Journal of Thermal Spray Technology最新文献

Thermal sprayed WC-based metal carbide coatings exceptional hardness and superior wear resistance, indicating significant application potential for surface protection of critical equipment in nuclear environments. Nevertheless, the facile activation of metal binders (such as Co) under prolonged nuclear radiation significantly restricts their stability during operation. In this study, a WC-FeNiCrCu_0.5 coating with high-entropy alloy (HEA) as a metal binder was fabricated by supersonic atmospheric plasma spraying (SAPS). The influence of WC particle size on the microstructure and tribological responses of the coating was comparatively studied. The results suggested that the WC-HEA coatings primarily consisted of WC, W₂C, W₂(C, O), and FCC phases. A tight bond was realized between WC and the metal binder inside the coatings, leading to high density. Notably, the inclusion of nano-sized WC as the hard phase achieved a synergistic enhancement of both hardness and toughness. This outcome significantly decreased the wear rate (6.75 × 10⁻⁶ mm³·N⁻¹·m⁻¹) and enhanced wear resistance. The wear mechanism of the coatings was mainly associated with abrasive wear, accompanied by oxidation wear. The wear debris mainly contained of Cr₂O₃, NiO, Fe₃O₄, and WO₃ phases.

In the large scale integration process of solid oxide fuel cells (SOFCs), high performance and highly stable interconnect materials have always been the focus of scholars’ attention. The low temperature stability of traditional metals and the relatively low electronic conductivity of ceramic materials compared with metal materials are the constraints on large scale integration (application). In this study, a new type of interconnect suitable for segmented-in-series SOFCs (SIS-SOFCs) has been developed and is introduced on the anode gas side (LST) of the LST/LSM dual-layer interconnect by mechanical mixing. The coating is prepared by atmospheric plasma spraying (APS), and a composite coating with high density, high electrical conductivity, and high stability that meets the requirements of SOFCs is obtained. The spraying behavior of the composite phase is systematically evaluated by means of phase analysis, in flight particle observation, etc. The ultra-high electrical conductivity of the composite coating further reduces the performance loss. The optimized SIS-SOFCs (n = 9) connected by the dual-layer interconnect has an output power of 25 W at 800 °C, and the maximum power density is 820 mW/cm² (Fuel gas: hydrogen at a flow rate of 2 L/min. Oxidant gas: oxygen at a flow rate of 2 L/min.) Compared with the maximum power density of 430 mW/cm² exhibited by the pure phase LST/LSM at 800 °C, it is increased by 90%. During the 100hrs constant current discharge (0.3A/cm²) test, the performance degradation rate of the cell with 10%SUS430 is 0%. In addition, a nonlinear relationship between the interconnect performance and the cell performance is established. These research results indicate that the composite interconnect prepared by atmospheric plasma spraying is an ideal material system for realizing the interconnect for the SIS-SOFCs.

The performance of thermal barrier coatings (TBCs) was limited by the formation of thermally grown oxide (TGO). Excessive growth of TGO could lead to the coating delamination and spallation, thereby significantly reducing the lifetime of TBCs. In this study, the composite powders (15 wt.% Ti₃SiC₂-CYSZ) were melted into the TBCs by laser alloying to obtain the self-healing TBCs. The microstructure, phase composition and TGO growth behavior of the self-healing TBCs during high-temperature cyclic oxidation were investigated. Results indicated that the high-temperature oxidation resistance of the Ti₃SiC₂-self-healing TBCs was better than that of the as-sprayed TBCs. The Ti₃SiC₂-self-healing TBCs primarily formed TiO₂ as oxidation products, with relatively low amounts of SiO₂. In the early stages of oxidation, the TGO growth rate of the Ti₃SiC₂-self-healing TBCs was higher than that of the as-sprayed TBCs. However, as oxidation time progressed, the oxidation products of Ti₃SiC₂ gradually filled the cracks within the coating, thereby realizing self-healing effect and impeding oxygen penetration, which slowed further TGO growth. Ultimately, the Ti₃SiC₂-self-healing TBCs exhibited a 37% reduction in TGO thickness compared with the as-sprayed TBCs, demonstrating superior high-temperature oxidation resistance. This study provided a new technological approach to enhancing the high temperature stability and durability of TBCs.

Graphite electrodes are widely used and consumed in electric arc furnaces (EAFs). The consumption of graphite electrodes accounts for a significant portion of steelmaking costs. Therefore, by reducing electrode consumption, the costs of steel production can be significantly reduced. In this study, to improve the oxidation resistance and surface electrical conductivity of graphite electrodes, Al and Cu/Al coatings were deposited on the graphite surface by wire arc spraying. The oxidation protective ability of the coated electrodes was investigated using repeated isothermal oxidation tests at 600 °C and 1200 °C for 6 h. The oxidation behaviour of the coatings was investigated using scanning electron microscopy (SEM) and X-ray analysis. Results indicate that the coatings efficiently enhanced the oxidation resistance of graphite at 1200 °C and reduced the weight loss rate of graphite by a factor of three after 6 h of oxidation. The excellent oxidation protection provided by the coating at 1200 °C is attributed to the formation of a dense, protective α-Al₂O₃ layer on the surface. Weight-loss measurements indicate that the oxidation performance of the coatings improved over long-term exposures. This could be due to pores being plugged by oxidation products, which hinder further oxygen penetration through the coatings. In contrast, the coatings provided inferior oxidation resistance for graphite at 600 °C. This is because the generated oxide phases did not provide protection against oxidation at 600 °C. After undergoing oxidation, the Al coating formed only Al₂O₃, while the Cu/Al coating resulted in the generation of CuO, Cu₂O, Al₂O_3, and CuAlO₂. As a result of the superior oxidation protection offered by Al₂O₃, the Al coating provided better oxidation protection than the Cu/Al coating. This study suggests that the high-temperature consumption of graphite electrodes might be reduced if they are coated with Al and Cu/Al.

Electronic interconnects benefit from copper due to its superior conductivity and low cost. Direct-write processes are desired for flexibility, ease and agility in mesoscale, hybrid and packaging electronics manufacturing. Vacuum cold spray (VCS) is an attractive process, but depends on optimization of many parameters to obtain efficient deposition and maximum fidelity. This study uses VCS with different powder feedstocks, nozzle diameters, nozzle standoffs and scan numbers to produce copper lines and pads on glass and silicon substrates. Electron microscopy reveals plasticity-based deposition, building films to thicknesses of several microns. Profilometry and image analysis portray the line profiles, with data fit to Gaussian curves to obtain accurate heights, widths and integrated cross-sectional areas. A figure of merit (FOM), combining height, rectangularity ratio and number of scans, is used to judge the deposition and geometric form of the lines. The FOM in this study has a wide range from 3 to 61 nm/scan. Both the line FOM and rectangularity are correlated with a drop in relative electrical resistivity. A 20-scan, 50-mm-long line is found to have a low electrical resistivity = 4.34 × 10⁻⁸ Ωm, just 2.5 times that of pure bulk copper. The results suggest that VCS copper holds promise for direct writing of interconnects, and the FOM approach is proposed for comparative studies in process development.

This study investigates the use of the internal diameter high-velocity oxygen fuel (ID-HVOF) technology for the deposition of bond coats in thermal barrier coatings, targeting potential applications in enhancing high-temperature protection of internal surfaces of gas turbine engines components. NiCoCrAlY and NiCoCrAlYHfSi powders, in both fine and coarse particle sizes, were applied using a kerosene-fueled ID-HVOF torch. Nitrogen was introduced into the combustion fuel at flow rates up to 150 lpm to extend the deposition window by promoting solid-state particle deposition, thus minimizing nozzle buildup, a key challenge in spraying fine metallic powders with ID-HVOF systems. An atmospheric plasma spray (APS) flash layer was applied to selected bond coats to enhance surface roughness and adhesion to the ceramic top coat. High-temperature performance was evaluated through isothermal and furnace cycle testing at 1150 °C. The combination of nitrogen addition and APS flash layer significantly improved TBCs performance, achieving 900 h in isothermal tests and 390 cycles in cyclic tests, surpassing the 248 cycle lifespan of a conventional APS benchmark coating. These findings highlight the strong potential of ID-HVOF for producing high-performance bond coats in next-generation TBC systems, offering a viable solution for coating internal surfaces in advanced gas turbine engines.

Environmental barrier coatings (EBCs) are necessary to achieve the long life required of SiC/SiC ceramic matrix components (CMCs) in the hot section of gas turbine engines. The most common EBC material in use today is ytterbium disilicate (Yb₂Si₂O₇) and has been the benchmark protection system since the early 2000s. As CMC use expands, the demand for EBC deposition and processing control will grow accordingly. Novel methods such as plasma spray-physical vapor deposition (PS-PVD) are also being evaluated for their capabilities in EBC deposition. Ytterbium disilicate powder was deposited on SiC substrates via PS-PVD to evaluate the effects of carrier gas chemistry and flow as well as torch traverse speed and powder injector orientation. Coating microstructure and phase were evaluated using x-ray diffraction and scanning electron microscopy. A range of coating compositions were generated, including a mixture of ytterbium monosilicate (Yb₂SiO₅) with the disilicate as well as configurations with excess silica (SiO₂).

A binder-free powder processing method is introduced for the preparation of Al₂O₃ nanoparticle-reinforced AA6061 composite powders intended for cold spray deposition. In this approach, 30 nm Al₂O₃ nanoparticles are uniformly laid down onto the surface of micron-sized AA6061 powder particles through natural electrostatic attraction, eliminating the need for any organic binders or dispersants. With only 1 wt.% nanoparticle addition, a network of nanoceramic particles is formed on the metal particle’s surface, producing a composite feedstock that retains the flowability and deposition characteristics of pure AA6061 powder. The decorated powders were successfully employed as feedstock in a low-pressure cold spray process, yielding coatings with embedded Al₂O₃ nanoparticles distributed along splat interfaces. Upon heat treatment at 430 °C for one hour, the nanoparticles effectively pinned dislocations and stabilized low-angle grain boundaries inside the splats, thereby suppressing recrystallization and grain growth. As a result, the coated composite exhibited remarkable thermal stability and maintained its hardness more than twice that of the AA6061 coating. The enhanced mechanical properties and microstructural stability are attributed to the synergistic strengthening mechanisms provided by the nanoparticles, including dislocation pinning and Orowan strengthening. These findings establish nanoparticle surface decoration as a simple and scalable approach for producing cold-sprayable metal matrix composite powders that achieve enhanced hardness and thermal stability with minimal ceramic reinforcement.

Graphical Abstract

In the present study, (Ti,Nb)N-based composite coatings with a thickness of 250 μm are prepared using reactive plasma spraying technology, and the effect of Nb content on structure, conductivity, and corrosion resistance is investigated. The (Ti,Nb)N-based composite coatings with a crystal size of 40-200 nm have multi-layered structures, and each layer is composed of NbTiN₂, Ti₃O, and Nb. As the Nb content increases, the density of the coating increases, and the Nb-30 wt.% coating exhibits the highest density. The Nb-30 wt.% coating exhibits the lowest interfacial contact resistance (12.58 mΩ cm²) under a compaction force of 1.5 MPa. In a simulated proton exchange membrane fuel cell (PEMFC) environment, the Nb-30 wt.% coating demonstrated superior corrosion resistance and stability. In the potentiostatic polarization tests at 0.6 and 1.2 V, compared with the other two coatings, the corrosion current density of the Nb-30 wt.% coating stabilizes first. The Nb-30 wt.% coating exhibits a higher corrosion potential and a lower corrosion current density compared to 45# steel. During prolonged corrosion testing, defects in the coating are gradually sealed by corrosion products generated from the reaction between the corrosive solution and the NiCrAlY bonding layer, resulting in a "self-sealing" effect and enhanced corrosion resistance.

This research focuses on the development of superhydrophobic TiO₂-based coatings by suspension flame spraying. Also, HVOF-, flame-, and plasma-sprayed powder coatings were studied as ref [erences. Furthermore, their hydrophobicity was improved by applying stearic acid to functionalize surfaces. In the flame spray process, both powder and suspension feedstock were studied, and the suspensions modified by adding epoxy and polydimethylsiloxane (PDMS) to examine their impact on coating properties. Among the conventional processes, plasma-sprayed coatings achieved a water contact angle (CA) of 145° while the suspension flame-sprayed coatings had CAs as high as 165°. This improvement was linked to structural changes like the formation of nanostructures. Coatings produced with solid powder feedstock did not show water droplet mobility, whereas the sliding angle decreased with the suspension feedstock and was reduced to less than 5° with epoxy and PDMS-modified suspensions. Incorporation of these polymers increased the stability of coatings under UV exposure and at low temperatures. Coatings with PDMS were more durable and stayed superhydrophobic for at least 180 days under UV exposure. In contrast, coatings without modifications became superhydrophilic within 23 days. This study demonstrates the potential of suspension flame-sprayed coatings for applications where robust superhydrophobic surfaces and environmental durability are needed.