This study presents a general overview of ceramic abradable coatings used in the high-pressure section of turbines that are sprayed over superalloys.

This study aims to investigate the influence of alumina in-flight particle characteristics on coating properties and deposition efficiency. To this end, velocity and surface temperature measurements were carried out on the in-flight particles. Resulting coatings were characterized in terms of porosity, hardness, and related to particle properties. The final goal was to obtain an optimized coating with low porosity, high hardness, manufactured with a high powder flow rate and deposition efficiency.

The aim of this study is to develop a solid shroud to minimize in-flight oxidation using the particle swarm optimization (PSO) algorithm. Additionally, the shroud is specially designed to use air as a cooling medium instead of water and is made from common stainless steel to help reduce equipment and process costs.

This study evaluates the surface protection of a waste-to-energy boiler wall using the Eutronic Arc Spray Gun 4 HFH. The test involved coating a 3.2 m² section of the boiler membrane wall with four materials: BTW 58 (FeCr-based), METCO 8294 (NiCrMo alloy), TAFALOY 71T (Inconel 625), and Metcoloy 4 (FeCr steel). Before spraying, the surface was grit-blasted to SA 3 finish with a roughness of 75–100 μm. Coatings were applied both with and without a Metco 8450 bonding layer. Additionally, two high-temperature ceramic coatings—Fireside and Tubearmor—were tested. The wear tests were conducted on-site in the boiler's third pass. After one year of exposure, samples were evaluated for condition, wear, and scale formation. BTW 58 and TAFALOY 71T, particularly when combined with Fireside ceramic coating, provided the most effective protection.

This paper proposes a new procedure for preparing enameled steels by thermal spraying the ceramic enamel followed by laser sintering and vitrification to obtain a smooth, corrosion-resistant, and anti-fouling coating. This study investigated the influence of enamel formulation, spraying methods, and laser parameters on the coating properties and characteristics, including microstructure, topography, phase composition, mechanical stability, and laser vitrification.

In this study, the effect of laser heat treatment on the deposition of oxide ceramic coatings has been examined preliminary. As the energy source, a fiber-laser irradiation experiment on the fine particle ceramic spray has been examined. This trial will give a new possibility to survey a new type of hybrid aerosol deposition, laser-assisted HAD.

This paper presents a comparative analysis of three coating types—W 2 C/WC12Co (Metco71NS), Cr 2 O 3 -4SiO 2 -3TiO (Metco136F), and Co25.5Cr10.5Ni7.5W0.5C (Metco45C-NS)—applied to disc harrow components, focusing on their microstructural and tribological properties.

Surface structures are of vital importance for the wetting behaviors of hydrophobic coatings. In this work, rare earth oxide coatings with different surface structures were deposited via the solution precursor atmospheric plasma spray (SPAPS) process and solution precursor vacuum plasma spray (SPVPS) process, respectively. The SPAPS coatings showed hierarchical cauliflower-like surface structures composed of micron-sized clusters and nanometer-sized particles, while the SPVPS coatings showed relatively flat topographies with small and short bumps. The formation of different surface structures in the SPAPS and SPVPS processes was investigated by modelling the movement of in-flight particles in the vicinity of the substrate. The properties of plasma jets and the characteristics of in-flight particles in the two processes were correlated. The effects of diverted plasma gas flow on the trajectories of particles impinging on the substrate and the resultant surface structures were elaborated, revealing different shadowing effects in the SPAPS and SPVPS processes. The SPAPS coatings were superhydrophobic due to the presence of hierarchical surface structures, which showed larger water contact angles and smaller roll-off angles than the SPVPS coatings. The correlations between the surface structures and wetting behaviors of different coatings were investigated.

Hybrid plasma spraying can be utilized to deposit novel coating microstructures by combining the simultaneous injection of a dry coarse powder and a liquid feedstock into the plasma jet. Using this approach, the coating microstructure contains both coarse powder-made splats and a dispersion of fine liquid-made splats. Furthermore, the so-called external feeding hybrid method allows the incorporation of fine particles of materials susceptible to decomposition at high temperatures thanks to the by-passing of the hot plasma jet and deposition of the temperature-sensitive material directly onto the coated surface from a suspension. In this study, microstructures of ceramic coatings with embedded self-fluxing sulfides were studied and the wear resistance of the system was evaluated using the dry sliding pin-on-disc method.

The application of thermally sprayed coatings on CFRPs has gained great interest to enhance thermal and tribological properties and several processes have been optimized. However, for the coating of internal surfaces of tubes there is no sufficient technical solution. This paper introduces a novel and unique process technique for coating the internal surfaces of CFRP tubes using the transplantation of thermally sprayed coatings. A negative shape tube with defined surface and material properties was used as a mandrel and coated using atmospheric plasma spraying (APS). The CFRP was then produced using filament winding onto the coating, and after curing, the specimen was separated from the mandrel. With this process innovation, CFRP tubes with internal ceramic or metallic coatings can be produced without any thermal degradation of the polymeric matrix or damage to the carbon fibers. Compared to conventional coating methods, this novel process technique has several advantages. It allows for the production of internal coatings with low roughness of R z = 10 μm as sprayed without post-processing. The specimens also have a significantly lower tendency to corrode compared to conventional coated CFRPs. A high adhesion strength of the coatings of 15.9 MPa was achieved and the hardness of the internal ceramic coating is 918 HV0.1

In addition to the proper functional properties, the adhesive strength represents one of the key criteria for industrial use of thermally sprayed coatings. Since conventional thermal spraying processes are almost carried out exclusively in air atmosphere, this leads to the oxidation of the particles and of interfaces within the coatings. As a result, conventional thermally sprayed metallic and metal-ceramic coatings are characterized by heterogeneous microstructures with interlamellar oxide fringes at the interfaces between individual splats and also between the coating and the substrate. This has a decisive influence on the bond strength and on the wear and corrosion protection properties of thermally sprayed coatings. The aim of this study is to present the potentials of thermal spraying processes carried out in a mixture of monosiliane and an inert gas at ambient pressure as an alternative to the known vacuum spraying process in order to prevent oxidation during the coating process. Using the example of arcsprayed coatings, it is demonstrated that the extremely low oxygen partial pressure in the silane-doped medium leads to coatings free of oxide seams with a reduced porosity and substantially enhanced properties.

In metal die casting as well as plastic injection molding, controlling the heat balance during the injection and solidification process can lead to fewer defects and a better component quality. An appropriate cooling channel design for the mold can help to control the solidification to a certain extent. But the heat control achievable by cooling channels is limited due to the high effective thermal mass, and therefore near-cavity energy input is of interest. In this paper, a simulation study is performed demonstrating the use of plasma sprayed ceramic coating as a heating coating at the cavity of the mold. The goal is to apply heat faster and locally focused during the solidification process in metal die casting as well as before the injection phase in plastic injection molding. The heat generation of these ceramic coatings is modelled using experimentally measured values and the effects of this approach on defects such as distortion and hot tearing is discussed.

Hybrid aerosol deposition (HAD) is a new coating method to deposit homogeneous nano-structured ceramic coatings. An accurate evaluation of the fabricated coating properties is required. In this study, α-Al 2 O 3 fine powder was sprayed by HAD. The obtained coatings were dense and uniform with a nanocrystalline structure. An X-ray diffraction measurement revealed that the fabricated HAD Al 2 O 3 coatings mainly consisted of α-Al 2 O 3 phase. The hardness and Young's modulus of the HAD Al 2 O 3 coatings were evaluated by a micro-Vickers method and a nanoindentation method using the Weibull distribution. The hardness of HAD Al 2 O 3 coatings measured by micro-Vickers was ~1400 HV (~15 GPa). The variation of mechanical properties of HAD coatings measured by the nanoindentation method was extremely small compared to those of plasma-sprayed coatings, which also indicates that HAD coatings contain less pores and cracks than plasma-sprayed coatings.

Aerosol cold spraying (ACS) is modification of low-pressure cold spray technology which allows to deposit ceramic and metal-based coatings. ACS technology in vacuum possesses the formation of films from sub-micro and nanoparticles directly at room temperature. The ACS technology is still under development to cover more application and discover solutions of spraying different kind of powders on different types of material substrate and optimizing spraying conditions to obtain the best results. The main objective of the present work is to develop a new ACS cold spray technology of Hydroxyapatite (HA) and Copper powder deposition onto both the implants and ceramic substrates. The new AD spraying system with radial injection of particles to be deposited is constructed and tried. An influence of technology parameters on the coating structure and properties are presented. In addition, the combined cold spray and sintering technology technique is further investigated for additive manufacturing applications.

Deposition of protective dense environmental barrier layers is a promising solution to improve the reliability and environmental durability of the next-generation turbines and other industrial applications. In this context, spraying of fine particles could enhance the formation of fine dense coating microstructures with improved properties. In AIST we are focusing on the spraying of the fine particles via different spraying technologies including suspension plasma spraying, as well as deposition of the fine solid particles directly by aerosol deposition (AD) and plasma-assisted aerosol deposition (so-called Hybrid Aerosol Deposition; HAD. The HAD is a new coating window to spray the fine ceramic particles via the implementation of a low-power rf-plasma source to assist the aerosol deposition at room temperature. This study introduced the feasibility of utilization of HAD as an outstanding technology for deposition of dense ceramic coatings on different substrate materials and 3D deposition capability. Highly dense and well-adhered Al 2 O 3 coatings without obvious observable cracks and bulk-like properties were successfully fabricated on different substrate materials of SUS 304, Aluminium, Al 2 O 3 and glass, via HAD of fine particles. The substrate material and its hardness significantly influenced the first deposition step, which determined the coating adhesion and properties. Furthermore, homogeneously uniform, dense, and crack-free coating with a strong adhesion has been fabricated successfully on cylindrical substrates with 6.3 mm diameter. During HAD spraying the plasma activated the surface of the particles without reaching to the molten state, then the activated particles impact and stuck with the substrate by room temperature impact consolidation mechanism. Therefore, the fabricated coatings had the same crystal structure as the starting feedstock powder, and the activated surface act as glue and improved the deposition efficiency and 3D capabilities. Herein, the deposition phenomena of HAD makes it as a promising candidate technology for development of environmental and sealing layers of highly dense microstructure, with the targeted crystalline phase structure, without stoichiometric composition nor phase transformation and improved deposition efficiency on multi-shape components in different fields such as environmental, thermal barrier coatings (TBCs), environmental barrier coatings (EBCs) and gas turbine applications.

Thermally sprayed ceramic coatings can be used for wear protection as well as thermal and electrical insulation. When exposed to environments with high humidity, the water absorption of the ceramic coating has a tremendous impact on the electrical insulation. In thermally sprayed ceramic coatings, water can easily be absorbed by the porous microstructure of the coating. A general result of the water absorption is the reduction of the dc resistivity. However, in the high frequency regime of ac loads, contrary results were observed for sealed Al 2 O 3 coatings on steel substrates. Specimens exposed to high air humidity have shown an increased ac resistance compared to dry specimens if frequencies above 1 MHz are considered. To analyse this phenomenon, a novel measurement technique was developed to investigate the influence of the water absorption of detached ceramic coatings on the ac resistivity at high frequencies. Moreover, the water absorption of the ceramic is measured gravimetrically. To ensure the results are also applicable to ceramic coatings on substrates, the morphology of the coating was analysed using electron microscopy and compared to reference specimens deposited on steel substrates from [1].

Thermally sprayed Al 2 O 3 -TiO 2 ceramic coatings provide exceptional hardness and corrosion and wear resistance, but the high velocities at which they are applied result in an inherently porous structure that requires some type of remediation. This study evaluates the effectiveness of ultrasonic aluminum phosphate sealing treatments on plasma sprayed Al 2 O 3 -40TiO 2 ceramic coatings. The sealants were applied with and without ultrasonication (20-40 kHz) and were assessed using SEM/EDX analysis, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Test data indicate that optimum sealing, corresponding to the highest values of corrosion protection and erosion resistance, are achieved under ultrasonication at 30 kHz for 5 hours.

This study investigates the microstructure and hardness of coatings produced by atmospheric plasma spraying using a commercial (Al,Cr) 2 O 3 solid solution (ss) powder blended with various amounts of TiO 2 . The microstructures were analyzed using SEM, EDS, and XRD measurements. It was shown that blending with TiO 2 reduces porosity and defect density while increasing deposition efficiency and microhardness. Small amounts of Ti in ss (Al,Cr) 2 O 3 splats were detected in coatings prepared from blends with higher TiO 2 content. Variations in aluminum and chromium content were also observed.

Cold spraying is a promising process for fabricating functional coatings. Because of the solid-state particle deposition, the electrical and chemical properties of the coatings are similar to those of the bulk materials. Mechanical properties, on the other hand, differ from those of bulk materials due to severe plastic deformation of the particles. Residual stress may thus be an important variable to track during cold spraying although the formation mechanism is not entirely clear. In this study, the residual stress of metallic (copper) and ceramic (titania) coatings is measured during the cold spray process. The results are presented and discussed.

A wide range of properties can be achieved in intermetallic coatings applied by gas detonation spraying (GDS). The properties of Fe-40at%Al GDS layers, however, may change when exposed to temperatures exceeding a threshold level. To characterize such changes, Fe-40at%Al GDS coatings were subjected to systematic dilatometric studies in which temperatures were cycled from room temperature to 1180 °C. The investigation revealed both irreversible and reversible phase transitions as described in the paper. Dilatometry measurements obtained from sintered samples made from the same powder are presented for comparison.