Search Results (199)

Water walls in power plant boilers are prone to failure under extreme conditions involving high temperature, corrosion, and wear, which severely threaten unit reliability and operational economy. In this work, a NiCr-Cr₃C₂ protective coating was deposited on SA213-T12 steel substrates using high-velocity oxy-fuel (HVOF) spraying, with arc-sprayed PS45 coating as a reference. The NiCr-Cr₃C₂ coating exhibited a dense, low-porosity structure with homogeneous dispersion of Cr₃C₂ hard phases in the NiCr matrix, forming a typical cauliflower-like composite morphology. During high-temperature sulfate corrosion tests at 750 °C, the NiCr-Cr₃C₂ coating demonstrated superior corrosion resistance, with a weight gain of only 2.7 mg/cm², significantly lower than that of the PS45 coating and the SA213-T12 substrate. The higher microhardness and lower friction coefficient also indicate excellent high-temperature wear resistance. The enhanced performance of the NiCr-Cr₃C₂ coating is attributed to the high Cr content, which promotes the formation of a continuous and protective scale composed of Cr₂O₃ and NiCr₂O₄, effectively inhibiting corrosive diffusion and penetration. This work demonstrates the application prospects of NiCr-Cr₃C₂ coatings on water walls of power plant boilers and guides the development of advanced HVOF coatings. Full article

A cost-effective Fe-Cr-Mo-B-Si-C metamorphic alloy (HXA5) was newly designed and fabricated as coating material using the high-velocity oxygen fuel (HVOF) thermal spray process, and its microstructure and dry wear resistance were investigated in comparison with a conventional HVOF WC-12Co coating. The HXA5 coating material consisted of a splat area and un-melted powder area. The splat area contained metallic glass, (Cr,Fe)₂B, Cr₂B, and minor Fe-based BCC phases, and the un-melted powder area was composed of Fe-based BCC, (Cr,Fe)₂B, and Cr₂B phases. Room-temperature wear tests revealed that HVOF HXA5 coating material exhibited wear resistance comparable to HVOF WC-12Co coating over ~8.4 km sliding and even superior performance at high-stress wear conditions. This superior wear behavior of HXA5 coating material was attributed to the minimal hardness difference between the metallic glass and boride, the plasticity of the metallic glass, and the formation of a lubricating tribofilm. The wear mechanisms and the influence of alloying elements on glass-forming ability were also discussed. Full article

The development of thin, wear-resistant coatings is a relevant area in the field of surface engineering, especially given the increasing demand for resource efficiency and reliability of machine elements. In this study, we investigate the structural and phase composition, tribological characteristics, and physical and mechanical properties of zirconium carbonitride (ZrCN) coatings deposited by high-velocity oxygen-fuel spraying (HVOF) on U8G carbon steel substrates. Particular attention is paid to the influence of spraying parameters, in particular air pressure, on the formation of coatings and their performance properties. X-ray phase analysis methods revealed the formation of Zr₂CN, ZrC, ZrN, ZrO₂, and Fe₃O₄ phases, with the dominance of the cubic phase ZrN(C) with a lattice parameter of a = 4.6360 Å. Tribological tests have shown that at an air pressure of 0.38 MPa, the minimum friction coefficient is achieved, presumably due to the formation of an amorphous CN_x phase with a self-lubricating effect. The wear mechanism is predominantly abrasive in nature; the width of wear tracks is 329–759 μm. The coatings demonstrate a significant increase in microhardness—up to 1512–1857 HV, which is 4–4.5 times higher than the substrate. The results of adhesion tests carried out in accordance with ASTM D4541-22 showed a maximum adhesion strength of 14.56 MPa. The results obtained confirm the high efficiency of thin ZrCN coatings obtained by the HVOF method as a promising solution for protecting metal surfaces subject to intense wear in tribological systems. Full article

This study examines advanced electrospark alloying (ESA) as a pulse-driven surface hardening technique for marine engineering components operating in corrosive and abrasive environments. Coatings were deposited using cobalt-based (Stellite 6), nickel-based (NiCrBSi), titanium-based (VT1-0), and boron-based (B₄C) electrodes, with pulse energies of 0.2–0.5 J, discharge frequencies of 100–200 Hz, electrode feed rates of 5–8 mm/min, applied loads of 15–20 N, and treatment durations of 40–60 s. The effects of processing parameters on coating microstructure, adhesion strength, microhardness, corrosion resistance, and wear behaviour were systematically evaluated. ESA treatments increased microhardness by 35–48% and adhesion strength by 22–30%, while reducing the corrosion rate from 0.043 mm/year to 0.025–0.027 mm/year and lowering wear volume loss by 40–47%. Compared with high-velocity oxy-fuel (HVOF) spraying and laser hardening, ESA achieved 37–58% lower energy consumption and 40–70% lower CO₂ emissions. These findings highlight ESA as an energy-efficient and environmentally sustainable option for on-site maintenance and modernisation of maritime equipment. Full article

Biocompatible coatings are widely employed in dental applications to enhance the biofunctionality of metallic implants exposed to the aggressive oral environment. Among them, hydroxyapatite (HAp)-based and carbide-reinforced coatings have been explored due to their favorable mechanical and biological performance. In this study, Cr₃C_-20(Ni20Cr)-20HAp-XSi coatings were deposited using the high-velocity oxy-fuel (HVOF) technique. The coatings were applied onto commercially pure titanium substrates, with the silicon content varied between X = 0, 5, 10, and 20 wt%. To evaluate the coatings’ corrosion resistance, electrochemical techniques such as potentiodynamic polarization curves, linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and open circuit potential (OCP) were employed. Artificial saliva was used as the corrosive medium at 37 °C for 168 h. The feasibility of producing carbide-HAp-Si coatings with excellent corrosion resistance and cytocompatibility via HVOF was demonstrated here, although some of the tested coatings (20 wt% Si) showed reduced electrochemical stability, attributed to faster dissolution processes and associated with a thinner coating layer, as confirmed by SEM analyses. X-ray diffraction (XRD) analyses revealed the formation of new phases in the coatings during thermal spraying, including Cr₂O₃ and Cr₇C₃. Additionally, MTT assays using 3T3-L1 fibroblasts showed no significant cytotoxic effects after 24 and 72 h of exposure to some of the coatings, confirming their biocompatibility for potential dental applications. Full article

Tribological processes in extreme environments pose serious material challenges, requiring coatings that resist both wear and corrosion. This review summarizes recent advances in protective coatings engineered for extreme environments such as high temperatures, chemically aggressive media, and high-pressure and abrasive domains, as well as cryogenic and space applications. A comprehensive overview of promising coating materials is provided, including ceramic-based coatings, metallic and alloy coatings, and polymer and composite systems, as well as nanostructured and multilayered architectures. These materials are deployed using advanced coating technologies such as thermal spraying (plasma spray, high-velocity oxygen fuel (HVOF), and cold spray), chemical and physical vapor deposition (CVD and PVD), electrochemical methods (electrodeposition), additive manufacturing, and in situ coating approaches. Key degradation mechanisms such as adhesive and abrasive wear, oxidation, hot corrosion, stress corrosion cracking, and tribocorrosion are examined with coating performance. The review also explores application-specific needs in aerospace, marine, energy, biomedical, and mining sectors operating in aggressive physiological environments. Emerging trends in the field are highlighted, including self-healing and smart coatings, environmentally friendly coating technologies, functionally graded and nanostructured coatings, and the integration of machine learning in coating design and optimization. Finally, the review addresses broader considerations such as scalability, cost-effectiveness, long-term durability, maintenance requirements, and environmental regulations. This comprehensive analysis aims to synthesize current knowledge while identifying future directions for innovation in protective coatings for extreme environments. Full article

The degradation process of HVOF-MCrAlY + APS-nanostructured YSZ (APS-nYSZ) thermal barrier coatings, produced using gas turbine OEM-approved MCrAlY powders, is investigated by studying the TGO growth and crack propagation behaviors in a thermal cycling environment. The TGO growth yields a parabolic mechanism on the surfaces of all HVOF-MCrAlYs, and the growth rate increases with the aluminum content in the “classical” MCrAlYs. The APS-nYSZ layer comprises micro-structured YSZ (mYSZ) and nanostructured YSZ (nYSZ) zones. Both mYSZ/mYSZ and mYSZ/nYSZ interfaces appear to be crack nucleation sites, resulting in crack propagation and consequent crack coalescence within the APS-nYSZ layer in the APS-nYSZ/HVOF-MCrAlY vicinity. Crack propagation in the TBCs can be characterized as a steady-state crack propagation stage, where crack length has a nearly linear relationship with TGO thickness, and an accelerating crack propagation stage, which is apparently a result of the coalescence of neighboring cracks. All TBCs fail in the same way as APS-/HVOF-MCrAlY + APS-conventional YSZ analogs, but the difference in thermal cycling lives is not substantial, although the HVOF-low Al-NiCrAlY encounters chemical failure in the early stage of thermal cycling. Full article

Many components in industry are subjected to high loads during operation and therefore often do not reach their intended service life. Conventional steels frequently do not provide sufficient protection against wear and corrosion. One solution is to coat these components using methods like thermal spraying to apply cermet coatings such as Cr₃C₂-NiCr or WC-Co-Cr. In light of increasingly strict environmental regulations, more eco-friendly alternatives are needed, especially ones that use little or no Cr, Ni, Co, or W. Another alternative is the recycling of powder materials, which is the focus of this research project. This study investigated whether filter dust from an HVOF system could be used to develop a new coating suitable for use in applications requiring resistance to wear and corrosion. This is challenging as the filter dusts have heterogeneous compositions and irregular particle sizes. Nevertheless, this recycled material, referred to as “Green Cermets” (GCs), offers previously untapped potential that may also be of ecological interest. An established WC-Co-Cr coating served as a reference. In addition to friction wear and corrosion resistance, the study also examined particle size distribution, hardness, microstructure, and susceptibility to crack formation at the interface and inside the coating. Even though the results revealed a diminished performance of the GC coatings relative to the conventional WC-CoCr, they may still be applicable in various industrial applications. Full article

Quasicrystalline coatings based on Al₆₅Cu₂₀Fe₁₅ are of increasing interest as potential alternatives to conventional wear-resistant materials due to their unique structural and tribological properties. This study explores the influence of air pressure during high-velocity oxy-fuel (HVOF) spraying on the phase composition, morphology, and wear behavior of Al₆₅Cu₂₀Fe₁₅ coatings deposited on U8G tool steel. Coatings were applied at a fixed spraying distance of 350 mm using three air pressures (1.9, 2.1, and 2.3 bar), with constant propane (2.0 bar) and oxygen (2.1 bar) supply. X-ray diffraction analysis identified the formation of Al₇₈Cu₄₈Fe₁₄ and Al_0.5Fe_1.5 phases, while scanning electron microscopy revealed a dense, uniform microstructure with low porosity and homogeneous element distribution across all samples. Tribological testing using the ball-on-disk method showed wear track widths ranging from 853.47 to 952.50 µm, depending on the air pressure applied. These findings demonstrate that fine-tuning the air pressure during HVOF spraying significantly influences the structural characteristics and wear resistance of the resulting quasicrystalline coatings, highlighting their promise for advanced surface engineering applications. Full article

Thermally sprayed carbide cermet coatings, particularly those based on tungsten carbide (WC) and chromium carbide (Cr₃C₂) and produced with the high velocity oxygen fuel (HVOF) process, are used in tribological applications as environmentally friendly alternatives to electroplated hard chrome coatings. These functional coatings are especially prevalent in the automotive industry, offering excellent wear resistance. However, their mechanical and tribological performances are highly dependent on factors such as feedstock powders, spray parameters, and service conditions. This review aims to gain deeper insights into the above elements. It also outlines emerging advancements in HVOF technology—including in situ powder mixing, laser treatment, artificial intelligence integration, and the use of novel materials such as rare earth elements or transition metals—which can further enhance coating performance and broaden their applications to sectors such as the aerospace and hydro-machinery industries. Finally, this literature review focuses on process optimization and sustainability, including environmental and health impacts, critical material use, and operational limitations. It uses a life cycle assessment (LCA) as a tool for evaluating ecological performance and addresses current challenges such as exposure risks, process control constraints, and the push toward safer, more sustainable alternatives to traditional WC and Cr₃C₂ cermet coatings. Full article

This paper investigates the tribological behavior of Stellite 6 coatings produced with high-velocity oxygen fuel (HVOF), with an emphasis on the transition between severe and mild wear regimes and the glaze layer formation. The development of these coatings involved two spray parameters modifying the oxygen fuel ratio and three post-heat treatment conditions at temperatures ranging between 600 °C and 1150 °C. The coatings were tested under conditions varying the normal load, temperature, sliding distance, and testing temperatures (up to 300 °C). The results show that the coating obtained from the HVOF process exhibited a microstructure different from the conventional bulk Co-alloys, significantly impacting the wear performance. The coating post-processing was essentialto enhance wear resistance at elevated temperatures. Full article

The HVOF (High Velocity Oxy-Fuel) thermal spraying method is widely used in surface engineering to produce coatings with high hardness, low porosity, and excellent crack resistance. Composite coatings with chromium carbide (Cr₃C₂) in a nickel–chromium (NiCr) matrix are commonly applied in demanding environments, such as the energy and transport sectors. This study compares the microstructure, mechanical, tribological, and corrosion properties of two coatings—Cr₃C₂-25(Ni20Cr)-10(Ni) and Cr₃C₂-25(Ni20Cr)—deposited on ductile cast iron using HVOF. The addition of 10 wt.% Ni enhances coating integrity, mechanical performance, and environmental resistance by improving ductility, reducing residual stress, enhancing wettability, and balancing hardness with improved crack, wear, and corrosion resistance. Microstructure analysis via LM (Light Microscopy) and SEM (Scanning Electron Microscopy), along with chemical and phase characterization using EDS (Energy Dispersive X-ray Spectroscopy) and XRD (X-ray Diffraction), revealed that the Ni-enriched Cr₃C₂-25(Ni20Cr)-10(Ni) coating exhibited a denser structure, lower porosity, and high hardness. Its microstructure consists of large, partially melted Ni particles and fine Cr₃C₂ and Cr₇C₃ carbides embedded in the NiCr matrix, some at submicron scales. Performance tests, including indentation (H_IT, E_IT, K_IC), scratch, and corrosion resistance assessments, confirmed that Ni addition improves crack resistance, wear durability, and corrosion protection. Consequently, these coatings demonstrate superior operational durability, making them more effective in challenging environments. Full article

This review paper presents a detailed analysis of the influence of high-velocity oxygen–fuel (HVOF) spraying parameters on the microstructure formation and performance characteristics of Cr₃C₂-NiCr coatings. Key HVOF parameters, including the spray distance, oxygen-to-fuel ratio, powder feed rate, and spraying temperature, are examined in relation to their impact on coating properties. Structural parameters such as density, porosity, adhesive strength, and microhardness, which determine the mechanical behavior of the coating, are analyzed. Special attention is paid to wear resistance mechanisms, adhesion to the substrate, and resistance to fatigue failure. Additionally, the thermal stability of the coatings, their coefficient of thermal expansion, and oxidation resistance are investigated. This study also evaluates the morphology and phase composition of the coatings under different HVOF spraying conditions. An overview of modern diagnostic techniques, such as electron microscopy and spectroscopy, is provided. Compared to traditional surface treatment methods, HVOF spraying offers superior coating density, higher adhesion strength, and enhanced wear and corrosion resistance, making it an effective solution for extending the service life of components. Based on the findings, this paper highlights promising applications of Cr₃C₂-NiCr coatings in the aviation, power engineering, and mechanical engineering industries, where high wear resistance and thermal stability are crucial. Full article

To enhance the erosion resistance of typical Cr₃C₂-NiCr coatings, the Cr₃C₂-TiC-NiCrCoMo (NCT) coating was developed and deposited by high-velocity oxygen fuel spray (HVOF). The erosion resistance and mechanisms of the coating were investigated using numerical simulations and experimental methods. A comprehensive calculation model for the coating erosion rate was developed, incorporating factors such as the properties of the eroded particles, the characteristics of the coating, and the conditions of erosion. The erosion rate of the NCT coating was calculated and predicted by the model, and the accuracy of these predictions was validated through experiments. The NCT1 (87.3 wt.% Cr₃C₂-NiCrCoMo/3 wt.% TiC)coating demonstrated exceptional erosion resistance compared to the original Cr₃C₂-NiCrCoMo (NCC) coatings with reduced erosion rates of 23.64%, 20.45%, and 16.22% at impact angles of 30°, 60°, and 90°, respectively. The addition of nano-TiC particles into the NCT1 coating enhances the yield strength, impeding the intrusion of erosive particles at low angles and supporting the metal binder phase, eventually reducing fatigue fracture under repeated erosion. However, excessive nano-TiC content degrades the erosion resistance due to the increase in pores and cracks within the coating. Full article

The effectiveness of a machining process can be determined by analysing the quality of the generated surface and the rate of tool wear. Stellite is highly challenging to machine, which is why it is primarily processed through grinding methods. This study concentrates on the impact of cutting parameters and tool wear (VB_b, KB_b) on the created surface roughness surface (Rt, Ra, Rz) during the orthogonal cutting of Stellite 6, which is overlaid on a steel surface, C45, prepared by means of HP/HVOF (JP-5000). The results indicate that the dominant influence on the change in the total roughness profile height value (Rt) is the mutual interaction of cutting speed and depth of cut at 16% (p < 0.000). The greatest impact on the change in the mean arithmetic deviation of the roughness profile (Ra) value is the interaction of cutting speed, tool front angle, and depth of cut with a 15% share (p < 0.000), as well as on the change in the Rz value (15%) and tool wear VB_b (25%). This investigation lays the groundwork for potentially substituting the processing of flat surfaces with hardened layers created by thermal spraying (such as Stellite 6) with grinding or methods that offer greater efficiency from both economic and technological perspectives. Full article