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CoCrNi medium‐entropy alloy (MEA) is a promising material for aviation and aerospace applications due to its excellent strength and ductility. However, its low surface hardness and poor wear resistance pose challenges for its tribological performance. To address this issue, electrochemical boronizing is explored as a potential solution, offering advantages such as a fast boronizing rate and low cost. This study demonstrates that electrochemical boronizing can significantly enhance the surface hardness and self‐lubrication performance of CoCrNi MEA, as well as retain impressive mechanical performance. Results show that a boronized layer with a thickness of about 50 μm is formed on the surface in 45 min. The boronized layer is mainly composed of Co2B, Ni2B, CrB, CoB, and Ni3B. After boronizing, the surface hardness of the sample increases by about 9 times, and the ultimate tensile strength and uniform elongation can reach 97% and 73% of the original sample, respectively. Compared with the original alloy, the friction coefficient and wear rate of boronized MEA are reduced by 38% and 85% under deionized water conditions, respectively. X‐ray photoelectron spectroscopy analysis reveals the generation of boron‐containing tribofilm on the wear scars, which significantly reduces friction and wear during the friction process. [ABSTRACT FROM AUTHOR]

To reduce the dosage of zinc dialkyldithiophosphates (ZDDP) in engine oil, the synthesis and characterization of a novel borate ester containing a phenylboronic group (BDDP) was reported. The thermogravimetric analysis results showed that BDDP had a better thermo-stability compared with that of commercial additives ZDDP and F10A. The tribological properties of the PAO 6 base oils containing BDDP, ZDDP and F10A were studied using a four-ball tester and SRV tribo-meter. The oil with a BDDP concentration of 0.8% showed tribological properties superior to those of the ZDDP and F10-containing oil under varying applied loads and elevated temperature conditions. The elemental composition of the tribological film generated on the worn surfaces of the steel balls was detected by X-ray photoelectron spectroscopy (XPS), and the results indicated that the tribological film was composed of Fe 2 B and B 2 O 3 . Thus, BDDP could be a candidate to replace ZDDP or reduce the dosage of ZDDP in engine oil. [ABSTRACT FROM AUTHOR]

The compatibility and effectiveness of nanoparticles with the existing additives in formulated oil are still unclear. In the present study, some lubricant additives were selected to modify nanoparticles to obtain friendly capped nano-MoS2. Various polyisobutyleneamine succinimide (PIBS) concentrations were applied to investigate the lubrication effectiveness of capped nano-MoS2. The results showed that the reduction in COF and wear volume of friendly capped nanoparticles without PIBS reached about 35% and 75% in comparison with those of the base oil respectively. However, the average coefficient of friction and wear volume loss of nano oil increased with PIBS concentration in the range of 0.05%-1%. By scanning electron microscope, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analysis, it is identified that (i) MoS2 tribofilm was formed on the wear track for the oil with nano-MoS2 and (ii) wear scar was smooth for nano-MoS2 with low PIBS concentration and without PIBS, while it showed plowing wear when containing high PIBS concentration. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The CoCrNi medium-entropy alloy (MEA) exhibits an impressive ductility, but its low hardness (∼352 HV) and poor wear resistance limit its engineering applications. In this study, a significant increase of surface hardness and enhancement of self-lubrication were achieved for the CoCrNi MEA using powder-pack boronizing. Results indicate that dual reaction layers with a total thickness of about 50 μm were formed on the surface. These two strengthened layers are mainly consisted of silicide (Ni 2 Si) and borides (CoB, Cr 5 B 3). The hardness of the affected region reaches to 11–21 GPa dependence on the cross-sectional depth, being about 6 times higher than that of untreated MEA. In the deionized water condition, the friction and wear rate reductions of the boronizing treated specimen reach to about 25% and 63%, respectively. Energy Dispersive Spectrometer (EDS) and X-ray Photoelectron Spectroscopy (XPS) analysis on the wear scars showed that a silicon/boron-containing tribofilm was formed under the water environment, which reduces the friction coefficient and enhances the wear resistance. Our study demonstrates that powder-pack boronizing is a powerful way to enhance surface hardness and self-lubrication properties of CoCrNi MEA. • Double-strengthened layers were observed on the boronized CoCrNi alloy surface. • An obvious improvement of surface hardness was obtained. • The self-lubrication performance of boronized CoCrNi MEAs in the water is excellent. • The self-lubrication enhancement was due to the formation of silicon-boron based tribofilm. [ABSTRACT FROM AUTHOR]

The boronizing treatment has been an effective way to strengthen and enhance the lubrication performance of alloys. However, the traditional power-pack boronizing method has been limited due to its time-consuming. Improving the boronizing efficiency is highly demanded for the strengthening and industry application of the high-entropy alloys (HEAs). In this study, the electrochemical boronizing strategy was applied to improve the surface hardness and self-lubrication performance of AlCoCrFeNi 2.1 eutectic HEA (EHEA). The microstructure, phase formation and hardness of boronized alloys were studied. Results confirm the high efficiency of electrochemical boronizing to form a boronized layer with a thickness of about 35 μm in 30 min. The surface hardness of the boronized AlCoCrFeNi 2.1 HEA reached to about 18 GPa due to the presence of NiB, FeB and Cr 3 B 4 in the boronized layer. Tribological tests reveal that the self-lubrication property of AlCoCrFeNi 2.1 HEA in water condition was significantly enhanced by the electrochemical boronizing treatment, e.g., the friction and wear reductions reach to about 25% and 80%, respectively. Lubrication mechanism investigation by X-ray photoelectron spectroscopy (XPS) analysis showed the formation of a H 3 BO 3 tribofilm on the sliding surface during the friction process, which effectively reduce friction and wear. This study provided a novel and fast approach for surface hardening and self-lubrication enhancement of HEA systems using the electrochemical boronizing strategy. • A boronized layer was obtained on the AlCoCrFeNi 2.1 alloy surface in 30 min. • The surface hardness was about 4 times higher than that of the original EHEA. • The self-lubrication performance of boronized EHEAs in the water is excellent. • The lubrication enhancement was due to the in-situ formation of H 3 BO 3 tribofilm. [ABSTRACT FROM AUTHOR]

The commonly accepted interlayer shear mechanism for layered materials as oil additives remains a challenge with the emergence of two-dimensional materials. In this work, the lubrication effectiveness of MoS 2 and BN nanosheets with a similar size was investigated as oil additives using block-on-ring tests. BN nanosheets reveal remarkable anti-wear performance and a reduction of wear depth of about 50%, whereas, the expected friction and wear reduction were not found for MoS 2 nanosheets. X-ray photoelectron spectroscopy (XPS) investigation indicates the generation of boron-based tribofilm for BN nanosheets and MoS 2 -complex tribofilm for MoS 2 nanosheets. Together with the thermal stability analysis, we found that it is the high strength tribofilm with high oxidation resistance, but not the layer structure, that plays a critical role in lubrication enhancement. This study highlights the advance of 'depositing tribofilm' mechanism in novel additive design. Image 1 • Layered materials with similar size and shape were selected. • Expected friction and wear reduction was not found for MoS 2 nanosheets in this study. • BN nanosheets reveal the remarkable anti-wear property with strong tribofilm strength. • It is a challenge to explain the results by using interlayer shear mechanism. • Depositing tribofilm mechanism would be preferable for novel particle additive design. [ABSTRACT FROM AUTHOR]

The influence of anti-oxidation property of nanoparticles on the tribological properties is rarely reported. In this study, the alkyl-functionalized graphene oxide (FGO) and alkyl-functionalized boric acid (FBA) were fabricated as oil additives to explore their lubrication effectiveness. FBA exhibited remarkable lubricating properties which reduced friction coefficient by approximately 24 % and the wear depth by about 94 %. However, the friction coefficient and wear depth of FGO were reduced by only 9.5 % and 44 %, respectively. Worn surface analysis shows a bunch of deep-plowing on rubbing surface in the case of FGO, while the wear scar was smooth and almost wear-free for FBA. Lubrication mechanism analysis by X-ray Photoelectron Spectroscopy revealed the formation of carbon-based tribofilm for FGO and boron-based tribofilm for FBA during rubbing. In the thermal behavior analysis, graphene oxide (GO) nanoparticles were completely decomposed at 650 °C, whereas, B 2 O 3 nanoparticles remained stable. It indicated that the excellent thermal stability and anti-oxidation property of boron-based tribofilm benefited to the lubrication enhancement. This study highlights the importance of oxidation resistance in designing novel nanoparticle additives, and the enhancement of oxidation resistance of GO will be a promising way to further application as oil additives. [Display omitted] [ABSTRACT FROM AUTHOR]