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].

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.

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 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.

In this study, the in-situ corrosion behavior of an Fe-based amorphous coating is investigated in a simulated deep sea environment (80 atm). FeMoCrYCB powder produced by gas atomization was deposited on 316L stainless steel substrates by HVOF spraying. The amorphous iron coatings exhibited greater pitting resistance than stainless steel under high hydrostatic pressures, evidenced by higher pitting potential, longer pitting incubation time, and reduced pitting growth. Passive films that formed on the amorphous coatings were also analyzed and found to be thicker, more uniform, and harder than those that developed on 316L stainless steel, indicating that the former are more difficult to break down and more resistant to Cl- ion penetration.

This work investigates the effects of sulfidation on plasma-sprayed Al-Mo and Mo coatings. Pure Mo powder and Al-Mo powder mixtures were sprayed on Inconel substrates with either a NiCrAlY or Mo bond coat. Oxidation and sulfidation tests were carried out in air and Ar-S 2 atmospheres, respectively, at temperatures of 973, 1073, and 1173 K. Coating samples were evaluated before and after testing via SEM and XRD analysis and weight measurements. The results show that Al-Mo coatings with a Mo bond layer provided the best protection against high-temperature oxidation and sulfidation corrosion.

Thermally sprayed aluminum (TSA) coatings have been successfully used to mitigate corrosion of carbon steel in offshore service, but concerns regarding its suitability in CO 2 -containing solutions have kept it out of the running for emerging carbon capture and storage applications. This paper presents the results of a 30-day test in which carbon steel specimens protected by TSA coatings were immersed in deionized water at ambient temperature in 0.1 MPa CO 2 . Acidity and corrosion potential were monitored during the test and dissolved Al 3+ ion content was analyzed at the completion. Based on experimental results, thermally sprayed aluminum is a viable candidate for corrosion mitigation in CO 2 -containing water as would be encountered in carbon capture and storage applications.

Commercially pure aluminum was arc sprayed on low-carbon manganese steel and electrochemical impedance spectroscopy (EIS) was carried on coating samples in a simulated marine immersion environment at 35 °C. A simple pore network circuit model was used to analyze the data and calculate the corrosion rate, which was estimated to be 5-15 μm/y from the charge transfer resistance value. After 9 months of exposure, the actual corrosion rate was found to be ~5 μm/y. The mechanism of protection offered by thermally sprayed aluminum (TSA) coatings is discussed.

In this study, a suspension containing Mg-Al-spinel nanopowder was deposited on bond-coated IN738 and stainless steel disks by suspension plasma spraying with and without substrate cooling. Coating surfaces and cross-sections were examined by SEM, EDS, and XRD analysis and thermal cycling tests were performed. SEM images of coatings obtained on cooled stainless steel show a unique columnar microstructure with a cauliflower-like surface. XRD spectra of the nanopowder and coatings revealed evidence of phase changes in the material deposited on cooled substrates. In preparing samples for thermal cycling tests, a YSZ layer was deposited on bond-coated IN738 prior to spraying the suspension. Double-layered Mg-Al-spinel/YSZ thermal barrier coatings produced on cooled substrates exhibited a thermal cycling lifetime of 2000 cycles at 1390°C, compared to 101 cycles for the TBCs sprayed without substrate cooling. The superior performance of the TBCs sprayed with substrate cooling is attributed to the densification of the coatings, revealed by SEM images, and possibly the formation of CaO-6Al 2 O 3 needles and Al 2 O 3 precipitates as identified by EDS measurements.

Thermal barrier coatings typically incorporate a YSZ topcoat and a metallic bond coat. During service, a reaction zone consisting of different thermally grown oxides forms at the interface. Although most such oxides are detrimental, one (α-Al 2 O 3 ) improves service life due to its barrier effect on oxygen diffusion. In this study, Al and AlOx films are deposited on metallic bond coats by dc magnetron sputtering prior to topcoat deposition. The resulting TBCs were thermally cycled to determine the effect of the interlayer films on service life and TGO formation. It is shown that the Al films transform in situ into dense Al 2 O 3 layers that act as oxygen diffusion barriers. TBCs with interlayer alumina, whether deposited directly or formed in situ, showed less cracking and were more mechanically stable during thermal cycle tests.

Superplastic forming (SPF) is an advanced sheet manufacturing process typically used for low- volume, high-value products. SPF dies made from refractory castables have a lower production cost than metal dies, but their brittle nature is a limiting factor. This work investigates surface degradation mechanisms in ceramic dies and how they are affected by the application of thermal spray coatings. Among the more notable accomplishments of the study is the development of a test rig that simulates die-part interface conditions during superplastic forming and monitors die wear, making it possible to predict ceramic die lifetime for different coatings.

This study investigates plasma erosion mechanisms in alumina and yttria coatings produced by air plasma spraying. Plasma exposure tests were conducted in ICP etchers using CF 4 , Ar, and O 2 as process gases. Etching rates were calculated based on height differences between masked and unmasked areas and coating cross-sections, surface morphologies, and phase distributions were analyzed. In the Al 2 O 3 layers, erosion increased with increasing CF 4 concentration and fluoridation of the coating surface was confirmed, suggesting that chemical erosion is the dominant mechanism. Although fluoridation occurred on Y 2 O 3 surfaces as well, the amount of erosion in CF 4 was the same as in the Ar environment. It is thus assumed that the fluoride formed on Y 2 O 3 surfaces is very stable and that physical erosion due to ion sputtering is the dominant mechanism.

The durability of columnar TBCs produced by PS-PVD are strongly influenced by the compatibility of the metallic bond coat and ceramic topcoat. Studies have shown that a smooth bondcoat surface improves thermal cycling performance and that further improvements are possible by optimizing the formation of the thermally grown oxide layer. In this work, preheating and the deposition of the first coating layer are varied in order to adjust oxide growth. The results show that thermal cycling lifetimes can be more than doubled without a major increase in manufacturing time.

This study investigates the influence of segmentation crack density on the strain tolerance of thermal barrier coatings produced by atmospheric plasma spraying. A Triplex II plasma gun is used to spray fused and crushed yttria-stabilized zirconia, forming thick deposits with high segmentation crack densities, low porosity, and low branching crack density, which is necessary for good interlamellar bonding. Thermal cycling and burner rig tests yield promising results in terms of lifetime and strain tolerance behavior and microstructural analysis shows that the segmentation crack network was stable during thermal shock testing. The main failure mechanism was delamination and horizontal cracking in the vicinity of the TBC-TGO (thermally grown oxide) interface.

In this investigation, two complex perovskite powders, Ba(MgTa)O and Ta(AlMgT)O, are deposited by atmospheric plasma spraying and evaluated for use as thermal barrier layers. Process parameters are optimized to provide sufficient melting without causing the formation of secondary phases. Deposited coatings are assessed based on composition, morphology, porosity, and thermal cycling lifetime. It is shown that the nature of the starting powders has a significant effect on the lifetime and performance of perovskite-based thermal barrier coatings.