Search Results (119)

AISI 316L stainless steel (316L SS) exhibits inadequate corrosion resistance in chloride-containing soils. Fe-based amorphous coatings (Fe-ACs), owing to their high Cr, Mo, and W contents and defect-free amorphous structure, are promising candidates for superior protection. In this work, the corrosion behavior of 316L SS and an Fe-based amorphous coating (Fe-AC) fabricated by high-velocity oxygen-fuel (HVOF) spraying was systematically compared by burial in Daqing saline soil (25% water content) with 0, 1.0, and 2.0 wt.% NaCl for 15–55 days. Corrosion rates were measured via mass loss, and surface morphology, elemental distribution, and phase constitution were characterized using OM, SEM/EDS, and XRD. Electrochemical impedance spectroscopy and potentiodynamic polarization were employed to assess passive-film stability and charge-transfer resistance. The Fe-AC consistently exhibited an extremely low corrosion rate (below 0.01 mm y⁻¹), nearly independent of NaCl concentration and exposure time, with only sporadic rust spots and the formation of a compact Cr/Mo/W-enriched passive film. In contrast, after 55 days in soil containing 2.0 wt.% NaCl, the 316L SS showed a corrosion rate of 0.0562 mm y⁻¹—six times that of the Fe-AC—accompanied by severe pitting (pit depth up to 3.6 mm) and loose corrosion products (γ-FeOOH and α-Fe₂O₃). Electrochemical tests confirmed that the charge-transfer resistance of the Fe-AC under the 0% NaCl condition reached 1.16 × 10⁶ Ω cm² and its breakdown potential exceeded 1.12 V, far outperforming 316L SS (2.30 × 10³ Ω cm² and 0.22 V, respectively). The novelty of this study lies in the systematic evaluation of the buried corrosion performance of HVOF-sprayed Fe-based amorphous coatings versus 316L SS in an actual saline soil and in elucidating the synergistic passivation mechanism of Cr, Mo, and W. This passive film effectively impedes chloride ingress and maintains high impedance over extended periods. Full article

Al-Cu-Fe quasicrystalline coatings were deposited on AISI 321 stainless steel substrates by high-velocity oxy-fuel (HVOF) spraying at oxygen pressures of 3.0, 3.5, and 4.0 bar. The influence of oxygen pressure on the phase composition, microstructure, porosity, corrosion behavior, thermal stability, and microhardness of the coatings was investigated using X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS), ImageJ porosity analysis, electrochemical corrosion testing in 3.5 wt.% NaCl solution, simultaneous thermal analysis (TGA/DSC), and microhardness measurements. XRD analysis revealed the formation of quasicrystalline-related intermetallic phases together with Al, Fe₃Al₁₃, FeAl, Fe₃O₄, CuFe₂O₄, Cu₂O, and CuO phases. The coating deposited at 3.5 bar exhibited the lowest porosity (5.37%), the most homogeneous microstructure, and the largest residual coating thickness after corrosion testing. SEM and EDS analyses indicated that corrosion preferentially initiated at pores, splat boundaries, and phase interfaces, while the coating produced at 3.5 bar demonstrated the most stable surface condition after exposure to a 3.5 wt.% NaCl solution. Thermal analysis showed that all coatings remained stable up to 900 °C. Sample (a) exhibited the lowest mass loss and the highest thermal stability, whereas sample (b) demonstrated the most favorable combination of structural integrity, phase ordering, coating density, corrosion-related performance, and thermal stability. Microhardness values of the coatings ranged from 754 to 778 HV, significantly exceeding that of the AISI 321 substrate. The results demonstrate that oxygen pressure is a critical parameter controlling the microstructure and functional properties of HVOF-sprayed Al-Cu-Fe coatings, with 3.5 bar providing the most balanced set of properties. Full article

Advanced thermal barrier coatings (TBCs) are essential for improving the efficiency and performance of gas turbine engines. Increasing engine operating temperatures and harsh service environments are pushing the current industry-standard 8 wt% yttria-stabilized zirconia (8YSZ) to its performance limits. High-rare-earth-oxide zirconates, such as Gd₂Zr₂O₇, have emerged as promising materials for next-generation engines due to their excellent high-temperature phase stability, lower thermal conductivity, and enhanced resistance to CMAS attack. In this work, dense vertically cracked (DVC) Gd₂Zr₂O₇/8YSZ bilayer coatings were developed using the air plasma spray (APS) process. Two approaches were employed for deposition of the NiCrAlYHfSi bond coat: (i) high-velocity oxygen fuel (HVOF), and (ii) APS flash-coated HVOF NiCrAlYHfSi bond coat. The durability of DVC TBC systems with the two bond coat types was evaluated by furnace cycling test (FCT) at 1125 °C. The TBC system with an APS flash-coated HVOF bond coat exhibited an FCT lifetime approximately twice that of the system with the HVOF bond coat alone. The improvement is primarily attributed to the higher surface roughness of the APS flash-coated bond coat, which enhances resistance to crack initiation, propagation, and linkage, thereby extending thermal cycling life. Full article

This study presents the fabrication of a Cr₃C₂-25NiCr/NiCr coating on Co₃W₃ steel utilizing high-velocity oxygen fuel (HVOF) spraying. The effects of the vacuum heat treatment process on the microstructures, mechanical properties, and wear mechanisms of the coating were systematically analyzed. The results indicated that the microstructure became denser following heat treatment. During the spraying procedure, decarburization resulted in transformation of the metastable phase structure into a stable one. In comparison to the sprayed coating, there was a 93.8% reduction in porosity. The precipitation of nano-secondary carbides shifted the mechanism of solid-solution strengthening to precipitation strengthening, resulting in a 29.1% increase in microhardness. Meanwhile, the thermal softening effect led to a 114.3% increase in fracture toughness. Wear experiments demonstrated that the friction-induced amorphous structure effectively mitigated stress concentration and inhibited crack initiation. The polycrystalline interface transition region between the nano-secondary carbides and the matrix facilitated the shedding of nano-secondary carbides, forming abrasive particles that generated a rolling effect, which significantly reduced the coefficient of friction. The semi-coherent interface between secondary carbides and NiCr decreased the interfacial energy and enhanced the bonding strength, effectively preventing the shedding of carbides during the wear process. Consequently, a dense microstructure, the type of interface, and high hardness and toughness were critical factors in enhancing its wear resistance. Full article

This study centred on the parametric optimisation and performance prediction of NiCr/WC-Co coatings produced by high-velocity oxygen fuel (HVOF) spraying. An L18 orthogonal experimental design based on the Taguchi method and the response surface method (RSM) was adopted to examine how key process parameters affect the microstructure, phase composition and hardness of the coatings. The results revealed that analysis of variance (ANOVA) indicated that travel speed, methane flow rate, powder feed rate, and stand-off distance were the primary parameters affecting coating hardness, collectively accounting for 76.25% of the total variance. Also, the RSM model established in this study demonstrates remarkably high predictive accuracy, with a coefficient of determination (R²) of 0.985 and an average prediction error of just 1.16%. Verification experiments were also conducted under optimal conditions. The measured hardness was 1352.7 ± 75 HV, in close agreement with the predicted value of 1365 HV. The coating, which was applied using HVOF spraying, had a dense layered structure and low porosity, and the decarburisation of the tungsten carbide was extremely minimal. In addition, interfacial bonding is improved and structural defects are reduced by the addition of a NiCr intermediate layer. It is demonstrated by the results that the Taguchi-RSM method is reliable for the optimization of HVOF spraying parameters and the prediction of coating hardness. Full article

High-velocity oxygen fuel (HVOF) spraying technology has been widely used to protect and repair the surface of mechanical parts and extend their service life. Spraying Fe-based amorphous alloy coatings can improve the corrosion resistance and fatigue resistance of the substrate. It is crucial to quantitatively elucidate the influence of process parameters on spraying behavior to achieve high-quality coatings. This study utilized a computational fluid-dynamics model to analyze the flight trajectories of flames and particles during HVOF spraying. Additionally, how parameters such as the O/F ratio, parallel barrel length, Laval nozzle diameter, and nitrogen flow rate affect flame and particle behavior was examined. These parameters were found to significantly impact the overall spraying process. As a result, the optimum structure and properties are obtained. In this study, the spray gun parameters were investigated to provide better guidance for the process and improve the quality and efficiency of the coating system. Full article

To gain deeper insight into the protective mechanism of tungsten carbide/diamond-like carbon (WC/DLC) duplex coatings, this study employed high-velocity oxygen-fuel (HVOF) combined with linear ion source (LIS) technology to deposit the WC/DLC duplex coating on the Ti₆Al₄V substrate. Their tribocorrosion behaviors were thoroughly investigated. The results show that the dense, uniform, and chemically inert DLC top layer acts as an effective barrier, preventing the corrosive medium from penetrating into the underlying WC cermet layer through pores. Consequently, the duplex coating exhibits a lower I_corr of 3.54 × 10⁻⁸ A/cm², compared with that of the single WC coating (1.08 × 10⁻⁶ A/cm²), demonstrating significantly improved corrosion resistance. Moreover, the DLC coating offers excellent tribological performance owing to the high hardness and self-lubricating characteristics. After depositing the DLC top layer on the HVOF-sprayed WC cermet, the COF is reduced to ~0.08, and the wear rate reaches only 5.64 × 10⁻⁸ mm³/N·m, indicating notably enhanced tribocorrosion resistance. In short, in such HVOF-PVD/CVD duplex coating systems, the PVD/CVD functional layer can improve the tribocorrosion performance of the HVOF interlayer by leveraging its intrinsic advantages, such as high hardness, low friction, dense and uniform microstructure, and chemical inertness. Full article

High-entropy coatings based on CoCrFeNiMn obtained by thermal spraying have demonstrated the potential to improve the wear resistance of traditional materials used in extreme conditions. The aim of the work was to study the effect of the oxygen/fuel ratio when using kerosene as fuel in the HVOF process on the microstructural characteristics of CoCrFeNiMn coatings, including phase composition, microhardness, elastic modulus, and wear resistance. Phase and microstructural transformations in gas-atomized powder during HVOF spraying were analyzed using XRD, SEM, and EDS methods. The tribological and mechanical properties of the coatings obtained were also evaluated. The results obtained are consistent with thermodynamic predictions based on the Scheil model for non-equilibrium conditions. The data obtained indicate the high potential of high-entropy CoCrFeNiMn alloys for use as protective coatings for industrial purposes. In addition, the results of the study emphasize the promise of using thermodynamic prediction of high-entropy alloys using Thermo-Calc software. The best mechanical and tribological properties were obtained in the HVOF 1 regime, which provided a maximum microhardness of 783.8 HV and a minimum wear rate of 7.45 × 10⁻⁵ mm³ × N⁻¹ × m⁻¹. Full article

Copper slag was introduced as a second phase into Cr₃C₂–NiCr coating to improve corrosion resistance and reduce material cost. Composite coatings with different copper slag/Cr₃C₂–NiCr ratios were prepared by high-velocity oxygen fuel (HVOF) spraying. The corrosion behavior was evaluated through electrochemical tests and immersion experiments, and the effect of coating composition on corrosion resistance was elucidated by microstructural and compositional analysis. To increase the addition of copper slag, the open-circuit potential of the coatings shifted positively, the corrosion current density decreased significantly, and both the polarization resistance and charge-transfer resistance increased markedly, leading to a notable reduction in corrosion rate. The coating with a copper slag-to-Cr₃C₂–NiCr mass ratio of 3:7 exhibited the best corrosion resistance. The improvement can be attributed to the reduced porosity and more compact structure resulting from the copper slag addition, as well as the homogeneous distribution of copper slag, which enhances the stability of the surface passivation layer. Full article

In this study, carbide-metal composite coatings (WC-10Co4Cr) were prepared via high-velocity oxygen-fuel (HVOF) spraying, and the influence of Mo₂C addition on the microstructure, mechanical properties, and wear performance was systematically investigated. The results indicate that Mo₂C is solid-soluted in WC during the preparation process, which induces lattice distortion. Mo₂C addition results in refinement of the grain size of WC particles, homogenization of the binder phase distribution, and reduction of the porosity of the coatings. An appropriate amount of Mo₂C addition significantly enhances coating performance. The coating containing 2 wt.% Mo₂C exhibited optimal properties. It demonstrated the highest microhardness and the lowest porosity, and wear tests revealed it had the lowest friction coefficient and wear rate at room temperature, which is primarily due to enhanced hardness and density that effectively suppressed abrasive wear. At 400 °C, the coating with 2 wt.% Mo₂C addition also showed the most stable and lowest friction coefficient. The generated Mo-containing oxides acts as a solid lubricant, isolating friction surfaces and mitigating both oxidative and adhesive wear. However, excessive Mo₂C content leads to an abnormal increase in the volume fraction of the binder phase, accompanied by reduced hardness. This induces a transition of the wear mechanism toward adhesive wear dominance, with complex nonlinear evolution characteristics. Full article

The paper presents the results of research aimed at verifying the possibility of creating renovation layers using HVOF (High Velocity Oxygen Fuel) technology. HVOF ceramic coatings represent a promising way to increase the efficiency, reliability, and sustainability of manufacturing processes. Molds for high-pressure injection of aluminum alloys were analyzed. The degradation mechanism of the functional surfaces of the molds was determined. The paper analyzes two types of HVOF coatings—Cr₂O₃-TiO₂ and Al₂O₃-TiO₂. For both coatings, a Ni-Al interlayer was used for mechanical stability, durability, and reliable functionality in demanding operating conditions. The interlayer is used in thermal spraying as a so-called bond coat—a layer that mediates adhesion between the metal substrate and the ceramic coating. EDX maps of chemical elements from the coating surface and cross-sections were determined. The tribological properties of the coatings were evaluated by a ball-on-disk test at 20 °C and 250 °C. SEM analysis of the surface after the tribological test was performed. The resistance of the coatings was evaluated by COF and friction resistance. Full article

This study fabricated six types of NiCr–Cr₃C₂ composite coatings using high-velocity oxygen fuel (HVOF) spraying and systematically evaluated their tribological behavior at 350 °C and 500 °C, along with their electrochemical corrosion performance in 3.5 wt.% NaCl solution. The objective was to elucidate how compositional design regulates the coatings’ microstructure, mechanical properties, and service performance. Results indicate that the 75NiCr–25Cr₃C₂ coating (C) formed a stable oxide film under both temperatures, exhibiting oxidation-dominated wear and the lowest friction coefficient and wear rate. When the temperature increased from 350 °C to 500 °C, the wear rates of coatings C, B, E, and F decreased significantly. Notably, coatings E and F, which contained CoCrFeNiMo high-entropy alloy, showed more than a 50% reduction in wear rate, demonstrating the contribution of the high-entropy phase to high-temperature wear resistance. At 350 °C, coatings B, D, E, and F experienced primarily abrasive wear; at 500 °C, however, E and F shifted to oxidative wear as the dominant mechanism, leading to a marked improvement in wear resistance. Electrochemical measurements revealed that coating E exhibited the best corrosion resistance, while the NiCr coating (A) performed the worst. The findings highlight that optimizing Cr₃C₂ content and incorporating high-entropy alloy elements can synergistically enhance both high-temperature tribological properties and corrosion resistance. Full article

To enhance the abrasive wear resistance of mechanical components operating in corrosive environments, this study fabricated WC-10Co-4Cr coatings using high-velocity oxygen-fuel (HVOF) thermal spraying technology. A L9 (3⁴) orthogonal array was designed to optimize four key process parameters (kerosene flow rate, oxygen flow rate, powder feed rate, and spraying distance) at three levels each, aiming for minimal porosity. The phase composition, microstructure, hardness, abrasive wear resistance, and corrosion resistance of the coatings were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), microhardness tester, wet sand rubber wheel abrasion tester, and electrochemical workstation. The results indicated that the optimal parameters were a kerosene flow rate of 0.0073 L/s, oxygen flow rate of 15.33 L/s, powder feed rate of 1 g/s, and spraying distance of 326 mm. The coating prepared under these conditions exhibited high density with a porosity of only 0.32% and a high microhardness of 1281 HV1. Compared to the AISI 1020 steel substrate, the optimized WC-10Co-4Cr coating demonstrated a 122-fold improvement in abrasive wear resistance and a better corrosion resistance, showcasing its excellent overall performance and great potential for wear-resistant surface protection in corrosive environments. 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