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The bonding of thermal-sprayed coatings largely depends on the substrate surface morphology. This study examines the effect of the substrate surface texture shapes on the adhesion strength of coatings. For that, it used plasma-sprayed Ni-based MoS2 coatings deposited on grit-blasted and laser-textured surfaces, and investigated the coating bonding strength (ASTM 633 pull-off test), and cross-sectional and fracture morphologies, as well as phase compositions and element distribution. The results showed that the surface texture shape has a significant effect on the improvement of coating adhesion. The coatings deposited on sinusoidal-textured surfaces had the highest adhesion strength (50.0 MPa), followed by coatings deposited on groove-textured surfaces, while dimple and dimple–groove textures resulted in the lowest coating adhesion strength. The coating fracture analysis revealed that cohesive failure occurred mainly at the texture positions, while adhesive failure occurred almost always in plain areas. Therefore, it could be concluded that, in the conditions of this study, the existence of plain areas and dimple textures did not improve coating adhesion. Factors such as coating bond mode, contact area ratio, and coating deposition quality should be comprehensively considered in texture design to improve coating adhesion. [ABSTRACT FROM AUTHOR]

Compared with their metal counterparts, the insufficient erosion resistance of polymer matrix composites (PMC) is a key issue for application in aero-engines. In this study, multilayered coatings were deposited on carbon fiber reinforced bismaleimide polymer composites using detonation spraying to improve their erosion resistance. The coatings consisted of a polymer–aluminum mixed transition layer, pure aluminum bond layer, and WC-17Co top layer The microstructure and bond strength of the coatings were characterized by using scanning electron/transmission electron microscopy and mechanical testing, respectively. Furthermore, solid particle erosion tests were conducted on coated and uncoated PMC at 25 and 250 °C using an air jet. The tests showed that the coatings 150 µm thick were well bonded to the PMC substrate. Substantial enhancement of the coating adhesion up to 16.5 ± 0.5 MPa was achieved by the optimization of the polymer–aluminum mixed transition layer. Under the same erosion conditions, the volume loss of the coated PMC was less than 1/10 of that of uncoated PMC, indicating the effectiveness of the coating to prevent the PMC from the foreign objects' impact damage. Finally, the coating erosion mechanisms are discussed. [ABSTRACT FROM AUTHOR]

In this work the method of response surfaces was used for the purpose of drawing up a mathematical model for the calculation (forecasting) of the adhesion of a flame sprayed coating of powdered aluminum on S 235 JR steel. Experimental work was conducted according to a fractional central-composite design at three levels. The adhesion of the coatings made with combinations of input parameters of the procedure according to the experiment plan mentioned is measured in line with the EN 582 standard. A mathematical model was derived describing the dependence of the experimentally obtained adhesion values on the input parameters of the procedure. The possibility of analyzing the influence of the parameters on the adhesion for a certain combination of input parameters has been presented with the use of perturbation plots. [ABSTRACT FROM AUTHOR]

We plasma-sprayed nickel coatings on stainless steel and cobalt alloy coupons heated to temperatures ranging from room temperature to 650 °C. Temperatures, velocities, and sizes of spray particles were recorded while in-flight and held constant during experiments. We measured coating adhesion strength and porosity, photographed coating microstructure, and determined thickness and composition of surface oxide layers on heated substrates. Coating adhesion strength on stainless steel coupons increased from 10–74 MPa when substrate temperatures were raised from 25–650 °C. Coating porosity was lower on high-temperature surfaces. Surface oxide layers grew thicker when substrates were heated, but oxidation alone could not account for the increase in coating adhesion strength. When a coupon was heated to 650 °C and allowed to cool before plasma-spraying, its coating adhesion strength was much less than that of a coating deposited on a surface maintained at 650 °C. Cobalt alloy coupons, which oxidize much less than stainless steel when heated, also showed improved coating adhesion when heated. Heating the substrate removes surface moisture and other volatile contaminants, delays solidification of droplets so that they can better penetrate surface cavities, and promotes diffusion between the coating and substrate. All of these mechanisms enhance coating adhesion. [ABSTRACT FROM AUTHOR]

Thermal spray techniques can fulfill numerous industrial applications. Coatings are thus applied to resist wear and corrosion or to modify the surface characteristics of the substrate (e.g., thermal conductivity/thermal insulation). However, many of these applications remain inhibited by some deposit characteristics, such as a limited coating adhesion or pores or by industrial costs because several nonsynchronized and sequential steps (that is, degreasing, sand blasting, and spraying) are needed to manufacture a deposit. The PROTAL process was designed to reduce the aforementioned difficulties by implementing simultaneously a Q-switched laser and a thermal spray torch. The laser irradiation is primarily aimed to eliminate the contamination films and oxide layers, to generate a surface state enhancing the deposit adhesion, and to limit the contamination of the deposited layers by condensed vapors. From PROTAL arises the possibility to reduce, indeed suppress, the preliminary steps of degreasing and grit blasting. In this study, the benefits of the PROTAL process were investigated, comparing adhesion of different atmospheric plasma spray coatings (e.g., metallic and ceramic coatings) on an aluminum-base substrate. Substrates were coated rough from the machine shop, for example, manipulated barehanded and without any prior surface preparation. Results obtained this way were compared with those obtained using a classical procedure; that is, degreasing and grit blasting prior to the coating deposition. [ABSTRACT FROM AUTHOR]

A durable ceramic thermal barrier coating is applied directly to a smooth, highly oxidation resistant intermetallic alloy in two layers. The first layer of ceramic is applied by low pressure plasma spraying and the second layer is applied by conventional atmospheric pressure plasma spraying. This approach would allow the use of plasma sprayed ceramic coatings in applications where a metallic bond coat is not desirable. [ABSTRACT FROM AUTHOR]