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

The method of simulating the wear performance under working conditions using a high-temperature ultra-high-speed wear testing machine was adopted to study the effect of feed rate variation on the wear behavior and scraping performance of the AlSi/hBN sealing coating and TC4 simulated blades. The macro and micro morphology of the coating and blades were analyzed by stereomicroscope and scanning electron microscope (SEM). The phase composition of the coating was analyzed by energy dispersive spectrometer (EDS) and X-ray diffraction. The results showed that, under the conditions of temperature of 450°C, line velocity of 300m/s, and feed depth of 500μm, the change in feed rate significantly affected the macro and micro morphology and wear mechanism of the AlSi/hBN sealing coating-TC4 simulated blades. At low feed rates, severe wear occurred, mainly manifested as grooving, adhesion transfer, and overheating mechanisms. At medium to high feed rates, good machinability was observed, mainly manifested as cutting and transfer of coating material to the blades.

Alkaline water electrolysis is currently the most promising approach to produce hydrogen. However, a main limitation for large-scale application originates from the significant energy loss caused by the coverage of bubbles on the electrode surface. Here, pore-graded Ni electrodes with a positive and negative gradient porous structure that boosts the desorption and release of gas bubble are reported, resulting in a greatly advanced mass transference. The electrodes are obtained from a blend of Ni and Al via high-pressure cold spray. The gradient porosity is realized by varying the addition of Al and chemical etching. As-sprayed electrodes are annealed to eliminate the residual stress and strengthen the adhesion of layers, hence improving their durability. As a result, the electrode with a positive pore-graded structure exhibits a better HER/OER performance when tested with a carbon rob counter electrode. Notably, when tested with an annulus counter electrode of Nickel foam, the electrode with a negative pore-graded structure achieves minimal HER/OER overpotential, outperforming other porous electrodes. This is benefited from improved bubble removal and mass transference capability. All prepared electrodes showed an excellent stability that after 500 cycles of HER/OER test without a large potential fluctuation.

Acquisition of a new LVPS and APS coating system at Delta Air Lines necessitated optimization of the coating parameters on both systems, especially for application of bond coat (LVPS) and top coat (APS) for a TBC coating system. To expedite the coating optimization, it was determined that a design of experiments (DOE) approach would best enable the establishment of the operating window for the two systems. Samples prepared were primarily evaluated for their performance while exposed to a cyclic oxidation cycle. Samples were also evaluated for the microstructure and composition using energy dispersive spectroscopy (EDS) analysis. Samples from the ceramic coating DOE were also evaluated for their erosion characteristics. Results indicate a low correlation between the individual bond coat parameters evaluated to the furnace cycle life. However, the top coat spray parameters were found to have a greater correlation to furnace cycle life and erosion performance.

As steam power plants continue to move towards higher operating temperatures in order to improve efficiency, materials exposed to the working fluid are subjected to accelerated degradations in the forms of surface oxidation and reduced mechanical properties. In this study, the oxidation behavior of two cobalt base alloys, CoCrMoSi (T14) and CoCrNiMoSi (T19), was evaluated in superheated steam (SHS, 0.1MPa) at 800 °C for up to 500 hours. After the exposure, both T14 and T19 alloys experienced weight gain caused by oxidation. Visual observation and SEM surface analysis revealed that T19 had greater extent of surface oxide spallation than that seen on T14. From the cross-sectional evaluation, however, a thin, adherent oxide layer was found to have formed on T19. T14 in fact had suffered from excessive internal oxidation and the surface oxide was uneven. Based on the results obtained so far, it is believed that the finer Laves phase combined with greater amount of Cr in alloy T19 have enabled the formation of a protective oxide layer and thus reduced the extent of internal oxidation. Due to the extensive oxidation ingress along the large Laves phase, it is concluded that T14 is not suitable for applications in SHS at 800 °C.

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].

The advantages of UV-curing polymers are well known and used in various coating and adhesive applications. Curing times of a few seconds and long application windows allowing an increased throughput in series production. The use of UV-curing polymers in sealers is beneficial, but so far insufficient due to only surface curing. With a newly developed dual-cure mechanism in sealers, it is now possible to combine deep penetration curing and surface curing. The hybrid sealers combine radical polymerization with subsequent polyaddition or polycondensation. The development of sealers for thermal sprayed (TS) coatings involves an extensive requirement profile. This includes properties such as corrosion protection, penetration depth and processing times. High penetration depths of the sealant into the coating system are important to ensure a protection over the full lifetime of the TS coatings. The depth of penetration of the developed sealers into various TS coatings was determined by measuring the gas permeability in a specially developed test procedure. The corrosion protection effect in combination with TS coatings was determined by measuring the cell voltage. In summary, two UV dual-cure sealers have been developed to seal TS coatings with deep penetration and corrosion protection.

This study developed microstructure-based finite element (FE) models to investigate the behavior of cold-sprayed aluminum-alumina (Al-Al2O3) metal matrix composite (MMCs) coatings subject to indentation and quasi-static compression. Based on microstructural features (i.e., particle weight fraction, particle size, and porosity) of the MMC coatings, representative volume elements (RVEs) were generated by using Digimat software and then imported into ABAQUS/Explicit. State-of-the-art physics-based modelling approaches were incorporated into the model to account for particle cracking, interface debonding, and ductile failure of the matrix. This allowed for analysis and informing on the deformation and failure responses. The model was validated with experimental results for cold-sprayed Al-18 wt.% Al2O3, Al-34 wt.% Al2O3, and Al-46 wt.% Al2O3 metal matrix composite coatings under quasi-static compression by comparing the stress versus strain histories and observed failure mechanisms (e.g., matrix ductile failure). The results showed that the computational framework is able to capture the response of this cold-sprayed material system under compression and indentation, both qualitatively and quantitatively. The outcomes of this work have implications for extending the model to materials design and under different types of loading (e.g., erosion and fatigue).

In subzero conditions, atmospheric ice naturally accretes on surfaces in outdoor environments. This accretion can compromise the operational performance of several industrial applications, such as wind turbines, power lines, aviation, and maritime transport. To effectively prevent icing problems, the development of durable icephobic coating solutions is strongly needed. Here, the durability of lubricated icephobic coatings was studied under repeated icing/deicing cycles. Lubricated coatings were produced in one-step by flame spraying with hybrid feedstock injection. The coating icephobicity was investigated by accreting ice from supercooled microdroplets using an icing wind tunnel. The ice adhesion strength was evaluated by a centrifugal ice adhesion tester. The icing performance was investigated over four icing/deicing cycles. Surface properties of coatings, such as morphology, topography, chemical composition and wettability, were analyzed before and after the cycles. The results showed an increase in ice adhesion over the cycles, while a stable icephobic behaviour was retained for one selected coating. Moreover, consecutive ice detachment caused a surface roughness increase. This promotes the formation of mechanical interlocking with ice, thus justifying the increased ice adhesion. Finally, the coating hydrophobicity mainly decreased as a consequence of the damaged surface topography. In summary, lubricated coatings retained a good icephobic level after the cycles, thus demonstrating their potential for icephobic applications.

Increasing operating temperature plays a critical role in improving the thermal efficiency of gas turbines. This paper assesses the capability of advanced thermal barrier coatings being developed for use in 1700 °C class gas turbines. Parts sprayed with these coatings were evaluated and found to have excellent durability and long-term reliability.

Developing effective heating systems to prevent ice accretion on the surface of wind turbine blades and aircraft wings is of great significance for extreme cold environments. However, due to high velocity impingement of water droplets and solid particles on the surface of these components, an appreciable degree of surface material degradation may occur. In this study, nickel-chromium-aluminum-yttrium (NiCrAlY) was chosen as a metal matrix material for a coating-based heating system. Pure ceramic powders, namely, alumina and titania, and a cermet powder, tungsten carbide-cobalt (WC-12Co), were mechanically admixed with NiCrAlY powder and deposited to fabricate reinforced metal matrix composite (MMC) coatings. The powders were deposited on cylindrical low carbon steel bars by using flame spraying. The specimens were placed in a wind tunnel to conduct a comparative investigation of their erosive wear resistance under water droplet impact. A cold spraying unit was used for solid particle impact erosion tests. The erosive wear rates were quantified by measuring mass loss. The experimentally obtained results showed noticeably lower wear rate in NiCrAlY-WC-12Co and NiCrAlY-titania coatings compared to the other coatings. The results suggest that certain MMC coatings could be effectively employed to decrease the erosion rate of coating-based heating elements.

In this study, different sets of plasma-sprayed YSZ thermal barrier coatings were deposited via Ar/H 2 and N 2 /H 2 plasmas and compared based on deposition efficiency (DE), thermal conductivity (TC), and furnace cycle testing (FCT). The top-performing coatings exhibited equivalent FCT lifetimes with TC values in the range of 1.15-1.25 W/mK at 1200 °C, but the deposition efficiency of those produced with N 2 /H 2 plasma was twice as high, resulting in a 55% reduction in production costs.

This study demonstrates the applicability of water-stabilized plasma (WSP) spraying for producing thermal barrier coatings (TBCs). A hybrid WSP torch was used to deposit yttria-stabilized zirconia (YSZ) topcoats from powder, suspension, and solution feedstocks. A NiCrAlY bond coat was also sprayed and Hastelloy-X alloy was used as the substrate material. Microstructure, phase composition, and thermal cycle endurance were evaluated. All coatings showed excellent stability and thermal cycle endurance, withstanding more than 700 cycles, and in one case, more than 900 cycles.

In this study, dicalcium silicate (Ca 2 SiO 4 ) coatings were deposited on stainless steel substrates by atmospheric plasma spraying. Salt spray and immersion tests were carried out to evaluate corrosion performance and XRD, SEM, and EDS were used to analyze phase composition and microstructure. During corrosion testing, calcium carbonate crystals appeared on coating surfaces and the pores were filled with hydration products, producing denser coatings. Potentiodynamic polarization curves and electrochemical impedance spectroscopy plots indicated that the corrosion resistance of the coatings increased after immersion in saltwater and artificial seawater, and in the latter case, a silica-rich layer was observed between the coating and the calcium carbonate crystals.

The aim of this work is to find a path toward a thermal barrier coating (TBC) that is more thermally stable and less thermally conductive than current 8YZS coatings. The concept of dual-phase composite ceramics is proposed in an effort to combine the desirable attributes of unique phase constitution, low conductivity, and high ceramic fracture toughness. In addition, efforts are made to optimize the spraying process for low-k ceramic topcoats by controlling the effect of key parameters on porosity, deposition rate, and deposition efficiency. Isothermal oxidation and thermal cycling tests are conducted to evaluate the performance of the low-k TBCs with promising results.

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.

The aim of this work is to develop and assess an eco-friendly carbon-based composite coating for piston ring applications. The coatings were produced from sugarcane waste and Mo, NiCr, and CrC powders using high-velocity oxyfuel spraying and thermal chemical vapor deposition. SEM-EDS and XRD analysis confirms the presence of carbides and oxides that cause coating hardness to increase with increasing temperature. At 550 °C, under a 20 N load with a sliding velocity 0.3 m/sec, the friction coefficient of the coating was found to be 0.2, the wear value was 130 μm, and friction force was 4N. The results indicate that the friction and wear properties of the coatings improve with increasing temperature due to the formation of tribo-oxidative films and the effects of graphitization associated with the presence of carbon.

This paper reports on the performance evaluation of stainless steel (SS) thermal spray coatings aimed at shielding lightweight aluminum (Al) brake rotor disks from excessive heat and providing an adequate tribological surface in contact with brake pads. Coating wear, corrosion and heat resistance performances were evaluated using pin-on-disk, cyclic corrosion tests and thermal cycling using a custom laser rig, respectively. Arc spray optimized coatings displayed lower or equivalent wear rates when compared with the baseline gray cast iron disks, with similar frictional behavior. However, arc spray coating exhibited low adhesion which limits the maximum coating thicknesses achievable and leads to early coating spalling after about 1000 thermal cycles. Arc sprayed coatings also corroded and delaminated under corrosion tests. Optimized cold spray coatings present high corrosion resistance and could resist above 10,000 thermal cycles without spalling. However, cold spray coatings exhibit wear rates at least 4 times those of the cast iron. Taking advantage of both types of coatings, it was found that the production of a duplex coating made of a cold spray bond coat and an arc spray top coat could meet the requirements for protecting Al disks, with near 50% weight reduction.

300M steel is one of most important aerial materials, which can be used for landing gear and flap & slat track. Some surface engineering technologies are needed to be adopted on its surface, because of its bad corrosion performance. WC10Co4Cr Coatings by high velocity oxygen-fuel spray processing (HVOF) is an environmental friendly method for this protection. In this paper, WC10Co4Cr coatings were prepared on 300M by optimized HVOF processing. And their corrosion performance has been estimated by neutral salt fog test, according with ASTM B117. The results indicate that the porosity gets larger and the hardness gets higher for the dissolution of bonding phases after the test. And for the optimized coatings, there are no corrosion products in the surface and interface between the coating and 300M steel, after 2000 hours ASTM B117 test. So the coatings have a good corrosion performance.

In the present work, commercially available NiCr and NiCr-TiC powder blends were deposited on boiler steel substrates by HVOF spraying. To evaluate coating performance, bare and coated steel samples were placed in the superheater zone of a coal fired boiler for 15 cycles. Weight change and thickness loss were measured and the results were used to establish erosion-corrosion kinetics. XRD and SEM/EDS techniques were used to analyze the microstructure and phase composition of as-sprayed and eroded-corroded specimens. The improvement in erosion-corrosion resistance provided by the coating may be attributed to the formation of nickel and chromium oxides and spinels.