Thermal barrier coatings have provided a revolution in the industry as they allow a higher operating temperature of equipment, improving the efficiency of gas turbines. However, one of the biggest challenges in terms of increasing the lifespan of TBC systems is the attack of fused silicates or simply CMAS (Calcium-Magnesium-Alumina-Silicate). CMAS are particles from the environment that can penetrate the TBC structure and cause delamination of the coating when exposed to high temperatures during thermal cycling. In this study, a plasma sprayed YSZ coating in the as coated and surface treated condition were given CMAS depositions from various preparation methods, and then subjected to thermal cycles at different evaluation temperatures and exposure times. The permeability of the ceramic layer and the penetration path of CMAS at different temperature levels were evaluated, as well as the penetration characteristics in relation to the microstructure of the ceramic layer. X-Ray diffraction and Scanning Electron Microscopy were used to characterize the applied CMAS and the penetration kinetics and conditions. Samples with longer exposure time had a considerable volume increase. The conditions to guarantee the formation of the silicate and its consequent wettability are also discussed.

Thermal spray is a versatile process that produces high-quality coatings possessing diverse properties such as superhydrophobicity, wear resistance, corrosion resistance, dielectric properties etc. Conventionally, powder feedstock is used in thermal spray, and this process is commercialised in numerous industrial processes. However, liquid feedstock based thermal spray is still in its development phases, due to limited information available on process parameters. Various parameters such as plasma/fuel gas, plasma current, feedrate, feeding angle, type of feedstock (suspension or solution precursor), feedstock concentration, feedstock viscosity, solvent, etc. significantly influence the thermal and kinetic energy exchange between plasma/flame and feedstock material. Suspension plasma spray (SPS) and suspension high velocity oxy-fuel spray (SHVOF), once optimised, can give rise to coatings with multiscale features. An in-depth understanding of the complex interaction between feedstock solution/suspension chemical-physical properties and plasma/flame jet characteristics is essential to understand its specific impact on coating properties and their application. This paper presents comparisons between two different TiO2 coatings, deposited by SPS and S-HVOF, and obtained by varying some of the fundamental spray deposition parameters. The surface morphology and cross-sections of the as-deposited coatings were compared through SEM/EDX. Further, surface wetting properties were analysed through measuring the static and dynamic contact angles.

Fluoropolymer and other polymer materials are extremely difficult to coat using solid-state deposition techniques such as cold spraying. In this study, fluoroethylene propylene (FEP) is cold sprayed onto a metallic substrate in order to investigate the effect of powder size, gas temperature and pressure, and substrate surface treatments. A powder modification technique that uses fumed nanoceramic particles as an additive to the feedstock is evaluated as well. The results show that the deposition efficiency of FEP is affected by particle size, gas temperature, and traverse speed as well as the added nanoceramic which, in this case, is either silica or alumina. It is also shown that the hydrophobic properties of the fluoropolymer are retained in the coatings and that adhesion between the coating and substrate plays a critical role.

In this study, icephobic polymer coatings were produced by flame spraying using different process parameters. Process optimization for low-density polyethylene (LDPE) coatings was achieved through design of experiments. The most icephobic coating was produced at a traverse speed of 900 mm/sec and a spraying distance of 250 mm. Although surface roughness affected ice adhesion, thermal effects proved to be the main factor influencing the performance of the coating. The higher the processing temperature, the smoother the surface and the greater the polymer degradation. It is also shown that coating degradation can be caused during post heating steps with similar consequences in the ice-shedding performance of the LDPE coatings.

This study assesses the durability of superhydrophobic surfaces that possess a scalable architecture similar in morphology to branching or corymbose coral. In the experiments, electrolytic copper powders with a coral-like morphology are cold sprayed onto metal, ceramic, and glass substrates, forming a textured copper layer with a structural hierarchy based on the morphology of the powder. After cold spraying, a flame treatment is applied, creating a porous layer of Cu 2 O over the pliable Cu surface, which further increases roughness. As a final step, a fluoroalkyl silane spray is applied to reduce surface energy. It is shown that the fluorinated surface retains its excellent water repellency after cyclic bending and folding, sand-grit erosion, knife-scratching, and even heavy loading with simulated acid rain. It also retains its adhesion to glass (17 MPa), ceramic (12 MPa), and metal (34 MPa) substrates.

Minimizing ice adhesion and preventing ice accumulation on different surfaces has remained in scientific focus from the mid 1900’s. Decades after, scientists are combatting the same challenges, which only outlines the complex nature of ice and ice adhesion related research. One approach to exploit passive coating technology for low ice adhesion utilizes slippery surfaces that combine porous solid material with lubricating liquid. This study presents a novel method in creating functional slippery liquid infused porous surfaces, SLIPS, by exploiting flame spray technique. We demonstrate the functionality of these thermally sprayed SLIPS in ice adhesion and wettability. The ice adhesion results confirmed the potentiality of thermally sprayed SLIPS as ice repellent surfaces with an order of magnitude lower ice adhesion strength compared to polished stainless steel.

In this study, cold sprayed Cu approximately 40 to 60 μm in thickness is deposited on 6063 and LD10 aluminum plate to improve wettability for low temperature soldering and to serve as a barrier layer to protect the substrate from gallium diffusion originating in the solder paste. The effect of the coating on wettability, diffusion, solder joint interface microstructure, and shear strength is investigated in detail.

A new method to fabricate micro-nano scaled surface with super-hydrophobicity is introduced in the present paper. Micro-nano hierarchical structure coatings based on silica (SiO 2 ) micron particles were successfully deposited on the stainless steel substrates by high-velocity oxygen fuel (HVOF) spraying which were modified by 1,1,2,2- Tetrahydroperfluorodecyltrimethoxysilane (FAS) to reduce surface energy. The influences of the HVOF process parameters on the wettability of the coatings were investigated. The coatings were characterized by scanning electron microscopy (SEM), 3D laser microscopy (LSM), and Fourier transform infrared spectrometer (FTIR). The results show that the as-sprayed surfaces exhibit micro-nano hierarchical structure. The water droplets are strongly adhesive to the as-sprayed surface, while by FAS absorbing treatment, the surfaces exhibit super-hydrophobicity, whose contact angle with water droplets are as high as 150°, and the water droplets tend to roll on the surface with extremely low adhesion with a sliding angle of 3°

This study investigates the effect of surface morphology on the wetting behavior of atmospheric plasma sprayed (APS) titanium dioxide. It is shown that with appropriate control of particle temperature and velocity and the use of stearic acid treatments, it is possible to achieve TiO 2 surfaces with water contact angles as high as 144°, which is close to a superhydrophobic state. Such coatings were found to exhibit a rough and irregular surface morphology and were obtained by increasing particle velocity while reducing particle temperature.

This study evaluates the wetting behavior of TiO2 coatings deposited by atmospheric and suspension plasma spraying. A design-of-experiments method is used to investigate the effect of different spray parameters on the water contact angle (WCA) of the coatings. Despite the hydrophilic nature of TiO2, coatings with WCAs as high as 140° were achieved by controlling various spray parameters. SEM imaging shows that these coatings have a cauliflower-like surface morphology that repels and sheds water.

This work deals with the flattening of alumina molten particles, called droplets, on stainless steel substrates either smooth or blasted and preheated at different temperatures. The blasted surface roughness has been limited to Ra= 1.4 µm to image the flattening droplet. Besides flattening and splat cooling, the wettability of melted millimeter-sized alumina drops on the same substrates was measured. The transition temperature, Tt, has been shown to be different between smooth and rough surfaces. For a smooth surface, Tt, is 170°C, and at 200°C 100% of disk shaped splats are obtained. For the rough surface, Tt is close to 300°C with porous splats, becoming almost dense at 450°C. Close to alumina melting temperature, wettability does not vary with the substrate preoxidation, which may not be the case when the temperature is much over the melting one as in plasma spray conditions.

Super-hydrophobic materials have broad application prospects in industry, agriculture and daily life. Not only the types of the materials but also the structure and the morphology of their surface have a significant impact on the hydrophobicity of materials. In this study, nano-structured TiO 2 coatings were deposited on glass surface by vacuum cold spray using agglomerated nano-TiO 2 powder and aggregated nanostructured TiO 2 powder to create nanostructured and micro-nano hierarchical structured TiO 2 surface. The surface morphology of nanostructured TiO 2 deposited surface was characterized by scanning electron microscopy and 3D laser microscopy. The influences of the surface morphology, annealing and fluoroalkylsilane adsorption treatment on the wettability of the surfaces were investigated. The results showed that the nanostructured TiO 2 coatings in the as-sprayed and annealed states were hydrophilic. However, after adsorbing treatment by fluoroalkylsilane, the nanostructured TiO 2 deposited glass surface exhibited super-hydrophobicity. The contact angle of water drops on TiO 2 coating surfaces became greater than 120° up to 170° depending on the local surface morphology. Moreover, micro-nano hierarchical structured TiO 2 coatings obtained by VCS using aggregated nano-TiO 2 after fluoroalkylsilane adsorption exhibited excellent super-hydrophobic performance and the contact angle was greater than 170° and water droplets tended to roll on the surface with extremely low adhesion.

The combination of thermally sprayed hard coatings with a polymer based top coat leads to multilayered coating systems with tailored functionalities concerning wear resistance, friction, adhesion, wettability or specific electrical properties. The basic concept is to combine the mechanical properties of the hard base coating with the tribological or chemical abilities of the polymer top coat suitable for the respective application. This paper gives an overview of different types of recently developed multilayer coatings and their application in power transmission under dry sliding conditions. State of the art coatings for dry sliding applications in power transmission are mostly based on thin film coatings like DLC or solid lubricants, e.g. MoS 2 . A new approach is the combination of thin film coatings with combined multilayer coatings. To evaluate the capability of these tribological systems, a multi-stage investigation has been carried out. In the first stage the performance of the sliding lacquers and surface topography of the steel substrate has been evaluated. For this purpose case-hardened steel substrates were laser textured and coated with different sliding lacquers. In the following stage thermally sprayed hard coatings were tested in combination with different sliding lacquers. For this test stage steel samples were coated with oxide ceramics, metal alloys and hard metals by high velocity flame spraying (HVOF) and high velocity suspension flame spraying (HVSFS). After a grinding process several types of sliding lacquers were applied by air spraying on the coated specimens. Wear resistance and friction coefficients of combined coatings were determined using a twin disc test-bed.

SOFCs for mobile applications require short starting times and capability of withstanding several and severe cycles. For such applications metallic cassette type cells with low weight and thermal capacity are beneficial where the active cell part is set in interconnects consisting of two sheets of ferritic steel. These cells are stacked serially to get higher voltage and power. This approach needs interconnect sheets that are electrically insulated from each other to prevent electrical short circuit. The technology discussed here is to use brazed metals, as sealants, and ceramic layers, as electrical insulators, which are vacuum plasma sprayed on the cassette rims. For reliable insulating layers, a variety of deposits were developed, starting from cermet-spinel multilayers with various compositions and constituents, where reactive metals (such as Ti, Zr) were part of the coatings, to pure ceramic layers. The qualities and characteristics of these coatings were investigated which included electric insulation at room temperature and at 800 °C (SOFC operating temperature), wettability of different brazes towards these deposits, phase stability and peeling strength. The single steps of development, characteristics of the insulating layers for SOFCs as well as some challenges that have to be taken into account in the process are described.

Large (3 x 3 x 0.05 m 3 ) refractory pieces (as the ones used for examples in smelters or incinerators) do not sustain regular glazing in a kiln, mostly due to high associated costs. Still, glass coatings could find use on such pieces due to their physical properties (durability, chemical inertia, tightness, etc.). Thermal spraying, using oxyacetylenic flame in particular, appears as a cost-effective solution permitting to circumvent the aforementioned disadvantages. This study aims at evaluating the quality of two types of coatings in terms of permeability. The first type considered coatings (resulting from a previous optimization of the spray operating parameters) sprayed directly on the substrates whereas the second one considered an additional brass underlayer manufactured by twin-wire electric arc spraying. The wettability of the glaze on the refractory substrate and on the brass underlayer was studied to comprehend the coating structural attributes (thickness, porosity, crazing, etc.) as well as their effects on the permeability. A specific measuring device was developed to assess permeability.

The flattening behavior of individual splats plays a fundamental role in the elaboration of thermal spray coatings. In the PROTAL process, an in-situ laser treatment is coupled with spraying operations. It was shown that a pulsed laser irradiation can effectively suppress the splashing phenomenon of splats. This aspect was primarily attributed to the efficient removal of surface adsorbates/condensates. But, it may also be enhanced by the modification of the surface topography that improves the surface wettability. Therefore, this study deals with the effects of the surface microroughness modifications on the surface wettability induced by the PROTAL process. Several roughness parameters characterizing the surface topography are also discussed from a static wettability point of view.

Thermal sprayed coatings are influenced by the wettabillity of the molten particles to substrates. The contact angles of several molten metal droplets are measured in air and vacuum. The flattening ratio is evaluated by taking into account of wettability. Comparing with the experimental data of the freefall droplet, it was concluded that the wettability to the roughened substrates influenced on the flattening characteristics.

A free falling experiment was conducted as a simulation of a thermal spray process. A flattening behavior of the freely fallen metal droplet impinged onto a flat substrate surface was fundamentally investigated. The substrates were kept at various designated temperatures, and the substrates coated with gold by PVD were also prepared in order to investigate the effect of a wetting at the splat/substrate interface on the flattening behavior of the droplet. A falling atmosphere was atmospheric pressure nitrogen to prevent the oxidation of the melted droplet, and the experiments under low-pressure condition were also conducted. A transition of the splat morphology was recognized in atmospheric pressure nitrogen experiments, that is, the splat morphology on a room temperature substrate was a splash type, whereas that on a high temperature substrate was a disk type. The cross-section microstructure of the splat obtained on the room temperature substrate was an isotropic coarse grain, whereas that on the high temperature substrate was a fine columnar. The grain size changed transitionally with increasing the substrate temperature. Transition temperature on the gold-coated substrate was higher than that on the substrate without coating. The cross-section microstructure of the splat obtained under low-pressure was a fine columnar even on the room temperature substrate. The results indicate that the metal droplet wets better under low-pressure condition than in atmospheric pressure nitrogen condition, and the wetting has a significant role in the flattening of the droplet.