The transition to electric vehicles (EVs) calls for sustainable advancements in automotive lubricants, as traditional fossil-fuel-based products pose environmental challenges. Palm oil-based biolubricants enriched with nanoparticles present a promising eco-friendly alternative that meets the thermal and tribological demands of EVs. This paper aims to analyze the development of nanoparticle-enriched palm oil-based biolubricants, aimed at improving the sustainability and performance of electric vehicle (EV) lubrication systems. The critical findings highlight that integrating nanoparticles such as graphene, titanium dioxide, and aluminum oxide into palm oil-based lubricants significantly enhances their tribological properties. These enhancements include a 26.21%–34% reduction in coefficient of friction (COF), a 12.99%–30% reduction in wear, and improved thermal stability. The study found that nanoparticle-enriched biolubricants outperformed traditional options in terms of friction and wear under high-temperature and pressure conditions, as supported by regression analysis. The study demonstrates that nanoparticle-enriched biolubricants offer a viable eco-friendly alternative to conventional lubricants, lowering the environmental impact by reducing greenhouse gas emissions and energy consumption. This innovation has significant implications for both the environment and industry, offering a sustainable solution that reduces dependency on fossil fuels, enhances EV efficiency, and aligns with global sustainability goals. Besides, this paper discusses biolubricants drawbacks and future studies direction.

CrN and diamond-like carbon (DLC) coatings are deposited on the surface of 431 stainless steel by the direct current magnetron sputtering technique. The surface morphology, micro-structure, hardness, friction, and wear properties of CrN, CrN/DLC and multi-layer composite DLC coatings are investigated by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, nanoindentation tester, scratch tester, and friction and wear tester. The results show that the surface of the single CrN coating is very rough for the columnar crystal structure with preferred orientation. When it serves as inner transition layers to form the composite DLC coatings, the surface gets much smoother, with reduced defects. The friction and wear results indicate that the composite DLC coatings exhibit lower coefficients of friction, and better wear and corrosion resistance in dry friction, deionized water, and seawater. In the dry wear and friction process, the single CrN coating is easily worn out, and severe friction oxidation and furrow wear both appear with a friction coefficient of 0.48. But the friction coefficient of a CrN coating in seawater is reduced to 0.16, and friction oxidation and wear loss are further reduced with water lubrication. The CrN/DLC coating has excellent tribological performance in three test concoctions and has the lowest friction coefficient of 0.08 in seawater, which is related to the higher sp³ bond content, density (1.907 g/cm³) and high degree of amorphization, contributing to high hardness and a self-lubrication effect. However, due to the limited thickness of CrN/DLC (1.14 µm), it easily peels off and fails during friction and wear in different testing conditions. In multi-layer composite DLC coatings, there are more sp² bonds with decreased amorphization, high enough thickness (4.02 µm), and increased bonding strength for the formation of different carbides and nitrides of chromium as transition layers, which gives rise to the further decreased average friction coefficient and the lowest wear loss. Therefore, the CrN coating alone has good wear resistance, and, as with the inner transition layer with a DLC coating, it can effectively improve the overall thickness and the bonding strength of the multi-layer films by optimizing the chemical compounds of DLC coatings. These results provide experimental support and reference for the design and selection of surface coatings for 431 stainless steels in different working conditions.

Ti/TiN/(Ti,N)-DLC/Ti-DLC/DLC coatings were deposited on 431 stainless steel using direct current magnetron sputtering technology under different bias voltages(0 V, −100 V, −200 V and −300 V). The microstructure and tribocorrosion performance of these DLC coatings in seawater was investigated. The results indicated that under the bias voltages, a denser and smoother surface of DLC coatings with a higher bonding strength between coatings and substrates was observed related to the increased incident kinetic energy of deposited ionized atoms. When the bias voltage was −200 V, the surface roughness reduced from 9.81 nm to 7.03 nm, and the bonding strength enhanced from 8.23 N to 8.86 N. What is more, the sp³ bond proportion and the disorder degree in DLC coatings both increased, which resulted in improved hardness and deformation resistance. However, when the bias voltage was −300 V, the increase of the amorphization was associated with a simultaneous rise in internal stress, which reduced the hardness and bond strength a little (8.72 N). DLC coatings can effectively improve the tribocorrosion properties of 431 stainless steel in seawater. When the voltage was −200 V, the average friction coefficient decreased from 0.35 to 0.07, with shallower wear traces and the wear loss of the DLC coating also being the smallest. The abrasive wear caused by metal oxides falling off the grinding ball, and the plastic deformation of the DLC coatings are the main wear forms. The high-density structure of DLC coatings under bias voltages can not only prevent the rapid expansion of cracks during deformation, but also provides a physical barrier to the erosion, which improves the corrosion and friction resistance in seawater. The optimization of bias voltage can improve the tribological performance of DLC coatings by regulating the carbon chain bond and microstructure. These results provide reference for DLC preparation and their potential engineering applications in stainless steel.

Diamond-like carbon (DLC) coatings doped with Ti and Ni elements were deposited on 316 L stainless steel substrate using magnetron sputtering technology. The morphology, microstructures, and performances of the coatings were detected using scanning electron microscopy, a Raman spectrometer, nanoindenter, scratch tester, and a tribological machine. The effects of element doping on the microstructures, friction and wear properties of DLC coatings were analyzed. The results revealed that Ti/Ni doping ensures the uniform cover and tight fit of DLC coatings on the substrate. Additionally, Ni-doped DLC coatings have a much smoother surface and denser texture with higher bonding strength and enhanced hardness (7.5 GPa) though Ti doping also can improve the bond strength to some extent. The presence of Ni both in the 316 L substrate and in Ni-doped DLC coatings improves interface matching, decreases structural differences, and increases bonding strength. Moreover, the presence of Ni effectively inhibits oxidation and corrosion in friction interfaces, stabilizes the friction coefficient, and enhances wear resistance. Therefore, based on this study, it was concluded that reasonable matching between the dopant elements and the substrates can effectively improve the performance of DLC coatings.