Abstract In general, similar MAX-Phase coatings are considered as oxidation protection layer for preventing disastrous reactions of the Zircaloy fuel rods during a cooling water failure in a nuclear power plant. For the present study on Aerosol Deposition, Ti3SiC2 was selected as MAX-phase model system due to the availability of property data and commercial powder. The as-received powder was milled to different nominal sizes. For revealing details on coating formation and possible bonding mechanisms, Aerosol Deposition experiments were performed for different particle size batches and process gas pressures. Microstructural analyses reveal that coating formation preferably occurs for particle sizes smaller than two microns. Using such small particle sizes, crack-free, dense layers can be obtained. The individual deposition efficiencies for the different particle sizes, particularly the critical size below which deposition gets prominent, vary with process gas flows and associated pressures. Detailed microstructural analyses of coatings by high resolution scanning electron microscopy reveal plastic deformation and fracture, both attributing to shape adaption to previous spray layers and probably bonding. In correlation to coating thickness or deposition efficiencies, respective results give indications for possible bonding mechanisms and a tentative window of Aerosol Deposition for Ti3SiC2 MAX-phases as spray material.

Abstract The porous architecture of coatings has a significant influence on the coating performances and thus should be properly designed for the intended applications. For simulating the coating properties, it is necessary to determine the numerical representation of the coating microstructure. In this study, YSZ coatings were manufactured by suspension plasma spray (SPS). Afterwards, the porous architecture of as-prepared coatings was investigated by the combination of three techniques, imaging analysis, Ultra Small Angle X-ray Scattering (USAXS), and X-ray transmission. A microstructural model for reconstructing the porous architecture of the SPS coating was subsequently computed according to the collected experimental results. Finally, the coating thermal properties were simulated based on the model and were compared with the experimental results.

Abstract Hybrid plasma spraying is emerging as the next potential technology leap in thermal spraying. The combination of high throughput and deposition rates of coatings sprayed from powders with the tailored functionality of liquid-feedstock sprayed coatings appears highly promising for a wide range of applications. Moreover, possible refined mixtures of different materials come readily with the utilization of multiple feedstocks with varying particle sizes. However, the practical aspects of hybrid coatings production are accompanied with several peculiarities not encountered when using distinct feedstocks. To deepen the understanding of this novel route, this paper presents fundamental hybrid coating formation principles and the effect of selected deposition parameters using multiple case-study material systems, such as Al2O3-YSZ, Al2O3-Cr2O3, and Al2O3-TiO2.

Abstract The pore microstructure of the spray coatings is complicated. However, it can be approximated with three systems, interlamellar pores, intralamellar cracks, and volumetric globular pores. This complex pore morphology can strongly influence the properties of the layer. This paper examines the NiCrAlY layers using the multi-small angle scattering technique to determine the pore system in detail. A model is created based on the analysis of the SEM examinations. The model shows that the inter-lamella system is of the utmost importance. Paper includes a German-language abstract.

Abstract Laser beam forming is a process in which metal is deposited directly, which combines the processes of high-performance laser alloying and the advanced method of rapid prototyping in order to be able to manufacture complex three-dimensional components directly. In this article, this technique is used to process Ni-based superalloys. Simple component geometries are used in order to be able to compare them with conventional alloys. The 718 superalloy is used. The characterization of the alloys produced included a complete microstructure analysis. Paper includes a German-language abstract.

Abstract With cold gas spraying, the particles of the spray powder are accelerated to speeds of over 500 m/s in a preheated gas jet. Due to the relatively low temperatures, the spray material does not melt in the gas jet, and the thermal load on the substrate is also low. This paper provides an overview of the state of the art of the system as well as layers and their properties. It shows a few examples of the applicability of the cold gas spray process. Various metals such as aluminum, copper, zinc, steel, nickel alloys, titanium, and niobium as well as powder mixtures and polymer powders have been sprayed onto a wide variety of substrate materials. The layers are examined metallographically and characterized. Possible applications are discussed on the basis of these results. Paper includes a German-language abstract.

Abstract Microstructural evaluation is a common approach for determining the quality of thermal spray coatings. The need for careful consideration of the mounting material is realized due to the inconsistent quantitative measurements attained, in this article, using automated image analysis to evaluate optical microscopic images. Various epoxy and embedding techniques are used. The layers selected for these investigations included both porous and dense, ductile EAS Cu-base layers, plasma-sprayed, porous nickel-aluminum, YSZ, tungsten carbide and dense HVOF-sprayed aluminum oxide-titanium dioxide, chromium carbide, and tungsten carbide layers. The results suggest a significant influence on the measured values and suggest that the embedding method must be carefully selected. Paper includes a German-language abstract.

Abstract Metallographic tests on thermally sprayed layers are fundamental components of the development of thermally sprayed layers and quality control during production. The aim of the investigations was to develop reliable and reproducible metallographic preparation methods for the different classes of layers. These methods should be able to reproduce the real microstructure of the layers. Layer preparation is expensive and cannot cover all combinations of parameters. Therefore, a statistical test plan was set up to optimize the metallographic preparation method. This paper presents the results of extensive investigations with a variety of polishing methods and their effects on the quality of the cuts. The main focus is on breakouts in the layer. The results show that the type of polishing cloth has an influence on the layer breakouts. The direction of rotation and the embedding medium have no significant influence on the quality of the cut. Paper includes a German-language abstract.

Abstract In this paper, the scope of the European Airline Committee for Materials Technology (EACMT) subcommittee was to standardize how thermal spray coatings are evaluated. In 1997, the EACMT working group defined the objectives for the sub working group for reviewing the total evaluation system of thermal spray coatings. Standardization of testing and manufacturing processes is a very important goal as all industries become more global in both the technical and business sense. The processes involved in the repair of aircraft engines are no exception to this world-wide trend. Original equipment manufacturers for the selection of thermal spray materials, laboratories are forced to use various criteria and systems for the examination and analysis of thermal spray coatings. Excellent progress has been made in elimination of non-value added test methods and special emphasis is being placed on defining a system for preparation of metallographic specimens and microstructural evaluation. Paper includes a German-language abstract.

Abstract In this paper, different methods for surface preparation are investigated before the MCrAlY adhesive layer is applied. Surface characteristics are analyzed and the adhesive layer is applied to surfaces consisting of nickel-alloyed superalloys using the low-pressure plasma spraying process. Various preparation processes are taken into account: dry and wet blasting with corundum, dry blasting with silicon carbides, and cryogenic cleaning with carbon dioxide. The properties of the nickel-base substrate surface before and after the preparation measures are examined from the point of view of the surface roughness morphology and hardness near the surface. The properties of the adhesive layer in the layer system are determined. These are determined by adhesion tests on the substrate and layer system by means of scratch tests and the LESAGE-CHICOT method. The layer thicknesses and the layer structure are determined by metallographic analyzes. The microhardness in the area of the layer and substrate is measured. Paper includes a German-language abstract.

Abstract As a rule, the main processes of friction surface destruction are contact fatigue damage, micro-contact grabbing wearing, abrasive, and oxide wearing. The considered mechanism of the mentioned processes proves that to reduce their intensity and harden friction surfaces it is effective to form surfaces of composite materials; containing Ni, Cr, Si, and Mn; hard structural inclusions (for example, a carbide phase); and a hard lubricant (for example, as molybdenum disulfide, calcium fluoride, and graphite). This paper presents studies on powders for thermal spraying of wear protection layers. The focus is on studies of the influence of the shape, size, and structure of mixed powders made of nickel and iron with dry lubricants, such as molybdenum disulfide and calcium fluoride, which are analyzed using SEM and metallographic methods. The examinations are supplemented by X-ray diffractometry. Paper includes a German-language abstract.

Abstract In order to properly characterize the entire deposition process, evaluation of the coating, including a reliable metallographic preparation technique which reveals the true microstructure, must be performed. Often, recommended metallographic sample preparation methods for thermally sprayed coatings are generic and are not tailored to specific materials. They are time-consuming and, in some cases, may provide inaccurate details (pull-outs, smearing, etc). This could lead to a wrong interpretation of the coating quality. The aim of the investigation was to develop new metallographic sample preparation procedures tailored to different types of coatings (metallic, ceramic, multilayer and composites), in order to reveal a more representative microstructure. A comparative study of different preparation procedures for the examination of various as-sprayed coatings is presented using an optical microscope. The coatings were deposited by atmospheric and vacuum plasma spray (APS and VPS) and high velocity oxygen fuel (HVOF) processes. A separate approach is recommended for choosing the right metallographic preparation procedure for ceramic, metallic, or composite coatings. Applied load and positioning of the mounted sample during preparation are identified as key factors in developing proper procedures. The microhardness of the coating must be considered when determining the applied load. Interesting practical trends in preparation procedures that may lead to superior coating representation and, in some instances, cost and time savings are presented.

Abstract Thermal Barriers Coatings (TBC) are mass-produced in several industrial fields: aeronautic, automotive or energetic industries. All production requires the same constant level of fest and reproducible quality control at the lowest cost. The metallographic process is the primary way to evaluate thermally sprayed coatings but it must be both highly very repeatable and fast, especially when metallography is used to keep the production at a constant level. Therefore the management and the organization of a metallographic laboratory is of prime importance in order to reduce the cost and to provide a quality structure. The present approach to the whole chain of characterization is based on the user's point of view. Generally speaking, metallographic control of widely used parts often seems to be considered to be an uninteresting and obtuse subject, since it has been in practice for so long. Despite the lack of the prestige associated with the subject, optimization of an appraisal post can provide very concrete and more importantly profitable, results.

Abstract The improvement of the tribologic characteristics of surfaces is an important application of thermal sprayed coatings. Also various ranges of application demand good antiadhesive characteristics. The tribologic and antiadhesive characteristics of fluorine containing polymers are very good. Since furthermore those polymers have the highest thermal resistance of all plastics it has been investigated if those polymers can be integrated in thermal sprayed oxide and carbide coatings. The aim was to improve the tribologic and antiadhesive characteristics. The processes Plasma- and HVOF-spraying have been used to apply the coatings. The polymers in the coatings were detected by examinations with the light-optical and the scanning electron microscope. To heighten the contrast for the light microscopy examinations the metallographic sections of the specimens were physically contrasted. To clearly identify the different phases with the scanning electron microscope EDX-analyses have been carried out. Samples have been tested to investigate the mechanical characteristics of the coatings. Paper text in German.

Abstract This paper provides results from experimental studies with regard to novel, thermally sprayed coatings for tribological applications, which consist of mechanical mixtures of cast iron powders (2.16% by weight C and 5.18% by weight Si) and solid lubricant (calcium fluoride or iron oxide) produced in an amount of 10 to 20% by volume. It was established that a basic phase of initial cast iron powder and detonation coatings is gamma-Fe and it is alpha-Fe in plasma coatings. Oxide inclusions which are products of cast iron oxidation are observed in coatings structure. Metallographic investigations showed an uniform distribution of solid lubricant inclusions in a metallic-matrix of coatings. Tribotechnical tests of coatings containing 20 vol. % calcium fluoride carried out in conditions of room temperature indicated that the best antifriction properties were obtained for coatings with calcium fluoride additions which were sprayed by supersonic air-gas plasma method. Paper includes a German-language abstract.

Abstract This paper contributes to the broadening of knowledge about process combinations in connection with thermally sprayed coatings. It describes the influence of a later annealing, nitriding, and carburizing on different thermal sprayed coatings. The connection between the processes is determined and optimal process parameters is adjusted for both processes. The paper analyzes the coating characteristics and the alterations of the substrate. The results of the metallographic and X-ray analysis as well as of the wear and corrosion tests are discussed. Prospects for possible further applications are given. Paper includes a German-language abstract.

Abstract This paper presents the electrochemical characterization of a chromium carbide-NiCr coating applied using high-speed flame spraying. It examines the behavior of the complete system, the steel, the steel coating, and the coating immersed in NaCl solution alone. The paper discusses electrochemical measurement methods such as the measurement of polarization resistance, anodic polarization, and open circuit potential. The tests are compared with each other and with results from metallographic examinations. The structure was characterized by light and scanning microscopy. In addition, an analysis of the residual water was carried out using an ICP technique. The paper also includes a study of the various mechanisms that could affect the behavior of such coating types in a corrosive environment. Paper includes a German-language abstract.

Abstract Laser shock processing (LSP) is a surface treatment similar to shot peening, in which the compressive stresses in the material are created by laser-induced mechanical impacts. The tensions are of sufficient intensity to modify the microstructure and properties. In this paper, the laser pulses are generated with a power density of 5 to 8 GW/centimetres square with a neodymium laser. The glass laser is used to treat Al+SiC composite coatings, which were initially applied using the high-speed oxygen fuel spray technique. The laser-processed samples are prepared metallographically and examined for their microstructure with a scanning electron microscope. The latter is also used to investigate the surface morphology of laser-treated samples. Finally, the microhardness and the vibration wear resistance of the coatings are tested and compared with the data obtained for the samples in the sprayed state. Paper includes a German-language abstract.

Abstract This article presents one of the most advanced technologies for the application of powder coatings, the detonation spray method. The devices for measuring the temperature and the velocities of the powder particles are presented and the results obtained are shown. The article deals with results from wear tests as well as from fatigue strength tests. The tests are carried out on the coatings of the Ni-Cr-B-Si type applied to C45 steel. In addition, X-ray examinations, linear distribution of the chemical elements, microhardness measurements and metallographic examinations are carried out. The coating properties of the detonation-sprayed layers are compared with the same coatings, which were applied by means of plasma or flame spraying. Paper includes a German-language abstract.

Abstract Thermally-sprayed coatings are applied to various materials to provide protection for beat-loaded parts as well as corrosion and wear. They also serve as a thermal barrier to reduce metal substrate temperatures. Microstructural analysis is used to characterize the substrate, the coating, and the adherence of the coating to the substrate. Accurate evaluation or these coatings depends heavily upon the quality of the polished surface produced by metallographic preparation. A well-prepared surface must first be free of plucked material and have minimal relief between the hard and soft constituents. The entire surface must be flat to allow a clear view of the interface and any reaction products that might be present in the coating or the substrate. Furthermore, the finished polished specimen must be scratch-free and have no resolution destroying films or stains. Various metal and oxide coatings on ferrous substrate material are used to demonstrate the excellent microstructural detail that is revealed when correct polishing procedures are used. These special techniques successfully address the problems normally encountered when preparing hard, brittle coatings or softer metallic coatings and substrates. As a result, clear microstructures are revealed across the specimen surface and valuable information is obtained.