Although inner-diameter (ID) thermal barrier coating (TBC) processes are well established for large aero/land-based turbine liners, the relationships between the processes, microstructures, and properties of coatings applied to smaller, highly confined passages (ID < 200 mm), such as combustor liners, exhaust manifolds, and pipes that face comparable thermal loads, remain largely undocumented. This study examines 8 wt.

One of the most cost-intensive components of proton exchange membrane water electrolyzers (PEMWE) are the anode-side Porous Transport Layers (PTLs), often comprised of titanium with a noble metal coating such as platinum. Replacing the noble metal coating is crucial to reduce the manufacturing costs of PEM electrolyzers. This study aims to replace conventional platinum coatings with titanium-niobium alloy coatings using magnetron sputtering. To evaluate the performance and stability of the coated PTLs, laboratory-scale tests have been conducted with PEMWE single cells. Post-mortem analysis of the PTLs included scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and resistance measurements. So far, the best results were achieved with alloy coatings consisting of 94 at.% titanium and 6 at.% niobium, as these coatings enabled stable PEMWE operation for 144h at 2.0V. TEM confirms that niobium is incorporated into the growing oxide scale. We assume that the pentavalent niobium atoms serve as donator sites in the oxide increasing its electric conductivity.

Low-pressure plasma-sprayed (LPPS) tungsten coatings of 300 mu m thickness were produced with optimized production parameters to demonstrate the feasibility of the process as a repair technique for eroded or damaged plasma-facing components. The samples were, in two separate experiments, exposed to Neon (Ne) and Deuterium (D) plasma to investigate the sputtering resistance and the deuterium retention, and compare the performance to similarly exposed reference bulk tungsten samples. After applying a total fluence of 2.1024 ions/m2s Ne ions with an ion impact energy of 100 eV at a sample temperature of 60 degrees C, the LPPS coatings showed a 0% to 20% higher sputtering yield than the similarly exposed reference bulk tungsten, indicating a slightly decreased performance. The deuterium plasma was characterized by 73 eV ions, and the exposure was run at a sample temperature of 250 degrees C, until the plasma fluence was 3.1025 ions/m2s. The deuterium retention, which was evaluated using nuclear reaction analysis as well as thermal desorption spectroscopy, demonstrated an enhanced performance of the LPPS coatings, indicated by a lower total D inventory potentially by outgassing. In addition, the spectra indicated a D desorption at lower temperatures than that for pure bulk tungsten for the LPPS coatings and a significant impact of the LPPS process parameters on the grain structure and, therefore, the retention performance.

Decarbonizing aviation aims to reduce greenhouse gas emissions from aircraft operations, paving the way for sustainable air travel. This endeavor requires adopting advanced technologies, alternative fuels, high-performance coatings and efficient engineering solutions that minimize environmental impact while maintaining performance and safety standards. Two of the most prevalent and cost-effective methods for applying protective and functional coatings to aerospace components are thermal spray and physical vapor deposition. These techniques enhance the durability and efficiency of several components, resulting in fuel savings and an extended service life across the aviation industry. This supports the broader aim of transitioning the aviation industry to net-zero emissions and sustainable growth. This roadmap explores how these two coating techniques can promote sustainable aviation and identifies the challenges and opportunities in the aerospace sector for researchers and manufacturers of thermal spray and physical vapor deposition (PVD) coatings. It also proposes research directions to address these challenges and discusses the role of AI, which is crucial for breakthrough technologies in process optimization and integration, new coating development and coating design optimization. The roadmap is organized into 20 concise subsections, each focusing on a specific topic. Renowned specialists in each area were invited to summarize the current status of their field, discuss the challenges it faces, and offer recommendations for necessary research and development to overcome these issues. Together, these contributions vividly highlight the essential elements of the field and the challenges that lie ahead. The innovative ideas and concepts outlined in the roadmap reveal that the future path is both expansive and far-reaching. A decade after the JTST released its roadmap on thermal spray, which emphasized the processes, coatings, and applications of thermal spray, the current roadmap shifts its focus to spray processes and vapor deposition methods aimed at decarbonizing aviation. Academic and industry experts are collaborating to share insights on how thermal spray and vapor deposition techniques and coatings can advance sustainable aviation and the necessary research to overcome associated challenges. This roadmap can serve as a valuable reference point for researchers aiming to understand the field’s trajectory and identify critical gaps to address.

Periprosthetic joint infections (PJIs) are a major complication in joint arthroplasty, leading to higher mortality, poorer outcomes, and increased failure rates in revision surgeries. Revision challenges include patient risk factors, bacterial resistance, and the need for implants that combine biological integration with antibacterial effects. The 45S5-bioactive glass (BG), with its unique osseointegration and antibacterial properties, shows promise over hydroxyapatite (HA), though its high-temperature crystallization limits the appropriate coating technologies. Using atmospheric plasma spraying (APS) with controlled thermal exposure, we successfully applied coatings of Ti-6Al-4V alloys with either HA or BG, while preserving bioactivity and mechanical properties of the BG coating. This study compared HA and BG coated Ti-6AI-4V discs in terms of cytocompatibility, effect on biofilm formation and macrophage immune response. In doing so, we demonstrated that both coatings showed comparable attachment and viability of human bone marrow stromal cells (BMSC). We found a significant reduction in biofilm formation of Staphylococcus epidermidis (SE) on the BG coatings, while a pro-inflammatory macrophage activation by bacterial colonization and biofilm formation was preserved. Overall, our study shows that BG exhibits the same properties as HA regarding BMSC attachment and survival, whereas it is superior regarding its anti-biofilm characteristics further allowing for macrophage immunocompetence against bacterial colonization. Therefore, incorporating BG coated implants into revision joint arthroplasty has the potential to enhance and advance current coating strategies by providing a multifunctional approach that combines osteoconductive and antibacterial properties.

For several decades, yttria-stabilized zirconia (YSZ) has been the state-of-the-art material for thermal barrier coatings (TBCs), e.g., in gas turbines, for temperatures up to 1200 degrees C. At higher temperatures, the YSZ undergoes detrimental phase transformations and strong sintering, which leads to early failure of the TBC system. Recently, it was shown that this early failure is correlated to the exact cooling rate applied. It was shown that the lifetime of a TBC system tested in a burner rig at 1550 degrees C was not reduced, when the cooling rates were reduced strongly, e.g., to 10 K/s. In the present study, a new, not yet in the literature reported, pyramidal topography was detected in YSZ samples being cycled at about 1550 degrees C. Analyses were performed using scanning electron microscopy and also transmission electron microscopy. The pyramidal structures were present immediately after preparation of cross sections and increased in amount and size during storage at room temperature in laboratory air.

Fully crystalline, dense environmental barrier coatings (EBCs) are required to protect SiC-based ceramic matrix composites, which are the advanced structural materials for hot-section components of gas turbines. Thermal spray technologies, which have been widely used for depositing thermal barrier coatings, are also applied to deposit EBCs. Avoiding the segmental cracks is one of the main challenges in depositing thermal sprayed EBCs. In this work, suspension plasma spraying (SPS) was used to deposit EBCs on the SiC substrates. The combustion of an ethanol-based suspension can bring plasma additional enthalpy. As a result of that, extremely high deposition temperatures (above 1200 degrees C) could be achieved. At such high deposition temperatures, fully crystalline crack-free Yb2Si2O7 coatings were successfully obtained. However, A relatively high amount of Yb2SiO5 phase was observed in the as-sprayed coatings. The high amount of the Yb2SiO5 phase was attributed to the high surface ratio of the particles formed during the suspension plasma spray.

The energy system and the chemical industry of the present and future require large quantities of hydrogen. A key technology for the production of green hydrogen is the polymer electrolyte membrane water electrolysis (PEMWE). However, investment costs are high due to the use of iridium, platinum and titanium. One way to reduce costs is to partially replace titanium used for the porous transport layers (PTL) by stainless steel. Therefore, we used 316L expanded metals and coated them with titanium by cold gas spraying (CGS) for corrosion protection. Thereby, the average layer thickness was reduced from 60+12 & micro;m to 48+16 & micro;m to 33+16 & micro;m. The corrosion stability of the expanded metals was evaluated by long-term measurements for up to 1006 h at 2.0 V, impedance spectroscopy, analyzing water samples and performing post mortem analysis of cross-sections of the membrane electrode assemblies (MEAs). With 48 & micro;m and 33 & micro;m thick coatings, cationic contamination caused by corrosion lead to increasing ohmic resistances and catalyst inactivation. In contrast, with thicker protective coatings of 60 & micro;m, PEMWE operation was conducted for 1006 h at 2.8 A cm-2 without any evidence of corrosion impact and with performance close to state-of-the-art PTLs. With this newly developed PTL, around 58% Ti-savings can be achieved compared to full titanium PTLs.

Abradable coating systems in aircraft gas turbines minimize the clearance between rotating blade tips and stationary liners, acting as sealants that improve engine efficiency. In this work, abradable liners made of a nickel-based superalloy substrate are coated with a CoNiCrAlY bondcoat, an intermediate Y2O3-stabilized ZrO2 (YSZ) layer, and a MgAl2O4 abradable top layer. The coated systems are evaluated using both thermal gradient cycling and incursion tests designed to replicate real operating conditions. To enhance bonding strength for thicker abradable coatings, laser ablation is applied to the bondcoat and YSZ layer to increase mechanical interlocking between layers. Furthermore, a combined dense and porous microstructure is introduced in the thick MgAl2O4 coating to lower the overall energy release rate while improving toughness near the interface. Three coating configurations are tested: (i) a standard high velocity oxygen fuel (HVOF) sprayed bondcoat with a standard atmospherically plasma sprayed (APS) YSZ/MgAl2O4 double-layer used as a reference, (ii) a laser-ablated HVOF bondcoat with a laser-ablated APS YSZ layer and a standard MgAl2O4 layer, and (iii) a laser-ablated HVOF bondcoat with a standard APS YSZ layer and a dense/porous MgAl2O4 layer. Both modified liners showed superior incursion performance and no failure after 1500 thermal cycles (125 h at 1390 degrees C).

One of the most cost-intensive components of proton exchange membrane water electrolyzers (PEMWE) are the anode-side Porous Transport Layers (PTLs), often comprised of titanium with a noble metal coating such as platinum. Replacing the noble metal coating is crucial to reduce the manufacturing costs of PEM electrolyzers. This study aims to replace conventional platinum coatings with titanium-niobium alloy coatings using magnetron sputtering. To evaluate the performance and stability of the coated PTLs, laboratory-scale tests have been conducted with PEMWE single cells. Post-mortem analysis of the PTLs included scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and resistance measurements. So far, the best results were achieved with alloy coatings consisting of 94 at.% titanium and 6 at.% niobium, as these coatings enabled stable PEMWE operation for 144 h at 2.0 V. TEM confirms that niobium is incorporated into the growing oxide scale. We assume that the pentavalent niobium atoms serve as donator sites in the oxide increasing its electric conductivity.

In the field of aerospace engineering, the efficiency of cooling mechanisms in high-temperature turbine airfoils and combustion chamber walls of jet engines is of great significance. The utilization of cooling holes and thermal barrier coating systems (TBCs) is crucial in protecting these components from the effects of high-temperature combustion gases. Additive Layer Manufacturing (ALM) techniques have emerged as a promising method for the fabrication of more efficient cooling holes with sophisticated geometries. In this study, ALM button samples with and without cooling holes were coated with High-Velocity Oxygen Fuel (HVOF) CoNiCrAlY bond coats and partially Yttria-stabilized zirconia (YSZ) top coats. The top coats were prepared by either suspension plasma spraying (SPS) or atmospheric plasma spraying (APS), using non-90 degrees spraying angles to avoid spraying directly into the cooling holes. Subsequent to this, the samples were exposed to thermal cycling in a furnace at 1100 degrees C, with the objective of comparing their lifetimes and failure mechanisms. The results indicated that the lifetime of the coatings was comparable when applied to samples with and without cooling holes, as well as when using APS and SPS. Stress concentrations that emerge at the complex hole structure appeared to be not critical for the lifetime under cyclic isothermal conditions, although they can influence the direction of preferred crack propagation.

This work employs burner rig testing to understand the modes of degradation of a CoNiCrAlY coated superalloy under thermo-cyclic service condition upon exposure to oxide, oxide-sulfate and sulfate deposits. The mixed oxide and oxide-sulfate deposits adhered to the Al2O3 TGO without reacting, likely due to the decomposition of sulfates and sequestration of reactive oxides into silicates. In contrast, sulfate-only deposits readily react with the TGO, forming less-protective calcium aluminates for all cycling conditions. While the TGO on the specimen heat treated isothermally remained protective, increased cycling frequency led to reaction product delamination depleting the Al-reservoir and oxidizing other coating elements.

In order to meet society's increasing energy needs and at the same time reduce the dependence on fossil fuels, it is essential to expand the production of renewable energies. However, a particular challenge of such energies is the discrepancy between energy production and demand. To bridge this gap, methods are needed to store the energy generated. One possibility is the production of green hydrogen by means of Proton Exchange Membrane Water Electrolysis (PEMWE), which can later be used to generate electricity. Consequently, it is crucial to develop costeffective and resource-conserving manufacturing methods for electrolyzer stacks. In this study, we compare a conventionally used porous transport layer (PTL) on the anode side, which consists of a titanium felt, with a new type of PTL made out of a stainless steel expanded metal coated with titanium. Cold gas spraying (CGS) was selected as the coating process, which, like the production of expanded metals, is highly scalable. In addition, cold gas spraying has the advantage that the deposition can take place under normal atmospheric conditions, as comparatively low gas temperatures prevent titanium from undergoing any phase changes. This study shows that it is possible to coat 130 mu m thin expanded metals without deformation or blockage. The microstructure was analyzed using scanning electron microscopy (SEM) and the phase composition was determined through X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The performance of different PTLs was compared by incorporating them into a proton exchange membrane (PEM) electrolyzer test cell. The newly fabricated PTL reached a current density of 2.6 A/cm2 at 2 V, which is only slightly lower than the benchmark value, reached with a full-body titanium felt, of 2.9 A/cm2. Compared to the full-body titanium felt, our new titanium-coated stainless steel-based PTL can reduce the amount of titanium needed by 68 %.

The residual stresses induced by the various process conditions in engineering components can have a significant impact on their structural integrity and performance. It is essential to ensure reliable control of the mechanical properties of structural components during the repair process, as this directly affects their performance and longevity. Cold gas spray, a solid-state deposition technique, involves the high-velocity impact of fine powder particles onto a substrate, resulting in the formation of a dense, metallurgically bonded coating. The aim of this study is to investigate the suitability of cold gas spraying parameters for the repair of large cavities in components made of Inconel 718. Two sets of parameters, approaching the limits of the spraying facility, have been utilized and analyzed using particle diagnostics. Experimental methodologies involve the characterization of residual stress profiles using techniques such as in situ curvature measurement and the incremental hole drilling method after the cold gas spray repair. Additionally, the microstructure and topography of the as-sprayed repair coatings are demonstrated. The results demonstrate the ability of cold gas spray to successfully fill deep repair cavities and adjust the residual stress state of such repair coatings by varying the processing parameters. Lower residual compressive stresses in the layer were achieved by utilizing gas parameters, wherein the particles impact the substrate at an elevated temperature and at a comparatively reduced velocity. Both conditions exhibited coatings with consistent microstructure, good adhesion and uniform topography without major defects. This research demonstrates the potential of cold gas spray as a viable and efficient repair method for large repair geometries, offering a promising avenue for enhancing the reliability and lifespan of critical engineering structures.

In this study, two particle-tracking velocimetry systems, the Oseir HiWatch HR2 and the Oseir HiWatch CS2 were tested. The particle-sizing velocimetry results were then compared with corresponding particle characteristics obtained using a Tecnar Cold Spray Meter and a Tecnar Accuraspray 4.0 unit. In addition, particle size distributions measured by laser diffraction were included for validation.

This work aims to contribute to our understanding of the importance of nitrogen in enhancing feedstock treatment in plasma spraying. Three different plasma gas compositions—a ternary argon-based composition, a ternary nitrogen-based composition, and a nitrogen-based composition without argon—were used with the Axial III™ plasma torch for suspension plasma spraying. The thermodynamic and transport properties of the plasma gas mixtures were calculated and compared. Based on these calculations, the Ability of Acceleration Factors (AAF) and the Ability of Heating Factors (AHF) were determined and correlated with the measured in-flight particle velocities and temperatures. Computational and experimental results indicate that transport properties, specifically thermal conductivity and viscosity, are key factors in thermal feedstock treatment. In this respect, a high nitrogen content is advantageous. Therefore, nitrogen can be considered a high-heat-transfer component of the plasma. Nitrogen also introduces a relatively high enthalpy. Enthalpy describes the amount of energy stored in the plasma gas that can be released. If the energy output is not enough to heat the feedstock adequately, especially when dealing with high feed rates of liquid feedstocks, the enthalpy of the plasma gas can become a limiting factor. In such cases, a high nitrogen content in the plasma gas is advantageous because the higher enthalpy provides more energy than an argon-based plasma. However, this requires a thermally resilient torch concept.

In all air plasma sprayed (APS) environmental barrier coating (EBC) applications, the predominant goal is to achieve maximum coating density, gas tightness, and/or hermeticity prior to subjecting it to harsh environments (i.e., high-temperature impingement of high-velocity water vapor). The microstructures of APS coatings are historically understood to be influenced by the input processing parameters. Beyond the local deposition rate (surface speed, feeding rate) explored in Part I, there are further extrinsic processing parameters such as plasma gas composition, feedstock choice, and anode orifice dimensions which can be tuned, but have not been fully explored in the context of EBCs. Screening these ancillary extrinsic inputs in a rigorous and systematic way presents challenges in determining which control variable(s) to select to gain meaningful insights. A constant particle temperature distribution (not average particle temperature) in the spray stream was held as a constraint, and the aforementioned extrinsic parameters were varied. As in Part I, a qualitative microstructural approach toward examining the presence (or absence) of advantageous vertical thin microcracks in the as-deposited coating was taken. For certain conditions, a Dense Vertically Macrocracked structure was achieved. Concurrent synthesis of these results offers further insights into process selection and parameter design can be gained.

The quality of low-pressure plasma-sprayed tungsten (W) coatings for application in fusion reactors was investigated under various spray process parameter settings for the following substrate materials: carbon fiber composite, Eurofer (a ferritic/martensitic steel with reduced activation), and tungsten. The deposited coatings with a thickness of approximately 130 µm were evaluated in terms of porosity, deposition efficiency, defects, and surface roughness. Selected parameter sets were applied to produce scaled-up coatings up to 500 µm in thickness on Eurofer and tungsten substrates. Regions of very low porosity of approx. 0.3

The cold gas spray process has emerged as a promising thermal spray technology since its introduction in the 1980s, offering lower operating temperatures and reduced oxidation effects compared to conventional thermal spray methods. This paper presents a comprehensive investigation of cold gas spray dynamics using Inconel 718 as a coating material. It focuses on particle diagnostics and numerical simulations associated with three commercially available nozzle geometries for the cold gas spray system used. Key findings include particle velocity measurements using two diagnostic instruments - a cold spray meter and a HiWatch system - compared with simulation models to analyze the relationship between particle trajectory and gas flow characteristics. Emphasis is placed on predicting the spray spot sizes, considering factors such as the type of powder injection (axial aligned or perpendicular orientated) and particle-flow interactions as determined by the divergent nozzle section. The spray profiles from both simulation and experiment showed a good agreement for the three nozzles, given the applied harsh spraying conditions of 4 MPa and 950 degrees C of the gas. The respective shock diamond structure did not significantly affect the particle dispersion, while a radial particle injection increased the overall particle velocity and temperature. Consistent particle velocities were obtained from both modeling and diagnostic tools for each of the three nozzles. In-situ curvature measurements revealed a general compressive residual stress state, which increases with larger spot size but not necessarily with the length of the divergent nozzle section as shown by findings from the CFD model.