Journal of Thermal Spray Technology最新文献

Laser-assisted cold spraying (LACS) is garnering significant interest as an innovative surface treatment technology that integrates cold spray technology with laser. However, the primary role of laser on in-flight particles remains underexplored. This study aims to elucidate the impact of laser on in-flight particles through meticulously designed experiments and comprehensive multi-physical field simulations, in which the in-flight iron and nickel particles were heated by the laser parallel to the substrates and deposited on the substrates, while the substrates were not heated by the laser. The cross-sectional microstructures, porosity, oxygen content and microhardness of the coatings were characterized to assess the effect of the laser on the in-flight particles. The heating behavior of the in-flight particles under varying velocity and laser power was evaluated using multi-physical field simulations. The results indicated that the microstructures and properties of the coatings, including porosity, flattening ratios, oxygen content and microhardness, were not significantly influenced by the laser irradiation. The simulations further revealed that the laser irradiation had negligible effect on the temperature variation of the in-flight particles, attributed to the short duration time of laser exposure. The investigation enhances our understanding of the mechanism of LACS.

A key factor to ensure a sustainable future for the air transport industry is electrification. Exploring new designs for permanent magnet electric motors could increase their potential. Unfortunately, complex shaped magnets cannot be produced easily using current fabrication methods. Cold spray additive manufacturing could eventually help to alleviate this problem by allowing the fabrication of magnets with complex geometries consolidated on electric motor parts. Furthermore, another aspect to increase the electric motors’ efficiency is the possibility to operate at higher RPM and with higher electrical currents, consequently generating more heat. Currently, most magnets are prepared with NdFeB, which is less tolerant to high-temperature exposure. This work reports on the cold spray additive manufacturing of samarium-cobalt (SmCo), a material of growing interest since it preserves most of its magnetic properties up to 350 °C. The permanent magnets were fabricated using a SmCo-Al composite powder mix in a standardized simple geometry to evaluate the impact of the fabrication parameters. The impact of the powder mix composition and the gas temperature on the magnetic properties is investigated. The results demonstrate that the use of cold spray would be effective for fabricating SmCo composite permanent magnets directly on the electric motor parts.

In this experimental study, diamond-reinforced Ni-P coatings were developed by flame and high-velocity air fuel (HVAF) spraying techniques using Ni-P capped diamond powder. Further, effect of heat-treatment on microstructure, structural, hardness and high temperature wear characteristics of the above coatings was investigated. After heat-treatment, high hardness was observed in HVAF coating compared to flame sprayed which is attributed to the high porosity of the latter as evident from the microstructure. Extensive diamond particle fragmentation was observed in the HVAF sprayed coating, providing motivation for including the lower velocity flame spraying in this work. It is interesting to note from the wear tests that coatings deposited by flame spraying exhibited superior wear resistance and low friction coefficient at high temperature, i.e., under dominated oxidative wear conditions, which is attributed to the soft matrix leading to diamond particles’ exposure and graphitization. However, hard and dense heat-treated HVAF sprayed coatings exhibited highest wear resistance in room temperature tests dominated by abrasive wear mechanism as evident from the wear track morphology. Raman spectroscopy and energy dispersive spectroscopy analysis (EDS) confirmed the graphitization for the flame sprayed coatings and formation of oxides in the wear tracks.

The Ti-6Al-4V alloy is widely used in aerospace applications for its excellent mechanical properties; however, it presents low wear resistance. It is often coated with a cermet using high-velocity oxygen fuel (HVOF) spraying to improve its wear performance. The Cr₃C₂-NiCr cermet becomes particularly interesting since it is non-carcinogenic, compared to traditional cermet coatings containing tungsten-cobalt compounds. While the improvement in wear resistance of Ti-6Al-4V with this coating has been demonstrated, its impact on the fatigue performance of the alloy remains to be studied. This is precisely the aim of this study, which focuses on the fatigue life of a Cr₃C₂-25NiCr-coated Ti-6Al-4V alloy. Among the various influencing factors, surface preparation represents a significant source of crack initiation, particularly in the case of sandblasted surfaces. Indeed, the inclusion of fragmented alumina particles can produce stress concentration zones. Thus, laser texturing, which is a method involving the creation of anchoring points through controlled ablation, can be considered today as a less harmful surface preparation technique. The results obtained from cyclic tensile fatigue tests with a stress ratio of 0.1 for these two surface preparation methods, both with and without the coating, are presented in this paper.

Cold spray has been extensively applied to deposit a range of materials in many industries. In the recent times, such a method has also shown its potential to deposit nickel-based superalloys, which currently are in demand due to their high tensile strength and corrosion resistance (especially at elevated temperatures); however, cold sprayed nickel super alloy coatings have poor mechanical properties due to the materials’ limited ability to undergo plastic deformation. Regarding this, numerous cold spray process modifications have been experimented, including preheating substrate and feedstock powder, applying laser irradiation, heat treating coatings post deposition, and heat treating feedstock powder, to promote plastic deformation, eliminate porosity and enhance inter particle bonding. Specifically, the important influence of external heat input on the underlying substrate and/or the incoming particles during cold spray deposition was highlighted in multiple studies. These studies indicated that the addition of external heat during cold spray increased the adhesion strength of the coatings due to an increase in the thermal softening effect of the deposited particles. In general, an attempt is made here to systematically review the influence of cold spray process modifications on the microstructure, mechanical properties and residual stresses of nickel super alloy coatings.

To achieve higher engine combustion efficiency while reducing emissions, it is necessary to address the challenges posed by elevated operating temperatures. High entropy alloys (HEAs) have emerged as promising materials for this purpose, offering exceptional properties at high temperatures, including synergistic effects and excellent resistance to oxidation and corrosion. In this study, a FeCoNiCrAl HEA was investigated as a bond coat material due to its excellent balance of strength and ductility, coupled with outstanding oxidation resistance. It was deposited using HVAF M3 and i7 guns equipped with different nozzles/powder injectors and pressures. Notably, this research marks the first study of the i7 gun globally for the HEA bond coat, coupled with the optimization of HVAF parameters for both i7 and M3 guns. Characterization of both powder and as-sprayed samples was carried out using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and field emission scanning electron microscopy (FESEM) techniques. The results revealed the formation of a dense and homogeneous microstructure. Additionally, isothermal oxidation tests were conducted to analyze the behavior of the thermally grown oxide. After 50 hours at 1000 °C, a dense, uniform, and thin alumina TGO layer was observed to have formed. These tests revealed that FeCoNiCrAl HEA exhibits significant potential to enhance oxidation resistance at high temperatures.

Aerosol deposition (AD) is capable of producing dense nanocrystalline ceramic films at room temperature. Most studies have focused on flat, smooth substrates, but the growing demand for miniature devices requires coatings on various substrates, including rough, structured, or patterned surfaces. This study investigates the influence of substrate structures in AD by depositing alumina coatings on patterned silicon (Si) substrates. The growth process and microstructure of coatings deposited on Si substrates with different pillar widths, heights, and spacings have been analyzed. Results show that coatings initially form in the valleys with particle fragments before covering the entire pattern and developing a uniform layer. We demonstrate that the relative size of the substrate patterns and powder particles significantly influences the coating microstructure, particularly in the valleys between the pillars. Dense coatings were deposited on all patterned substrates except those with deep, narrow valleys, where only accumulated powders were found in the grooves.

In the process of High velocity oxygen fuel (HVOF) spraying, micron-sprayed particles are bound to oxidize under high temperature oxygen-containing environment, particle oxidation and burning are the key factors affecting coating quality. However, how to quantitatively evaluate and control particle oxidation is the bottleneck problem faced by the industry. In this paper, a three-dimensional transient calculation model of flame flow during HVOF thermal spraying WC-12Co process was established, and the computational fluid dynamics and discrete phase surface reaction model were combined to calculate and reveal the distribution characteristics of flame flow and the oxidation degree for particles during the spraying process. The calculation showed that the oxide layer thickness of particles varies greatly with different particle sizes. The oxide layer thickness of particles with 5 μm size is about 90 Å, and the oxide layer thickness of particles with 60 μm size is only about 8 Å. By adjusting the process parameters of oxygen/fuel ratio, particle size and nitrogen mass flow rate in the model, the output samples of sprayed particle flight temperature, velocity and oxide layer thickness can be obtained. On this basis, the sample data were statistically analyzed based on Genetic Algorithm-Back Propagation (GA-BP) neural network model, and the optimal process parameters for preparing the optimized coating were determined: particle size 27 μm, oxygen/fuel ratio 3.1, nitrogen mass flow rate 0.000363 kg/s. Experiments were carried out with optimized parameters, the results show that the optimized coating has fewer defects, lower oxide content and higher hardness and wear resistance. This study provides an important theoretical basis for quantitative preparation of high quality HVOF spray coatings.

Developing new materials and alloys for coatings is increasingly crucial to reduce costs in manufacturing. Inconel, a widely used alloy, is known for its chemical inertness and resistance to high temperatures, but it lacks sufficient resistance to erosive wear. This study evaluated the wear resistance of Inconel 718 and Inconel 718 + 10% NiNb coatings produced by laser cladding, focusing on cavitation and slurry erosion. Scanning electron microscopy (SEM-EDS), x-ray diffraction, and microhardness profiling were employed to analyze the microstructure and wear. Cavitation erosion tests followed the ASTM G32 standard (2016), and slurry erosion resistance was tested according to ASTM G73-10 (2017). Mass loss and wear rates were assessed for both coatings. The laser-cladding IN718 and IN718 + 10% NiNb coatings exhibited solidification structures with fine dendrites, low dilution, no cracks, and minimal porosity. Adding 10% NiNb refined the microstructure, reducing dendrite size and improving the overall coating quality. This also resulted in a 45% increase in microhardness for the IN718 coating. A higher dispersion in microhardness was observed in the IN718 + 10% NiNb coating. The addition of 10% NiNb promoted the formation of thicker interdendritic zones in an interconnected network, with a higher concentration of the Laves phase. This enhancement increased cavitation resistance and improved slurry erosion resistance by 33% at a 60° impact angle. However, at a 30° impact angle, the improvement was less effective. This study demonstrates the potential of IN718 + 10% NiNb coatings for applications demanding enhanced cavitation and slurry erosion resistance, particularly at higher impact angles.