wear properties of PAOs had been improved significantly as compared to the base oils. It was also observed that MWCNTs exhibited excellent anti-wear properties than friction properties. The possible reasons for the improvement in friction and wear properties are discussed with the aid of various analytical tools.

This current study emphasized the tribological performances of COOH-functionalized multiwalled carbon nanotubes (MWCNTs) dispersed in two different grades of polyalphaolefins (i.e., PAO 4 and PAO 6). The friction and wear properties have been estimated using SRV 5 tribometer with “ball on disc” configuration. Prior to tribo-testing, MWCNTs were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), and Fourier transform infrared spectroscopy (FTIR). The varying dose of MWCNTs (0.025-0.15 wt.%) was incorporated into both PAO base oils to obtain the optimized lubrication behaviour. The test results revealed that PAO 4 exhibited a reduction in friction coefficient (~27%) and wear volume (~88 %) at a dose of 0.05 wt.% and 0.025 wt.% MWCNTs, respectively. However, in PAO 6, the minimum coefficient of friction and wear volume was obtained at a concentration of 0.075 wt.% and 0.05 wt. % of the additive. The results evidenced that PAO 6 based nanolubricants demonstrated the best frictional characteristics while attained the best anti-wear performance with PAO 4 based nanolubricants. For the better unveiling of the lubrication mechanism of MWCNTs, worn surfaces were characterized using various analytical techniques such as scanning electron microscopy (SEM), scan probe microscope (SPM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron microscopy (XPS).

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The lubricating greases employed in this study were formulated with polyalphaolefin (PAO) 100 as the base oil and 12‐lithium hydroxystearate as the thickener. The sol–gel method was used to produce the LaF3 nanoadditives. The oleic acid‐treated LaF3 (i.e., OA‐LaF3) and carboxylic acid‐treated MWCNTs (i.e., COOH‐MWCNTs) were blended in the formulated grease samples and used as nanoadditives. The detailed microstructural and chemical properties of chemically treated nanoadditives were investigated using HR‐TEM, XRD, FTIR and XPS analyses. Using a four‐ball tester, the effect of different concentrations of nanoadditives on the tribo‐performance of greases was investigated. Tribo‐test results revealed the role of nanoadditives in PAO‐based grease lubrication performance. COOH‐MWCNTs and OA‐LaF3 nanoadditives outperformed PAO grease in terms of physicochemical and tribo‐performance for steel‐steel tribo‐pair. The improved tribo‐performance is attributed to the formation of tribo‐film on the contact interfaces via nanoadditives. The development of tribo‐film was confirmed by XPS analysis of worn surfaces.