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[Display omitted] • Integration of thermal regulation and friction reduction functionalities in a nanocomposite coating for electronic packaging. • Inspired by Camponotus ants, coatings with hierarchical micro/nanostructures were developed for efficient radiative cooling and friction reduction. • Utilization of PEO for rapid and eco-friendly coating fabrication, offering potential for large-scale production of multifunctional radiative cooling materials. • Achieving high infrared emissivity and substantial reduction in LED temperature (21.5 °C), alongside outstanding friction reduction performance. To date, the demand for electronic packaging materials with combined highly efficient heat dissipation and low friction attracts intensive attention. There have been hardly any reports of coatings that provide simultaneous radiative cooling, thermal conduction, and friction reduction properties. In the present work, a novel biomimetic nanocomposite coating is gown on the titanium alloy substrate. The coating consists of a TiO 2 ceramic layer adorned with hemispherical protrusions and is enriched with hexagonal boron nitride (h-BN) flakes and CNTs on the surface. The optimal microstructures are determined through Finite Difference Time Domain (FDTD) simulation calculations and then prepared using plasma electrolytic oxidation (PEO). The results show that the hierarchical micro/nanostructures enable the coating to achieve an infrared emissivity of ∼ 0.9 within the 3–14 wavelength range, whilst h-BN and CNTs contribute to the thermal conduction of the TiO 2 -BN/CNTs ceramic coating. The advantage of the biomimetic nanocomposite coating over the bare titanium alloy is that the coating facilitates a reduction in the equilibrium temperature of a 5 W LED by around 21.5 °C. In addition, the coating exhibits outstanding friction reduction performance with a low friction coefficient (COF) of 0.15 over a sliding distance of 94.2 m, benefitted from the lubrication effect of h-BN and CNT. This work introduces a straightforward and environmentally friendly approach to fabricating bifunctional thermal regulation materials. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (h -BN) is considered a very promising anti-friction material, however, how to assemble them densely and uniformly on metal surfaces remains a challenge. In this study, CNT-assisted plasma electrolytic oxidation (PEO) with the addition of h -BN nanoparticles was employed to create a double-layer coating on titanium alloy, demonstrating exceptional tribological characteristics. The CNTs not only acted as lubricating phases to improve the anti-friction performance but also as additives to facilitate the transition from the nanocomposite coating to the double-layer coating. The later stage of the PEO process with CNT doped in the electrolyte produces an interesting sudden rise in current density, which generates strong and dense discharge that facilitates the deposition and sintering of h -BN. As a result, the double-layer coating has a higher adhesion and hardness as well as more h -BN nanoparticles incorporated into the coating compared to coatings without CNTs-assisted deposition. Further, the double-layer coating exhibits a lower friction coefficient (∼ 0.11), attributed to the high release rate of h -BN under shear to form a lubrication film in conjunction with CNTs on the contact surface. The simple technique offers a novel approach to fabricating self-lubricating ceramic coatings on light alloys, which has huge potential for application in the anti-friction materials field. [Display omitted] • CNT-assisted PEO method achieves dense TiO 2 -hBN/CNT double-layer coating. • The coating exhibits low COF (∼0.11). • Simple method offers potential for self-lubricating coatings on light alloys. [ABSTRACT FROM AUTHOR]

Plasma electrolytic oxidation (PEO) coatings were formed, respectively in three silicate-based, phosphate-based and aluminate-based electrolytes on niobium, with the aim to explore the relationships between electrolyte composition, dielectric breakdown behavior and corresponding corrosion resistance. The initial growth stages of the anodic coatings were studied, and result shows that an impedance falling stage (from about 200 V to 400 V) starts at the emergence of spark discharge accompanied with the surface morphology evolution from compact to porous. The PEO coatings were characterized through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods. Results show the coatings fabricated in (NaPO 3) 6 electrolyte provide the best corrosion resistance. It attributes to the effective thickness of the compact inner layer rather than the entire thickness of the coating that decrease diffusion of corrosion medium. Unlabelled Image • Porous oxide formation at spark occurrence explained coating impedance decrease. • The sustained inner and outer growth of the coating caused impedance rebounding. • Coatings produced in (NaPO 3) 6 electrolyte exhibited the prior corrosion resistance. • The outstanding corrosion resistance depends on inner barrier layers of PEO coating. [ABSTRACT FROM AUTHOR]

• A fractal-patterned coating is designed for superhydrophobicity and passive cooling. • The coating is fabricated by plasma electrolytic oxidation and hydrothermal treatment. • The coating with high emissivity enhances the passive heat dissipation efficiency. • The coating has robust water-repellence, self-cleaning and anti-corrosion properties. Effective surface passive cooling and superhydrophobicity is vital for promoting more flexible application of energy power system for aircraft and aerospace. Here, we experimentally demonstrate a fractal-patterned coating on TA15 titanium alloy for superhydrophobic and passive cooling performance through plasma electrolytic oxidation and hydrothermal treatment successively. The coating exhibits excellent corrosion resistance and self-cleaning properties, largely thanks to the fractal structure and low surface energy. Additionally, the micro-hole's infrared trapping effect and TiO 2 lattice absorption significantly increase the emissivity over the thermal wavelength range. When functioned on a titanium radiator, such a coating can reduce the temperature by as much as 9.3 °C. Therefore, the passive heat dissipation and superhydrophobic multi-functional coatings are expected to be a promising candidate for heat exchange equipment that requires exposure to harsh external environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • A highly compact ceramic coating is formed on SiC p /Al composite surface by PEO. • The coating obtained at +500 V/−80 V (i.e., N80) has high electrical insulation. • The compact coating structure provides a good long-term anti-corrosion ability. • The coatings display a high infrared emissivity value in the waveband of 8–20 μm. PEO coating microstructure on SiC p /Al composites under the influence of negative pulse are comparatively studied. Results show that the cross-sectional porosity is significantly reduced to 5.1%. The electrical insulation performance of coatings initially improves and then declines as the negative voltage rises from 0 V to 120 V, which is attributed that either an excessively low or excessively high negative voltage is insufficient to improve the internal defects of the coating. Among all the coatings, the coating obtained at +500 V/−80 V (i.e., N80) possesses better electrical insulation (with breakdown voltage of 736 ± 15 V, dielectric strength of 16.3 ± 0.3 V/μm, electrical resistivity of 1.51 × 1011 Ω∙cm), better dielectric performance, higher optical band gap value, making it appropriate for usage as electronic packaging or dielectric materials. The impedance modulus at low frequency of N80 coating is two to three times higher than that of N0, N40, and N120 coating, providing a long-term anti-corrosion ability for the substrate, during the 72-hour immersion. Additionally, the coatings display a high infrared emissivity in the waveband of 8–20 μm (>0.9) to achieve good radiation and heat dissipation effect. Thus, a reasonable negative voltage used in coating preparation does effectively diminish internal structural defects, enhancing coating performance. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel superhydrophobic Al 2 O 3 /cerium hexadecanoate double-layer coating was designed. • The composite coating was fabricated by combining plasma electrolytic oxidation and electrodeposition. • The high emissivity double-layer surface enabled a significant LED temperature drop. • The composite coating showed superior self-cleaning, anti-corrosion and adhesion strength. Abstract To enhance the heat dissipation and anti-corrosion performance simultaneously, a superhydrophobic Al 2 O 3 /cerium hexadecanoate (Al 2 O 3 /CH) composite coating with high adhesion strength has been fabricated by plasma electrolytic oxidation and subsequent electrodeposition. The Al 2 O 3 /CH composite coating with a contact angle of 165.5° shows excellent water repelling and self-cleaning ability owing to the micro/nano structure and low surface energy. The composite coating enhances the corrosion potential of pure Al from −0.742 to −0.730 V and lowers the corrosion current density by two orders of magnitude. Thanks to the high emissivity in the wavelength range from 2.5 to 25 μm, the Al 2 O 3 /CH coated sample enables the operation temperature of a 5 W LED to drop approximately by 9.3 °C compared with Al substrate. In addition, the Al 2 O 3 /CH composite coating exhibits higher adhesion strength than that of the CH single layer. Therefore, the superhydrophobic coating is expected to be a promising candidate for heat dissipation and anti-corrosion applications. [ABSTRACT FROM AUTHOR]

Plasma electrolytic oxidation (PEO) coatings fabricated on 6061 aluminum alloy under different applied voltages (400 V, 500 V and 600 V) were used to investigate the plasma discharge induced ‘local over-growth’ characteristics across substrate/coating interface. The instant microdischarges across the local plasma channels induce the ‘micro molten pool’ products and then solidify rapidly to form ‘over-growth’ oxides region extending into substrate. A thin bonding layer composed of nanocrystalline and amorphous Al 2 O 3 with a constant thickness of ~600 nm is always forming on the interface. The intact interface structure of the “local over-growth” characteristic patterns was presented perfectly by both microdischarge-sculpted substrate side ‘pits’ and electrochemically detached coating side ‘protrusions’. The patterns demonstrate that the over-growth ‘pits’ and ‘protrusions’ gradually grow up with increasing applied voltage, which is attributed to the larger discharge channels and molten pools caused by the increased size and intensity of plasma discharges. The speculative ‘over-growth’ mechanism of discharge event during plasma electrolytic oxidation process is described. This work provides insights to control ‘over-growth’ characteristics of substrate/coating interface by tailoring electrical parameters or electrolytes composition. And this strategy has a potential application to fabricate micro-nano structure or optimize outstanding performance of PEO coatings. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel double-layer nanocomposite coating is prepared via a facile one-step PEO-SDSN technique. • The addition of nanoparticles creates interesting rising and falling changes in current. • A new fabrication strategy of multifunctional coatings by tailoring particles species is proposed. • The instant, dense discharges are induced by Highfield, high temperature and bubbles accumulation. • Such intense discharges significantly improve the growth rate of nanocomposite coating. A novel double-layer structural nanocomposite coating was prepared via one-step plasma electrolytic oxidation-synchronous deposition & sintering of nanoparticles (PEO-SDSN) technique under unique threshold conditions of concentration of added nanoparticles, electrolyte temperature, and applied voltage. The special discharges at the coating/electrolyte interface lead to the directional migration, deposition and sintering of organic (eg. PTFE) or inorganic (eg. SiC) nanoparticles, combined with the dynamic growth equilibrium of bottom oxide layer and outer nanoparticle deposition & sintering layer. Different from traditional PEO, the addition of nanoparticles creates interesting rising and falling changes in current and corresponding discharging characteristics. The underlined formation mechanism of the double-layer coating was detected by OES combined with discharging phenomena and coating structure evolution. Moreover, compared with the single PEO coating, the double-layer structural nanocomposite coating has better comprehensive performances, such as corrosion protection, and low and stable friction coefficient. The PEO-SDSN technique is energy saving, more importantly, it provides a brand-new fabrication strategy for a series of double-layer multifunctional coatings by tailoring the nanoparticles species. Eventually, the potential applications and guiding strategies of double-layer nanocomposite coating are presented. [ABSTRACT FROM AUTHOR]