The system of atmospheric corrosivity classification was specified by ISO EN 9223 and this system is implemented into other standards for protective coating choice (paint coating, metalic coating, duplex system, etc.). The corrosivity category is also important for accelerated testing of choosen protective systems - duration of test. Due to changing and varying environmental situation in Europe the actual data is necessary to use the suitable values. The specific microclimates are presented too.
In the present study, surface laser boronizing technique was applied to improve wear resistance of maraging steel (MSt) parts manufactured by selective laser melting (SLM). Samples for investigation were manufactured of DIN 1.2709 steel powder using Concept Laser M3 equipment. Continuous 1 kW CO2 laser was applied at 0.5-4.0 mm laser spot and 250-1500 mm/min laser operating speed, providing power density between 796 and 50955 W∙cm-2 and heat input between 4.0 and 24.0 J∙mm-1, respectively. Before laser-processing, amorphous boron paste was preplaced on samples surface. The appropriate melt pool geometry was applied at 0.5 mm laser spot, for which XPS analysis revealed increase in boron concentrations from ~3.1 to ~5.7 wt. % with laser speed increase from 500 to 1500 mm/min. XRD analysis revealed domination of Fe3B type borides along with presence of FeB, Fe2B type borides and presence of reflections attributable to austenitic and martensitic phases. The microstructure of laser-boronized layers exhibits evolution from fine dendritic boride-based eutectic plus Fe-based solid solution microstructure having ~630-780 HK0.5 hardness (at 500 and 750 mm/min laser speed) to superfine lamellar nanoeutectic (at 1000 and 1250 mm/min; ~1000-1030 HK0.2) and further to submicron-sized grain boride structure (at 1500 mm/min; ~1770 HK0.2). The obtained hardness is up to three times higher than that of MSt after aging (~600 HK), indicating that laser boronizing technique may be promising in term of the improve of MSt wear resistance.
DLC films have special properties, which are of great interest in fields of tribology, including the high hardness and the low coefficient of friction. These properties are limited because of shortcomings in adhesion of DLC films on steel. So far, metallic adhesive layers like titanium and chromium are established options for the improvement of the adhesion of DLC films on steel. However, it is hardly investigated how plasma nitrided surfaces increase the adhesion by itself.
Starting point for this research were the different surface modifications, which can occur through plasma nitriding. The surface can consist of a compound layer of γ ‘-nitride and/or
ε-nitride or it is also possible that there is no compound layer. These surface modifications differ in their composition, crystal structure, bond type, as well as their solubility and diffusion velocity of carbon.
By means of a two-stage nitriding process, it was ensured that the hardness depth profile of all three surface modifications were similar. Thus, the “eggshell” effect should have no significant influence on the research. Afterwards, the nitrided specimens were DLC coated by PACVD. Tests, executed on a scratch test rig, indicate that plasma nitriding can improve the adhesion of DLC films. LC2 values of up to 60 N could be achieved. Typical values of LC2 DLC films with metallic adhesive layers are about 25 N. During the investigations, it also became apparent that adhesion in this system is influenced by other factors, such as environmental conditions and polishing processes.
Cold spray (CS) is a promising technology for the restoration of worn parts manufactured from numerous materials. The most important benefits are the preclusion of phase transformation caused by bonding by plastic deformation at low temperatures, providing oxide-free coatings with internal compressive residual stresses. The deposition of Ni-superalloys, namely Inconel, is a challenging task due to the insufficient acceleration of powder particles while using nitrogen as a processing gas. This leads to a low deposition efficiency (DE) and the formation of rather low-quality coatings. This study presents the first results of the restoration of artificial defects fabricated on a real turbine blade manufactured from Inconel 713LC (substrate) and the influence of the substrate preheating. This work aims to validate the Inconel 713LC as a material suitable for cold spraying. The powder particles, substrate, and coatings were characterized by the scanning electron microscopy (SEM). The powder particle size varied from 22 to 53 µm. The X-ray diffraction was performed to assess the phase composition and the hardness measurement for comparison of the powder particles and the coating hardness. Metallographic analysis was conducted to study the interface between coating and artificial defects and to evaluate the restoration capability of cold sprayed Inconel 713LC. The Inconel 713LC coating was successfully deposited onto the real turbine blade with artificial defects. The geometry of defects has a significant influence on the quality of the coating. Phase transformations studied by means of X-ray diffraction were not detected.
The boronizing is a thermochemical process in which the boron atoms are introduced into the steel surfaces. During this process, the boride layers with high hardness, wear- and corrosion-resistance are formed. In this study, the RoyAlloy (0.05 wt.% C; 12.6 wt.% Cr; 0.4 wt.% Si and 1.2 wt.% Mn) steel was powder-boronized at 900, 950, 975, 1000 or 1050 °C, and for 1, 3, 5, 7 or 10 h. The boronized samples were analyzed by X-ray diffraction analysis (XRD) to analyze their phase composition, and by scanning electron microscope to analyze their thickness and morphology at the interface with the substrate. To investigate the chemical elements redistribution during the boronizing process, the EDS mapping and EDS point analysis were used. The treatments produced boride layers with a thickness from 8 to 168 µm, depending on the boronizing parameters. During the boronizing process, the chromium was redistributed between the boride layers, where creates the chromium borides, and the transient region underneath the boride layers, where creates the particles with the biggest amount of chromium. The slightly higher amount of chromium was found in Fe2B layer, compared to the FeB layer. The silicon was focused at the layer - substrate interfaces. The concentration of manganese was slightly higher in substrate compared to the boride layers.
The possible differences in the protective performance of Zn and MIO pigmented epoxy coating for different times of exposure performed in 0.05 M NaCl were confirmed by new interpretation of ENA data in combination with single frequency (1kHz) impedance test results. By this approach changes of resistivity and dielectric constatnts (identified on tested coating systems in the end of the exposures performed in diffrent time) can be related to the delamination tendency as well as changing possibilities for new defects formation in tested type of coating for longer times of exposure.
Laser cladding, which is surface modification technology, is based on melting with a laser beam by spraying powder on the base metal and generated by depositing the layers. In this study, the Metco 42C martensitic stainless steel powder material was cladded on the FGS600-3A ductile cast iron used in sheet metal forming molds. The effect of energy input on porosity and microhardness was investigated. The digital image processing method was used for porosity analysis. The energy input had a significant effect on the pore formation. The lower energy input (1.1 kW laser power, 14 mm/s scanning speed) resulted in lower porosity. The cladding thickness varied depending on the scanning speed parameter due to affecting powder efficiency, high thickness was obtained at 6 mm/s low scanning speed. In the upper layer of the cladding, high hardness values were achieved due to the martensitic phase formation. The bottom layers of cladding had lower hardness values because of the tempering of the hard martensitic phases by subsequent cladding processes. Significant increase in hardness at cladding zone was attributed to carbon transfer from the base metal. This remarkable increase in hardness was much higher at lowest energy input (1.1 kW laser power and 14 mm/s scanning speed). However, it is clear that this will increase the risk of crack formation because of brittleness. On the other hand, at the higher energy input, this significant increase in hardness is at a lower level due to rest-austenite formation and excessive annealing with subsequent cladding processes.
Infrared thermography is a fast and illustrative nondestructive testing method, which is widely used for the inspection of metallic and non-metallic materials. Previously it was used mostly for defects indication. However, modern devices and software allow an application of a quantitative estimation of parameters of the defects. This contribution presents a novel infrared thermographic method for quantitative defect depth estimation. The majority of known thermographic techniques are based on a 1D heat transfer model and does not take into account 3D heat transfer. These methods are applicable only for large defects, in which lateral size can be assumed as infinite. In contrast, the presented technique takes into account the lateral dimension of defects and a finite thickness of the tested material. The method is based on a modification of the 1D analytical solution obtained by Almond et al. and a nonlinear optimization procedure. The algorithm was verified by numerical modelling and experiments. The applicability of the method for the defect depth evaluation in the steel parts was demonstrated.
Laser cladding is a modern technology for the repair of forming tools. The paper describes the optimization of the cladding and the main process parameters monitored, It discusses the comparison of several cladding powders of H13 tool steel, M300 maraging steel and Capilla 66 martensitic steel. The microstructures and mechanical properties and their influence on the resulting tool life are documented. The lifetime is verified on real tools in real operation.
This paper investigates the influence of thermal spray parameters of high velocity oxygen fuel (HVOF) process on the properties of cermet coatings prepared from commercially available Amperit 551 WC-CrC-Ni powder. Three different processing parameters were applied in order to optimize the production process and achieve preeminent mechanical properties and fully dense material without microstructural defects. The deposition was carried out by GLC5 gun and the powder particles velocity and temperature in spray stream were monitored by Accuraspray Tecnar diagnostic tool. The quality of deposited coatings was analyzed by means of light microscopy, scanning electron microscopy, and X-ray diffraction. The chemical composition of used powder and sprayed WC-CrC-Ni coating was determined by energy dispersive spectroscopy. It was found that the spray parameters have a negligible effect on the resulting microstructure and phase composition of the coating. However, the porosity and surface roughness were significantly affected by the variation in process parameters. To assess the basic mechanical properties of HVOF sprayed coating instrumented Vickers hardness measurements were utilized. The coating hardness reached mean values over 1500 HV 0,1 and the indentation modulus varied from 168-279 GPa.
Superalloys are used in a wide range of application areas in aviation, aerospace and nuclear energy industries. Inconel 718 is a nickel-based superalloy that provides remarkable mechanical properties and surface stability at elevated temperatures. The surface of Inconel 718 can be modified by several techniques in order to further improve its surface properties such as oxidation and wear resistance. Among several surface modification techniques, hot-dip aluminizing (HDA) is a highlighted one as an easy and cost-effective technique. It is also one of the high temperature coatings (HTC) techniques that utilize diffusion mechanisms. In the scope of this study, effect of HDA and subsequent diffusion annealing (DA) on high temperature wear behavior of Inconel 718 superalloy were investigated. Inconel 718 samples were first hot-dip aluminized in an Al-12 wt.% Si molten bath at 700°C for 2 minutes and subjected to diffusion annealing at 700°C for 10 hours afterwards. Morphological and structural analyses were carried out by using SEM-EDS and XRD, reciprocating wear tests of bare, HDA and HDA+DA samples were conducted at room temperature, 300°C and 600°C. The results revealed that aluminum rich and nickel rich aluminide phases were formed after HDA and HDA+DA processes, respectively. Wear tests results showed that the wear rate of the HDA+DA sample was approximately found to be three times lower than the HDA samples and four times lower than the bare Inconel 718 at room temperature. With increasing temperature, the wear rate of the bare alloy continuously decreased, while higher wear rates were observed for HDA +DA samples at elevated temperatures with respect to that of room temperature. Dominant wear mechanism was discussed based on the wear track morphology examined by SEM.