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 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.

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.

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.

In order to overcome the problem of insufficient abradability of existing metal based coatings that cannot meet the requirements of harsh working conditions, this article designs two types of metal based abradable sealing coating materials based on the particle structure of "peeling medium", and studies the basic performance and simulated working condition service performance of the coatings. The research shows that, after undergoing a 1000 hour heat exposure test at high temperature, the two coatings still maintain good hardness, bonding strength, and abradability, indicating that under long-term high-temperature service environment, the two coatings can fracture at the location where the abradable components are exposed, thereby maintaining the abradability and good thermal stability that meet the requirements of use.

Coating thickness is considered to be one of the most important characteristics of thermal spray coatings. Therefore, it has long been the goal to be able to predict the coating thickness that ensues when coating an arbitrary part. A commonly applied approach is to determine the coating deposit based on a series of spray spot tests and use that for modeling the coating. Another option is to conduct spray bead tests, which better reflect the conditions during the coating. This work suggests a novel approach for in situ acquisition of the spray beads and their analysis. The acquisition is based on a 3D camera to scan the sample before and after depositing of a spray bead. The approach allows for their streamlined evaluation, enabling better understanding of spray bead formation and their modeling. The suggested analysis of spray beads includes uncertainty evaluation. This enables estimation of model prediction uncertainties which has been omitted in previous works on the topic. The analysis shows that a relative expanded uncertainty of 10% (at 95% level of confidence) can be expected for the coating thickness prediction for the simplest scenario of coating a flat sample sprayed perpendicularly at a constant spray distance and spray speed.

The multi-layered thermal barrier coatings (TBC) are commonly used in the systems exposed to extensive heat, such as jet engines or gas turbines. The testing of coatings' performance is usually carried out using electric or gas furnace. Concentrated solar power (CSP) could provide cost-effective and environmentally friendly alternative using natural energy source. Moreover, it can also simulate materials exposure in real applications, e.g., in solar power-plants. In this study, possibility of using concentrated solar power to test the performance of hybrid YSZ-based TBCs prepared by hybrid water/argon-stabilized plasma (WSP-H) technology was studied for the first time. In service, TBC top-coat layer may be exposed also to so-called CMAS air-borne particles occurring in the atmosphere which may melt at elevated temperatures and penetrate the coating microstructure, inducing crystallographic and volumetric changes therein. Therefore, testing with the presence of CMAS particles was also included in this study to observe its influence on the coating microstructure under solar irradiation. Changes of the coating microstructures were studied using SEM analysis and X-ray diffraction.

Atmospheric plasma spraying (APS) is characterized by complex interactions between input, process and output variables. Process control relies heavily on human expert knowledge and experience. Process diagnostics can provide additional information to the operator and support cognitive processes in task execution. When using non-cascaded torch systems, significant plasma fluctuations occur, affecting the coating quality. High-frequency fluctuations can only be detected by suitable diagnostic systems and interpreted by experienced APS operators. In this study, the state of the plasma jet (area, fluctuation) is investigated depending on total plasma gas flow rate (50 vs. 65 l/min) and the H 2 content of plasma gases (17, 20 and 23 vol. %) using high-speed camera pictures. To evaluate plasma fluctuation effects, particle temperature and velocity as well as resulting coating properties (thickness and porosity) are determined for two ceramic systems. The results show that fluctuations of the plasma jet have a significant effect on the particle state and coating quality. The use of a high-speed camera to evaluate the stability of the plasma jet is an attractive method that, when properly integrated, has the potential to provide the human operator with important information to allow rapid assessment of input parameters or the condition of the plasma torch.

Additive Manufacturing (AM) processes offer geometrical freedom to design complex shaped parts that cannot be manufactured with conventional processes. This leads to new applications including aerospace propulsion systems where the Ni-superalloy based material has to withstand high operating temperatures. In this contribution, the influence of heat treatment and surface conditioning of the additively manufactured Inconel 718 substrates on the thermocycling performance of suspension sprayed YSZ coatings was investigated. The different surface conditions included as-built, sandblasted and milled substrate surfaces with and without heat treatment. YSZ coatings were applied using suspension plasma spraying (SPS) with commercial available suspensions. Thermal cycling tests (FCT) at 1100°C, 1300 °C, and 1500 °C were applied to coating systems until failure occurred. The microstructures of the samples were characterized before and after thermal cycling. The performance of the coatings was mainly influenced by the coating morphology and FCT test conditions and less by the state of the AM substrates. Columnar-like YSZ SPS sprayed coatings on AM Inconel 718 substrates seemed to be a promising candidate for rocket engine applications.

The development of thermal spray processes usually requires an analysis of the complex coating microstructure. In order to inspect critical areas of a coating, destructive testing methods such as the preparation of cross-sections are commonly used. In this work, the suitability of largely non-destructively measured polarisation curves for the quality assessment of thermal sprayed AISI 316L coatings is investigated. Therefore, a 3.5 % NaCl gel electrolyte was developed to prevent the corrosive medium from infiltrating the porous and micro-cracked microstructure characteristic for thermal sprayed coatings. In addition, a measuring cell based on the 3-electrode arrangement was designed to simplify the setup, reduce the measurement time and enable mobile measurements directly on the component surface at a later stage of development. The effects of process-related differences in the microstructure of HVAF and APS AISI 316L coatings on the polarisation curve was investigated by determining the corrosion current density. The microstructure of the AISI 316L coatings was analysed by optical microscope, SEM and EDS, focussing on the porosity and oxide content. The results clearly show that the potentiodynamic polarisation curves of the AISI 316L coatings differ significantly depending on the spray process used and microstructure created. Even small changes in the oxide content within a coating can be detected. Therefore, electrochemical measurement methods using gel electrolyte offer an interesting opportunity to evaluate the quality of thermal sprayed AISI 316L coatings in a largely non-destructive manner.

The scanning acoustic microscopy (SAM) technique is used for studying the character and interface quality of cold sprayed Fe coatings deposited onto notched Al-based substrates. Three notch geometries were used: a rectangular notch, a trapezoidal notch with a flat bed, and a trapezoidal notch with a cylindrical bed. Scanning electron micrographs demonstrated an increased porosity and cracks at the areas where the spraying direction was not perpendicular to the surface of the substrate. The SAM measurements were then performed on thin plates cut vertically across the notches such that the scanned area included the locations of the increased porosity and their surroundings. The resulting distributions of longitudinal wave velocities and their attenuation revealed that the affected area is more complex and the mechanical response of the coatings could be limited not only at areas of the visible porosity, but also in their vicinity.

In order to improve the quality of coating, the causes of defect are analyzed in this paper. The research innovative uses single factor experiment combined with MATLAB to fit out the relationship between porosity and laser power, scanning speed, thickness, overlap rate. The multivariate quadratic equation is derived in this paper. It provides a solution to avoid defects in the aspect of laser cladding process.

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.

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].

The advantages of UV-curing polymers are well known and used in various coating and adhesive applications. Curing times of a few seconds and long application windows allowing an increased throughput in series production. The use of UV-curing polymers in sealers is beneficial, but so far insufficient due to only surface curing. With a newly developed dual-cure mechanism in sealers, it is now possible to combine deep penetration curing and surface curing. The hybrid sealers combine radical polymerization with subsequent polyaddition or polycondensation. The development of sealers for thermal sprayed (TS) coatings involves an extensive requirement profile. This includes properties such as corrosion protection, penetration depth and processing times. High penetration depths of the sealant into the coating system are important to ensure a protection over the full lifetime of the TS coatings. The depth of penetration of the developed sealers into various TS coatings was determined by measuring the gas permeability in a specially developed test procedure. The corrosion protection effect in combination with TS coatings was determined by measuring the cell voltage. In summary, two UV dual-cure sealers have been developed to seal TS coatings with deep penetration and corrosion protection.

Thermally sprayed coatings can be used in structural health monitoring devices where the coatings can reveal defects in the real-time integrity of the component through changes in mechanical, thermal or modal properties during service. In this emerging application, the mechanical properties of the coating are strongly affected by the interfacial bond between the coating and the substrate. This paper presents an analytical study of the interfacial stress distribution based on piezoresistive-stress constitutive relation of a coating layer. Both a single layer coating- and a bilayer coating-substrate system were considered. An analytical solution of the interfacial stress was developed by solving a Fredholm-Volterra singular integro-differential equation of a coating-substrate model using Chebyshev polynomials. Numerical simulation was conducted to analyze the effects of geometric and effective material properties of the coating-substrate system on the interfacial stress distribution. It was found that the susceptibility of the piezoresistive layer to delamination primarily relies on thicknesses of the coating layers and the stiffness of the intermediary insulating layer and substrate.

Hydraulic turbines, valves, and pumps operate in environments where they are exposed to cavitation phenomena and corrosion, which can result in mass loss, leading to reduced performance and failure. HVOF spraying has been used to repair eroded surfaces on such components and new alloys are being developed to reduce repair costs. This investigation assesses the cavitation resistance of FeMnCrSiNiB alloy coatings deposited by HVOF spraying. Corrosion rates and oxidation potentials are measured under different conditions and compared to stainless steel coatings normally used on water turbine runners.

Aluminum castings have limited strength and stiffness and tend to exhibit brittle fracture behavior under fatigue loading. These properties can be significantly improved, however, as this study shows, by reinforcing cast aluminum parts with magnesium metal-matrix composite structures. In order to obtain a bond between the cast Al and fiber-reinforced Mg composite surfaces, Al alloy (Al 99 and AlSi 12 ) layers were deposited on the Mg structures by thermal spraying. The mechanical properties of the bonding were assessed via single-lap shear and adhesive tensile tests along with optical microsection analysis. Hybrid aluminum alloy AlSi 10 Mg castings incorporating coated Mg-MMC inserts were also produced and examined, validating the general approach, while revealing that heat input to the MMC structure must be reduced through design or process adaptations.

Nondestructive Evaluation and Testing (NDE&T) techniques have been played vital roles in property characterization, process development and quality control of various thermal spray coatings. Besides conventional NDE&T lab methods such as eddy current test (ECT) for thickness measurement and fluorescent penetrant inspection (FPI) for cracking detection, some latest NDE techniques have been developed, demonstrated and applied to evaluate and characterize thermal sprayed coatings recently. The improved and innovative NDE methods provide more capable and accurate measurement to inspect on surface morphology, 2D and 3D coating porosity, oxide content, interface debonding, as well as other types of coating features, defects or specific properties. In this work, some non-contact NDE techniques and their applications were investigated and discussed based on several case studies of thermal sprayed coatings. Laser confocal microscopy had been used for characterizing surface morphologies and roughness profiles of HVOF WC-based coatings with 2D and 3D mapping methods. In particular, thermal wave imaging and ultrasonic micro imaging methods were used to detect the suspicious existence of lateral coating separation within or at the MCrAlY coating-substrate interfaces. Laser dimension sensoring method exhibited the extended capability of in-situ coating thickening measurements on turbine blade and vane. The latest non-contact NDE techniques demonstrated their unique and strong capability for in-situ and ex-situ coating characterization, process and quality control and coating failure analysis.