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.

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.

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.

This paper describes recent improvements in metal supported solid oxide fuel cells produced by plasma spraying. By optimizing the process, incorporating nano-micro structured electrodes, and introducing additional layers to prevent interlayer diffusion, the power density of these cells has doubled, voltage has increased to 1.1 V, degradation rates have been cut in half, and redox stability has improved. Although upscaling to larger substrates initially caused distortion in the metal supports, the problems were successfully overcome.

In this study, plasma sprayed ceramic coatings with different amounts of SiC and MoSi 2 particles dispersed in a ZrB 2 matrix were produced and tested. The results show that MoSi 2 addition in ZrB 2 -SiC samples improves high-temperature oxidation resistance without affecting mechanical properties. Demonstrative components were manufactured and tested in simulated operating conditions by means of a plasma wind tunnel. Preliminary results indicate that thermal sprayed ceramics are well suited for use in space re-entry vehicles.

In this investigation, Ni-20Cr alloy powder was deposited on SA 516 boiler steel by cold spraying. The oxidation kinetics of both coated and uncoated samples, evaluated in molten salt, followed a parabolic rate. The rate constant of the Ni-20Cr coated steel was much lower than that of the bare boiler steel. X-ray diffraction, SEM-EDX, and X-ray mapping were used to analyze the oxidation products of the coated and uncoated boiler steel. The uncoated steel exhibited intense spalling and peeling of its oxide scale, which may be due to the formation of Fe 2 O 3 oxides. The Ni-20Cr coating reduced the weight gain of the steel by more than 87% possibly due to the formation of nickel and chromium oxides.

This study evaluates Fe-Si intermetallic powders as an alternative to powders currently used to coat furnace walls in pulverized coal fired boilers. The developed powder mainly consists of Fe 2 Si, which has a relatively low melting point among iron silicides. The powders were deposited on CrMo steel substrates by HVOF and atmospheric plasma spraying and the resulting coatings were subjected to corrosion and erosion testing. Under conditions simulating the operating environment in a low NO X boiler, the HVOF sprayed Fe-Si coatings exhibited sulfidation resistance nearly equal to that of Cr-Ni layers, and in high-temperature erosion tests, the APS intermetallic coatings with boron additions were found to be more erosion resistant than conventional Cr 3 C 2 -NiCr coatings.

This paper presents the results of long-term thermal cycling tests on plasma-sprayed thermal barrier coatings, including coating samples produced with functionally graded materials. The role of oxidation is also considered based on the results of elemental analysis. The authors explain how the coatings were produced and tested and present and analyze the test results. The thermal barrier coatings formed with functionally graded materials were found to be relatively unaffected after the long-term thermal cycling test and showed no signs of oxidation. Paper includes a German-language abstract.

This study examines the high-temperature erosion characteristics of carbide cermet coatings produced by HVOF spraying. The coating materials tested include three Cr 3 C 2 cermets, WC, and WC-Cr 3 C 2 . A low carbon steel and an arc-sprayed iron-base coating are also tested for reference. A nozzle-type elevated-temperature erosion tester is used to spray bed ashes collected from several coal-fired boilers. Coating samples are analyzed and compared based on composition, surface morphology, erosion wastage, and hardness relative to that of the bed-ash particles. From the comparisons, a number of conclusions are drawn. Paper includes a German-language abstract.

The aim of this study is to find a coating that can improve the wear resistance of bushings and sleeves used in continuous hot-dip galvanizing facilities. In the experiments, a number of wear-resistant alloys and their carbide composites are applied to stainless steel substrates by plasma transferred arc (PTA) surfacing and the resulting deposits are characterized based on XRD and SEM analysis, microhardness measurements, and pin-on-disk sliding wear tests conducted in a molten Zn-Al bath at 470 °C. Changes in microstructure during solidification are discussed and correlations are made with phase composition, hardness, wear behavior, and suspected wear mechanisms. Paper includes a German-language abstract.

Studies on atmospheric plasma spraying have generally focused on the influence primary parameters such as gas flows and plasma current. However, the APS process is also influenced by a large number of disturbance variables including electrode wear, cooling system irregularities, and disruptions in powder injection. This study investigates both the cause and effect of each of these factors in the context of aluminum oxide spraying. Numerous measurements are made showing how electrode wear, cooling fluctuations, flow measurement inaccuracy, and variations in powder feed rates affect in-flight particle characteristics, deposition efficiency, and layer thickness. Paper includes a German-language abstract.

Tungsten coatings on copper substrates were produced and subjected to thermal shock loads in an electron beam device. The aim was to minimize the erosion rates thus caused. They are basically dependent on the level and type of porosity. Moreover, material erosion can also be directly influenced by the spraying parameters in coatings with the same relative density. In this connection, the chamber pressure, powder size and spraying distance play a decisive role.

The Laser Megajoule (LMJ) is designed to produce, in laboratory, fusion energy with a significant gain. Such an energy could be achieved by imploding a small capsule filled with a DT mixture. Fusion experiments produce a large emission of neutrons, x-rays, laser scattered light and debris which impose a first wall protection for the laser target chamber made of a low Z and refractory material. As boron carbide appeared to be a good candidate, among others, it was decided to evaluate the potentiality of plasma sprayed B4C coatings for this application. This paper deals with the optimization of plasma spraying conditions to build up coatings that satisfy specifications required for the first wall. Coating general properties are presented as well as outgassing performances. Specific x-ray and laser tests were performed to evaluate coating behavior close to real LMJ working conditions.

The paper discusses the testing methodology and identifies the analytical protocols, with proper validation, in order to evaluate the compatibility of thermal spray coatings in the food production technology, according to EU and FDA applicable standards. A brief state-of-the-art analysis of the international standards on food additives and human health is given, namely on indirect food additives (as defined in 21 CFR 170.3(e)), that can migrate into the food during the process. An outline of the test protocols, based on contact between coating and food simulating solvents in a set time/temperature conditions, are presented, and the main phases for the proposed testing methodology, as the choice of the simulating solvent, the migration cell design and the time/temperature conditions, are discussed. Finally the proposed methodology and protocols are validated through a thermal spray coating for food process application test case.

Fatigue properties of the Al 2 O3 plasma-sprayed SUS316L stainless steel rod specimens coated on different spraying conditions have been studied in a physiological saline solution (0.9 % NaCl solution) to evaluate the potential of surgical implant application. Fatigue tests were conducted in push-pull loading at the stress ratio of R = -1, and frequency of 2 Hz. Microstructure related with fatigue damage was examined by SEM and TEM. The fatigue strength of Al 2 O 3 plasma-sprayed metals significantly depended on spraying conditions: the effects of spraying on fatigue strength decreased with increasing the applied stress amplitude. As-blasted specimens were higher in fatigue strength than Al2O3 plasma-sprayed specimens. It was found that the plasma spraying had significant effects on fatigue crack growth behavior in the early stage of crack propagation. Fatigue cracks preferentially originated from dents that had been caused on the substrata metal surface subjected to grit-blasting. These results are discussed with both the compressive residual stresses due to the grit blasting which was carried out prior to plasma spraying and the corrosion-resistance of the alumina deposit.