Durable Icephobic Slippery Liquid-Infused Porous Surfaces (SLIPS) Using Flame- and Cold-Spraying

Icing and ice accretion cause severe problems in different industrial sectors, e.g., in aircrafts, aviation traffic, ships, solar panels, and wind turbines. This can lead to enormous economic losses and serious safety issues. Surface engineering can tackle these problems by designing surface structures to work as icephobic coatings and, this way, act as passive anti-icing solutions. In this research, slippery liquid-infused porous structures were fabricated using flame- and cold-spraying to produce polymer (LDPE and PEEK) coatings, and impregnated with a silicone lubricant. Microstructural details, surface properties, wetting behavior, and cyclic icing–deicing behavior were evaluated via ice adhesion measurements, which show the potential performance of SLIPS designs. All these SLIPS showed low or medium-low ice adhesion after the first icing-deicing cycle and the best candidate showed stable performance even after several icing-deicing cycles.publishedVersionPeer reviewe

Microstructure-based thermo-mechanical modelling of thermal spray coatings

This paper demonstrates how microstructure-based finite element (FE) modelling can be used to interpret and predict the thermo-mechanical behaviour of thermal spray coatings. Validation is obtained by comparison to experimental and/or literature data.Finite element meshes are therefore constructed on SEM micrographs of high velocity oxygen-fuel (HVOF)-sprayed hardmetals (WC-CoCr, WC-FeCrAl) and plasma-sprayed Cr2O3, employed as case studies. Uniaxial tensile tests simulated on high-magnification micrographs return micro-scale elastic modulus values in good agreement with depth-sensing Berkovich micro-indentation measurements. At the macro-scale, simulated and experimental three-point bending tests are also in good agreement, capturing the typical size-dependency of the mechanical properties of these materials. The models also predict the progressive stiffening of porous plasma-sprayed Cr2O3 due to crack closure under compressive loading, in agreement with literature reports.Refined models of hardmetal coatings, accounting for plastic behaviours and failure stresses, predict crack initiation locations as observed by indentation tests, highlighting the relevance of stress concentrations around microstructural defects (e.g. oxide inclusions).Sliding contact simulations between a hardmetal surface and a small spherical asperity reproduce the fundamental processes in tribological pairings. The experimentally observed "wavy" morphologies of actual wear surfaces are therefore explained by a mechanism of micro-scale plastic flow and matrix extrusion

Durability of Lubricated Icephobic Coatings under Various Environmental Stresses

Icephobic coatings interest various industries facing icing problems. However, their durability represents a current limitation in real applications. Therefore, understanding the degradation of coatings under various environmental stresses is necessary for further coating development. Here, lubricated icephobic coatings were fabricated using a flame spray method with hybrid feedstock injection. Low-density polyethylene represented the main coating component. Two additives, namely fully hydrogenated cottonseed oil and paraffinic wax, were added to the coating structure to enhance coating icephobicity. Coating properties were characterised, including topography, surface roughness, thermal properties, wettability, and icephobicity. Moreover, their performance was investigated under various environmental stresses, such as repeated icing/deicing cycles, immersion in corrosive media, and exposure to ultraviolet (UV) irradiation. According to the results, all coatings exhibited medium-low ice adhesion, with slightly more stable icephobic behaviour for cottonseed oil-based coatings over the icing/deicing cycles. Surface roughness slightly increased, and wetting performances decreased after the cyclic tests, but chemical changes were not revealed. Moreover, coatings demonstrated good chemical resistance in selected corrosive media, with better performance for paraffin-based coatings. However, a slight decrease in hydrophobicity was detected due to surface structural changes. Finally, paraffin-based coatings showed better resistance under UV irradiation based on carbonyl index and colour change measurements.publishedVersionPeer reviewe

Effects of multiple wetting incidents, shear and sliding friction on lubricant stability in SLIPS

Surface icing almost invariably derives from the precursory step of liquid water encountering the surface. Thus, slippery liquid infused porous surfaces, SLIPS, must possess steady wetting durability, and lubricant stability to function as a reliable hydro−/icephobic surface design especially in outdoor applications. Additionally, they should maintain their phobic performance under shear forces, and possess low sliding friction to act as a slippery, multirepellent surfaces. These characteristics are needed in variable applications ranging from moving and rotating blades to steady surfaces, operating in altering climate conditions. More profound durability testing is needed to examine the loss of surface functionality when the lubricant is depleted from the structure via various routes. In addition, the durability tests should be designed to serve the application-related purposes and thus, to reveal performance differences between slippery surfaces for further analysis and targeted end-use development. Here, we tested the wetting durability and stability of SLIPS with multicycle Wilhelmy plate by dipping the surfaces multiple times in water bath. Additionally, we examined the effects of centrifugal and friction-based shear stress to investigate the lubricant depletion from the structure. Tests that measure the durability and the stability of SLIPS designs are in great need in further developing functional slippery surfaces for real outdoor application coatings which encounter environmental stresses, e.g., wetting and icing. Acknowledging the material differences under specific stresses will guide designing the slippery surfaces towards more specific and functionable end-use applications.publishedVersionPeer reviewe

Wetting Behavior and Functionality Restoration of Cold-Sprayed Aluminum-Quasicrystalline Composite Coatings

Coating design is an efficient strategy to engineer wettability of surfaces and adjustment of the functionality to the necessities in industrial sectors. The current study reveals the feasibility of functional aluminum/quasicrystalline (Al-QC) composite coatings fabrication by cold spray technology. A commercially available Al-based quasicrystalline powder (Al-Cr-Fe-Cu) was combined with aluminum alloy (Al6061) feedstock materials to make coatings with various compositions. A set of cold spray process parameters was employed to deposit composite coatings with different QC-Al ratios and Al6061 coatings as counterparts. The wettability of the coating surfaces was measured by static water droplet contact angles using a droplet shape analyzer and investigation of the dynamic of water droplet impact by high-speed imaging. Through microstructural studies, the Al-QC composites revealed dense structure, well-integrated and adherent deposits, providing structural reliability and enhanced hydrophobic behavior. In the last step of this work, composite coatings were deposited over eroded cold-sprayed Al6061 and a selected composite to demonstrate the feasibility of repairing the damaged part and function restoring. The results and approach used in this work provide understanding of cold-sprayed Al-QC composite coatings manufacturing and their wetting behavior state for cross-field applications.publishedVersionPeer reviewe

Ice resistance of hydrophobic fluoropolymerized nanostructured alumina films for antireflective coatings

The functionality and durability of nanostructured alumina coatings exposed to atmospheric icing has been assessed to probe their usability in practical applications and to estimate the need for further development of the coatings. In particular, the changes in surface microstructure and in optical performance as well as in the wetting characteristics of the surfaces are reported. Without a hydrophobicity treatment the alumina nanostructures are superhydrophilic and do not endure large environmental changes. Hydrophobicity treated fluoropolymerized nanostructured alumina provides characteristics with partial anti-icing capabilities, enhanced durability, and excellent transmission levels of >95%, but the performance degrades in cyclic icing/de-icing. However, the hydrophobic nanostructured alumina outperforms both the nanostructured and planar alumina coatings and possesses increased durability and stability even under harsh conditions, such as the atmospheric icing. This indicates a clear need to use a hydrophobicity treatment for the nanostructured alumina antireflection coatings to be used in any environments. Therefore, its utilization in applications where little or occasional exposure to icing or other humidity and temperature changes is favorable over standard planar coatings. Further process optimization of the hydrophobicity treatment is still needed for better durability for cyclical icing exposure.publishedVersionPeer reviewe

The effect of mechanical and thermal stresses on the performance of lubricated icephobic coatings during cyclic icing/deicing tests

Evaluating the performance of icephobic coatings interests various industries, such as aviation, maritime, energy, and transportation. Recent developments on icephobic coatings have consistently highlighted the need for durable icephobic surfaces in cold conditions. This study investigates the icing performance and durability of lubricated polymer coatings under cyclic icing/deicing tests. Coatings were made of polyethylene and a solid lubricant and manufactured using flame spray technology. Icing was performed by accreting ice in an icing wind tunnel. Deicing was conducted by removing ice with a centrifugal ice adhesion tester. Surface properties, such as surface morphology, roughness, wettability and chemical composition, were measured before and after the cyclic tests. The results showed stable icephobic behaviour for some coatings, while the performance of others decreased over the cycles. The cyclic tests caused mechanical damage to the surfaces, producing erosion, scratches and, for some coatings, surface cracks. These defects resulted in increased surface roughness and reduced hydrophobicity. However, no chemical changes were revealed for any of the surfaces. Moreover, the causes of cracks were attributed to the difference in thermal expansion behaviour of substrate and coating materials. This result highlights the importance of materials and process parameters selection in flame sprayed coatings designed for cold applications.publishedVersionPeer reviewe

Arc-Sprayed Fe-Based Coatings from Cored Wires for Wear and Corrosion Protection in Power Engineering

High wear and corrosion of parts lead to an increase in operating costs at thermal power plants. The present paper shows a possible solution to this problem through the arc spraying of protective coatings. Cored wires of the base alloying system Fe-Cr-C were used as a feedstock. Rise of wear- and heat-resistance of the coatings was achieved by additional alloying with Al, B, Ti, and Y. The wear and heat resistance of the coatings were tested via a two-body wear test accompanied by microhardness measurement and the gravimetric method, respectively. A high-temperature corrosion test was performed at 550 °C under KCl salt deposition. The porosity and adhesion strengths of the coatings were also evaluated. The microstructure was investigated with a scanning electron microscope (SEM) unit equipped with an energy dispersive X-ray (EDX) microanalyzer, and the phase composition was assessed by X-ray diffractometry. The test results showed the positive influence of additional alloying with Y on the coating properties. A comparison with commercial boiler materials showed that the coatings have the same level of heat resistance as austenite steels and are an order of magnitude higher than that of pearlite and martensite-ferrite steels. The coatings can be applied to wear- and heat-resistant applications at 20–700 °C

Tribological Assessment of Cold Sprayed Aluminum-Quasicrystal Composite Coatings

Cold spray (CS) technology has proven an enormous potential in the production of composite coatings, enabling a production of materials with superior qualities such as enhanced tribological behavior. This study aims to investigate the tribological properties of CS Al-based composite coatings reinforced by quasicrystalline (QC) particles. Two different Al alloys were used as the matrix, AA 6061 and AA 2024, and mixed with Al-based QC particles (Al-Cr-Fe-Cu) at different Al/QC ratios. A room-temperature ball-on-disc test was then used to evaluate the wear resistance of the CS composite coatings in air and compared to those of the CS non-reinforced Al alloy coatings as well as cast counterparts (AA 6061-T6). We have demonstrated that CS could be employed to produce dense and thick Al-QC composites. Further, the addition of the QC particles into the structure increased the wear resistance of the matrix resistance up to 8 times.Peer reviewe