In this study, nine coating systems of Yb 2 Si 2 O 7 /Si-HfO 2 EBCs with varying spraying process parameters were deposited on silicon carbide (SiC) substrates using the air plasma spraying (APS) process and an orthogonal experimental method. The effects of variations in spraying distance, current, and hydrogen flow rate on spraying power and coating bond strength were investigated.

The commonly used method for preparing EBCs is atmospheric plasma spraying (APS), but it has problems such as easy oxidation of the coating, low spraying power, and low substrate temperature, resulting in the coating having multiple pores, cracks, and insufficient density. The new plasma spraying physical vapor deposition (PS-PVD) technology can solve these problems. This article compares the microstructure, mechanical properties, and phase composition of EBCs prepared using APS and PS-PVD processes.

The primary goal of this research work is to enable methane decomposition in absence of inert conditions as well as comparatively lower catalyst activation temperatures using thermally sprayed optimized catalytic coatings. Preliminary tests of twin-wire arc thermally sprayed coatings of metal alloys confirm the decomposition of methane gas.

In the present study, isothermal oxidation behavior of two multi-layered thermal barrier coatings (MLTBCs) has been investigated. Moreover, the property of the produced coatings were compared with a conventional bilayered TBC. For this purpose, nanostructured and micro YSZ were used as ceramic powder feedstocks and TBCs were deposited by air plasma spray (APS) procedure.

This study investigates the effects of varying particle size and particle size distribution of stoichiometric Yb 2 Si 2 O 7 feedstock powder on SiO volatilization, Yb 2 SiO 5 secondary phase formation, and crack behavior in Yb 2 Si 2 O 7 EBCs.

In this study, we explore the optimization of aerosol deposition parameters to achieve novel TiO 2 -Fe 3 O 4 graphene oxide composite coatings. Our approach focused on systematically evaluating deposition parameters, including chamber pressure, number of passes, gas flow rate, and sample holder speed, to optimize coating performance.

This study focuses on the development of thermally sprayed coatings for magnetic data storage. In the con-text of Industry 4.0 and the associated digitization of production, there is more demand than ever for suitable data storage on components in order to be able to automatically identify and process products. The resistance of certain sprayed coatings to harsh environmental conditions, make them a promising alternative compared to other solutions for dynamic data storage such as the RFID chips already available on the market. This area of application results in the requirement for a high stability of the written data against external influences such as temperature, wear or interference fields. These requirements can be met by the tailored choice of material including a sufficient magnetic anisotropy of the sprayed coatings. The influence of the spraying process on the formation of the magnetic material properties in the applied coatings is discussed with the aim of being able to change and optimize them in a targeted manner. The characterization of the produced samples is done by structural and magnetic analysis methods

This work focuses on the processing and deposit by suspension plasma spraying (SPS) of ZrO 2 -based ceramic materials for Thermal Barrier Coatings (TBC's) applications. The system of interest is ZrO 2 -16mol%Y 2 O 3 -16mol%Ta 2 O 5 (16YTZ). This ceramic has been reported to keep a non-transformable tetragonal phase (t'-phase), suitable to overcome the thermodynamic limits of the mostly used conventional 7-8wt.% yttria stabilized zirconia (YSZ). The research consists into evaluate the t'-phase stability and performance of the 16YTZ SPS coating. Synthesis of 16YTZ and, the evolution of the resulting microstructure in the dense ceramic and in the coating are a central part of the study. Sintering behavior in dense ceramics prepared from both precursor derived and milled powders is evaluated. Microstructural characterization by XRD, SEM and RAMAN spectroscopy of the as-deposited ceramic coating is presented and discussed.

In this study, the in-situ technique was used to observe crack formation and growth in multilayer suspension plasma spray (SPS) thermal barrier coatings (TBCs). Utilizing synchronized three-point bending (3PB) and scanning electron microscopy (SEM), coupled with digital image correlation (DIC), we provide real-time insights into strain field dynamics around cracking zones. Bending-driven failure was induced in both single and composite-layer SPS coatings to investigate the crack behavior in these columnar-structured multilayer TBCs. The real-time observations showed that columnar gaps can facilitate crack initiation and propagation from the coatings' free surface. The composite-layer SPS coating exhibits lower susceptibility to vertical cracking than the single-layer SPS coating, possibly due to the presence of a gadolinium zirconate (GZ) dense layer at the coating's free surface that enhances the bonding strength within the coating's columnar structure. The splat structure of the bond coat (BC) layer contributes to the crack path deflection, thereby potentially improving the SPS coating' fracture toughness by dissipating the energy required for crack propagation. Moreover, it was revealed that grit particles at the BC/substrate interface seem to promote crack branching near the interface, localized coating delamination, and serve as nucleation sites for crack development. Hence, optimizing the grit-blasting process of the substrate before BC layer deposition is crucial for minimizing the possibility of crack formation under operational conditions, contributing to enhanced durability and prolonged lifespan. This study underscores the critical role of in-situ observation in unravelling the complex failure mechanisms of multi-layered coatings, paving the way for the design of advanced coatings with enhanced structural complexity and improved performance for more extreme environments.

The ingestion of siliceous particulate debris into the gas turbine engines during operation caused the deposition of so-called CMAS (calcium-magnesium-alumino-silicate) on the hotter thermal barrier coating (TBC) surfaces. The penetration of these particles into the TBC at temperatures above 1200°C caused the loss of strain tolerance and premature failure of the TBCs. To mimic real-world conditions, a commercially available CMAS precursor dust powder was sprayed onto 8YSZ coatings using an atmospheric plasma spraying process. The substrate temperature was maintained at an average of 1100°C and 525°C during spraying. The effect of the spraying parameters on the deposition, microstructure, and composition of the CMAS coatings was investigated. In addition, to understand the CMAS build-up on the high-temperature surfaces, the CMAS splat formation behavior was also analyzed on the polished samples at temperatures ~1100°C. SEM/EDS analyzes were performed to identify and quantify the elements of the CMAS deposits. It was found that the surface temperature, deposition time, and different nozzles could play a significant role in having different phases of CMAS deposits.

This contribution gives an overview concerning basic principles of cold spraying (CS) and current trends in respective applications. As powder spray technique dealing with solid impacts, cold spraying results in coatings of high purity and unique properties, not attainable by other spray methods. Particularly within the last two decades, cold spraying developed from laboratory scale to a reliable industrial process. The presentation summarizes current models and key parameters in order to achieve and to improve bonding and coating qualities, and gives examples for applications in electronics, mechanical part repair and additive manufacturing.

Previous own works revealed that novel partially amorphous Fe-based alloys have a combination of proper-ties that are beneficial for the application in liquid hydrogen (LH2) tanks, viz low thermal diffusivity, little porosity, and good adhesion. The influence of cryogenic temperatures or hydrogen on coating tensile strength, on the other hand, has not been investigated yet for this material. However, this is crucial for the long-term durability of the coatings under hydrogen and other alternative fuels. Thus, in this work, tubular coating tensile (TCT) tests were performed at room temperature and cryogenic temperatures. In addition, hydrogen charging was carried out to identify a possible regime that is sufficient for TCT tests under the influence of hydrogen. Subsequently, the fracture surfaces were evaluated analytically, optically and profilometrically. Under cryogenic conditions, a significant increase in tensile strength and a finer structure of the fracture surfaces was observed.

One of the promising thermal barrier coatings (TBC) options for use above 1250 °C has been La 2 Ce 2 O 7 (LC). This work explored the role of dual layered ceramic coatings in the top layer of the TBC system that has been prepared using atmospheric plasma spraying (APS). Above the NiCrAlY bond coat, 8 mol.% yttria stabilized zirconia (8YSZ) coating has been deposited with optimized APS parameters. Over the top layer (8YSZ), another layer that comprises composite with LC and 8 wt.% of 8YSZ (spray dried) has been deposited. Investigations into the hot-corrosion behavior of 8YSZ-LC based TBC subjected to Na 2 SO 4 +V 2 O 5 salt at 950 °C for 4 hours. A porous layer made mostly of LaVO 4 , CeO 2 , CeO 1.66 and YVO 4 was developed on the LC+8wt.% YSZ layer after being subjected to a hot corrosion test in Na 2 SO 4 +V 2 O 5 salt. Dissociation of LC and 8YSZ leads to the formation of new phases, such as CeO 1.66 , CeO 2 , LaVO 4 and YVO 4 as the corrosion by-products in the extreme environment. The findings indicated that delamination has occurred due to the phase transformation, cavities and cracks in the 8YSZ-LC based TBCs. The molten salt's hot corrosion mechanisms of the 8YSZ-LC based TBC are discussed in detail. Further, the potential use of 8YSZ-LC based dual coatings and scope for the future work have been derived from the current study.

Hybrid plasma spraying combines deposition of coatings from coarse powders and liquids (suspensions or solutions) so that the benefits of both routes may be combined. In this study, failure evolution of early-stage thermal barrier coatings (TBCs) with hybrid YSZ-YSZ and YSZ-Al 2 O 3 top-coats deposited by hybrid water/argon-stabilized plasma torch was evaluated. In-situ bending experiment was carried out in SEM to assess potential influence of the secondary miniature phase addition on the coating failure during mechanical loading. Adapted high-resolution open-source strain-mapping code GCPU_Optical_flow was used to track evolution of the local coating failure. For the tested coatings, addition of miniature phase did not weaken the hybrid coating microstructure as the crack propagation was practically insensitive to the presence of the secondary phase and dissimilar splat boundaries. Main micromechanisms of the top-coat failure were thus splats cracking, loss of cohesion (splat debonding), and mutual splat sliding.

Suspension plasma spraying (SPS) is increasingly studied to produce finely structured coatings with dense and columnar microstructures for promising thermal barrier coatings especially in aerospace application. However, this process involves many parameters and complex phenomena with large spans of time and space scales in many physical mechanisms, like droplet break-up, liquid droplet evaporation, and various physical phenomena occurring within the suspension droplet, making it difficult to master. Especially, understanding the interactions of liquid drop submitted to plasma with the submicronic suspended particles is essential for material process optimization and control. For SPS understanding, a meaningful modelling of suspension treatment requires a prior analysis of these physical mechanisms and their characteristic times. This study details the different phenomena, their significance and characteristic timescales as well as the selection of the main governing forces acting between the different continuous and discrete phases (plasma, liquid, submicronic particles). We explore associated mechanisms: droplet breakup, carrier liquid evaporation, convective mixing and submicronic particle diffusion within the droplets. These mechanisms involve mass and heat transfer, that should condition particle agglomeration morphology before melting.

Thermally sprayed coatings of self-fluxing alloys are mainly fused using an autogenous flame. This subsequent fusing step reduces the porosity of the coating and achieves a pronounced metallurgical bonding. Therefore, an enhancement of the coating adhesion and intersplat cohesion as well as the corrosion and wear resistance are achieved. During this non-automated fusing step, the coating quality is significantly influenced by the operator's handling of the flame fusing process. By means of an alternative fusing using laser, can improve the reproducibility and automatability. In this work, the effect of different laser parameter settings and structural defects on fusing depth, microstructure evolution and tribological properties of thermally sprayed self-fluxing coatings and bulk materials is discussed. Gas atomized powder of conventional NiCrBSiFe self-fluxing alloy was processed by powder flame spraying and by spark-plasma sintering (SPS) as reference state. The findings reveal the potential of laser fusing to achieve a significant improvement in the coating quality and property profile of a wide variety of initial structures related to the process conditions.

Coating adhesion by thermal spraying method requires sufficient surface roughness on particle scale particles impacting the surface, particularly in the case of plasma spraying with particle melting state. Grit blasting process is mainly used to create the fine asperities required for spread particles to adhere. To further increase adhesion, the use of laser texturing for metallic substrates is benefit and is already well documented in literature. In the case of ceramic substrates such as alumina, grit blasting with corundum particles is no longer effective in creating a roughness of a few micrometers. Laser texturing therefore appears to be a potential candidate for generating adhesion in coatings. In this work, adhesion mechanisms of three different coatings produced by Atmospheric Plasma Spraying (APS) on a textured alumina substrate were investigated. The influence of substrate surface texturing by two different laser methods, a pulsed nanosecond laser and a continuous laser, was studied. YSZ was chosen as a potential Thermal Barrier Coating (TBC) and Al 2 O 3 and Y 2 O 3 were selected as bondcoats to observe the variation of adhesion mechanisms on ceramic substrates. Textured patterns and coating microstructures were observed by numerical and electron microscopy. Different adhesion mechanisms occurred depending on coating material. Either the geometrical parameters of the pattern and the surface roughness developed by a nanosecond laser and a continuous laser respectively, can promote mechanical anchoring and thus, a real adhesion.

Bond coats are used to protect the superalloy from oxidation and to serve as a bond between the ceramic thermal barrier coating (TBC) layer and the superalloy. During high temperature exposures, a thermally grown oxide (TGO) layer forms between the bond coat and the topcoat due to oxygen diffusion, leading to coating failure in the components. This study aimed to investigate the microstructure evolution of three TBCs with different cold-sprayed bond coat alloys after undergoing isothermal heat treatments. The TBCs were heat treated at 1100 °C for durations of 12, 25, and 50 hours to observe the effects of temperature on the microstructure and phase distribution. The microstructure of heat-treated bond coat alloys was examined using scanning electron microscopy and x-ray diffraction. The findings are discussed in relation to the characteristics of the coating alloy and the application process.

To achieve the optimum quality of thermal spray coating, the material must be applied by controlled, smooth and steady movement. This is best executed by robots. Complex geometries such as hydro turbine parts, hot gas casings or gas turbine blades are difficult to coat with common methods of robot programming such as teach-in. These methods take longer time and tedious calculations to generate robot coating paths. SoftART - a Switzerland based company - has developed a software-based offline programming process to produce robot paths quickly and accurate for an optimized coating result. Based on the 3D-model of the workpiece, the target points of the robot are calculated in a line pattern. Then, the spray direction for each point gets determined with optimized spray angle, considered collision avoidance and robot reachability. Based on this raw data, the line movement will be smoothed to avoid uneven accelerations of the robot axis to produce a uniform coating result. Finally, the data gets postprocessed and a robot specific, ready to run movement program will be generated. This offline programming process is well tested on many different parts and industries and fits best when you have either a complex geometry or many similar parts, which must be coated individually.

Whenever farming tools are used, the focus is on wear resistance. As the wear rate differs with local soil conditions, the progress of wear and thus the time for tool change is difficult to identify. Hence, component failure and breakage as well as the unknown retention of components or parts thereof in the field are possible undesirable consequences. This demands not only a better wear-resistant coating, but also a wear limit indicator to determine the time for tool change more precisely. This helps in reducing the fuel consumption and increasing the quality of soil. Therefore, the aim of this study is the development and application of a coating system with increased wear resistance compared to original OEM parts (Original Equipment Manufacturer) and integrated optical wear indication. Preliminary own tests demonstrated that arc-sprayed hard-facing coatings can increase the wear limit. Thus, in the current work two different types of thermal sprayed coatings are analyzed with regard to their wear resistance behavior. After positive wear test results, field testing on farmland was carried out. Further investigations concerned microstructure, optical as well as profilometry surface analyzes.