Chromium Coatings Research Articles

Fuel performance modelling of Cr-coated Zircaloy cladding under DBA/LOCA conditions

Chromium coatings are being developed for advanced technology fuel (ATF) claddings, offering negligible corrosion during normal operation, improved resistance to high-temperature steam oxidation, and superior high-temperature strength, the latter two being of utmost relevance during design basis accidents (DBAs). Demonstrating the improved response of Cr-coated Zircaloy requires the development or extension of fuel performance codes to coating simulations.In this work, material models and correlations for Cr-coated Zircaloy cladding have been derived or obtained from the literature and implemented into TRANSURANUS and the FRAPTRAN-TUmech suite. These extended tools have been used to simulate two complementary LOCA tests: QUENCH-L1 rod 4 (out-of-pile bundle test on fresh Zircaloy cladding) and IFA-650.10 (in-pile single rod test on high-burnup Zircaloy-UO2 fuel), enabling a gradual cross-verification of results between codes and a comparative performance analysis between coated and uncoated cladding.The results indicate negligible impact of coating properties other than creep on the burst time. While the superior high-temperature creep resistance of coated cladding slightly delays the burst time, additional burst data would be necessary to draw sound conclusions on the balloon size. Regarding the modelling approach, treating the coated cladding as a composite material through the definition of effective properties might result in worse performance relative to uncoated cladding, contradicting experimental observations. Therefore, the separate modelling of the coating and the cladding is recommended.

Evaluation of wear and corrosion resistance in acidic and chloride solutions of Cathodic Arc PVD chromium nitride coatings on untreated and plasma nitrided AISI 4140 steel

Chromium nitride ceramic like coatings are well known for their hardness and wear resistance, especially under severe conditions. When deposited on mild steel, nitriding is required for such applications to create a gradient hardness profile and improve the coating adhesion and the system's mechanical properties. Corrosion resistance is also necessary since these chromium coatings are recommended for applications in the plastic mould and injection industry. Therefore, in this work, the combination of a nitriding without white layer pretreatment and CrN coating was studied in a chloride and an acidic electrolyte, to asses if the diffusion layer also plays an important role as a corrosion protection treatment. Coating microstructure, adhesion to both nitrided and non-nitrided steel, wear resistance, and corrosion resistance in chloride and acidic media were evaluated. For comparison, bare and nitrided steel were also examined. Results indicated an improvement in the adhesion for the duplex treatment (nitriding + CrN). The CrN coating demonstrated a considerably lower coefficient of friction and wear rate compared to both non-nitrided and nitrided steel. Regarding corrosion, the iron nitride layer provides some protection in chloride environments; however, in acidic media, only the CrN coating plays a protective role. In both media, localized attack occurred at sites where the coating had defects, such as pores or pinholes through which the electrolyte comes into contact with the substrate. The duplex treatment proved to be the most effective surface treatment for AISI 4140, achieving excellent tribological properties, good adhesion, and high corrosion resistance in both neutral chloride and acidic solutions.

Improving the tribological and corrosion behavior of Ni[sbnd]B coating with low boron content from optimized lead-free bath on aluminum alloys

This study focuses on producing environmentally friendly, lead-free nickel‑boron (NiB) coatings as an alternative to hard chromium coatings. Using the electroless method, the NiB coatings were fabricated from a lead-free bath, and the effects of varying B and Ni concentrations on the coatings' chemical composition, surface morphology, hardness, corrosion resistance, and wear performance were investigated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to analyze surface morphology and phase composition. Corrosion performance was evaluated using potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS), while wear behavior was tested at sliding speeds of 20, 30, and 40 cm/s. The study highlights the critical role of sliding speed on wear mechanisms, friction coefficient, wear rate, and surface morphology. The analyses revealed that the optimal NiB coating, containing 34 g/L Ni and 3 g/L B, exhibited the highest hardness, the lowest corrosion rate, and the highest wear rate performance. The values obtained from these analyses were 891 HV for hardness, 8.87 × 10−6 mpy for corrosion rate, and 2.21 × 10−4 mm3/N·m for wear rate. The use of analysis of variance (ANOVA) identified key factors influencing these properties. The findings suggest that optimizing boron and nickel concentrations significantly enhances NiB coatings' corrosion resistance and wear performance, making them suitable for industrial applications.

STRUCTURE FORMATION OF Ni−P ALLOY ELECTROCOATINGS WITH INCREASED CORROSION RESISTANCE

Purpose of research. The main factors that reduce the protective properties of electrocrystallized coatings are the formation of volumetric defects − pores, as well as the occurrence of microgalvanic couples at grain boundaries, that is, on surface defects of the crystalline structure. Creating a non-porous structure in electrocoatings, eliminating the formation of surface defects in metal/alloy layers, as well as the possibility of replacing chromium coatings, which are obtained from toxic electrolytes, are urgent tasks. Materials and methodology. In the work, it was proposed to use electrocoatings with Ni−P alloy as protective layers on products that increase corrosion resistance. An X-ray determination of the phase composition of Ni−P electrochemical deposits was carried out. The surface morphology and corrosion resistance of coatings were studied. Results. Samples of electrochemical coatings of pure nickel and nickel-phosphorus alloy were studied. It has been established that during the formation of nickel coatings with the addition of phosphorus ions, the surface morphology has practically no pores, amorphization of deposits occurs, due to which the protective properties, namely, corrosion resistance, are improved. Scientific novelty. Factors have been identified that influence the increase in corrosion resistance of coatings − the absence of a porous structure and the formation of an amorphous state. Conclusions. The influence on the structure and properties of electrochemical coatings of a nickel-phosphorus alloy has been studied. It has been established that the addition of phosphorus ions to the nickel plating electrolyte leads to the formation of an amorphous structure in the coatings, and layers of the Ni−P alloy appear practically without the presence of pores. It has been established that the effect of increasing the corrosion resistance of the electrochemical coating with a nickel-phosphorus alloy (by 30 %) is due to the formation of an amorphous structure of the solidifying metal liquid while preventing the crystallization process during electrochemical deposition.

Adhesive built-up edge on tool steels due to friction and wear

When processing metals by cutting, there are a number of materials prone to growth. This phenomenon leads to a change in the geometry of the cutter, cutting forces and surface quality, final dimensions of the part. In friction nodes: shaft-sleeve, piston-sleeve, etc. this phenomenon causes jamming. In this work, experimental studies of the processes of dry friction of tool steels with coatings were carried out to evaluate the effectiveness of reducing the growth process. As a result, it was established that the nature of formation, destruction and size of growth of materials prone to growth depends on the chemical composition of the material and modes of friction. High-strength chromium-manganese steels are most prone to growth and microseizures. It is shown that the well-known recommendation of increasing speed cannot always be used to prevent build-up, but it can be achieved by using single-layer and multi-layer coatings with a defect-free structure and moderate friction modes. It was found that electrolytic single-layer nickel and chromium coatings contribute to the formation of growth on the studied materials and this phenomenon does not depend on the modes of friction, while the same chemical coatings, which have an almost defect-free structure, are almost not prone to growth formation.

Features of cavitation wear of chrome electrolytic coatings

Cavitation wear is a pervasive phenomenon on water transport. The parts of ship propulsion system as well as the water-cooled surface of cylinder liners of high-speed ship diesels are subjected to cavitation attack. Bright chromium deposits are used to protect the water-cooled surface of liners. Nevertheless, the effect of cracks appearing in the electrolytic chrome coating upon depositing on the cavitation resistance of coating is still an open relevant problem. The goal of the study is to analyze the kinetics and mechanism of the destruction of the bright chrome electrolytic deposit under cavitation attack. The cavitation resistance of chrome electrolytic coatings after grinding and after polishing was studied. The chrome electrolytic coatings were obtained on the plates (90 × 30 × 7 mm in size) made of cast iron SCh21. The chrome was deposited on one side (90 × 30 mm) of the plate placed vertically by flow anodic jet chrome plating in standard electrolyte (kg/m3): chrome anhydride — 250; sulfuric acid — 2.5; trivalent chrome — no more than 5; trivalent iron ions — no more than 10. The electrolyte was prepared using distilled water of a single distillation. The parameters of depositing: electrolyte temperature is 50°C; the current density amounts to 60 A/dm2. Four samples cut from the same plate were used. The coatings on the first two samples were ground using the abrasive paper number 320. The coatings on the second pair of samples were first ground successively on the abrasive paper of different grit: 320, 500, 800, 1000, and 1200, and then polished on the cloth with GOI paste. The cavitation wear tests were carried out on a magnetostrictive vibratory rig in fresh water, the frequency and amplitude of the rig horn vibration was equal to 22 kHz and 28 μm, respectively. The spacing between the chrome-plated sample surface and the horn butt was 0.5 mm. The wear of the samples was evaluated by periodical weighing during testing. The wear of the ground samples turned to be significantly higher, than that of polished samples. The photographs of the surface after different duration of the cavitation attack show that the initial cracks formed on the coating during chrome plating are the centers of cavitation destruction. To reduce the negative impact of initial cracks on the cavitation resistance of the bright chrome electrolytic coatings deposited on the water-cooled surface of the cylinder liners of diesels it is shown expedient to include polishing in the technological process of depositing chrome coatings.

Corrosion of Chromium Coating Fabricated on Zircaloy-4 Substrate.

In the nuclear industry, coated cladding is a topical problem and it is chosen as the near-term and most promising ATF (Accident-Tolerant Fuel) cladding concept. The main objective of this concept is to enhance the accident tolerance of nuclear power plants and accordingly, the performance of cladding is expected to be improved. This work assesses the corrosion performance of a Zircalloy-4 alloy coated with a thin chromium coating by MS (magnetron sputtering), tested under a CANDU (CANada Deuterium Uranium) reactor primary circuit simulated condition (LiOH solution, 10 MPa, 310 °C, pH = 10.5). The anticorrosive performance is evaluated by a gravimetric analysis, a metallographic analysis, X-ray diffraction, electronic microscopy, and electrochemical methods. A four times less gain mass was noticed compared to uncoated Zircaloy-4, indicating a smaller corrosion rate. The SEM micrographs illustrate that the coatings are still adherent, and they are keeping the initial morphological characteristics during the autoclaving process. A SEM cross-section analysis shows values of the thickness of the coatings between 0.8 and 1.46 µm. By XRD, the presence of Cr2O3 oxide is identified. Electrochemical testing confirms good stability and good corrosion performance of Cr coating over time under autoclave conditions.

Insights in the wettability of hard chromium coated steel for cold rolling applications

The use of toxic Cr (VI) in the chrome plating process poses significant health risks, highlighting the urgent need to find sustainable alternatives for many applications such as cold rolling. Understanding key properties of functional chrome coating in lubricated industrial processes, especially its wetting properties that can support lubrication, low friction, and durability, is essential for the development of safer coating processes. However, the wetting properties of hard chromium coating are not fully understood. This study investigates the wetting characteristics of chromium coatings in comparison to uncoated steel. The study explores the dynamic wetting behavior by conducting contact angle measurements with water and lubricant oil, determining surface free energy using the sessile drop method, and characterizing the surface through X-ray photoelectron spectroscopy analysis. The findings reveal that a standard hard chrome coating exhibits superior wettability by both water and oil and higher surface energy compared to uncoated steel. The research, supported by theoretical modelling, highlights that factors are not limited to chromium alone, but rather involve a multilayer system that includes chromium oxide and organic contaminations, which have a substantial impact on surface properties and wettability. Increased levels of organic contamination on the chrome-coated surface, are shown to result in weaker intermolecular interactions with the contacting fluid, leading to reduced surface affinity to water and consequently result in higher contact angles. Our findings provide critical insights into the intricate nature of chromium coatings and lay foundations for developing sustainable alternatives.

Insights into 1200 °C steam oxidation behavior of Cr coatings with different microstructure on Zircaloy-4 alloys for enhanced accident tolerant fuel cladding

In order to improve the 1200°C steam oxidation properties of Cr-coated zirconium alloy accident tolerant fuel cladding tubes, chromium coatings with various micro-structures were fabricated by bipolar high-power impulse magnetron sputtering technology. The microstructures of chromium coatings transforms from unconsolidated column structure to dense & column-oblate structure with the bias voltage increase. Hardness and elastic modulus values of optimal chromium coatings are approximately 19.1 GPa and 374.8 GPa, respectively, which are 2.09 and 1.60 times higher than those of chromium coatings with unconsolidated column structures. Optimal chromium coatings with dense & column-oblate structures display preferable 1200°C steam oxidation resistance because of possession lower weight gain value and thicker Cr2O3 oxide layer after 2 h exposure periods. The fabrication strategy of chromium coatings with dense & column-oblate structure is expected to pave the way for enhancing 1200 °C steam oxidation resistance for Cr-coated zirconium alloys.

Relationship between Texture, Hydrogen Content, Residual Stress and Corrosion Resistance of Electrodeposited Chromium Coating: Influence of Heat Treatment.

Electrodeposited chromium plating continues to be widely used in a number of specialized areas, such as weapons, transport, aerospace, etc. However, the formation of texture, hydrogen content and residual stress can degrade the serviceability and lead to material failure. The effect of post heat treatment processes on the relationship of texture, hydrogen content, residual stress and corrosion resistance of hexavalent [Cr(VI)] chromium coatings deposited on Cr-Ni-Mo-V steel substrates was investigated. Macrotexture was measured by XRD. Microtexture, dislocation density and grain size were studied by EBSD. With the increase of the heat treatment temperature, it was found that the fiber texture strength of the (222) plane tended to increase and subsequently decrease. Below 600 °C, the increase in the (222) plane texture carried a decrease in the hydrogen content, residual stress, microhardness and an increase in the corrosion resistance. In addition, crack density and texture strength were less affected by the heat treatment time. Notably, relatively fewer crack densities of 219/cm2, a lower corrosion current density of 1.798 × 10-6 A/dm2 and a higher microhardness of 865 HV were found under the preferred heat treatment temperature and time of 380 °C and 4 h, respectively. The hydrogen content and residual stress were 7.63 ppm and 61 MPa, with 86% and 75% reduction rates compared to the as-plated state, respectively. In conclusion, in our future judgement of the influence of heat treatment on coating properties, we can screen or determine to a certain extent whether the heat treatment process is reasonable or not by measuring only the macrotexture.

Corrosion Resistance of Coatings Based on Chromium and Aluminum of Titanium Alloy Ti-6Al-4V.

Improvement of wear, corrosion, and heat-resistant properties of coatings to expand the operational capabilities of metals and alloys is an urgent problem for modern enterprises. Diffusion titanium, chromium, and aluminum-based coatings are widely used to solve this challenge. The article aims to obtain the corrosion-electrochemical properties and increase the microhardness of the obtained coatings compared with the initial Ti-6Al-4V alloy. For this purpose, corrosion resistance, massometric tests, and microstructural analysis were applied, considering various aggressive environments (acids, sodium carbonate, and hydrogen peroxide) at different concentrations, treatment temperatures, and saturation times. As a result, corrosion rates, polarization curves, and X-ray microstructures of the uncoated and coated Ti-6Al-4V titanium alloy samples were obtained. Histograms of corrosion inhibition ratio for the chromium-aluminum coatings in various environments were discussed. Overall, the microhardness of the obtained coatings was increased 2.3 times compared with the initial Ti-6Al-4V alloy. The corrosion-resistant chromaluminizing alloy in aqueous solutions of organic acids and hydrogen peroxide was recommended for practical application in conditions of exposure to titanium products.

Chromium Coatings Applied to Zr Alloy Claddings by Cathodic Arc Ion Plating: Effect of Nitrogen Inclusion on Limiting Columnar Defects

The effect of nitrogen on an anticorrosive Cr coating for the Zr alloy cladding of nuclear fuel rods is investigated. It is aimed to reduce the number of typical columnar defects generated in Cr‐based coatings when using the cathodic arc ion plating method through reactive nitrogen inclusion and improve the oxidation resistance. Under a working pressure of 5 Pa and an arc current of 60 A in a chrome target, Cr‐based coatings are fabricated under varying N2/Ar gas flow ratios and substrate biases. The growth structures, crystallography, and corrosion behavior of the coatings are characterized using scanning electron microscopy, X‐ray diffraction, and potentiodynamic polarization tests. The Cr coating exhibits a typical columnar structure with voids, pores, and columnar defects. In comparison, through nitrogen inclusion, when the nitrogen content of the Cr‐based coating is less than 15 at%, the Cr(N) coating shows a “featureless structure” similar to an amorphous structure, resulting in fewer voids and defects. Potentiodynamic polarization tests reveal that the Cr(N) coating, featuring a distorted body‐centered cubic‐Cr structure, exhibits a significantly low corrosion current in the passive region. The protection efficiency of the Cr(N) coating is calculated to be 96.9%, confirming its superior substrate protection capabilities compared with chromium nitride coatings.

Multi-Parameter Complex Control of Metal Coatings on Ball Plugs of Pipeline Shut-Off Valves

The greatest losses during gas transportation occur in the elements of shut-off valves, the operating parameters of which, among other things, depend on the thickness and hardness of the protective coating of the ball plugs. The study of the parameters of nickel–phosphorus and chrome coatings on ball plugs of serially produced shut-off valves, including control of their thickness and hardness, was carried out. Based on the test results, deviations in the actual parameters of coatings from the requirements of technological documentation were revealed, the necessity of their complex control was substantiated, recommendations on the choice of methods and equipment were formulated, and the main provisions of the test methodology were developed.

The effect of chromium-based coatings on corrosion behavior of alloy Zr1Nb in 70ppm Li+ water environment

Recent research indicates that one of the leading candidates for Accident Tolerant Fuels (ATF) are chromium-based coatings deposited on the commercially used zirconium alloys. The chromium-based coatings seem to improve the corrosion kinetics of underlying zirconium in both primary water and steam, where zirconium fails to meet the safety requirements. It is well known that the corrosion kinetics of zirconium can be negatively influenced by high concentrations of lithium ions. To evaluate the effect of chromium-based coatings on corrosion behavior of zirconium alloys in water containing elevated concentrations of lithium, Cr and CrN/Cr multilayer coated Zr1Nb alloy was tested in high temperature water containing 70 ppm Li+. Using Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectroscopy (EDX), we have found that the chromium coating could have a positive effect on the underlying material as it behaves as a good diffusion barrier for oxygen and Li+ions. On the other hand, CrN/Cr coating, due to not sufficient structural integrity of the multilayer, showed non-protective behavior to the Zr1Nb alloy. Our results suggest that certain chromium coatings can significantly enhance corrosion resistance in lithium containing water environments.

Mitigation mechanisms of ash deposition and adhesion by different coatings on heated surfaces at macro and molecular scales

Research on the mitigation of ash deposition on coals rich in alkali and alkaline earth metals using coatings is limited. Existing research methods, mainly focusing on ash composition and melting characteristics, cannot fully elucidate the key mechanisms underlying ash adhesion properties on various coated surfaces. Therefore, this study explored the mitigation mechanisms of nickel and chromium coatings on ash deposition using a drop tube furnace, custom-made ash adhesion strength tester, and molecular dynamics. The results revealed that nickel and chromium coatings effectively mitigated ash deposition, with a more significant effect at temperature less than 1000 °C. Above 1000 °C, the ash melting led to a significant increase in ash adhesion strength, diminishing the inhibitory effect of coatings. The key minerals, Na2SO4, Ca2MgSi2O7, and Ca2Al2SiO7, mainly physically adsorbed onto the NiO(001) and Cr2O3(001) surfaces. The binding energy of these minerals with NiO(001) and Cr2O3(001) was significantly lower than that on α-Fe2O3(110) surfaces. The α-Fe2O3(110) system was more stable, and minerals readily adhered to the α-Fe2O3(110) surface, whereas none of these minerals readily bound to NiO(001) and Cr2O3(001), maintaining their adhesion state. Consequently, nickel and chromium coatings demonstrated excellent resistance to ash adhesion and deposition, with nickel coatings being more effective.

Control of the preferential orientation and properties of HiPIMS and DCMS deposited chromium coating based on bias voltage

This study investigates the effects of varying bias voltages on the crystallographic orientation and properties of DCMS + HiPIMS-deposited chromium coatings. Under bias voltages varying from 100 to 500 V, dense Cr coatings were obtained, and the deposition rate decreased by 13 %. The bias voltage significantly impacts the hardness, crystallographic orientation, electrical conductivity, and bonding strength of the coating. As the bias voltage increases, the hardness of the Cr coating gradually increases. The crystallographic orientation of the coating is governed collectively by surface energy, strain energy, and sputtering effects. The preferential crystallographic orientation of the Cr coating transitions from (222) to (110), subsequently changing to a mixed preferential crystallographic orientation of (110), (211), and (222). Under the combined influence of thermal effects and ion bombardment, a (110) preferential crystallographic orientation was obtained at a bias voltage of 300 V, featuring moderate hardness and optimal wear resistance. This study establishes that the electrical characteristics of the coatings have a significant correlation with bias voltage levels.

Surface crack propagation of electroplated chromium coating and cotton fabric with dry friction

Electroplated chromium coatings are commonly used to improve the wear resistance of metal parts in the cotton textile industry, and surface crack is an important feature. This study investigates the tribological properties and surface crack propagation of the electroplated chromium coating in dry friction contact with cotton fabric. It is found that the coating has excellent tribological properties, with the friction coefficient eventually stabilized at 0.11 and the average wear rate of 0.0038 mm3/h. The cotton fabric mainly exhibits a polishing effect on the coating during friction, and the failure of the coating is in the form of delamination failure within the coating. Crack propagation is mainly due to the friction of cotton fabric, the main cracks of the mesh crack structure hardly propagate, while the short cracks extending on the main cracks undergo propagation behavior. Short cracks propagate vertically along the friction direction and eventually develop into the main crack level. The tangential stress generated by friction acts on the crack tip, which is the main cause of crack propagation. The plastic zone generated at the crack tip affects the distribution of the stress field and the effect of the plastic zone on crack propagation is analyzed.

Metallization of polypropylene substrates through surface functionalization and physical vapor deposition of chromium coatings

Physical vapor deposition (PVD) of chromium coatings represents an interesting alternative to electroplating to obtain metallized plastic parts for a variety of manufacturing sectors. This process is however hampered by the limited adhesion of the metallic layer on the underlying polymeric substrates. Within this context, PVD metallization of polypropylene substrates has so far been particularly challenging given the low surface energy and poor wettability of this commodity plastics. To address this issue, a comprehensive approach is proposed here to enable the production of PVD-metallized PP substrates with excellent and stable interlayer adhesion. The adhesive properties of the PP substrate are modified by a selective UV-induced photografting process in which vinyl-, glycidyl- or 2-hydroxyethyl methacrylate species are covalently attached to the PP surface, as confirmed by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and surface wettability measurements. Based on the chemistry of the photografted functionality, different resin systems are selected and investigated for use as primers to enable subsequent chromium deposition, including acrylic, epoxy and polyurethane systems. The effect of the photografting process on the adhesion between PP and the primers is systematically assessed by means of pull-off tests, highlighting a significant improvement of the adhesion force after surface functionalization with appropriate grafting agents. Finally, functionalized PP substrates are chromated through PVD, obtaining homogeneous and crack-free chromium surfaces upon judicious selection of suitable primer-grafting agent combinations. This also led to outstanding interlayer adhesion and micromechanical performance. This work provides the first demonstration of chromium-metallization of PP substrates via PVD for metallized plastic components with excellent surface characteristics, and paves the path for the design of mechanically durable and aesthetically-compliant PVD-metallized PP components.

Evaluation of chromium coatings deposited by standard and bipolar high-power impulse magnetron sputtering (HiPIMS & B-HiPIMS) for nuclear power applications

Chromium coatings, as deposited onto Zircaloy-4 through direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS), are evaluated for usage in advanced nuclear fuel applications. While traditional magnetron sputtering has been documented extensively in literature, HiPIMS remains relatively novel and unexplored within this application space, especially when the sputtering source voltage waveform is modified with the addition of a positive “kick pulse”, as in the case of bipolar HiPIMS (B-HiPIMS). Rigorous analysis of the microstructure and residual stress state of these coatings are correlated to electrochemical observations and 84-day, 360 °C autoclave weights gains to predict the performance of the films within a non-irradiated pressurized water reactor (PWR) environment. Under this scrutiny, differences and similarities are revealed between DCMS, HiPIMS, and B-HiPIMS. It is demonstrated that monolithic Cr coatings deposited by HiPIMS and B-HiPIMS outperform those deposited by DCMS, while exhibiting an order of magnitude reduction in autoclave weight gain relative to the Zircaloy-4 nuclear grade material.

Resistance of HVOF-Sprayed Cr3C2-25NiCr and WC-10CO-4Cr coatings to cavitation and erosion by mud jetting

This study investigates chromium carbide-based coating material’s cavitation and erosion resistance with 25% nickel-chromium. (Cr3C2-25NiCr) and Tungsten carbide coating with 10% cobalt and 4% chromium (WC-10CO-4Cr) coatings deposited by high-velocity oxygen fuel (HVOF) thermal spraying. The coatings were characterized by microstructure, porosity, hardness, and fracture toughness. Cavitation tests were performed in distilled water and water-sand mixtures to assess the synergistic effect of erosion and cavitation. Erosion tests were conducted using a mud jet at different impact angles (30°, 60°, 90°). The Cr3C2-25NiCr coating exhibited higher cavitation resistance due to its higher fracture toughness and lower porosity. However, the WC-10CO-4Cr coating showed superior erosion resistance, attributed to its finer and more homogeneously distributed carbides. The dominant wear mechanisms were micro grooving, carbide detachment, and cracking. The impact angle significantly influenced the erosion rates, with ductile materials like CA6NM steel being more susceptible at lower angles, while brittle coatings showed the opposite behavior. The findings highlight the importance of coating properties and test conditions on the wear performance, providing valuable insights for selecting suitable coatings for hydropower applications.