Research and Testing Institute Plzen (Czechia)

This study investigates the fretting wear mechanisms of plasma-sprayed wollastonite-zirconia (CaSiO 3 -ZrO 2 , WaZr) composite coatings, both unreinforced and reinforced with carbon nanotubes (WaZr-CNT), for bioimplant applications. The developed coatings are compared with conventional hydroxyapatite (HA) coatings on titanium substrates. Microstructural analysis reveals that CNT reinforcement leads to a denser, more uniformly bonded WaZr-CNT coating through effective splat bridging and pore sealing. Mechanical characterization shows that WaZr-CNT coatings possess higher microhardness and lower elastic modulus than unreinforced WaZr coating. During fretting tests at a 200 µm displacement amplitude, the WaZr-CNT coating exhibited an approximately 83 % reduction in energy dissipation compared to HA coatings and a 75 % reduction compared to WaZr coatings, indicating significant improvement in fretting resistance. While HA and WaZr coatings underwent splat fracture and generated considerable amount of wear debris, the WaZr-CNT coating produced almost no debris and maintained intact splat boundaries. The novelty of this work lies in the development and evaluation of CNT-reinforced WaZr coatings that for the first time undergo fretting tests and demonstrate superior fretting wear resistance under cyclic sliding contact compared to unreinforced WaZr and conventional HA coatings.

The aim of the work was to assess the nature and causes of defects – cracks in the welds of membrane wall panel tubes (MW) of a thermal power plant boiler made of T24 steel. This steel is intended to produce MW evaporators and superheaters for power plant units operating in the area of supercritical steam conditions. Its advantage, compared to the originally used materials, is higher creep resistance. The main expected advantage of the steel was to obtain optimal properties of welded joints without subsequent post-weld heat treatment (PWHT).

Twin Wire Arc spraying (TWAS) is a well-established method to deposit metallic coatings to protect mechanical components from wear and corrosion. In this work were used coatings that can be divided into two groups: FeCr-based ones and NiCr-based ones. The microstructure, and mechanical properties such as hardness, adhesion, abrasion and erosion resistance were evaluated on these coatings. The wear behavior of the coatings was investigated by Solid Particle Erosion resistance test and by Dry sand/Rubber wheel abrasion test. The aim of this work is to study the wear mechanism by SEM observation of worn tracks.

Abstract This study evaluates the surface protection of a waste-to-energy boiler wall using the Eutronic Arc Spray Gun 4 HFH. The test involved coating a 3.2 m² section of the boiler membrane wall with four materials: BTW 58 (FeCr-based), METCO 8294 (NiCrMo alloy), TAFALOY 71T (Inconel 625), and Metcoloy 4 (FeCr steel). Before spraying, the surface was grit-blasted to SA 3 finish with a roughness of 75–100 μm. Coatings were applied both with and without a Metco 8450 bonding layer. Additionally, two high-temperature ceramic coatings—Fireside and Tubearmor—were tested. The wear tests were conducted on-site in the boiler's third pass. After one year of exposure, samples were evaluated for condition, wear, and scale formation. BTW 58 and TAFALOY 71T, particularly when combined with Fireside ceramic coating, provided the most effective protection.

This study investigates the application of infrared (IR) thermography for evaluating thermal-sprayed coatings, focusing on distinguishing coatings subjected to different thermal treatments and varying porosity levels.Experimental thermographic analysis demonstrated the capability of IR thermography to differentiate between coating variants.The Fourier transform method and phase analysis at low frequencies proved remarkably effective.This approach enabled the visualization of areas with differing thicknesses in the thermographic images and facilitated detailed analysis through phase-frequency plots.The results highlight the potential of IR thermography as a powerful, non-destructive tool for characterizing thermal-sprayed coatings, offering insights into their structural and thermal properties.This method holds promise for quality control and optimization in industrial applications involving thermal spray processes.

Cold spray deposition of metals and alloys has gained considerable attention due to its advanced applications across various industries. This technique offers numerous advantages, including the absence of phase changes and oxidation. However, the process presents challenges due to its inherent complexities. Plastic deformation is crucial for the successful deposition of powder particles during cold spray. Therefore, achieving an optimal level of plastic deformation is essential. Fracture toughness is one of the important properties that can help understand the degree of plastic deformation in cold-sprayed coatings. Yet, measuring fracture toughness in these coatings is challenging because most evaluation methods are destructive and require large sample sizes. This study investigates the feasibility of predicting the fracture toughness of cold-sprayed coatings. Specifically, the micro-scratching method is employed to predict the fracture toughness of cold-sprayed IN625 coatings. IN625 is selected because of its high-end applications in sectors such as nuclear, marine, and aerospace component manufacturing. In addition to evaluating fracture toughness, the deposited coatings undergo rigorous testing and characterization to establish the microstructure-process-property relationship. The scaling of frictional force and fracture toughness confirms the validity of using scratch data for fracture toughness calculations. Hence, fracture toughness of the resulting coatings was successfully evaluated.

The focus of this research is to examine the feasibility of using laser texturing as a method for surface preparation prior to thermal spraying. The experimental part includes the thermal spraying of a Stellite 6 coating by High Velocity Oxygen Fuel (HVOF) technology on laser-textured substrates. The thermal spraying of this coating was deposited both on conventional substrate material (low carbon steel) and on substrates that had been previously heat treated (nitrided steel). The properties of the coatings were analysed using scanning electron microscopy (SEM), optical microscopy (OM) and Raman spectroscopy. Adhesion was assessed through a tensile adhesion test. The results showed the usability of laser texturing in the case of carbon steel, which was comparable or even better than traditional grit blasting. For nitrided steel, the problem remains with the hardness and brittleness of the nitrided layer, which allows for the propagation of brittle cracks near the interface and thus reduces the adhesion strength.

The preparation of surfaces for coating processes is indispensable for maximal adhesion and good coating results. These technical surfaces can be treated by chemical, mechanical, or physical procedures. In thermal spray coating, grit blasting is a standard process for surface preparation. This mechanical roughening and activation of the surfaces is fast and easy to handle. On the negative side, the grit gets wasted and the generated pattern is inflexible. Therefore, attempts to substitute grit blasting with a laser application is discussed in this article. Herein, a theoretical evaluation of high‐speed laser surface texturing (LST) is performed to find limits and points for the optimization of these processes. To estimate the surface processing rates, continuous wave, nanosecond, and ultrashort pulse laser machined dimples and grooves are investigated, and results of the spray coatings are presented afterward. The steel substrates are coated with Stellite 6 and tungsten. Adhesion tests and coating structures are analyzed. In terms of the optimization of the laser texturing, in situ temperature measurements show the influence of the laser process speed on the thermal load of the substrate. The influence of the number of scanning repetitions on heat accumulation during LST is also analyzed.