Cold spray (CS) is a solid-state process for depositing metal powder, accelerated by a high-velocity gas such that it bonds to the substrate metal through kinetic impact energy. Although the technology is finding applications in non-load bearing repair and coating applications, work is needed in the quality control procedures for CS for its use in load bearing structural applications. in this study, the viability of electrical conductivity and through thickness ultrasound wave velocity measurement methods are studied to serve as a means for nondestructive quantitative measurement methods for quality control in CS and potentially other additive manufacturing (AM) methods. Eddy current, ultrasound, porosity, hardness, and uniaxial tensile strength tests were conducted on copper and aluminum samples that were manufactured using CS. Ultrasound measurements of longitudinal wave velocity and eddy current electrical conductivity measurements showed good correlation with process conditions that were varied to control particle velocity to intentionally produce samples with varying deposition quality. Influence of process conditions on particle velocity was confirmed via particle image velocimetry. Porosity, hardness, and tensile test results were further correlated to ultrasound wave velocity and electrical conductivity measurements. The results of this work show that nondestructive testing methods can be effectively used to quantitatively assess the cold spray products for quality control purposes.

In conventional powder processing, there has been considerable work on classifying feedstock powders based on particle size distribution, morphology, microstructure and composition, since these influence processability and final properties. Cold spray is a new application for powders and conventional characterization may be insufficient to assess powder cold sprayability. In particular, metallic powders have an oxide layer, which breaks during impact with the substrate or with another coating layer during cold spray; this fragmentation facilitates bonding. It has been suggested that the thickness of the oxide layer can influence the mechanism of fragmentation; thicker oxides are easier to remove, revealing clean metal surfaces that can metallurgically bond. Consequently, not all high-purity powders or powders that are stored in ambient conditions have the potential to give good coating properties after cold-spray. This work focuses on surface oxidation of the powders, characterizing the variation of oxide film aspects with size and composition of nominally pure copper powders using X-ray Photoelectron Spectroscopy (XPS). The results indicate the presence of Cu (I) and Cu (II) oxide species on the surface of as-received, naturally aged and heat-treated powders; their thickness is determined using the depth profiling feature.

As it has been demonstrated that the use of the observation equipment applied on the spray process helps to gain a better coating in terms of properties, non-intrusive observation equipment (Control Vision Inc's SprayCam) is used in the current work for the observations of the jet and particles during the spray process. The application of such in-situ observation techniques concerns the field of cold spraying and brings new insights into the formation process of cold sprayed coatings. The build-up of coatings operated with different parameters (copper powder, nozzle, etc.) are recorded with an extreme short unit of time and then analyzed with the help of digital techniques such as image processing. The basic theories on cold spraying were previously verified by simulation and then compared to experimental results considering the distribution of flying particles involving in the build-up of the coating. The accumulation of data collected by in situ processing techniques during the spray allows understanding the complete steps of the coating formation consequently could bring the entire cold spraying mechanism to a higher level of research.

With an increasing demand for lower fuel consumption of different means of transportation, the demand for lightweight construction materials is rising. In this frame, usually metallic parts can be replaced by components consisting of fiberreinforced plastics. On the other hand, the components lose their electromagnetic field (EMF) shielding properties, which are required for many applications such as housings for electrical components. This issue can be solved by applying electrically conductive foils or meshes, often by a manual process that increases the time of production and process. In this publication, the application and parameter influence of thermally sprayed electrically conductive coatings for EMFshielding applications is discussed. Laser structuring is used as a novel surface preparation process, for the subsequent thermal spray process. The influence of the used laser-parameters is discussed accordingly. The coatings are applied by the wire-arc spray with Zinc feedstock as well as the atmospheric plasma spray (APS) process with Copper feedstock. It was found that coating properties such as adhesion strength, EMF-shield strength as well as electrical properties are provided by the proposed technology.

The quality of feedstock powder is a critical factor in determining the properties of coatings deposited using cold spray (CS). However, most commercially available powders are not designed or optimized for CS applications, making it challenging to tailor powders to desired quality. In this research, we investigated and compared the cold-sprayability of four different Cu powders produced by electrolysis and gasatomization methods. We assessed the powders' microstructure, particle morphology and size distribution to understand the effect of manufacturing methods on Cu powder characteristics. We also studied the flowability of the powders using the shear cell method and evaluated their mechanical properties and deformability for CS using nano-indentation. Our results showed that gas-atomized powders with equiaxed grains exhibited promising flowability and deformability for CS applications, outperforming the other powders tested. Specifically, the spherical morphology of gas-atomized powders provided less surface area than the irregular-shaped electrolytic powder, reducing the interaction of surface forces and contributing to smooth powder flow. Additionally, the gasatomized powder with small dendrites in the microstructure exhibited the highest nano-hardness value (HIT= 1.6±0.1 GPa), while the porous electrolytic Cu powder had the lowest value (HIT= 0.7±0.2 GPa). In conclusion, we found that gas-atomized Cu powders with equiaxed grains may hold promise as the optimised feedstock for CS application, considering both effective metrics of flowability and deformability.

Viruses and microbial pathogens can survive for hours on fabrics. This paper reports that copper-doping of natural and synthetic fabrics inactivates, within minutes, a human COVID surrogate pathogen. The fabric is embedded with copper particles by twin-wire arc thermal spray. The long-lasting fabric surface simultaneously provides good breathability, it is scalable and cost-effective. Virucidal activity is not affected by repeated washing of the fabric. Importantly, copper-embedded material will provide effective protection against all classes of pathogens, regardless of their mutation rates and infection strategies. It also can provide protection against all classes of pathogens, regardless of their mutation rates in industrial and residential filters.

Aerosol cold spraying (ACS) is modification of low-pressure cold spray technology which allows to deposit ceramic and metal-based coatings. ACS technology in vacuum possesses the formation of films from sub-micro and nanoparticles directly at room temperature. The ACS technology is still under development to cover more application and discover solutions of spraying different kind of powders on different types of material substrate and optimizing spraying conditions to obtain the best results. The main objective of the present work is to develop a new ACS cold spray technology of Hydroxyapatite (HA) and Copper powder deposition onto both the implants and ceramic substrates. The new AD spraying system with radial injection of particles to be deposited is constructed and tried. An influence of technology parameters on the coating structure and properties are presented. In addition, the combined cold spray and sintering technology technique is further investigated for additive manufacturing applications.

In line with the industrial trend of additive manufacturing, cold spray as a non-laser-based process is becoming increasingly important for many fields of application. For the evaluation of additive manufacturing of winding components made of copper for large electrical high-voltage machines, material and component properties such as electrical conductivity, mechanical load capacity and the component size that can be produced are of particular importance. In this context, the cold spray process offers advantages over laser-based additive manufacturing processes such as laser powder bed fusion (LPBF) or laser cladding by using the kinetic energy of the copper powder particles to generate particle bonding. To investigate the electrical conductivity as well as the mechanical load capacity of cold spray parts, specimens were machined out of cold sprayed bulk copper deposits. The characteristic values were obtained with regard to the direction of deposition, which is defined by the direction of the robot’s movement. Thus, for the investigation of the component properties, specimens were provided that had been produced both aligned lengthwise and crosswise as well as vertically to the direction of deposition. The results of the investigations show that both the electrical conductivity and the mechanical load capacity of the specimen have a strong dependency of the specimen orientation with respect to the direction of deposition. Furthermore, it could be shown that by increasing the deposition height, there is an increasing oxygen content in the sample material, combined with increasingly significant defect networks. These effects have a negative impact on the electrical conductivity as well as on the mechanical load capacity. As a conclusion, further need for investigation is identified in the optimization of the process parameters as well as in the deposition strategy for the additive manufacturing of large-volume components with cold spray.

This study aims to develop a metal-based compatibilizing sublayer on a Carbon Fiber-Reinforced Polymer (CFRP) composite to overcome the erosion issue of polymer substrate using the cold spray deposition technique. The objective is to contribute to the in-situ repair of aircraft structures. Two cases of sublayers, i.e., Al-based sublayer (1126 μm thick) and Cu-based sublayer (547 μm thick), have been prepared and co-cured with the CFRP substrates by pressure assisted molding process. Gas-atomized copper powders were deposited on a reference sample of aluminum panel (A-0) and on two functionalized composite substrates (A-1 and C-1) by a high-pressure cold spraying (HPCS) process. The results show that cold spray deposition onto the Al-based sublayer leads to a coating formation whereas the Cu-based sublayer is strongly eroded by the supersonic collision of copper powders. Scanning electronic microscope (SEM) morphologies were used to investigate the HPCS deposition mechanisms on various configurations of substrates. It was found that the high deposition efficiency of case Cu/A-0 was achieved by metallic bonding, evidenced by the significant flattening powders and agglomeration phenomenon of multiple particles. The copper particles of case Cu/A-1, encapsulated by the deformed aluminum powders, could anchor to the substrate via mechanical interlocking, whereas only pure localized fracture of epoxy and exposed broken carbon fibers were observed on the substrate of case Cu/C-1. The results demonstrated the feasibility of an Al-based sublayer-assisted cold spray process for the thermosetting CFRP composite to achieve a successful deposition of copper powders, which also emphasized the necessity to search an optimal material coupling between sublayers and coatings.

Abradable seal coatings are widely employed in the gas turbine of aero-engine, which not only strength enough to resist the impact of external particles and airflow, but also excellent wear resistance. In the current study, we concentrate on APS sprayed Aluminum Bronze Polyester abradable coating that can be used in turbo engines both for seals and clearance control. A composite thermal spray powder, substantially in the form of clad particles each of which has coarse polyester powders and sub-particles of Cu-Al alloy powders, was prepared using mechanically clad process. Abradable seal coating was prepared by atmospheric plasma spraying. The microstructure, hardness, bonding strength, thermal shock resistance and corrosion resistance of coatings were researched. Properties of the coating were able to meet the application requirements. The coating microstructures and phase compositions were evaluated via SEM. The corrosion mechanisms of the coating were compared by analyzing the cross-sectional and top surface microstructures of the as-sprayed and eroded coatings.

Unlike their metal counterparts, composite structures do not readily conduct away the electrical currents generated by lightning strikes. Cost reduction and expected production growth of the next middle range airplanes require automated manufacturing process of polymer components. The development of an automated technology to metallize polymer based composite for lightning strike protection is the aim of the CO3 project (EU Grant agreement: ID831979). In this study, thermal and electrical conductivities of composites were achieved by cold spray deposition of Cu or Al coatings. Critical points to be addressed were substrate erosion during cold spray, lack of polymer-metal adhesion and poor deposition efficiency. Several strategies were tested: i) a thin polymer film was cocured at the substrate surface before cold spraying, to enable implantation of metallic particles in the film, helping coating build-up and protecting the fibers of the composite. ii) Cold spraying a mix of metal and polymer powders to improve coating adhesion and prevent fiber damage. iii) Supercritical Nitrogen Deposition technology, prior to cold spray, to mechanically anchor metallic particles into the polymer. Subsequent cold spraying of purely metallic coatings was more efficient and showed better adhesion. All coatings were tested in terms of adhesion strength and electrical conductivity.

In this study, a new physically-based finite element approach is proposed to model and predict the superficial oxide layer removal and the occurrence of localized metallic bonding during particle impacts. The process physics, based on explosive welding theory and experiments, and method implementation is presented. Prediction of critical velocity of copper is obtained and compared to experimental data to validate the model. Moreover, the model is also able to show the bonding locations at the interface between particles and substrate. The predicted bonding locations are consistent with experimental data from literature for several metals.

Grinding wheels are usually manufactured by powder metallurgical processes, i.e. by moulding and sintering. Since this requires the production of special moulds and the sintering is typically carried out in a continuous furnace, this process is time-consuming and cost-intensive. Therefore, it is only worthwhile for medium and large batches. Another influencing factor of the powder metallurgical process route is the high thermal load during the sintering process. Due to their high thermal sensitivity, superabrasives such as diamond or cubic boron nitride are very difficult to process in this way. In this study, a novel and innovative approach is presented, in which superabrasive grinding wheels are manufactured by thermal spraying. For this purpose, flat samples as well as a grinding wheel body were coated by low-pressure (LP) cold gas spraying with a blend of a commercial Cu-Al2O3 cold gas spraying powder and nickel-coated diamonds (8-12 μm). The coatings were examined metallographically in terms of their composition. Afterwards, the grinding wheel was conditioned for the grinding application and the topography was evaluated. This novel process route offers great flexibility in the combination of binder and hard material as well as a costeffective single-part and small-batch production.

A previous study showed that Cu can be cold sprayed onto carbon fiber-reinforced polymers (CFRPs) if a Cu interlayer is deposited prior to low-pressure cold spraying. In this present study, Cu was cold sprayed onto CFRP substrates that were coated with either Sn (cold spray) or Ni electroplating. Two layers of Cu powder were also cold sprayed onto a Cu-plated CFRP substrate to investigate the effect of a second particle layer on impacting particles. Test results showed that the relative hardness between the particle and substrate has a major effect on deformability, impact mode, and deposition efficiency (DE), which explains why Cu could not be cold sprayed onto Sn or Ni interlayers and why the deposition efficiency of Cu-on-Cu substrates is lower than that of one pass spraying. In summary, the results suggest that Cu can be successfully cold sprayed at low pressures onto electroplated Cu due to their similarity in hardness.

This study investigates the in-flight behavior of particles during cold spraying by means of high-speed shadowgraph photography using a laser imaging system. It also characterizes the particle jet outside the nozzle for different powder sizes (<10 µm to 155 µm) and densities (copper, aluminum). Observations of the jet reveal two low-pressure cold spray flow regimes, one stable, the other unstable, the effect and control of which are discussed.

This study compares the performance of circular and rectangular cold spray nozzles based on numerical simulations and experimental results. It shows how nozzle geometry and gas pressure affect the velocity and temperature of copper particles at various points in their travel. The goal of the investigation is to establish a nozzle design that achieves a uniform spray pattern with suitable particle impact velocity for the materials and temperatures involved. It was found that a rectangular nozzle with an expansion ratio in the range of 11-12 can provide a more uniform particle velocity with high deposition efficiency at a reasonable gas pressure.

This paper describes a process that has been developed for producing thick composite coatings with friction and wear properties that were once only achievable in diamond-like carbon (DLC) films. The process is based on cold spraying and the use of surface modified metallic powders. In this investigation, two such powders were prepared by placing either copper or titanium particles on a negatively biased stainless steel tray and then coating them with a DLC film by pulse plasma chemical vapor deposition. The powders are then cold sprayed onto aluminum plates, creating metal-matrix composite coatings. The thickness of the Cu-DLC composite coating is 250 µm and that of the Ti-DLC coating is 435 µm. In each case, the presence of dispersed DLC in the metal matrix was verified by Raman spectroscopy. Sliding wear tests were also conducted, revealing that the Cu-DLC composite has a lower coefficient of friction than copper film, while the Ti-DLC composite has lower specific wear rate than titanium film.

In this study, copper-doped bimodal WC-Co powders are applied to steel substrates by high-velocity oxyfuel spraying and the coatings are evaluated based on their microstructure and high-temperature wear performance. It is shown that the addition of copper reduces coating porosity without affecting the structure of the WC. It also inhibits the decomposition of WC and has a solid diffusion function. The friction coefficients and wear rates determined at different temperatures were found to be consistently low with minimum values being obtained at 450 °C. At high temperatures, the soft copper flows to the surface, forming a self-lubricating film that reduces friction and wear.

An internationally recognized best practice for disposing used nuclear fuels is to store them in specially designed containers in deep geological repositories. One type of spent fuel container is a carbon steel canister with a cold-sprayed copper coating. The aim of this study is to assess the impact of various factors on the ductility of this protective copper layer. The current investigation finds that there can be significant variability in ductility when feedstock powder size and chemical composition are changed while keeping spraying and heat treatment conditions constant. Test results show that the ductility of nitrogen-sprayed copper decreases with increasing hardness, but can be improved by raising annealing temperature from 300 to 600 °C. The effects of substrate geometry and process variations are discussed as well.

This work addresses some of the challenges associated with depositing copper on PEEK by cold spraying. Getting copper powder to adhere to the PEEK substrate is not difficult at first, but deposition efficiency falls rapidly during coating build-up. Without heating the propellant gas, a copper coating will not form, even at the highest gas pressures. Increasing prechamber pressure is necessary, but requires an increase in gas temperature to 400°C to reach a deposition efficiency of 70%. Subjecting PEEK to such heat causes delamination issues that offset the deposition efficiency gained.