Journal of Thermal Spray Technology最新文献

Cold spray is an additive manufacturing and coating process in which powder particles are accelerated to supersonic speeds without melting them and then deposit on a surface to form a layer of a coating. Process parameters and materials affect the characteristics of manufactured parts and therefore must be chosen with care. Machine learning (ML) techniques have been specifically applied in additive manufacturing for tasks such as predicting and characterizing porosity. Machine learning algorithms can learn how a variation in the input spray parameters affects annotated output data, such as experimentally measured part properties. In this work, a dataset was developed from experiments reported in published academic papers, to train ML algorithms for the porosity prediction of cold spray manufactured parts. Data cleaning steps, such as null value replacement and categorical feature handling, were applied to prepare the dataset for the training of different ML models. The dataset was split into training and testing portions, and floating feature selection and hyperparameter optimization were performed using parts of the training set. A final evaluation of all trained models, using the test portion of the dataset, showed that a prediction accuracy with an average deviation of 0-2% porosity of the predicted values compared to the true values can be achieved.

Graphical Abstract

Herein, the effects of Gd₂O₃ on the laser cladding NiCoCrAlYTa coatings in terms of microstructure, phase structures, high temperature oxidation behaviors were investigated. The results showed that the addition of Gd₂O₃ changed the composition of coating phases, promoted homogeneous phase distribution, reduced porosity and improved coating density. During oxidation at 1100 °C for 150 h, the increase in the content of added Gd₂O₃ (at mass fractions of 0, 0.5, 1, 2, 5 and 10%) exhibited an initial inhibitory and then increased effect on the weight-gain rate of the coatings. Overall, 1% Gd₂O₃ addition resulted in the greatest improvement in the oxidation resistance of the coatings, with 49.58% decreases in oxidation kinetic constants, respectively, compared with those of unmodified coatings. However, at a Gd₂O₃ content of 10%, the thermally grown oxide on the coating surface exhibited large flaking areas. The high-temperature oxidation kinetic parameters of the coatings exhibited an inverted parabolic form with increasing Gd₂O₃ content. The higher Gd₂O₃ content led to the formation of excessive oxygen diffusion channels along grain boundaries, which is the reason for the decrease in the anti-oxidant performance of the coating.

Owing to its reflectivity, Copper manufacturing has always been challenging through laser-based additive manufacturing. In this study, we demonstrate additive/bulk manufacturing of copper using high velocity air fuel (HVAF) spray technology, an emerging variant in the thermal spray family. Rapid deposition of millimeter scale copper parts with good mechanical integrity and decent ductility, comparable to that of cold spray, has been shown feasible. The mechanical properties measured along different built directions showed no significance to be considered anisotropic. Electron backscattered diffraction analysis revealed the possibility of developing favorable bimodal grain distribution with a high volume fraction of ultrafine grains (>50%). However, the intersplat porosities and continuous pores were found to be detrimental despite the low overall porosity. HVAF technology demonstrates great potential and appears to be a promising process methodology for bulk/additive manufacturing of metals with a rapid production rate.

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Polymers have proven to be challenging to cold spray, particularly with high efficiency and quality when using inexpensive nitrogen (N₂) and air propellants. Helium (He), when used as a process propellant, can improve spray deposit properties but is often undesirable due to its limited availability and high cost. In this study, additives of multiple particle sizes and materials were mixed with polymer powder in an effort to improve the performance of polymer sprays using mainly N₂ as a process propellant. The effects of hard-phase additives on deposit microstructure were investigated by precise ion beam polishing of deposit cross sections and subsequent electron microscope imaging. Additional metrics including the density and post-spray composition of deposits were investigated to quantify the peening effect and the amount of embedded additive. Additives, regardless of size, were observed to embed in the spray deposits. Additionally, hard-phase additives demonstrated nozzle cleaning properties that continually remove polymer fouling on the nozzle walls. Inversely, sprays with polymer powder and no additives tended to clog the nozzle throat and diverging section because of continual fouling.

In this study, the role of feedstock powder in influencing the characteristics of cold spray deposition is explored. Four distinct types of Cu feedstock powders, derived through electrolysis and employing varied gas atomization methods, are applied to a Cu substrate via low-pressure cold spray coating. We investigated the impact of feedstock powder on the resultant coatings' microstructure and mechanical properties. A comprehensive statistical model is developed, considering the cold spray parameters, weight change, coating thickness, and discerning their significance and interactions. Optimal conditions for carrier gas temperature and pressure are identified at approximately 400 °C and 1.99 MPa, respectively, consistent across all Cu powders. Velocity analysis reveals particle velocities ranging from 373 to 564 m/s under these optimal conditions. Coatings deposited using satellite-free gas-atomized powder, characterized by enhanced sphericity, exhibit superior characteristics, including minimal porosity (0.66 ± 0.35%), high flattening ratio (3.57 ± 1.51), elevated microhardness (107 ± 3 HV) and high bonding strength (20.7 ± 2.3 MPa). In contrast, coatings deposited with gas-atomized powder featuring microsatellite particles and electrolytic powder with irregular shapes display distinct properties. The observed trends are attributed to lower oxygen content and reduced oxide levels near the surface of the more spherical, satellite-free powder. This powder also demonstrates heightened plastic deformation during deposition. The increased peening effect of satellite-free gas-atomized powder during cold spray results in elevated dynamic recrystallization near the substrate surface, leading to smaller grains at the interface. Microstructural evolution analysis, utilizing electron backscatter diffraction, further elucidates the heterogeneous deformation and grain refinement occurring in Cu splats during cold spray coating.

The surface modification technology based on high current pulsed electron beam (HCPEB) can eliminate the porous structure of thermal sprayed coatings and obtain amorphous coatings with excellent corrosion resistance. In this study, Al-Co-Ce master alloy and powder were firstly prepared, followed by the preparation of an Al-Co-Ce alloy coating on Q235 steel substrate using high velocity flame (HVOF) spraying technology. Finally, HVOF sprayed coating was irradiated and remelted by HCPEB to change its porous crystalline microstructure into dense and amorphous form which greatly enhances its corrosion resistance. The combination of thermal spraying and HCPEB surface remelting proposed in this study provides a new process for preparing Al-Co-Ce amorphous alloy coatings.

Graphic Abstract

Diagram of surface structural transformation of Al-Co-Ce coating

Cold spray (CS) is a rapid additive manufacturing method for deposition of metallic materials at rates significantly exceeding the laser-based methods, while retaining high deposit quality and low process cost. The mechanisms of the high-rate, extensive deformation of the materials in the CS process were recently intensively studied on macro- and meso-levels. In this paper, we introduce positron annihilation spectroscopy as a viable and reliable analytical method to study lattice defects created in the cold sprayed materials on the atomic-scale level. For the first demonstration, four different base metals were selected (Al, Cu, Ni, and Ti). A high density of dislocations was observed in all four deposits. In addition, deposits of fcc metals (Al, Cu, and Ni) also contain a considerable concentration of vacancy clusters. The results show that the extremely fast deformation in cold spray deposition process prevents recovery of vacancies which tend to agglomerate into clusters.

Cold spray (CS) technology has proven a great potential in the production of composite coatings, enabling the production of materials with superior qualities such as enhanced tribological behavior. This study aims to investigate the tribological properties of CS Al-based composite coatings reinforced by quasicrystalline (QC) particles. Two different Al alloys were used as the matrix, AA 6061 and AA 2024, and mixed with Al-based QC particles (Al-Cr-Fe-Cu) at different Al/QC ratios. A room-temperature ball-on-disc test was then used to evaluate the wear resistance of the composite CS coatings in air and compared to those of the non-reinforced Al alloy CS coatings as well as a cast counterpart (AA 6061-T6). We have demonstrated that CS could be employed to produce thick and dense Al-QC composites that can retain up to about 50 wt.% QC reinforcement in the structure. The incorporation of the QC particles increased the wear resistance by a factor of 7.

For metal-supported solid oxide fuel cells, gadolinium-doped cerium ceria (GDC) is one of the most promising electrolyte materials due to its high ionic conductivity at medium and low temperatures. However, using traditional sintering method to prepare GDC electrolytes at high temperature can lead to interdiffusion between the metal supports, electrolytes, and electrodes, which can seriously impact cell performance. In this paper, the GDC electrolytes were prepared using atmospheric plasma spraying technology, which could avoid the issue of high-temperature sintering. The effects of different spraying distances on the microstructure, interface, and cell performance were studied. The results show that the cell performance is optimal when the spraying distance is 80 mm. The open-circuit voltages of the single cell at 500, 600, and 700 °C are 0.866 V, 0.82 V, and 0.75 V, respectively. The peak power densities at these temperatures are 66.2, 182.8, and 386 mW/cm², respectively. It provides a reference value for the commercialization of metal-supported solid oxide fuel cells prepared by plasma spraying.

With multiple merits compared with thermal spray, cold spray technology is widely applied for various application fields. As part of an intelligent cold spray repair system, an approach for three-dimensional (3D) damage region contour extraction is proposed, which is without nominal Computer-Aided Design models and prior knowledge of damaged workpieces. Moreover, due to partially image processing based, the computation load of the proposed method is lower caused by partially avoiding the 3D point cloud processing. According to the results, it is capable to handle the uneven, sparse and unorganized point cloud to precisely extract 3D contour of damage region. The effectiveness of the proposed approach is highlight. Furthermore, the proposed methods on 3D cloud point to grayscale conversion, two-dimensional (2D) edge detection on images, 3D contour reconstruction from 2D edge are also promising for point cloud processing in other application fields.