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In order to extend the life of boilers by applying an anti-corrosion coating without the need to dismantle them, it is advisable to find coatings that can be applied using cheaper and portable techniques, such as Twin Wire Arc Spray technology (TWAS). In this study, we compare selected NiCr-based coatings and two uncoated steel substrates (steel 1.7715 and 1.4903). Two coatings, Cr3C2 - 25% NiCr and Hastelloy C-276 are deposited using High velocity oxygen-fuel technology (HVOF) and three coatings, NiCrTi, NiCrMo, and Inconel 625, are deposited using TWAS. In addition to the corrosion weight gain during 50 cycles of loading in an 18% Na2SO4 and 82% Fe2(SO4)3 salt environment at 690 °C evaluated using the gravimetric method, the microstructure and phase composition of the coatings were analyzed on the samples after the exposure in order to compare the properties and gain a deeper understanding of the corrosion kinetics. Coating cross-sections and free-surfaces were observed with a scanning electron microscope (SEM) with an energy-dispersive (EDX) system. The phase composition was investigated using X-ray diffraction (XRD) and Raman spectroscopy. No significant differences were observed between the TWAS and HVOF coating methods for the coatings compared. Due to the similar corrosion products found on all coatings, a very effective corrosion protective layer was formed on the surface, forming a barrier between the corrosive environment and the coating regardless of the used deposition technology. Therefore, for industrial use on the inner surface of coal-fired boilers we recommend NiCrTi, NiCrMo, or Inconel coatings prepared with the more cost-effective and portable TWAS technology.

The components of rail vehicles are strained by a number of sources, whether operational, natural, or effects caused by passengers. For protection against these influences, the number of types of surface protection is frequently used. The project called "Increasing of resistance of rail vehicles components by the means of modern thermal spraying technologies" deals with improving the performance and service life of rail vehicle components by thermal spraying. In the project, more than ten components are selected for coating by different material sprayed by different methods of thermal spraying. This paper is focused on coating made by Twin Wire Arc Spraying. Three materials of coating sprayed by TWAS were tested and their mechanical properties were evaluated in this paper. These materials are pure molybdenum, Fe13Cr, and Zn15Al. The Ball on Flat, Dry Sand/Rubber wheel Test, and Erosion Wear Resistance Test were done. The molybdenum coating showed very good sliding properties. This material can find its application for rolling components such as rollers, or rollers carriers. The Fe13Cr and Zn15Al coatings showed a very good erosion resistance. The Zn15Al had even a better erosion resistance than Fe13Cr. Both of these materials can be used, where this type of wear resistance is required, for example for walkable footplates. The Fe13Cr had also a very good abrasive resistance in contrast with Zn15Al, which can't be recommended for application where abrasion resistance is required. The spraying of real components is also shortly presented in this paper.

High velocity oxy-fuel spraying (HVOF) being one of thermal spraying techniques, is deployed in many commercial applications mostly for very hard wear and/or corrosion resistant coatings. Supersonic speed of the spraying jet combined with temperatures around 5500 K is utilized to spray most metals, metallic alloys, cermets and superalloys [1][2][3]. Typical HVOF coatings are compact, dense, with very low porosity, low to moderate oxidation level and high bonding strength to substrate [1]. Cermets and superalloys are standardly commercially applied HVOF materials, demanded for superb wear resistance, high hardness, abrasion and erosion resistance and overall great performance in high stress and/or high temperature environments. Proper testing methods are required to evaluate quality of deposited coatings and consequently choose coating with optimized properties for demanded application. There are many testing methods standardly and widely used for evaluating properties of thermally sprayed coatingssuch as superficial indentation, micro and nanoindentation on cross section of the coating, tensile adhesion strength test, many tribological tests, etc. [1]. This article concerns modified TCT (tubular coating tensile test) for testing cohesion strength of the coatings with the use of common tensile test equipment. In this paper, specimen assembly, coating deposition, testing procedure and calculation of results is described. Cohesion strengths of five HVOF commercial coatings: Stellite 6, Hastelloy C 276, Cr3C2-25NiCr, WC 10Co4Cr and NiCrFeSiBC are evaluated.

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