Use of nanoparticles as lubricant additives in wind turbine gearbox

The increasing demand for reliable and efficient lubrication in offshore wind turbine gearboxes, particularly under harsh conditions involving water ingress, humidity, and variable loading necessitates the development of advanced lubricant additives with enhanced tribological performance. This research presents a novel, systematic investigation into the synergistic behaviour of copper oxide (CuO) and molybdenum disulphide (MoS₂) nanoparticles (NPs) as lubricant additives in poly alpha olefin (PAO) oil. Unlike previous studies that predominantly examine these nanoparticles individually and under limited environmental conditions, this work offers the first comprehensive evaluation of hybrid CuO/MoS₂ NPs systems under boundary and rolling–sliding contacts, combined with the effects of water contamination, relative humidity, and nitrogen (inert) atmospheres. The study further establishes, for the first time, a direct link between nanoparticle dispersion stability, tribofilm chemistry, and friction–wear performance across these conditions.
To enhance dispersion stability, the nanoparticles were surface modified with oleic acid (OA), and their physicochemical characteristics were confirmed using Fourier Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analyser (TGA). Dispersion stability was quantified statistically through Dynamic Light Scattering (DLS) and Zeta Potential (ZP), revealing that optimal OA concentrations significantly reduce agglomeration and support long-term stability.
Tribological behaviour was assessed using a pin on reciprocating plate and Mini Traction Machine-Spacer Layer Imaging Method (MTM-SLIM) tribometers in conditions relevant to wind turbine gearbox, while tribofilm composition and structure were analysed using Energy Dispersive X-ray Spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS), Secondary Ion Mass Spectrometry (SIMS), and Focused Ion Beam Transmission Electron Microscopy (FIB/TEM) techniques.
Scanning Electron Microscopy (SEM), White Light Interferometry (WLI), Atomic Force Microscopy (AFM) were employed on the wear scar to provide a multi scale and complementary assessment of the surface after tribological testing: SEM was used to visualise the micro scale wear features and identify dominant wear mechanisms, as well as to detect the presence and distribution of tribofilm forming elements through EDX analysis; WLI provided precise, 3D surface profilometry to quantify wear depth, wear volume, and overall topography across the entire wear track; and AFM enabled nanometre scale examination of surface roughness and tribofilm texture, capturing fine details such as nanoscale smoothing, asperity deformation, and continuity of the protective layers. Together, these techniques offered a comprehensive understanding of how the different lubricant formulations influenced surface damage and tribofilm formation, linking friction and wear behaviour to the underlying surface transformations.
The results demonstrate that OA-modified hybrid CuO/MoS₂ nanolubricants reduce friction and wear significantly, relative to base oil (BO), outperforming single-component nanoparticle systems and conventional additives. Environmental testing shows that water and humidity deteriorate tribofilm formation, while nitrogen inhibits oxidation and preserves the lubricious sulphide and oxide phases within the tribofilm.
A key novelty of this research lies in the development of a mechanistic model that explains how nanoparticle dispersion stability governs the formation, chemistry, and durability of tribofilms. This model integrates the statistical stability data (DLS, ZP) with the experimentally observed tribofilm composition (XPS, EDX, SIMS, TEM), enabling a unified interpretation of lubrication behaviour across all operating conditions. The model provides a new conceptual framework for predicting the tribological performance of nanoparticle based lubricants in real world applications.
Overall, this work advances the state of the art by demonstrating a previously unrecognised synergistic mechanism between CuO and MoS₂ NPs, revealing their environmental sensitivities, and establishing a mechanistic–statistical foundation for the design of next generation nanolubricants for wind turbine gearboxes and other high demand mechanical systems