TiO₂-BN/CNTs coating with radiative cooling and reduced friction

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 TiO₂ 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 TiO₂-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.