Journal of Thermal Spray Technology最新文献

In this paper, a novel hard nickel composite coatings were fabricated by wide-band laser cladding technique. The effects of Si alloying on the composite coatings were investigated by microstructure characterization, phase identification, microhardness and wear resistance. Results showed that the in-situ precipitated phases in the laser molten pool were composed of the γ-Ni solid solution and hard phases such as Cr₂₃C₆, CrSi, Cr₅B₃. With the increase of Si element, the morphology of the precipitated phases changed significantly. When the added content of Si was 1.0 wt.%, the precipitated phase was a mainly block morphology. As the added content of Si was increased to more than 2.0 wt.%, the main precipitated phase was transformed into a long stripe morphology. With the increase of Si content, the stripe-like precipitated phase was gradually refined and finally becomes density needle-like precipitates. Element distribution analysis showed that the block precipitated phase was enriched in Cr, W and Si elements. Additionally, the enriched elements in the long strip precipitation phase were essentially the same as those in the block precipitation phase. The added Si element was highly involved in the in-situ reactions of precipitated phase. The TEM results showed that the precipitated phases contained the crystal structures of Cr₅B₃ and Cr₇C₃. The pin-on-disc wear tests revealed that the composite coating with the addition of 6 wt.% Si exhibited the best wear resistance in the experimental group. The average friction coefficient was about 0.6 and the wear mass loss rate was about 2.38 × 10⁻⁵ g/m under counter-abrasive conditions. The worn surface analysis indicated that the wear mechanism of composite coatings was mainly abrasive wear. The refined needle-like precipitated phase was closely bound to the matrix and thus not easy to peel off, providing a significant improvement in the wear resistance of the laser cladding coatings.

Metal-supported solid oxide fuel cells have broad application prospects in distributed power generation, transportation, military, and other fields. The electrochemical performance of the cell is still a challenge in commercial applications. Regulating the anode microstructure and optimizing polarization characteristics are effective methods. In this study, atmospheric plasma spraying technology is chosen to prepare the Ni-Gd_0.2Ce_0.8O_1.9(GDC) anodes using different low plasma powers (18, 21, 24 kW), which is cost-effective and efficient. The power effect on anode microstructure and electrochemical performance is investigated. The results show that as the plasma power decreases from 24 to 18 kW, the anode’s gas permeability and three-phase reaction boundary (TPB) gradually increase. Reducing the spraying power can decrease polarization resistance and improve power density. The 18-kW anode exhibits the lowest polarization resistance and the best output performance. Open-circuit voltage and maximum power density are 1.03 V and 0.89 W cm⁻² at 750 °C, respectively. The polarization resistance and total resistance are 0.19 and 0.40 Ω cm², respectively. The experimental results prove that atmospheric plasma spraying can realize the rapid and low-cost anode preparation for high-performance MS-SOFC.

This work investigated the trade-off among cavitation erosion resistance, corrosion resistance, and antifouling properties in HVOF-sprayed WC-10Co4Cr coatings. By adding 316L stainless steel (316L) and copper to WC-10Co4Cr coatings, this work aimed to enhance their antifouling ability while maintaining their cavitation erosion and corrosion resistances, presenting a comprehensive evaluation of the modified coatings, including their microstructure, hardness, fracture toughness, and resistance to cavitation erosion, corrosion, and biofouling. The results revealed that Cu addition significantly improved the antifouling property but at a cost of the compromised cavitation erosion and corrosion resistances. In contrast, 316L enhanced the cavitation erosion and corrosion resistances but did not effectively improve the antifouling property. The dual addition of Cu and 316L demonstrated a balanced performance in all three aspects. This research contributed to the development of HVOF-sprayed WC-CoCr coatings suitable for marine environments, suggesting further optimization possibilities by altering Cu and 316L contents.

In this work, Fe-based alloy coatings were prepared on the surface of ductile iron by laser cladding. To improve its wear resistance and consider the economic and time cost of other post-treatment processes, laser remelting was chosen to strengthen the coatings. The effect of laser remelting energy density (0−11.45 J/mm²) on the phase composition, microstructure evolution, hardness, and wear resistance of the coatings were investigated. The results show that the coating consists of γ-(Fe, Cr) and carbides and that remelting energy density has little effect on its phase composition. After remelting, the hardness uniformity of the coating was significantly improved, but increasing the remelting energy density had little effect on it. The hardness and wear resistance of the coatings were inversely related to remelting energy density. At a low remelting energy density of 5.66 J/mm², the hardness and wear mass loss of the coating were 111.49% and 54.36% of the original coating, respectively. The mechanism for the improved hardness and wear resistance is the microstructure refinement induced by laser remelting. Increased remelting energy density reduces the microstructure refinement of the coating, but the coatings still showed good hardness and wear resistance due to the diffuse distribution of carbides at higher remelting energy density conditions of 9.43-11.45 J/mm².

A high-performance Al₂O₃-PF composite coating was prepared on the surface of polymer matrix composite materials using supersonic high-energy plasma spraying technology. The bonding strength between the composite coating and the matrix was used as the evaluation index. The spraying process parameters were optimized using orthogonal experimental design method. Subsequently, the optimal process was verified based on single factor experimental method, further exploring the influence mechanism of Ar flow rate, spraying current, spraying voltage, and second powder feeding position on the composite coating. Analysis shows that spray voltage, Ar flow rate, and spray current have a significant impact on the experimental results and are the main influencing factors; the second powder feeding position has a relatively small impact on the experimental results and is a secondary influencing factor.

Cold-sprayed composite coatings have several advantages; however, some properties, such as hardness and abrasion resistance, are lower than those in plasma- or HVOF-sprayed deposits. This work showed that the use of surface diode laser processing allowed the development of (Cr₃C₂-25(Ni20Cr))-(Ni-graphite) cermet coatings with good adhesion to the steel substrate, and increased properties in the near-surface zone, below which the properties of cold-sprayed coatings were retained. Studies of the microstructure in the micro/nanoscale of the laser-treated coatings showed strong grain refinement after surface treatment. Cr₇C₃ carbide of various shapes and sizes was formed in the structure; while, a several hundred nanometre layer of Cr₂O₃ oxide appeared on the coating surface. The changes occurring in the microstructure have resulted in increased mechanical and tribological properties of the laser-treated zone of deposits.

This work aimed to explore the effect of cBN (cubic boron nitride) content on the microstructures and wear-corrosion resistance of the CoCrFeNiTi_0.8-xcBN (x = 0, 2, 4, 6 wt.%) particle-reinforced high-entropy alloy coatings. Laser cladding technology was used to prepare the coatings on TC18 substrate. The microstructures, volume wear rates and polarization curves were characterized. The results showed that the CoCrFeNiTi_0.8-xcBN coatings had an optimal forming quality under the process parameters: laser power of 1500 W, scanning rate of 12 mm/s and overlapping rate of 60%. As the cBN content increased, plenty of TiN and TiB₂ hard particles formed in situ in the coatings, significantly improved the wear resistance. As a result, the volume wear rate of CoCrFeNiTi_0.8-6cBN was only 4.0% and 16.5% of that of TC18 substrate and CoCrFeNiTi_0.8 coating, respectively; the wear mechanism changed from adhesive wear + oxidative wear to abrasive wear + oxidative wear gradually. Moreover, CoCrFeNiTi_0.8-xcBN coatings can effectively inhibit the infiltration of corrosive media by dense organizational characteristics and the physical barrier effect of oxidation-protective films. After 480 h of neutral salt spray (NSS) test, the CoCrFeNiTi_0.8-xcBN coatings exhibited excellent corrosion resistance, both of the appearance and protection rating reached level 10. Therefore, it can be used as the wear-corrosion-resistant coating for the TC18 substrate in a NSS environment.

The purpose of this study is to investigate the effect of copper powder oxidation on the deposition efficiency, microstructure, wear and corrosion resistance. The gas-atomized copper powders in the as-received (Cu-Safina and Cu-FST) and oxidized states (Cu-treat, oxidized in air, 25 °C for 5 months; Cu-treat1, oxidized at 100 °C for 1 h; and Cu-treat2, oxidized at 200 °C for 1 h) were used to prepare the coatings by cold gas spray (CGS). XPS analysis detected Cu₂O and CuO for all feedstock powders, increasing for oxidized ones. The deposition efficiency and thickness of the coatings followed the order: Cu-Safina > Cu-FST > Cu-treat1 > Cu-treat > Cu-treat2. For oxidized coatings, SEM images showed more defected microstructure, increase in pores, and microcracks. Cu-FST coating showed a sliding wear rate of (0.13 ± 0.01) × 10^-4 mm³ N⁻¹ m⁻¹), and abrasive wear rate of (3.2 ± 0.2) × 10⁻⁴ mm³ N⁻¹ m⁻¹. Gas-atomized powder coatings showed a better corrosion resistance performance. The electrolyte did not reach the substrate/coating interface for t ≥ 700 h and the coatings resisted for 2000 h in salt fog tests. However, oxidized coatings showed low corrosion resistance due to the presence of cracks and defects, and the coating/substrate was severely damaged after ≈100 h in 3.5wt.%NaCl solution.

WC-based coatings are found efficient in providing excellent tribological properties to the structures and components subjected to harsh wear and erosion environments. High-velocity oxy-fuel (HVOF) spraying is known as one of the best techniques to deposit such coatings. However, there still exists scope for further microstructural refinement and improvement in the mechanical properties of the as-sprayed HVOF coatings. Laser remelting has proven to be an appropriate process to achieve such improvement in as-sprayed WC-based coatings. In the current investigation, laser remelting at two different power levels was done on the HVOF-sprayed WC-NiCr coating on stainless steel specimens. The post-processed coatings were analyzed using a scanning electron microscope, x-ray diffraction, x-ray photoelectron spectroscopy, and ImageJ software to study the microstructural changes. Microhardness and surface roughness measurements were also performed to study the mechanical changes. The laser remelting resulted in a smoother coating surface, having lower porosity, lower surface roughness, and higher microhardness as compared to the as-sprayed HVOF coatings. The highest reduction in the porosity was found to be around 72%, whereas, an increment of around 21% in the microhardness was witnessed. These two parameters are crucial for the tribological performance of the coatings. The current study also gives direction to further study these remelted coatings in tribological conditions.