Grown by reactive unbalanced magnetron sputtering in a mixed N2 and CH4 gaseous medium, heterogeneous nanocomposite coatings in the Ti-Al-V-N-C system show extraordinarily excellent tribological performance of coated machining tools. Using analytical high resolution TEM, EELS, FEG-SEM, XRD, and Raman spectroscopy, this paper reports detailed structural and chemical characterization of the coatings grown at various CH4: N2 ratios. Meanwhile, the mechanical and tribological properties were also measured, including hardness, Young's modulus, residual stress and the dry-sliding friction and wear at varying environmental humidity. When CH4 gas was introduced in the deposition, the structure of the coatings has been found to experience a change from nano-scale TiAlN-VN multilayer architecture to a complex mixture of columnar grains of nc-TiAlV(N,C)/a-C nanocomposites and inter-column network of sp 2 -type amorphous carbon. Carbon incorporation and segregation also shows remarkable influence on the columnar growth model by leading to finer grain size. As compared to the carbon-free nitride coating, the nanocomposite coatings showed substantially reduced residual stress owing to the freecarbon precipitation, whereas the coatings maintained comparable hardness to the carbon-free TiAlN/VN. Their tribological properties were found to be strongly dependent on the environment. In humid air at RH > 30%, the coatings showed low friction coefficient less than 0.4 and extremely low wear rate at a scale of ~10 -17 m 3 N -1 m -1 .
A novel but simple path for the preparation of superhydrophobic and superhydrophilic coatings has been demonstrated via a recently developed technology, namely suspension high velocity oxy-fuel spraying.Potential uses for robust superhydrophobic coatings include antifouling applications such as aeroplane wings, ship hulls, offshore wind turbine blades, or the above-deck structures on ice breaker vessels.Several fabrication techniques have been reported for preparing inorganic superhydrophobic surfaces, but existing coatings either lack the necessary robustness for engineering applications and/or their deposition methods are not suitable for industrial scale-up. In this work, the industrially established HVOF coating process was adapted to use a liquid suspension of commercially available nano-particles (titania-TiO 2 , and hexagonal boron nitride-h-BN) as feedstock to produce nanostructured suspension HVOF TiO 2 /h-BN coatings for the first time on stainless steel. Results indicate that agglomerates in the nano-feedstock can be dispersed by h-BN due to poor mutual wettability between h-BN and molten TiO 2 . It also inhibits the anatase-to-rutile transformation of TiO 2 during coating deposition by inhibiting sintering of TiO 2 in the HVOF flame. The resultant coating becomes superhydrophobic when the addition of h-BN reaches 10 wt% due to the presence of hierarchical nano-texture on the surface. The superhydrophobicity (contact angle of 163-170 ) is maintained over a long period of time (>13 months, test still ongoing) and remains stable after exposure to light and tape test. A potential route for industrial preparation of robust water-repellent coatings is therefore highlighted by the study.
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