A method measuring the thermal conductivity and the interfacial thermal resistance of thermal barrier coatings (TBCs) which consist of metallic bond-coats (BCs) and ceramics top-coats (TCs) on superalloys was newly developed. It was based on the areal heat diffusion time method analysing the heat diffusion across multilayers. The developed method was experimentally verified using the BC and the TBC specimens coated by APS. It was found that there were the interfacial thermal resistance not only between the TC and the BC but also between the BC and the substrate. Furthermore, the thermal conductivities of the BC and the TC obtained from the BC and the TBC specimens by this method considering the interfacial thermal resistance were in good agreement with those measured from the free-standing specimen of each coating. Thus, it was confirmed that the newly developed method is effective to evaluate the thermal conductivity and the interfacial thermal resistance of the TBC.

Despite their light weight, 2.3 times lighter than Al, polymers are limited to application with low thermal, wear, and abrasion demands. The enhancement of the functional surfaces of the polymers using thermal spraying techniques is a challenging task due to the thermal degradation of polymers, the low wettability, and the disparate atomic properties. The twin-wire arc spraying (TWAS) process comprises two contradictory features. Almost all spraying particles are in a molten state on the one hand, and on the other hand, the spray plume has the lowest heat output among the different thermal spraying techniques. Therefore, it is a promising spraying technique for the required surface improvement. The surface of the 3D-printed parts was metalized using two successive layers. The first layer is a TWAS coating made of low-melting ZnAl 4 to avoid thermal degradation and provide a bond coat. The topcoat is also applied using a TWAS process and was made out of Ni-WC-Co as cored wires. The top hard coating has improved the wear resistance of the polymers by 14.6 times. The erosion of the coated and uncoated specimens was determined using a low-pressure cold gas spray gun. Ni-WC-Co coating led to more than five times higher erosion resistance.

“Testing Method for Thermal Cycle and Thermal Shock Resistance of Thermal Barrier Coating (TBC)” is a Japanese Industrial Standard (JIS) newly established by the Minister of Economy, Trade, and Industry in 2008, after deliberations by Japanese Industrial Standards Committee, in accordance with the Industrial Standardization Law. The standard specifies a testing method that evaluates the spalling resistance of TBCs based on operating conditions in gas turbines. This paper provides an overview of the standard along with examples of its use.

The thermal shock resistance of plasma-sprayed thermal barrier coatings (TBCs) with different top coats was investigated according to the Japanese Industrial Standard "Testing methods for thermal cycle and thermal shock resistance of thermal barrier coatings" (JIS H 8451:2008). Three types of ceramics powders, namely, Al 2 O 3 , 8 mass % Y 2 O 3 -stabilized ZrO 2 (YSZ) and La 2 Zr 2 O 7 (LZ) were used in the top-coat spray. After the specimens were subjected to a thermal shock, the tensile adhesive strength of the TBCs was measured and the thermal shock resistance as defined in JIS H8451 was determined. The thermal shock properties of the TBCs were found to depend strongly on the chemical composition of the top-coat material. For TBCs with Al 2 O 3 and LZ, the adhesive strength decreased with increasing thermal shock temperature difference (ΔT). On the other hand, little change in the adhesive strength was observed with increasing ΔT for YSZ TBC. From these results, the thermal shock resistance, ΔTc, was determined to be 480 °C for Al 2 O 3 , 680 °C for LZ and more than 880 °C for YSZ TBC. Furthermore, the influence of thermal shock on the adhesive strength of TBCs was investigated in detail through observations of cross-sectional microstructures and fracture surfaces after adhesive testing.

Carbon-fiber-reinforced plastic (CFRP) rolls are increasingly employed in manufacturing equipment due to their light weight, high stiffness, and low inertia and flexure. These rolls, however, are rarely used without a surface coating due to their lack of wear resistance and gripping properties. This paper examines the effects of thermal shock on an experimental carbide-type cermet coating deposited by atmospheric plasma spraying on a CFRP test roll. After thermal shock testing, coating cracks and peeling were observed. The underlying cause was determined and an improved coating, a nickel-base composite with high thermal shock resistance, has been developed, tested, and put to use in a papermaking line, where the rolls have been maintenance-free for more than four years.

The corrosion resistance of thermal barrier coatings against CMAS deposit at high temperature is significantly affected by the microstructure of the coatings. Enhancing the bonding ratio between splats can reduce the inter-connected pores and then obstructs the penetration of the molten CMAS into the coatings. In this study, atmospheric plasma sprayed ZrO2 contains 8 wt. % Y2O3 (8YSZ) coating with improved lamellar bonding ratios was deposited with full-molten droplets at an enhanced deposition temperature. The microstructure of the dense 8YSZ coating and conventional 8YSZ coating before and after thermal exposure with CMAS were characterized. It was clearly revealed that by adjusting the microstructure and designing a ceramic layer with high bonding ratio, the corrosion resistance of the thermal barrier coating could be enhanced. Moreover, by designing double-ceramic-layer (DCL) TBCs composed of a porous ceramic layer and well-bonded ceramic layer, the TBCs with high CMAS corrosion resistance and low thermal conductivity can be achieved.

A numerical model is developed to study the effects of the contact resistance, droplet impacting droplet temperature, and substrate temperature on the droplet solidification rate and temperature of the droplet under the condition when the substrate can melt and re-solidify. Two-dimensional simulations show that the interface velocity is small in the area of poor contact with an irregular solidification interface shape. During the impact of Molybdenum on a steel substrate, Mo solidifies while the steel substrate melts.

For more than two decades researchers have been working on thermal barrier coatings to improve the performance of diesel engines. However, these coatings have still not achieved widespread application in conventional diesel engines. The original motivation for this work was the improvement of fuel economy, since even a few percent improvement would result in huge savings in the transportation industries, but the coatings also effect exhaust emissions, component wear, and the sensitivity of engines to fuel quality. Wear at high temperatures, where conventional lubricants are not effective, is a serious problem in low heat rejection engines. Ceramic materials such as thermal barrier coatings in cylinder liners must have an acceptable wear rate and coefficient of friction. In this work we compare the wear behaviour of nanostructured thermal spray zirconia coatings with conventional zirconia coatings. First, process parameters that allowed the nanoparticles present in the feedstock powder to be retained in the coating were found. Then pin on disc wear tests of the two types of coatings were carried out at room temperature. The coating containing retained nanoparticles exhibited a lower coefficient of friction and less wear loss under discontinuous testing than the conventional coating.

Thick Nanostructured PSZ- NiCoCrAlY graded TBCs were got by air plasma spraying. The results reveal the morphology and phase transformation of TBCs by means of SEM and XRD. The plasma spray process results in a characteristic layered structure consisting of lamellae, unmelted nano-particles and an inter-lamellar porosity. The test results of thermal shock show that the graded coatings have different failure behavior, which caused by thermal stress, radial cracks penetrating and substrate oxidation. The failure mode was the spallation of top coat due to thermal stress. The improved strain tolerance of the top coat was benefited from the high coating porosity, the segmentation cracking, the fine-splat size and the unmelted nanoparticles. It has been found that the lamella consists of nanoscale columnar grains parallel to the spraying direction.

At the present, components which require both nitriding and locally a thermal sprayed coating or nitrided components which should l)e reworked are usually nitrided before spraying and the area to be coated is masked during nitriding or is prepared before spraying by locally removing the nitrided layer by grinding. Seen technically, advantages are to be expected if the nitriding process can be carried out after spraying. Moreover a post-nitriding of thermal sprayed coatings is of interest for improving coating characteristics, mainly wear resistance. Understanding the behaviour of sprayed coatings during nitriding in comparison to bulk materials will help to understand generally the behaviour of such coatings in gas atmospheres at increased temperatures. The objectives of the project are the investigation of the interaction between thermal spraying and nitriding, and the optimisation of both processes to achieve improved bonding, wear and corrosion characteristics respectively to get nitriding of the substrate through the coating without spalling or cracking. Furthermore the behaviour and structural changes of different coatings at increased temperatures are determined. The metallographic, X-ray, wear and corrosion results of the resulting compound coatings and parts are presented. Possible new applications are discussed. The project is funded by the German Research Ministry.

The development of corrosion resistant sprayed coating without sealing is required to increase reliability of the thermal spray coating method and to expand the field of application for the wet corrosion environments. The conventional wire flame sprayed Al coating on the steel substrate without sealing has poor resistance against aqueous corrosion, so as to be restricted in use in practical fields. A duplex coating composed of sprayed Al on a 80Ni-20Cr alloy undercoat was proven to have sufficient resistance in a hot, near neutral aqueous environment through a trial use in a vegetable oil process. In this paper, mechanism of the corrosion resistance of the duplex coating is clarified by electrochemical measurements of the corrosion potential and the anodic polarization characteristics.

Inconel thermal spray coatings are potential candidates for wide industrial applications. However, the coating structure resulting from thermal spray processes characterized by unmelted particles, oxides and porosity can severely hinder their corrosion resistance in aggressive media. The aim of the present work was to optimize elaboration parameters in order to enhance their chemical stability. Electrochemical criteria were used to identify the ability of those coatings to form a passive film in a sulfuric acid solution and also to determine their local corrosion resistance in a chloride solution. Results show that the passivity state is strongly conditioned by the coating microstructure. Coatings free of unmelted particles exhibit a notably reduced passive current density while the localized corrosion resistance seems conditionned by the amount of interlamellar oxide.

The elevated temperature erosion resistance of experimental amorphous thermal spray coatings was determined in a laboratory elevated temperature erosion tester. Test conditions attempted to simulate the erosion conditions found at the combustor waterwall tubes in fossil fuel fired boilers. Erosion tests were conducted on four experimental amorphous thermal spray coatings, using the bed ash retrieved from an operating coal fired boiler. An experimental arcspray process was used to spray coatings. These results were compared with erosion test results of two common structural materials, two commercially available arc-sprayed coatings, and a proprietary HVOF coating. Test results indicated that the Duocor coating had the highest erosion resistance among the four experimental coatings, it showed equal resistance to the HVOF coating (DS-200). Compared to AISI 1018 steel, both Duocor and DS-200 coatings reduced material wastage by 26-fold. Other test results indicated that the XJ-16, 60T and Armacor M coatings had equal erosion resistance reducing material wastage approximately 7-fold, while Armacor CW reduced by 10-fold. Only slightly better than the unprotected 1018 steel, the X-20 coating performed poorly on erosion tests. The high erosion resistance of Duocor and DS-200 coatings was attributed to their high densities and fine splat structures.

Flame sprayed PEEK (poly-ether-ether-ketone) coatings, with an amorphous structure, were subjected to isothermal treatments with annealing temperatures from 180 to 300 °C and holding time from 1 to 30 min. The coating structures were studied by means of DSC (Differential Scanning Calorimetry) and XRD (X-Ray Diffraction) analyses. All annealed coatings exhibit semi-crystalline structures. Coexistence of thick and thin lamellae in the spherulites of annealed coatings can be deduced from the analysis results. The Knoop hardness and the interfacial adhesion of the coatings were examined. The annealed coatings exhibit higher hardness than the amorphous ones. The formation of the thick lamellae is the determinant factor for improving the coating hardness. However, the annealed coatings exhibit a weak adherence to the substrate. Some fissures or spherical porosities could be observed, in certain zones, on the coating/substrate interface. The formation of these fissures and porosities could be ascribed to the coating residual stress and the big volume contraction during the crystallisation that occurred under the annealing condition.

Many properties (thermal, electrical, mechanical) of thermal sprayed coatings are strongly linked to the real contacts between the “piled-up” splats. The quality of this contact depends on droplet parameters at impact (size, temperature, velocity) and substrate parameters (temperature, topography). Two different techniques have been developed in order to study the plasma sprayed particle behaviour at impact. The first one allows direct observation under direct current (dc) plasma spray conditions, while the latter one, based on the millimetre sized free falling drop, enables the visualization of flattening phenomena, but at larger scale. These two techniques bring complementary approaches and results. The latter show that flattening time and cooling rate of the lamellae (metallic and ceramic) are improved with the stainless steel substrate surface modification at the nanoscale when corresponding to a positive skewness parameter obtained by preheating it over the transition temperature. Experiments of wettability show that the presence of nanopeaks increases the contact angle of the liquid on the substrates and reduces thermal contact resistance at interface. It has also been shown that, when adsorbates and condensates are not eliminated from the surface, even with a positive skewness, the thermal contact resistance is increased.

The advantage of cored wires, a new type of material in thermal spraying, is that it is easy to control their composition and convenient to develop new materials. This research is aimed at developing the Fe-Cr-Ni austenitic stainless steel corrosion-resistance thermal-sprayed cored wires with rare earth elements added. The experiments are conducted with arc spraying. The anodic polarization curves of the sprayed coatings of the developed wires and of the 1Cr18Ni9 solid wire are drawn by using MODEL 351 corrosion measuring system in the 0.5mol/L sulfuric and 3.5wt.% sodium chloride solution at a temperature of 20° C . For the sake of comparison, the substrate and the 18-8 wrought stainless steel are also measured. Results to date indicate good usability of thermal sprayed coatings in all the developed wires. Owing to added rare earth elements, the corrosion-resistance of coatings increases in the 0.5mol/L sulfuric solution. The wires with RE-3 added have exhibited good corrosion-resistance. Deterioration of the corrosion-resistance in the 3.5wt.% sodium chloride solution is caused by generation of crevices and inclusions between the deposited particles.

HVOF coatings of 80Ni-20Cr and 50Ni-50Cr powders were carried out on 9Cr-1Mo steel substrate. The coating thickness was around 60 µm. The coated specimens were steam oxidized in four different temperatures, ranging from 600 to 750°C. The steam oxidized specimens were taken out from the chamber at 10, 100 and 1000 hours to examine their protectiveness against scale growth. X-ray diffraction, scanning electron microscope and electron probe microanalysis were carried out on the steam-oxidized specimens in reference with as-coated conditions. Both 80Ni- 20Cr and 50Ni-50Cr coatings show neither scale growth at the interface nor de-lamination in the coating structure. Fe, and Ni diffusion was found in the case of 80Ni-20Cr coatings. The diffusion increased with increase in the temperature and test duration. On the other hand, 50Ni-50Cr coatings, showed an excellent performance in all tested temperatures. The effect of Cr content in the coating, change in phase and compound formation during oxidation, and their influence on the diffusion process will be discussed in detail.

Thermal spray of Al was carried out on the modified 9Cr-1Mo steel to evaluate the steam oxidation resistance of the sprayed Al coating. Atmospheric plasma spray process (APS) was used to coat aluminum on sandblasted 9Cr-1Mo steel substrate. The coating thickness was around 40 µm. The coated specimens were steam oxidized in four different temperatures, ranging from 600 to 750°C. The results show that the scale growth occurred in the interface between coating and substrate subsequently it penetrated into the coating structure. Al diffused into the alloy substrate with high solubility. The diffusion increased with increase in the steam temperature and test duration. Diffused aluminum formed the high hardness intermetallic compound in the substrate near the coating/substrate interface. With increase in the test duration, the intermetallic compound moved towards the bulk and at prolonged aging, it became dissolved. This was identified from the decrease in the micro hardness values at coating/substrate interface at prolonged duration. The scale growth at the substrate surface of Al sprayed steel was much controlled compared to the uncoated specimens.

This work assesses the effects of defects in thermally sprayed chromia via multiscale modeling and imaging techniques. Defect distributions in coating samples are identified by way of image processing and synthetic 3D microstructures are generated from extracted statistical information. The properties of the microstructures are determined by subjecting them to simulated tensile testing, and the significance of different types of defects is evaluated through defect-containing coating models. The approach is able to handle complex defect morphologies, including pore, crack, and splat boundary clusters, making it a versatile tool for assessing the influence of defects on component performance.

This study investigates the influence of heat treatment on the oxidation resistance of thermal barrier coatings. The coating systems examined incorporate an APS YSZ topcoat and a HVOF NiCo bond coat. Isothermal heating tests were conducted to determine how heat treat sequences affect interdiffusion between the bond layer and substrate and the microstructure of the bond coat and ceramic topcoat. Before and after heating, specimen cross-sections were studied by SEM and EDX analysis. Preliminary results indicate that the oxidation resistance of YSZ-NiCo coatings can be improved with a suitable heat treatment, in some cases, extending elevated-temperature service life by as much as 500 h. Abstract only; no full-text paper available.