Tribological Evaluation of Lead-Free MoS2-Based Solid Film Lubricants as Environmentally Friendly Replacements for Aerospace Applications

Solid lubricants, such as MoS2 have been widely used in the aerospace industry with the primary purpose of reducing the friction and wear of tribological interfaces. MoS2 based solid film lubricants are generally doped with other compounds, which can help overcome some of their limitations related to environmental conditions. For instance, compounds like Sb2O3 and Pb have been traditionally used to improve the endurance life of these lubricants. However, with the recent zest in transferring to eco-friendly lubricants, there is a strong push to eliminate Pb based compounds. The main purpose of this work is to better understand the influence of Pb based compounds on the tribological behavior of MoS2 based solid film lubricants as well as to critically evaluate the performance of Pb free lubrication strategies. More specifically, the baseline ‘non-green’ lubricant was doped with Pb compound and Sb2O3 and the Pb compound in the ‘Green’ alternative lubricant was replaced by more Sb2O3. The wear test was done using a ball-on-disk tribometer for specific loads and for 5000 cycles. Ex-situ analysis was conducted using Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), and micro-Raman to capture the interfacial processes of these lubricants at different loads. Overall, the non-green lubricant performed better in terms of the tribological behavior (i.e., lower friction and wear), which was attributed to the formation of a dense MoS2-based tribo-/transfer-film with the basal planes oriented in the parallel direction to the sliding. The finding on the interfacial phenomena provided critical insights into the development of novel green alternatives that may have the ability to replace Pb based compounds in the future for a sustainable environment.

Effect of Carbon Target Current on Ultralow Frictional Behavior of CrCN Coatings under Glycerol Lubrication

The aim of this paper is to find an effective way to reduce the friction and wear of steel. CrCN coating was deposited on AISI 304 stainless steel by magnetron sputtering technology, and the friction and wear properties of the coating under glycerol lubrication were studied. The hardness of CrCN coatings on stainless steel surface can reach to 17.87 GPa when the carbon target deposition current is 2A. The CrCN coating presents low friction coefficient (COF) under the lubrication of glycerol, a highly efficient green lubricant. When the load is 0.5 N, the lowest friction coefficient is only 0.01. XPS analysis on the wear track suggested that glycerol decomposed during sliding and a fluid lubricating layer was formed, which provides ultralow friction. The paper shows that the glycerol could be used as an efficient lubricant for the CrCN coating.

On the Tribological and Oxidation Study of Xanthophylls as Natural Additives in Castor Oil for Green Lubrication

The present study focuses on an introductory analysis of the use of three xanthophylls as additives for green lubricant applications. For this purpose, the additives were characterized by FTIR and 1H-NMR techniques, and the bio-lubricants were described by their physical properties. The effect of the natural compounds on the friction and wear properties of bio-lubricants were evaluated by sliding friction tests under boundary conditions, as confirmed by an analysis of the lubricating film thickness. The antioxidant capacity was analyzed by FTIR spectroscopy. It was observed better wear protection in castor oil with xanthophylls than without these additives. The wear rate was reduced up to 50% compared with neat oil. Lesser beneficial effects were appreciated in friction coefficient since it was increased 25%. The best contribution was observed with astaxanthin as an additive. In addition, a significant improvement in the oxidation of castor oil, complemented with this additive, was exhibited by FTIR analysis. It was found that xanthophylls could be employed as additives for totally biodegradable lubricant applications since they have better tribological and antioxidant behavior than current additives.

Development and Application of a Novel Green Water-Based Drilling Fluid

In response to the technical and environmental protection requirements of water-based drilling fluids, this study independently developed a series of green supporting treatment agents for water-based drilling fluids such as the green loss reducer HB-1, green inhibitor HB-2, and green lubricant HB-3, etc., and proposed a green water-based drilling fluid system (HBDF) with good comprehensive performance. The proposed system has a heat resistance of 150°C, a HTHP (high temperature and high pressure) filtrate loss of 12 mL, a biological toxicity EC50 value greater than 105 mg/L, and a biodegradability BOD5/CODCr value of 16.2%. Now the developed HBDF system has been applied in more than 10 wells in SL oilfield, and the field application results show that the proposed HBDF system has stable rheological and filtrate loss performance, good anti-pollution ability, and easy and simple maintenance operations; after drilling, the biological toxicity of the drilling fluids can meet the environmental protection requirements, which has provided a technical reference for the research of green drilling fluids and the green development of SL Oilfield.

Experimental Evaluation on Tribological Performance of the Wheel/Workpiece Interface in NMQL Grinding With Different Concentrations of Al2o3 Nanofluids

As a result of the growing need for environmental protection and the increasing number of health problems faced by workers, traditional lubricants are gradually being replaced. Nanofluids, which contain nanoparticles in the proper base fluid, can serve as a low carbon, “green” lubricant. Nanofluids show improved heat transfer capability and lubricating properties. Therefore, increasing lubricating effects is an effective way to improve machining performance. The tribological properties of grinding wheel/workpiece interface with different concentration of Al2O3 nanofluid micro-lubrication grinding were studied. The influences of the force ratio, viscosity and contact angle of Al2O3 nanofluids with different concentrations on the grinding force and the surface quality of workpieces are discussed. The best concentration of Al2O3 nanofluid with good lubrication performance in grinding zone was obtained.

Experimental Evaluation on Tribological Performance of the Wheel/Workpiece Interface in NMQL Grinding With Different Concentrations of Al2o3 Nanofluids

As a result of the growing need for environmental protection and the increasing number of health problems faced by workers, traditional lubricants are gradually being replaced. Nanofluids, which contain nanoparticles in the proper base fluid, can serve as a low carbon, “green” lubricant. Nanofluids show improved heat transfer capability and lubricating properties. Therefore, increasing lubricating effects is an effective way to improve machining performance. The tribological properties of grinding wheel/workpiece interface with different concentration of Al2O3 nanofluid micro-lubrication grinding were studied. The influences of the force ratio, viscosity and contact angle of Al2O3 nanofluids with different concentrations on the grinding force and the surface quality of workpieces are discussed. The best concentration of Al2O3 nanofluid with good lubrication performance in grinding zone was obtained.