Search Results (62)

In this study, a novel reverse friction stir processing (FSP) was adopted to investigate the effects of multi-pass reverse FSP on the microstructure, microhardness, bonding strength, and tribological properties of NiCrBSi coatings deposited on 6061-T6 aluminum alloy via atmospheric plasma spraying (APS). The results demonstrate that reverse FSP effectively eliminates pores, unmelted particles, and interlamellar defects in the as-sprayed coating without causing mechanical damage to the coating surface inside the processed zone. With an increase in processing passes, a micron-scale diffusion zone forms at the coating/substrate interface, transforming the bonding mechanism from mechanical interlocking to metallurgical bonding. Mechanical property tests reveal that compared with the as-sprayed state, the microhardness and tensile bonding strength of the three-pass FSPed coating are increased by 26.0% and 171.1%, respectively, indicating significantly improved mechanical properties. Tribological tests demonstrate that the main wear mechanism of the as-sprayed coating is severe abrasive wear. After multi-pass FSP, the wear mechanism of the coating transforms into a mixed wear mechanism. Among them, the FSP3 coating exhibits mild abrasive wear accompanied by local adhesive wear. Full article

Thermally sprayed, self-fluxing NiCrBSi-based coatings, subsequently flame-remelted, exhibit notable abrasion and corrosion resistance. While flame remelting facilitates the formation of a homogeneous, pore-free microstructure and promotes adhesion to the substrate, it suffers from low processing efficiency and introduces considerable thermal loads into the material. In contrast, electron beam remelting (EBR) offers enhanced efficiency, reduced heat input, and the potential to achieve metallurgical bonding with the substrate. This study investigates the influence of EBR parameters on the microstructure, hardness, and elemental distribution of NiCrBSi-based coatings. Four powder compositions—with and without tungsten or tungsten carbide (WC) additives—were deposited via thermal spraying and subjected to EBR. The resulting coatings were analyzed using light and scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Vickers microhardness testing. The optimized EBR process yielded dense, crack- and pore-free coatings with uniform elemental distribution and effective metallurgical bonding. Maximum matrix hardness values up to 881 HV0.1 were achieved, confirming the efficacy of EBR in enhancing the structural and mechanical integrity of thermally sprayed NiCrBSi coatings. It was also found that the addition of different reinforcement phases to the NiCrBSi matrix can significantly affect the overall microstructure and properties of the matrix itself. Full article

The nickel (Ni)-based alloy cladding layers on the surface of 6061 aluminum alloy are fabricated successfully using an optimized laser cladding process. An analysis has been conducted to compare the influence of two types of Ni-based powders on the phase composition, macroscopic morphology and microstructure of the cladding layers. The study also elucidates the micro-hardness and friction property of the cladding layers fabricated by two types of Ni-based powders. The results reveal that phases including Al₃Ni, Al₃Ni₂, and α-Al are formed in the pure Ni cladding layer. Nonetheless, in the Ni–Cr–B–Si cladding layer, a new phase characterized by needle-shaped Cr₇C₃ is observed. Mechanical properties characterization of the cladding layers reveals a notable improvement in microhardness and friction properties compared to the 6061 aluminum alloy substrate. The best properties are achieved in the Ni–Cr–B–Si cladded layer, which demonstrates a microhardness of 714 HV, almost 8.1 times superior to that of the substrate. Its friction and wear rate is merely 21% of that of the base aluminum. Our results are expected to provide significant insights into the design and production of aluminum materials with great resistance to wear. Full article

This paper investigates the applicability of plasma transferred arc (PTA) cladding for extending the service life of biomass shredder tools. The study evaluates the possibility of replacing Hardox 500 steel with a lower-cost structural steel S355J2 whose functional surfaces are modified by PTA cladding. Three commercially available powder fillers were examined: CoCrWNi (PL1), FeCoCrSi (PL2), and NiCrMoFeCuBSi (PL3). The quality and performance of the cladded layers were assessed through hardness measurements, microstructural analysis using SEM and EDX, and tribological testing focused on abrasive and adhesive wear at room temperature. The results showed that the PL1 cladding achieved the highest surface hardness, reaching up to 602 HV0.1, due to the presence of hard carbide phases. In contrast, the PL2 cladding exhibited the best resistance to abrasive wear, demonstrating the lowest mass loss for both as-deposited and machined surfaces. The PL3 cladding showed intermediate performance in terms of wear resistance. Overall, the findings indicate that PTA cladding using an FeCoCrSi-based filler on an S355J2 substrate represents a promising and cost-effective alternative to Hardox 500 for biomass shredder applications. Full article

Co-combustion in a refuse incinerator is a primary method for treating aged refuse (AR). Given the high contents of heavy metals and chlorine in AR, it is crucial to investigate their release and fate during co-combustion to achieve environmentally sound treatment. This study investigated the release and volatilization of heavy metals (Cd, Cr, Zn, Ni, Cu, Pb) and HCl during the co-combustion of AR and municipal solid waste (MSW) through chemical thermodynamic equilibrium analysis. The effects of several parameters on the volatilization of heavy metals and HCl were analyzed, including incineration temperature, the N₂/O₂ ratio, the degree of refuse classification, the blending ratio of AR, and the effects of conventional calcium-based additives. The results showed that high temperature promoted the volatilization of Cd, Pb, Cu, Ni, and HCl. A lower N₂/O₂ ratio suppressed Zn and HCl volatilization. A higher degree of MSW classification (with lower proportions of kitchen and wood waste) and an increased AR blending ratio enhanced Zn fixation. CaO at high temperature only suppressed HCl volatilization, with a minor effect on heavy metals. Two modified calcium-based additives (CaBSiO₄OH and CaB₅SiO₉(OH)₅) with strong high-temperature Cu removal capabilities were explored, and their risk index was analyzed. Full article

The high-temperature and hot corrosion behavior of Diamalloy 2002 coatings with a WC/Co–NiCrFeBSiC composite structure applied to a 316 L stainless steel surface using the atmospheric plasma spraying (APS) method was investigated. The coatings were held at 900 °C in air for 5, 25, 50, and 100 h and in a molten salt bath of Na₂SO₄ + V₂O₅ at 900 °C for 1, 3, and 5 h. SEM, EDS, and XRD analyses revealed that the oxide layer on the surface thickened with increasing temperature and corrosion duration, forming NiO, Cr₂O₃, and mixed metal oxides. These oxide phases created a protective barrier effect by limiting diffusion between the coating and the substrate. Despite a slight increase in porosity and minor WC dissolution under long-term oxidation conditions, the coatings maintained their structural integrity up to 900 °C, demonstrating significant resistance to high-temperature oxidation and molten salt corrosion. These results demonstrate that Diamalloy 2002 coatings provide an effective surface protection solution in abrasive and oxidizing high-temperature environments. Full article

Self-fluxing Ni-based coatings (NiCrFeBSiC) were deposited through gas-flame spraying and evaluated in three conditions: as-sprayed, flame-remelted, and furnace-heat-treated (1025 °C/5 min). Phase analysis (XRD) revealed FeNi₃ together with strengthening carbides/borides (e.g., Cr₇C₃, Fe₂₃(C,B)₆); post-treatments increased lattice order. Cross-sectional image analysis showed progressive densification (thickness ~805 → 625 → 597 µm) and a drop in porosity from 7.866% to 3.024% to 1.767%. Surface roughness decreased from Ra = 31.860 to 14.915 to 13.388 µm. Near-surface microhardness rose from 528.7 ± 2.3 to 771.6 ± 4.6 to 922.4 ± 5.7 HV, while adhesion strength (ASTM C633) improved from 18 to 27 to 34 MPa. Wettability followed the densification trend, with the contact angle increasing from 53.152° to 79.875° to 89.603°. Under dry ball-on-disk sliding against 100Cr6, the friction coefficient decreased and stabilized (0.648 ± 0.070 → 0.173 ± 0.050 → 0.138 ± 0.003), and the counterbody wear-scar area shrank by ~95.6% (0.889 → 0.479 → 0.0395 mm²). Wear-track morphology evolved from abrasive micro-cutting (as-sprayed) to reduced ploughing (flame-remelted) and a polishing-like regime with a thin tribo-film (furnace). Potentiodynamic tests indicated the lowest corrosion rate after furnace treatment (CR ≈ 0.005678 mm·year⁻¹). Overall, furnace heat treatment provided the best structure–property balance (lowest porosity and Ra, highest HV and adhesion, lowest and most stable μ, and superior corrosion resistance) and is recommended to extend the service life of NiCrFeBSiC coatings under dry sliding. Full article

This study was conducted to evaluate the high-temperature protection performance of new hard coating systems. Woka 7202 (Cr₃C₂-NiCr) and Diamalloy 2002 (WC-NiCrFeBSiC) powders were coated onto 316L stainless steel substrates using the atmospheric plasma spraying (APS) method and subjected to isothermal oxidation (5–100 h) and hot corrosion (55% V₂O₅ + 45% Na₂SO₄, 1–5 h) tests. Although the coatings exhibited a laminar microstructure and some pores, cracks, and oxide-containing regions, they did not show any flaking or structural integrity deformations during the tests. Microstructural changes, oxide layer morphology, and the phases formed were examined in detail. The findings demonstrate that these coating systems not only provide chemical and structural stability against existing high-temperature environments, but also meet the requirements of next-generation thermal protection needs. In this regard, the study provides directly applicable information for the coating design and performance optimization for turbine blades, energy production equipment, and similar industrial components exposed to high-temperature oxidation and hot corrosion. Full article

Rail transport is an essential component of global logistics as it supports heavy loads and reduces transportation costs. However, rail tracks often suffer from wear, fatigue, and cracking, which increase maintenance costs and shortened service life. One potential approach to enhance the mechanical properties of rail surfaces is the application of laser cladding (LC) technology combined with deep rolling (DR), which increases the microhardness of the coating layer. This study aimed to examine the effects of four nickel-based cladding materials: Colmonoy 42, Colmonoy 56, Colmonoy 63, and NiCrBSi + 17WC. The experimental results showed that the laser cladding process significantly increased microhardness. Combined with the deep rolling process, Colmonoy 63 demonstrated the best response, achieving the highest microhardness of 943.47 HV, an increase of 24.78% compared to the rail treated with laser cladding. Therefore, the findings of this study indicated that combining the laser cladding process with deep rolling is an effective method for improving the surface properties of rails. Full article

Aiming to enhance the surface properties of low-carbon steel, NiCrBSi coatings containing 10 wt.% Nb were fabricated via pulsed laser cladding. Samples were realized with laser power ranging from 2800 to 3200 W. Scanning electron microscopy (SEM), coupled with energy-dispersive X-ray (EDX) analysis, was used to examine the microstructure and chemical composition. X-ray diffraction (XRD) was employed to evaluate the new phases formed within the coatings compared to the initial powder composition. Hardness measurements and corrosion resistance in a 3.5% NaCl solution were conducted to evaluate the effect of the Nb alloying on the properties of the cladded layers. In all cases, good metallurgical bonds were formed between the coatings and the substrate. However, the coatings produced at low laser power were thinner, and the substrate experienced more intense thermal exposure, resulting in increased dissolution of iron from the substrate. Increasing the laser power significantly enhanced the hardness of the coating compared to coatings produced using lower power. These phenomena can be the result of improved powder cladding efficiency, which can lead to thicker coatings with enhanced corrosion resistance. The results suggest that Nb addition can lead to improved mechanical behavior and corrosion resistance, but the process is highly dependent on the parameters and mainly on the laser power. 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

This paper presents a comprehensive analysis of recent advancements in the application of thermal spraying techniques to enhance the durability and wear resistance of agricultural machinery components, with a particular focus on disc harrow assemblies. Given the harsh conditions under which tillage tools operate—characterized by abrasive wear, impact stresses, and chemical exposure from various soil types—thermal sprayed coatings have emerged as a viable solution to extend the service life of these components. The study discusses various deposition methods, particularly Atmospheric Plasma Spraying (APS), and evaluates their effectiveness in creating high-performance surface layers that resist wear, corrosion, and mechanical degradation. The review also summarizes experimental and field test results for coatings based on materials such as NiCrBSi, WC-Co-Cr, TiO₂, Al₂O₃, Cr₂O_3, and ceramic–metal composites, highlighting their significant improvements in hardness, friction reduction, and resistance to delamination and oxidation. The paper highlights research using thermal spraying techniques, especially APS for agricultural applications, with emphasis mostly on components intended for soil processing and requiring good resistance to abrasive wear. Full article

In this study, NiCrBSi composite coatings reinforced with 5–15 wt.% TiC particles were prepared using laser cladding to investigate the influence of the TiC content and laser beam power on the coatings’ quality, structure, and properties. Penetrant tests revealed the presence of cracks in the composite coatings, which were reduced with the higher laser power due to a decrease in cooling rate. A macroscopic analysis showed that pure NiCrBSi coatings exhibited a high quality and were free of defects, while the addition of TiC particles led to the formation of large pores, particularly in coatings produced with a lower laser power. Microstructural characterization was conducted using Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD). The microstructure of the pure NiCrBSi coatings consisted of an austenitic matrix with chromium-based precipitates (carbides and borides). Variations in structural morphology across different regions of the coatings and under varying laser powers were described. When TiC particles were added, partial dissolution occurred in the molten pool, enriching it with titanium and carbon, which subsequently led to the precipitation of titanium carbides. The average microhardness of the composite coatings increased by 28%–40% compared to the pure NiCrBSi coating, while the erosion resistance remained comparable. Solid particle erosion tests in accordance with the ASTM G76-18 standard resulted in average erosion values of the pure NiCrBSi coating of 0.0056 and 0.0025 mm³/g for the 30° and 90° impingement angles, respectively. Full article

The mechanical properties of surfacing layers are significantly affected by the precipitation and evolution of carbides in nickel-based alloys. At present, the study of carbide precipitation in a Ni-Cr-B-Si surfacing layer is described by using the phase field method. In this paper, the true Gibbs free energy of the M₂₃C₆ carbide phase in Ni-Cr-C ternary alloy was established by the CALPHAD method and thermodynamic database. The growth and coarsening process of M₂₃C₆ carbide was simulated based on phase field method. The microstructure of M₂₃C₆ carbide of Ni-Cr-C alloy at 1373 °C isothermal aging time was observed by scanning electron microscope (SEM). The results show that the growth and coarsening of the precipitated M₂₃C₆ carbide phase are undergone through multiple processes during isothermal aging. First, a single precipitate core is formed, and then the single precipitate continues to coarsen and grow, forming a lamellar structure. Two precipitates contact to form a single rod-like structure, and multiple precipitates form slender rod-like structures. Finally, the contacting elongated rod-like structures grow, forming a typical layered eutectic carbide. The precipitation behavior, growth, and coarsening process of M₂₃C₆-type carbides in Ni-Cr-B-Si series alloys are explored through phase field simulation and experimental research in this paper. A theoretical basis is provided for the rational control and distribution of carbides in surfacing layers. A reference is also offered for optimizing the nickel-based superalloy materials used for surfacing the surface of descaling rolls. Full article

Laser cladding technology is an effective method for producing wear-resistant coatings on damaged substrates, improving both wear and corrosion resistance, which extends the service life of components. However, the fabrication of hard and brittle materials is highly susceptible to the problem of cracking. Using gradient transition layers is an effective strategy to mitigate the challenge of achieving crack-free laser-melted wear-resistant coatings. This study presents the cracking issue of laser cladding Ni60B (NiCrBSi) coatings on 38CrMoAl (18CrNiMo7-6) steel by designing a gradient transition layer infused with varying amounts of Ni powder. We examine how different levels of Ni doping in the transition layer influence the fabrication of the Ni60B coating. The results indicate that the cracking mechanism of Ni60B is primarily due to the brittleness and hardness of the fusion cladding layer, which can result in cold cracks under residual tensile stress. Increasing the nickel content in the transition layer reduces the difference in thermal expansion coefficients between the cladding layer and the substrate. Additionally, the nickel in the transition layer permeates the cladding layer due to the laser remelting effect. The physical phase within the cladding layer transitions from the initial CrB, M₇C₃, and γ-Ni solid solution to γ-Ni solid solution and Ni-B-Si eutectic, with a small amount of boride and carbide hard phases. As the nickel doping in the transition layer increases, the proportion of the toughness phase dominated by Ni elements significantly rises, leading to a decrease in the hardness of the fused cladding layer. However, the average hardness of the fusion cladding layer in crack-free samples was measured at 397.5 ± 5.7 HV_0.2, which is 91% higher than that of the substrate. Full article