This study aims to comprehensively examine and analyze the basic mechanical properties, oxidation resistance, high-temperature hardness, fretting wear, and simulated operating conditions of CuAl/PHB coatings. The objective is to investigate the optimal combination of resistance to fretting wear and abradability for these coatings.

This study explores the steam oxidation behavior of pure chromium coatings applied using high-velocity oxygen fuel spraying on Zircaloy-4 cladding substrates designed for accident-tolerant fuel applications. The research addresses the urgent need to improve the performance of fuel cladding materials during severe nuclear accidents.

In this paper, oxidation behavior of three hardmetal coating compositions with different Cr 3 C 2 content deposited on 1.4828 (AISI 309) or 2.4856 (Alloy 625) substrates was investigated. Heat treatment was performed in a tube furnace in a slight air flow (2 l/h) in the temperature range 500-900 °C for 2–32 days.

To achieve higher engine combustion efficiency while reducing emissions, it is necessary to address the challenges posed by elevated operating temperatures. High Entropy Alloys (HEAs) have emerged as promising materials for this purpose, offering exceptional properties at high temperatures, including synergistic effects and excellent resistance to oxidation and corrosion. In this study, a FeCoNiCrAl HEA was investigated as a bond coat material due to its excellent balance of strength and ductility, coupled with outstanding oxidation resistance. It was deposited using HVAF M3 and i7 guns equipped with different nozzles/powder injectors and pressures. Notably, this research marks the first study of the i7 gun globally for the HEA bond coat, coupled with the optimization of HVAF parameters for both i7 and M3 guns. Characterization of both powder and as-sprayed samples was carried out using X-ray Diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), and Field Emission Scanning Electron Microscopy (FESEM) techniques. The results revealed the formation of a dense and homogeneous microstructure. Additionally, isothermal oxidation tests were conducted to analyze the behavior of the thermally grown oxide. After 50 hours at 1000 °C, a dense, uniform, and thin alumina TGO layer was observed to have formed. These tests revealed that FeCoNiCrAl HEA exhibits significant potential to enhance oxidation resistance at high temperatures.

The growth kinetics of thermally grown oxide (TGO) silica in Yb-disilicate (YbDS) environmental barrier coatings (EBCs) significantly affects the durability of EBCs. The oxygen permeability can control the TGO growth kinetics and thus could play an essential role in determining EBCs life. Therefore, the oxygen permeability constant of YbDS and TGO is systematically evaluated and quantified in terms of thermodynamics using defect reactions and the parabolic rate constant (kp), respectively. Dry oxygen and wet oxygen conditions as well as different temperatures, partial pressures and top coat modifiers are investigated. The results offer evidence that the oxygen permeability constant for the YbDS top coat is an order of magnitude higher than for the TGO. As such, the TGO hinders the oxidant diffusion stronger, proving to be the diffusion rate controlling layer. Moreover, water vapor strongly increases the oxygen permeability with defect reactions playing a key role. It is suggested that the mass transfer through the top coat is primarily by outward ytterbium ion diffusion and inward oxygen ion movement, with the latter being dominant, particularly in wet environments. The effect of top coat modifiers on oxidant permeation is composition sensitive and seems to be related to their interaction with oxygen ions and their mobility.

MCrAlX powder compositions (M=Ni, Co and X=Y, Hf, Si or combination) are often thermally sprayed (TS) via vacuum plasma spray (VPS), low pressure plasma spray (LPPS) or high velocity oxy-fuel (HVOF) to produce high temperature oxidation and hot corrosion resistant bond coats (BC) for thermal barrier coatings (TBCs). Cold spray (CS) technology is currently considered as a promising alternative to the traditional TS solutions having the advantage of delivering oxide-free and very dense metallic coatings at relatively lower costs compared to VPS and LPPS. Here, we first present high-pressure CS deposition of NiCoCrAlY and NiCoCrAlYHfSi and discuss the influence of feedstock properties on the deposited BCs. CFD numerical simulation is employed to tailor the spray conditions based on the feedstock characteristics. Secondly, we present the laser assisted cold spray (LACS) deposition of NiCoCrAlYHfSi BCs using a low-pressure CS system. We show that LACS can be successfully used to deposit this particular powder while eliminating nozzle erosion and low deposition efficiency disadvantages observed during conventional CS. Lastly, high temperature isothermal oxidation of a TBC architecture having LACS BC is presented.

The hot-section components of modern gas turbines (e.g., turbine blades and vanes) are typically manufactured from Ni-base superalloys. To develop the γ/γ' microstructure that imparts superior thermomechanical and creep properties, Ni-base superalloys usually require three distinct heat treatments: first a solution heat treatment, followed by primary aging, and finally secondary aging. To achieve oxidation resistance, MCrAlY coatings are applied on the superalloy components as either environmental coatings or bond coats for thermal barrier coatings. In this study, the effects of different processing sequences on MCrAlY coating characteristics and short-term isothermal oxidation performance were investigated. Specifically, cold spray deposition of NiCoCrAlTaY coatings was carried out on single-crystal Ni-base superalloy substrates that underwent various degrees of the full heat treatments prior to being coated. The remaining required heat treatments for the superalloy substrates were then performed on the coated samples after the cold spray deposition. The microstructures of the CMSX-4 substrates and NiCoCrAlTaY coatings were characterized after each heat treatment. Isothermal oxidation performance of the coated samples prepared using different sequences was evaluated at 1100°C for 2 hours. The results suggested a promising procedure of performing only solution heat treatment on the superalloy substrate before coating deposition and then primary aging and secondary aging on the coated samples. This processing sequence could potentially improve the oxidation performance of MCrAlY coatings, as the aging processes can be used to effectively homogenize coating microstructure and promote a thin thermally grown oxide (TGO) scale prior to actual isothermal oxidation.

In this paper, a diffusion kinetic model was applied to simulate the microstructure development in a MCrAlY-superalloy system at high temperatures. Both simulation and experimental results showed that γ+γ’ microstructure was obtained in the coatings due to Al depletion after oxidation. With the help of the modelling, the mechanism of the formation of the diffusion zones in the single crystal (SC) superalloy can be also analyzed. The results revealed that the inward diffusion of Al from coating affected the depth of secondary reaction zone (SRZ) with the precipitation of TCP phases while the depth of inter-diffusion zone (IDZ) was decided by the inward diffusion of Cr.

This study investigates the potential of cold-sprayed tungsten coatings for use in nuclear fusion reactors. Three commercially available tungsten powders were selected from which six series of feedstock were prepared. The feedstocks were deposited on aluminum, steel, and stainless steel substrates using high-pressure nitrogen cold spraying. The coatings produced were characterized based on SEM, EDX, and XRD analysis and were found to be free of oxides with levels of tungsten that were previously unachieved. The results indicate that cold spraying is a viable technology for applying tungsten-base coatings to critical components in nuclear fusion equipment.

Light water reactors (LWR) use zirconium-alloy fuel claddings, the tubes that hold the uranium-dioxide fuel pellets. Zr-alloys have very good neutron transparency, but during a loss of coolant accident or beyond design basis accident (BDBA) they can undergo excessive oxidation in reaction with the surrounding steam environment. Relatively thin oxidation-resistant coatings on Zr-alloy fuel cladding tubes can potentially buy coping time in these off-normal scenarios. In this study, cold spraying, solid-state powder-based materials deposition technology has been developed for deposition of oxidation-resistant Cr coatings on Zr-alloy cladding tubes, and the ensuing microstructure and properties of the coatings have been investigated. The coatings when deposited under optimum conditions have very good hydrothermal corrosion resistance as well as oxidation resistance in air and steam environments at temperatures in excess of 1100 °C, while maintaining excellent adhesion to the substrate. These and other results of this study, including mechanical property evaluations, will be presented.

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.

Nickel-aluminum alloys are widely used in harsh environments due to their corrosion resistance, high melting temperature, and thermal conductivity. In this work, Ni-5wt%Al coatings were deposited by twin-wire arc spraying (TWAS) on tool steel using a design of experiments approach to study the effect of process parameters on coating microstructure and performance. Test results presented in the form of process maps show how N2 pressure, stand-off distance, and current affect in-flight particle velocity and temperature as well as coating thickness and oxide content. Using this information, optimized coatings were then deposited on test substrates and subjected, along with uncoated tool steel, to several hours of molten aluminum attack. The coated samples showed no signs of physical or chemical damage, whereas the uncoated substrates experienced oxidation, aluminum infiltration, and formation of Fe-Al intermetallics.

The effect of deposition pressure on the microstructure and ablation behavior of ZrB2 coatings deposited by very low pressure plasma spraying is investigated. The results show that under a chamber pressure less than 50 kPa, as the spray chamber pressure decreases, the porosity of the coating deposited at the same distance decreases, and the coating prepared under 100 Pa presents the lowest porosity of 1.79 %. Furthermore, among the ZrB2 coatings deposited at 100 Pa, 5 kPa, 10 kPa and 50 kPa, the dense coating deposited at 100 Pa showed the lowest ablation rate of 0.33 μm/s, 0.75±0.08 mg/s.

In this study, nitrogen is employed rather than helium to cold spray MCrAlY coatings at relatively low process settings. Recycling of the non-deposited particles during the spray is also explored, and the characteristics and cold sprayability of recycled powder are compared with that of as-received feedstock powder. The resulting MCrAlY coatings from the two powders, though different thicknesses, show similar dense microstructures, low oxide inclusion, and smooth surface finish, all of which contribute to improved oxidation behavior.

This work investigates the high-temperature oxidation kinetics of CoCrAlSiY coatings with different Si concentrations. Hot-corrosion resistance is determined at 800 and 900 °C via hot salt coating, thermal shock resistance is measured at 1050 °C, and the oxidation and corrosion products are analyzed through mineralogical and micro analysis. The results show that Si promotes the formation of an Al 2 O 3 film that improves oxidation and corrosion resistance, but excessive amounts reduce thermal shock resistance.

This study assesses the effect of laser melting on MCrAlY-coated copper substrates. CoNiCrAlY, NiCoCrAlY, and NiCrAlY powders were applied to copper alloy substrates by atmospheric plasma and HVOF spraying. Sample surfaces were then laser melted and coating properties were determined and correlated with coating composition, surface morphology, and cross-sectional microstructure. Laser melting not only caused the coatings to fuse to the substrate, but also precipitated the formation of an aluminum oxide surface layer that reduced the oxygen content in the coating. As a result of this finding, the coating samples were heat treated in order to measure their high-temperature oxidation resistance.

This study investigates how Al and Ta diffusion affects the growth of surface oxides in NiCoCrAlYTa coatings and the interdiffusion that occurs between coatings and single-crystal substrates in high-temperature oxidation processes. HVOF-sprayed layers were tested at temperatures between 900 °C and 1100 °C and the corresponding oxidation behavior of Al and Ta was assessed. It was found that higher amounts of Al in MCrAlY coatings promote the selective oxidation of Al 2 O 3 and that the addition of Ta increases the stability of the γ’-Ni 3 (Al,Ta) phase.

A novel composite MCrAlY coating with a fine dispersion of sub-micron Al 2 O 3 particles were sprayed by high velocity oxygen fuel (HVOF) thermal spraying for high temperature oxidation protections. The presence of Al 2 O 3 could reinforce the metallic MCrAlY coatings, in a similar way to ODS alloys (oxide dispersion strengthening). It could also enhance the oxidation resistance owing to the dispersion of Al 2 O 3 on the surface as nucleation sites, which promotes the early formation of a coherent α-Al 2 O 3 scale. This is essential for an effective protection against oxidation attack, especially for these applications at relatively lower temperatures (<900 °C) with slower growing Al 2 O 3 . In this study, a suspension route was employed to achieve a uniform dispersion of 0-10 wt.% Al 2 O 3 particles with commercial MCrAlY powders. A liquid fueled HVOF spray gun (MetJet IV) was used to deposit the composite MCrAlY-Al 2 O 3 coatings onto 304 stainless steels substrates. The composite coatings were examined thoroughly by field emission gun scanning electron microscopy (FEGSEM) with energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. Isothermal oxidation at 900 °C was carried out to study the effect of Al 2 O 3 on the growth of oxide on the coatings surface. The composite coatings exhibited superior oxidation behavior against the conventional metallic coatings with the formation of nearly exclusively Al 2 O 3 on the coatings surface and inhibited NiO growth.

MCrAlY(M=Ni, Co, or Ni-Co)coatings with good high temperature oxidation resistance have attracted great interest. They are widely used in gas turbines as protecting layers, such as thermal barrier coatings and seal coatings. Among many methods developed for preparing MCrAlY coatings, electroplating has drawn great attention due to its perfect bond strength, precise controllability, good coating ability for complex shape and so on. In this paper, the MCrAlY coatings have been prepared by a composite plating way. During this process, the CrAlY particles are wrapped with Ni clad layer. The thickness of the composite coatings is controlled at 150- 200 μm. The plating tests results indicate that the density of the clad layers mainly depend on the electroplating time. After that, these coatings are heat treated under the vacuum condition to make elements diffuse, forming homogeneous M(Ni)CrAlY component. The high-temperature oxidation resistance tests of the prepared coatings show good antioxidant ability at 1000 °C under air condition.

The work concerns a study of the properties of cold sprayed Ti coatings. This material is an attractive choice for many applications because it exhibits high strength-to-weight ratios, very good oxidation resistance, corrosion resistance and biocompatibility. Cold spraying is applied to deposit Ti coatings and elements as additive manufacturing process, however it needs higher critical velocity for deposition than other, more ductile metals. Nowadays nitrogen as cheap gas is used as working gas in cold spray process, however application helium as accelerating gas allows to obtain elements with higher strength. It allows to understand the mechanism of cohesion between sprayed particles. In carried out experiment Ti powder with angular shape was applied in the cold spraying process. The coatings were sprayed by means of Impact Innovations 5/8 system with nitrogen and addition of helium onto 7075 Al alloy. The investigations revealed that the cold sprayed Ti coatings with addition of helium as working gas exhibit better mechanical properties, lower porosity and roughness.