Microstructure,friction and corrosion resistance properties of a Ni–Co–Al2O3 composite coating

Ni–Co–Al₂O₃ composite coatings were prepared by pulsed electrodeposition and electrophoresis–electrodeposition on aluminum alloy. The content of Al₂O₃ particles of the Ni–Co–Al₂O₃ composite coating prepared by electrophoresis–electrodeposition was significantly higher than the composite coating prepared by pulsed electrodeposition. The composite coating prepared by electrophoresis–electrodeposition exhibited a better anti-wear performance than that prepared by pulsed electrodeposition. The morphology, composition and microstructure of the composite coatings were determined by means of X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The hardness and friction properties of the samples were tested on the microhardness tester and the friction and wear loss tester respectively.

Ni–Co–Al₂O₃ composite coatings were prepared by pulsed electrodeposition and electrophoresis–electrodeposition on aluminum alloy.     

A study on the tribological property of MoS2/Ti–MoS2/Si multilayer nanocomposite coating deposited by magnetron sputtering

Pure MoS₂ coatings are easily affected by oxygen and water vapor to form MoO₃ and H₂SO₄ which cause a higher friction coefficient and shorter service life. In this work, five kinds of MoS₂/Ti–MoS₂/Si multilayer nanocomposite coatings have been deposited by using unbalanced magnetron sputtering with different modulation period ratios. The tribological tests and nano-indentation experiments have been carried out in order to study the tribological and mechanical properties of the multilayer nanocomposite coating. The results show that the hardness and internal stress of the multilayer nanocomposite coatings are superior to those of the pure MoS₂ coating. The polycrystalline columnar structures are effectively inhibited and the coating densification increases due to the multilayer nanostructure and the doped elements of Ti and Si. The nanocomposite coating with a modulation period ratio of 100 : 100 shows the lowest friction coefficient and wear rate. The multilayer nanocomposite coatings exhibit excellent tribological property under a heavy constant load. Interfaces in multilayer nanostructure coating is able to hinder the dislocations motion and the crack propagation. The doped elements of Ti and Si with nano-multilayer structure enhances the mechanical and tribological properties of MoS₂ coating. This study provides guidelines for optimizing the mechanical and tribological properties of MoS₂ coating.

Pure MoS₂ coatings are easily affected by oxygen and water vapor to form MoO₃ and H₂SO₄ which cause a higher friction coefficient and shorter service life.     

Competitive and sequence reactions of typical hydrocarbon molecules in diesel fraction hydrocracking – a theoretical study by DFT calculations

The molecular structures of hydrocarbon molecules determine the competitive and sequence reactions in the diesel hydrocracking process. In this study, the hydrocracking reactions of typical hydrocarbons with various saturation degrees and molecular weights in diesel fractions synergistically catalyzed by the Ni–Mo–S nanocluster and Al–Si FAU zeolite are investigated. The results show that the two major rate-controlling steps in saturated hydrocarbon hydrocracking are dehydrogenation on the Ni–Mo–S active sites and the cracking of the C–C bonds on the FAU zeolite acid center. Moreover, the major rate-controlling step in cracking the cycloalkyl aromatic hydrocarbons is the protonation of the aromatic ring. Moreover, the aromatic hydrocarbons presented an apparent advantage in competitive adsorption on the Ni–Mo–S active sites, whereas hydrocarbons with higher molecular weights demonstrated a moderate adsorption advantage on both Ni–Mo–S active sites and FAU zeolite acid centers.

The molecular structures of hydrocarbon molecules determine the competitive and sequence reactions in the diesel hydrocracking process.     

Preparation of ultra-high mechanical strength wear-resistant carbon fiber textiles with a PVA/PEG coating

Polyvinyl alcohol (PVA) is an organic polymer that is non-toxic, harmless to the human body, and has good biocompatibility. Polyethylene glycol (PEG) is a polymer that has good lubricity and compatibility. The unique graphite structure of carbon fibers can promote the potential application of carbon–fiber composites in tribology. This study explores the relationship between two kinds of organic polymer compounds and carbon fiber cloth (CFC), specifically a PVA/PEG composite coating that is impregnated on the CFC surface. The CFC is synthesized by chemical cross-linking, and the CFC composites (PVA/PEG/CFC) were synthesized. The tribological properties of PVA/PEG/CFC were tested under different concentrations, loads, and velocities. The effects of the different lubricants, surface morphologies, and tensile strengths on the mechanical and tribological properties of PVA/PEG/CFC were studied. In comparison to the original CFC, the friction coefficient and wear morphology of the composite material were reduced and the friction coefficient trend was stable. The addition of PVA/PEG improved the surface lubrication performance of the composite material and reduced the average friction coefficient. In addition, under the different lubrication mechanisms, oil as a lubricant can significantly reduce the friction coefficient and surface wear. In summary, the biocompatible coating process that is proposed in this study can effectively improve the tribological properties of the surface of the CFC.

Polyvinyl alcohol (PVA) is an organic polymer that is non-toxic, harmless to the human body, and has good biocompatibility. Polyethylene glycol (PEG) is a polymer that has good lubricity and compatibility. As a new coating material, PVA/PEG has good mechanical properties.     

Corrosion resistance of Ni–P/SiC and Ni–P composite coatings prepared by magnetic field-enhanced jet electrodeposition

To extend the working life of 45# steel, Ni–P and Ni–P/SiC composite coatings were prepared on its surface by magnetic field-enhanced jet electrodeposition. This study investigated the effect of magnetic field on the corrosion resistance of Ni–P and Ni–P/SiC composite coatings prepared by conventional jet electrodeposition. The surface and cross-sectional morphologies, microstructure, and composition of the composite coatings were determined by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD), respectively. The corrosion resistance was studied using a LEXT4100 laser confocal microscope. The introduction of a stable magnetic field was found to improve the surface morphology of the coatings, increase the growth rate, and reduce the agglomeration of nano-SiC (3 g L⁻¹, 40 nm) particles, thus significantly improving the corrosion resistance of the coatings. The corrosion potential of the Ni–P coating increased from −0.78 V (0 T) to −0.46 V (0.5 T), and the corrosion current density decreased from 9.56 × 10⁻⁶ A dm⁻² (0 T) to 4.31 × 10⁻⁶ A dm⁻² (0.5 T). The corrosion potential of the Ni–P/SiC coating increased from −0.59 V (0 T) to −0.28 V (0.5 T), and the corrosion current density decreased from 6.01 × 10⁻⁶ A dm⁻² (0 T) to 2.90 × 10⁻⁶ A dm⁻² (0.5 T).

We investigated the effect of magnetic field on Ni–P and Ni–P/SiC composite coatings prepared by jet electrodeposition.     

Enhanced thermal conductivity and tensile strength of Al–17Si–3.5Cu with SiC-nanoparticle addition

The morphology and size of primary Si has a significant influence on the thermal conductivity (TC) and strength of Al–17Si–3.5Cu. In this study, the effect of a 1–3 wt% SiC nanoparticle (SiC_nps) addition on TC and tensile strength of Al–17Si–3.5Cu was investigated. Nanoparticles distributed at the interface between primary Si and Al led to a significant refinement of primary Si; for example, a primary Si size of 2 μm with 3 wt% SiC_nps addition was achieved. TC of SiC_nps/Al–17Si–3.5Cu improved with an increase in nanoparticle content. Nanoparticles distributed at the interface between Si and Al reduced the interfacial thermal resistance. Thus, the effective TC of eutectic Si increased. Owing to the refinement of the primary Si and the increased interfacial thermal resistance, originating from the high content of SiC_nps at the interface, the effective TC of primary Si decreased. Compared with Al–17Si–3.5Cu, contribution to the improvement of the TC of SiC_nps/Al–17Si–3.5Cu resulted mainly from eutectic Si. Due to the refinement of primary Si, the tensile strength of SiC_nps/Al–17Si–3.5Cu improved with an increase in SiC_nps content. When the SiC_nps content was 3 wt%, the yield strength, ultimate tensile strength and elongation of SiC_nps/Al–17Si–3.5Cu were ∼176 MPa, 418 MPa and 7%, respectively, which were improved by 37.5%, 53.7% and 218%, respectively, when compared with Al–17Si–3.5Cu.

An interfacial nanocomposite layer was proposed to investigate the effect of SiC_nps on interfacial thermal resistance between Si and Al.     

Composite protective effect of benzotriazole and 2-mercaptobenzothiazole on electroplated copper coating

Benzotriazole (BTAH) and 2-mercaptobenzothiazole (MBT) are mixed to passivate electroplated copper coatings. The growth process of passive films is comprehensively analyzed from the surface potential, microstructure and chemical composition by potential–time curve, FESEM and XPS. Meanwhile, the corrosion resistance of copper coatings with different passivation treatments is evaluated by potentiodynamic polarization curves and electrochemical impedance spectroscopy. During the composite passivation process of BTAH and MBT, the copper coating undergoes the following steps: chemical dissolution of the copper coating, preferential adsorption of MBT, formation of Cu(i)–BTA complex film and Cu₂O, and synergistic growth of Cu(i)–BTA and Cu(i)–MBT. A protective film with a thickness of about 233 nm, containing the inner layer of BTA–Cu(i) and MBT–Cu(i) and the outer layer of MBT–Cu(i) and Cu₂O, is formed on the copper coating after composite passivation. The composite passivation film significantly improves the corrosion resistance of copper coatings, and its corrosion inhibition efficiency for copper coatings reaches 90.7%, which is far better than that produced by using BTAH or MBT alone.

Benzotriazole (BTAH) and 2-mercaptobenzothiazole (MBT) are mixed to passivate electroplated copper coatings.     

Facile hydrothermal synthesis of ternary Ni–Co–Se/carbon nanotube nanocomposites as advanced electrodes for lithium storage

Ternary Ni–Co–Se/carbon nanotube nanocomposites have been successfully prepared via a one-step hydrothermal strategy. When used as electrode materials for lithium-ion batteries, the Ni–Co–Se/CNT composite exhibits good lithium storage performances including excellent cycling stability and outstanding specific capacity, good cycling stability, and high initial coulombic efficiency. A high specific capacity of 687.8 mA h g⁻¹ after 100 charge–discharge cycles at a current density of 0.5 A g⁻¹ with high cycling stability is achieved. The excellent battery performance of Ni–Co–Se/CNT should be attributed to the synergistic effect of Ni and Co ions and the formed network structure.

A Ni–Co–Se/CNT composite exhibits outstanding Li-ion storage performance with respect to high reversible Li-storage capacity, high cyclability and high rate performance.     

Effect of phosphorus content on mechanical properties of polymeric nickel composite materials with a diamond-structure microlattice

Periodical and ordered polymer–nickel-coated composite materials with a diamond-structure microlattice and various contents of phosphorus (4.10 wt%, 8.01 wt%, 12.25 wt%, 16.08 wt%, 20.21 wt%) were fabricated via electroless nickel–phosphorus (Ni–P) coating onto diamond-structured polymeric templates using a 3D printing stereo lithography apparatus. With the increase in P content, the crystal morphology transfers from crystal to non-crystal. By controlling identical 1.0 μm-thickness of 5 different content coatings onto templates, the properties of 5 different microlattice composites were tested by uniaxial compression. To confirm the thickness and P content, several mathematical models were developed to direct the subsequent experiments and all theoretical predictions are in agreement with factual characterization. The composite with 8.01 wt% phosphorus content and density of 240.4 kg m⁻³ performs best, with the maximum compressive strength reaches 1.08 MPa, which is 2.1 times higher than that of polymer templates.

Ordered polymer–nickel microlattices are fabricated by electroless plating on diamond templates by 3D printing and are tested by compression. Fittings are used for tests and accord well. Composite with 8.01 wt% P presents best performance, 1.08 MPa.     

A study on the local corrosion behavior and mechanism of electroless Ni–P coatings under flow by using a wire beam electrode

The local corrosion behavior and mechanism of Ni–P coatings in a 3.5 wt% sodium chloride solution with different flow speeds (0 m s⁻¹, 0.5 m s⁻¹, 1 m s⁻¹) were investigated through a wire beam electrode (WBE) with morphological, elemental and electrochemical analyses as well as numerical simulations. It was found that the microstructure of the Ni–P coating was in the shape of broccoli and possessed satisfactory compactness and uniformity. The numerical simulations showed that the speed increased and the static pressure decreased at the local area. Combined with WBE, it was found that the average corrosion potential decreased at that area. The results indicated that the corrosion tendency and corrosion rate of the Ni–P coating were larger at higher speeds, and the corrosion resistance could be improved by the electroless Ni–P coating. WBE was helpful in revealing the local electrochemical information of the Ni–P coating.

The local corrosion behavior and mechanism of Ni–P coatings in an NaCl solution with different flow speeds were investigated through a wire beam electrode with morphological, elemental and electrochemical analyses as well as numerical simulations.     

Electroless deposition of Ni–P/Au coating on Cu substrate with improved corrosion resistance from Au(iii)–DMH based cyanide-free plating bath using hypophosphite as a reducing agent

The green cyanide-free gold deposition is an important development direction in electroless gold plating. However, the commonly Au(i) based cyanide-free gold plating bath always suffers from severe corrosion to the Ni–P layer and unsatisfactory service life of the bath. In this work, a green and environmentally friendly cyanide-free gold plating bath was developed with hypophosphite added as a reducing agent into the Au(iii)–DMH (5,5-dimethylhydantoin) based plating bath to retard the corrosion of the Ni–P layer. SEM micrographs combined with XRD and XPS analysis indicated that the electroless deposited gold was pure and compact. And XRD also revealed that the oriented deposition of gold was growing preferentially on Au (111). Corrosion tests, including salt spray tests, potentiodynamic polarization tests, and electrochemical impedance spectroscopy tests, indicated that the obtained Cu/Ni–P/Au coatings had significantly improved corrosion resistance performance with the loading of hypophosphite as the reducing agent. The baths remained transparent and no turbidity or precipitates were detected for 210 days, reflecting good stability. The detection for the Ni²⁺ concentration in the bath showed that adding hypophosphite could retard the replacement reaction between Au³⁺ and the Ni–P layer in part and this is important for decreasing the severe corrosion of the Ni–P layer. Moreover, Au was inactive for catalyzing the oxidation of hypophosphite during the deposition process which was confirmed furthermore via quantum chemical calculations. Therefore, our developed green cyanide-free electroless gold deposition process can beneficially provide research value and application prospects in microelectronic industry.

In the Au(iii)–DMH based cyanide-free electroless gold plating bath, the added hypophosphite inhibited the black pad and improved the corrosion resistance of the Cu/Ni–P/Au coating.     

Synthesis of biodiesel from waste cooking oil catalyzed by β-cyclodextrin modified Mg–Al–La composite oxide

In this study, Mg–Al–La composite oxide loaded with ionic liquid [Bmim]OH was used as a catalyst for the synthesis of fatty acid isobutyl ester (FAIBE) via transesterification between waste cooking oil and isobutanol. Mg–Al–La composite oxide was synthesized from the β-cyclodextrin (β-CD) intercalation modification of Mg–Al–La layered double hydroxides. The structure of the catalyst was characterized via XRD, BET and EDS. The results showed that the interlayer space of the catalyst was increased due to β-CD intercalation modification. The IL/CD–Mg–Al–La catalyst exhibited significant catalytic activity and regeneration performance in transesterification due to large interlayer space and strongly alkaline ionic liquid. The yield of FAIBE achieved was 98.3% under the optimum reaction condition and 95.2% after regeneration for six times. The viscosity–temperature curve of FAIBE was determined and the phase transition temperature was −1 °C. The pour point of FAIBE was only −10 °C, which exhibited excellent low temperature fluidity.

In this study, Mg–Al–La composite oxide loaded with ionic liquid [Bmim]OH was used as a catalyst for the synthesis of fatty acid isobutyl ester (FAIBE) via transesterification between waste cooking oil and isobutanol.     

Semisolid Al–Ga composites fabricated at room temperature for hydrogen generation

Usually, Al–Ga alloys are prepared by heating materials to hundreds of degrees for a long time, and the alloys obtained are in the solid state. Although some Ga-rich liquid Al–Ga composites have been developed lately, the mass percentage of Al is small, due to which the hydrogen generation rate and efficiency are limited. Besides, an alkaline solution is indispensable in these studies, which is also a limitation. In this paper, a semisolid Al–Ga composite has been fabricated by mixing liquid gallium and fragmented aluminium foils at room temperature, which is an effective means to generate hydrogen from pure water. With the increase in the Al proportion, the mixture changes from a liquid to a cement-like semisolid material morphologically. Furthermore, an application of the fuel cell taking advantage of the hydrogen released from the composites is given. This method does not require a high-temperature device and only requires water to produce hydrogen once the semisolid Al–Ga composite material is fabricated. Therefore, this is a new approach for making more portable and safer devices for hydrogen production.

A semisolid Al–Ga composite fabricated at room temperature is used as a novel material to generate hydrogen from pure water.     

Cu nanoparticles decorated WS2 nanosheets as a lubricant additive for enhanced tribological performance

Tungsten disulfide–polydopamine–copper (WS₂–PDA–Cu) nanocomposites were first prepared by a green and effective biomimetic strategy and then used as a lubricant additive in polyalkylene glycol (PAG). The biomimetic strategy is inspired by the adhesive proteins in mussels. WS₂ nanosheets were decorated by uniformly dispersed Cu nanoparticles (Cu NPs). The WS₂–PDA–Cu nanocomposites with good dispersion stability, showed better friction reducing and anti-wear properties than WS₂, Cu NPs and WS₂–Cu dispersed in PAG base oil. The average friction coefficient and wear volume were reduced by 33.56% and 97.95%, respectively, at 150 °C under a load of 100 N for the optimal concentration of 0.9 wt%. The lubrication mechanism was discussed.

Tungsten disulfide–polydopamine–copper (WS₂–PDA–Cu) nanocomposites were first prepared by a green and effective biomimetic strategy and then used as a lubricant additive in polyalkylene glycol (PAG).     

Ni–Al–Cr superalloy as high temperature cathode current collector for advanced thin film Li batteries

To obtain full advantage of state-of-the-art solid-state lithium-based batteries, produced by sequential deposition of high voltage cathodes and promising oxide-based electrolytes, the current collector must withstand high temperatures (>600 °C) in oxygen atmosphere. This imposes severe restrictions on the choice of materials for the first layer, usually the cathode current collector. It not only must be electrochemically stable at high voltage, but also remain conductive upon deposition and annealing of the subsequent layers without presenting a strong diffusion of its constituent elements into the cathode. A novel cathode current collector based on a Ni–Al–Cr superalloy with target composition Ni_0.72Al_0.18Cr_0.10 is presented here. The suitability of this superalloy as a high voltage current collector was verified by determining its electrochemical stability at high voltage by crystallizing and cycling of LiCoO₂ directly onto it.

A novel cathode current collector based on a Ni–Al–Cr superalloy is presented here. The suitability of this superalloy as a high voltage current collector was verified by crystallizing and cycling of LiCoO₂ directly onto it.     

Electrochemical performance of porous Ni-alloy electrodes for hydrogen evolution reaction from seawater electrolysis

The hydrogen evolution reaction in seawater is investigated using porous Ni–Cr–Fe, Ni–Fe–Mo, Ni–Fe–C and Ni–Ti electrodes, prepared by elemental powder reactive synthesis methods. The open porosity of the four kinds of electrode materials is 23.05%, 20.47%, 25.27%, and 29.05%, respectively. The electrochemical performance of the four kinds of electrodes has been researched by polarization measurement, cyclic voltammetry and electrochemical impedance spectroscopy. The preliminary results demonstrate that the porous Ni–Cr–Fe electrode has superior catalytic activity and relatively good long-term stability for hydrogen evolution reaction in seawater. The high efficiency and reasonable stability of the porous Ni–Cr–Fe electrode catalyst demonstrate its promising applications in the rising hydrogen revolution.

The hydrogen evolution reaction in seawater is investigated using porous Ni–Cr–Fe, Ni–Fe–Mo, Ni–Fe–C and Ni–Ti electrodes, prepared by elemental powder reactive synthesis methods.     

Effects of thermal treatments on the hydrophobicity and anticorrosion properties of as-grown graphene coatings

Graphene grown on metal substrates has been reported to provide efficient and robust hydrophobicity during water vapor condensation on metal surfaces. However, due to the intrinsic negative coefficient of thermal expansion (CTE) of graphene, the potential thermal stress in real application environments can cause CTE mismatch and then damage the protective graphene coatings, leading to loss of surface hydrophobicity and anticorrosion properties. In this study, the effect of thermal treatments on anticorrosion properties and subsequent hydrophobicity of the graphene surface has been investigated. The as-grown graphene on nickel (Ni–Gr) is explored in terms of survival under severe thermal cycling (up to 14.62 °C s⁻¹) and effectively maintains its surface properties. As a comparison, the as-grown graphene on copper (Cu–Gr) easily peeled off from the metal surface due to the thermal stress and intercalation of oxides. The thermal treatment at 200 °C under ambient atmosphere can elevate the corrosion rate 2.2 times and 29 times on the Ni–Gr and Cu–Gr surfaces compared to situations without thermal treatments, respectively. This study shows that the Ni–Gr surface is significantly more robust than the Cu–Gr surface as a sustainable hydrophobic surface in a complicated thermal environment.

Thermal treatments can significantly affect the anticorrosion properties and the subsequent surface hydrophobicity of graphene-metal systems with varied interfacial bonds.     

Wear and corrosion resistance of Co–P coatings: the effects of current modes

In this work, Co–P coatings were deposited from a chloride-based bath by direct current (DC), pulse current (PC) and pulse reverse current (PRC) methods, respectively. The effects of current modes on the microstructure, composition, microhardness, wear resistance and corrosion resistance of the Co–P coatings were explored. Results showed that the P content in the Co–P coatings increased and the surface roughness decreased in the sequence of DC, PC and PRC methods. The coatings with low P content deposited by DC and PC methods are crystalline with fcc and hcp structures, respectively, while the coating with high P content deposited by the PRC method is amorphous. Comparing to DC and PC methods, the PRC method can evidently improve the microhardness, wear resistance and corrosion resistance of Co–P coatings. The excellent wear and corrosion resistance of the Co–P coatings deposited by the PRC method could be attributed to its high P content, smooth surface and amorphous structure.

The P content in the Co–P coatings increased in the sequence of DC, PC and PRC methods. The PRC Co–P coating has better wear and corrosion resistance than DC and PC Co–P coatings.     

Boronate sol–gel method for one-step fabrication of polyvinyl alcohol hydrogel coatings by simple cast- and dip-coating techniques

The self-assembly of polyvinyl alcohol (PVA) and benzene-1,4-diboronic acid (DBA) is employed as a sol–gel method for one-step fabrication of hydrogel coatings with versatile functionalities. A mixture of PVA and DBA in aqueous ethanol is prepared as a coating agent. The long pot life of the mixture allows for the coating of a wide range of materials with hydrogel films by simple cast- and dip-coating techniques. The resultant films show negligible dissolution in water and the intrinsic hydrophilicity of PVA provides the films with functional properties, such as improved antifogging property and resistance to protein and cell fouling. The self-assembling process shows adaptive inclusion properties toward nanoscale materials, such as metal–organic coordination polymers and inorganic nanoparticles, affording composite films. Furthermore, the coating film exhibits a unique secondary functionalization reactivity toward boronic acid-appended fluorescent dyes, through which a variety of materials are converted into fluorescent materials.

The self-assembly of polyvinyl alcohol (PVA) and benzene-1,4-diboronic acid (DBA) is employed as a sol–gel method for one-step fabrication of hydrogel coatings with versatile functionalities.     

Triboelectrochemical friction control of W- and Ag-doped DLC coatings in water–glycol with ionic liquids as lubricant additives

In the last years, diamond like carbon (DLC) coatings doped with both carbide forming and non-carbide forming metallic elements have attracted great interest as novel self-lubricating coatings. Due to the inherent properties of DLC, the doping process can provide adsorption sites for lubricant additives depending on the chemical and electrochemical state of the surface. Ionic liquids (ILs) are potential lubricant additives with good thermal stability, non-flammability, high polarity, and negligible volatility. These characteristics make them also ideal for polar fluids, like water-based lubricants. In this work, three different DLC coatings (DLC, W- and Ag-doped DLC) were deposited on stainless steel substrates and their friction in dry and lubricated conditions in water-based lubricants was studied. Three ILs, tributylmethylphosphonium dimethylphosphate (PP), 1,3-dimethylimidazolium dimethylphosphate (IM) and 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate (BMP) were used as additives and compared with a well-known organic friction modifier (dodecanoic acid). The results showed better mechanical integrity, toughness and adhesion of the doped coatings compared to the undoped DLC. The Ag-doped DLC coating had the best mechanical properties of all the coatings. W formed tungsten carbide precipitates in the DLC coating. Two different additive-adsorption mechanisms controlled friction: a triboelectrochemical activation mechanism for Ag-DLC, and an electron-transfer mechanism for W-DLC resulting in the largest reduction in friction.

This study proves that friction can be electrochemically controlled in metal-doped DLCs using ILs as friction modifying additives in water-based lubricants. The type of friction control depends on the type of dopant (carbide or non-carbide forming) and its oxidation state.