Numerical studies directly quantifying particle-substrate adhesion under different spray process parameters during impact remain scarce, primarily due to the lack of consideration for adhesion models. This study addresses this gap by investigating bonding behavior under varying spray conditions using a single-particle model with the PD numerical method, incorporating adhesion forces.

This study examines the effects of N 2 and He process gases and heat treatment on the microstructure and mechanical properties of 3D-printed pure copper produced using a low-pressure cold spray system. Microstructural analysis is performed through optical microscopy, while tensile tests are used to evaluate mechanical properties. Samples processed with N 2 demonstrate improved plastic deformation, leading to reduced porosity compared to those processed with He.

This study analyzes the influence of reactive elements like H 2 regarding hydrogen embrittlement to determine whether the porous structure of the plasma sprayed coating itself, or the thermal treatment with H 2 is influencing the cohesion and microstructure. To exclude substrate-related influencing factors during testing, tensile rods of thermally sprayed coatings were manufactured.

This study focuses on the deposition and post-processing behavior of commercially pure copper produced using cold spray additive manufacturing (CSAM) with compressed air. By evaluating the microstructural evolution and mechanical performance of as-deposited and heat-treated copper samples, this work aims to provide insights into optimizing CSAM processes for industrial applications.

The performance and, as a consequence, the application of functionalized fiber-reinforced plastic (FRP) are limited due to low adhesion strengths between the metal coating and the polymer-based substrate. Common pre-treatment methods, to successfully apply a metal coating by thermal spraying on commercial FRP, are mechanical blasting, etching or thermal treatment. Moreover, additional layers made of metal wire or sand have been integrated into the FRP surface. A promising material-sensitive pre-treatment method for FRP substrates is laser micro structuring. This method avoids uncontrolled damage of surface-near fibers and offers an increased interface area. Unique for pulsed laser structuring is the opportunity to achieve a clamping effect between the functional coating and the FRP by a trench-like structure.

Cold spray metallization of carbon fiber-reinforced polymers (CFRP) has attracted increasing interest for potential applications in providing lightning strike protection (LSP) to aircraft. This study aims to assess the LSP performance of cold-sprayed copper and aluminum coatings on a Polyaryletherketone (PAEK)-based carbon fiber-reinforced thermoplastic polymer (CFRTP). Lightning strike tests with a peak current of 70 kA were performed on full-surface copper and aluminum coatings, and grid-patterned aluminum coatings. The lightning strike process was captured by a high-speed camera to investigate the fracture behavior of the cold-sprayed CFRTP specimens. Results revealed that the full-surface copper coating, which had higher electrical resistivity and was thinner than the aluminum coating, experienced explosive coating fractures. Conversely, the aluminum coating incurred less damage, effectively protecting the underlying CFRTP from lightning current without visible ply lift or carbon fiber fracture. Furthermore, grid-patterned aluminum coatings also exhibited LSP capabilities, with their denser mesh reducing both the area of coating fractures and the thermal damage to the CFRTP surface.

Air quality in buildings is often controlled by various Heating, Ventilation, and Air Conditioning (HVAC) systems. These systems are equipped with air filters to reduce dust and aerosol load in the air. Ambient aerosol particles may contain different organic matter such as pollen, bacteria, and fungi. In warm and humid indoor air conditions, the presence of such air particles may result in the growth and transmission of infectious bacteria, fungi, and mold spores.

High-performance polymers such as poly(ether ether ketone) (PEEK) are appealing for a wide variety of industrial and medical applications due to their excellent mechanical properties. However, these applications are often limited by relatively low thermal stability and conductivity compared to metals. Many methods developed to metallize polymers, including vapor deposition and thermal spray processes, can lead to poor quality control, low deposition rate, and high cost. Thus, cold spray is a promising potential alternative to rapidly and inexpensively produce polymer-metal composites. In this study, we investigated the deposition characteristics of metalpolymer composite feedstock, composed of PEEK powder with varying volume fractions of copper (Cu) flake added, onto a PEEK substrate. We prepared the Cu-PEEK composite powder in varying compositions by two methods: hand-mixing the powders and cryogenically milling the powders. Scanning electron microscopy (SEM) of the feed mixtures shows that cryogenically milling the polymer and metal powders together created uniformly distributed micron-scale domains of Cu on PEEK particle surfaces, and vice versa, as well as consolidating much of the porous Cu flake. In lowpressure cold spray, the relatively large volume fractions of PEEK in the composite mixtures allowed for lower operating temperatures than those commonly used in PEEK metallization (300-500 °C). While the deposition efficiencies of each mixture were relatively similar in single-layer experiments, deposits formed after multiple passes showed significant changes in deposition efficiency and composition in PEEK-rich feedstock mixtures. SEM of deposit surfaces and cross-sections revealed multiple co-dominant mechanisms of deposition, which affect both the porosity and final composition of the deposit. Though present in all samples analyzed, the effects of cryogenic milling were more prevalent at lower Cu concentrations.

As a supersonic solid-state deposition process, Cold Spray (CS) has a unique role among other thermal spray techniques as it uses compressed and heated gas to accelerate particles to a critical velocity. CS can be an expensive process, especially when helium is used as a processing gas. In recent thermal spray developments, High-Velocity Air Fuel (HVAF) has taken a specific place in terms of providing dense and strong coatings similar to CS, but also coatings with less oxidation than High- Velocity Oxy-Fuel (HVOF). In contrast to these techniques, HVAF uses a mixture of fuel and air, instead of pure oxygen as in HVOF, to accelerate particles. Therefore, HVAF appears as a relatively cheaper and environmentally friendly alternative for the deposition of a wide variety of materials. The aim of this research is to produce fully dense copper coatings with limited oxidation using an inner diameter (ID) HVAF system and to compare the microstructure with CS copper coatings. Coating microstructures, surface roughness, and microhardness are studied using different characterization methods such as Scanning Electron Microscopy (SEM). Through this paper, the influence of both spray processes, CS and ID-HVAF, on the deposition of copper coatings is discussed. Cross-sectional studies of different coatings show a fairly dense microstructure for CS and ID-HVAF coatings. Moreover, it is discussed how the copper coating properties can change upon modifying the spray parameters.

During the impact and solidification of thermal spray droplets on a substrate, the density increases when the droplet solidifies. Depending on the material, the changes in density could be significant. For example, aluminum oxide's density changes by 66%, while the changes are 12% and 19% for nickel and copper, respectively. For zirconia, this change is 24%. The effect of such densification on the dynamic of the droplet impact and the formation of porosity could be dramatic. In this study, the effect of shrinkage of a molten droplet during solidification on droplet impact is numerically investigated for several materials. Results for the impact of molten alumina, nickel, copper, and zirconia droplets on both smooth and rough surfaces are presented. The results of variable density cases are compared with those assuming constant density. The effect of thermal shrinkage is particularly vital in the interaction of two impacting droplets. The shrinkage promotes the formation of additional pores.

In cold spray (CS) additive manufacturing process, micrometer scale particles accelerated through a supersonic nozzle are targeted on a surface with velocities in the rage of 300-1500 m/s in solid state. The impact energy of the particles leads them to deform plastically with high shear energy near the impact interface and adhere to the surface metallurgically, mechanically, and chemically. Using CS, deposition of metals, metal matrix composites, and polymers are achieved with high adhesive/cohesive strength and low porosity. Sensitivity of the CS additive manufacturing process to the variabilities in the process parameters are still being understood. Among the process parameters, particle morphology can have significant implications on drag forces, and therefore, on the particle impact velocity. This in turn affects the deposition efficiency (DE) and the quality of products. In this work, a new approach is introduced for computing DE by incorporating particle sphericity and its variation into one-dimensional numerical models. Size, sphericity, and the variability of size and sphericity of aluminum, copper, titanium, and tantalum particles are measured from static optical microscope images. The data is used for predicting impact velocity, temperature, and DE. The model results are then compared with particle velocity measurements.

Metals were deposited on components made by 3-D printing with polyvinyl alcohol (PVA), a water-soluble polymer. The polymer was then dissolved, leaving a metal layer whose surface topography was the negative of that of the polymer. This is a rapid and low-cost alternative to 3D printing directly using metal, but to succeed it is essential for the sprayed metal to adhere to the polymer substrate. Tests were done in which aluminum and copper were sprayed using a twin-wire arc spray system onto 3D printed coupons, 50 mm x 50 mm in size, made from polylactic acid (PLA), PLA mixed with metal (aluminum, copper) or carbon fiber, and PVA. Adhesion depended on substrate roughness (minimum 1-2 μm) and substrate temperature (above the glass transition temperature but below the melting temperature of the polymer). It was shown that surface features could be made with high resolution on metal components using this technique.

Low pressure cold spraying is an attractive technique for onsite metal coating fabrication due to its compactness and portability. However, the bonding strength of the coating prepared by low pressure cold spraying is generally low, which restricts the further applications in engineering and industrial fields. To improve the bonding strength, pre-treatment on substrate surface can be an effective procedure. In this study, a low-temperature plasma treatment was applied to a pretreatment technique, and the effect of the treatment on particle bonding was compared with that of a laser treatment. Copper coatings on aluminum and copper substrates were selected and studied as basic metal materials. The SEM observation results show that the particle adhesion rate significantly increases by the laser and plasma treatments, due to the removal of the native oxide films on the substrates. The particle bonding on the plasma-treated substrate reveals better interfacial adhesion with less gap compared with the laser-treated one. The pre-treatment by low-temperature plasma can be an attractive technique to assist the cold spraying process due to the oxide removal ability and no thermal effect which can apply a wide range of materials.

Metal surface characteristics play a significant role in interacting with their biological environment. Copper surfaces have been identified for their antimicrobial properties. Improvement of antibacterial and antiviral performances can be tailored by surface microstructure modification. Severe plastic deformation is an effective surface modification procedure to improve the mechanical performance of metal surfaces. This technique can be adapted to obtain surface grain refinement and induce surface roughness. In this work, cold spray shot peening is used to modify copper substrate surfaces and study the effects on their antibacterial properties. To modify the grain structure of copper, different shot-peening parameters were examined. The surface roughness and microstructure were investigated by employing optical and scanning electron microscopy. The bactericidal activity of copper substrates after shot peening treatment is discussed and a comparison between the bacterial load on treated (shot-peened surface and cold sprayed copper coating) and untreated surfaces (as-received) is provided. Testing of the surfaces after their exposure to the biological environment demonstrated improved microbial inactivation performances for surfaces that had undergone grain refinement without exceeding a certain roughness value.

In cold spray, high adhesion of soft materials on hard substrates is commonly achieved by using helium as the propelling gas. This is the case of copper coatings on steel where adhesion may reach values as high as 60 to 80 MPa (glue failure), however, helium is a limited, expensive natural resource, and the use of more abundant nitrogen gas is preferred in an industrial setting. Unfortunately, when using nitrogen gas, little to no adhesion is obtained. In order to eliminate the use of helium gas we studied how laser assisted cold spray could lead to an improvement in adhesion of nitrogen sprayed copper coatings. In this work, several laser parameters (e.g., power and spot size) and process parameters (traverse speed, relative position laser spot vs. gas jet) were varied at a coupon level. Upon optimization, an equivalent adhesion to the coatings prepared with helium was obtained. Furthermore, the cross section of the coatings showed that the copper particles penetrated the steel, similar to what is observed when using helium gas. Optimization of these parameters for application to large diameter (~559 mm) cylinders was also performed. A discussion on the mechanisms which contribute to achieving high adhesion considering the use of helium versus laser assistance is provided.

Cold spraying is a promising process for fabricating functional coatings. Because of the solid-state particle deposition, the electrical and chemical properties of the coatings are similar to those of the bulk materials. Mechanical properties, on the other hand, differ from those of bulk materials due to severe plastic deformation of the particles. Residual stress may thus be an important variable to track during cold spraying although the formation mechanism is not entirely clear. In this study, the residual stress of metallic (copper) and ceramic (titania) coatings is measured during the cold spray process. The results are presented and discussed.

This study demonstrates a two-step laser cladding process for copper substrates in which cold spraying is used as a powder preplacing method to overcome problems associated with the high laser reflectivity of copper as well as the effects of high-temperature oxidation. In the first step of the process, Inconel powders are cold sprayed onto pure copper, producing a layer with a thickness of about 250 μm and a porosity of 0.88%. This is followed by a 3.5 kW laser remelting treatment using a 1030 nm laser with a spot size of 2.5 mm. Examination and testing of the as-sprayed and remelted layers show how the laser treatment improves coating microstructure, hardness, density, and metallurgical bonding.

This study investigates the microstructure and efficiency of coating-based heating elements produced by deposition of various powders, including aluminum oxide (Al 2 O 3 ), alumina-titania (Al 2 O 3 -TiO 2 ), nickel-chromium (NiCr), and copper, using flame spraying, suspension plasma spraying, high-velocity oxyfuel (HVOF) spraying, and cold spraying techniques. The main goals are to assess the dielectric strength of flame and plasma sprayed alumina, compare the electrical resistivity of HVOF and flame sprayed NiCr, and obtain coating cross-sectional images to shed light on the challenges and potential of different heating element designs. The Al 2 O 3 layer produced by suspension plasma spraying appeared to be more reliable due to its cauliflower-like structure, corundum content, and hygroscopic properties. Resistivity was found to be higher in the flame sprayed NiCr than in the HVOF deposit mainly due to discontinuities and imperfections such as cracks, pores, and oxygen content. The micrographs taken from sample cross-sections show penetration of flame-sprayed NiCr into the flame-sprayed Al 2 O 3 and Al 2 O 3 -TiO 2 layers, which decreases the effective thickness of the dielectric. However, interlocking between NiCr and Al 2 O 3 -TiO 2 coatings can be beneficial when cohesion is a concern.

The economic feasibility of using thermal-sprayed heat generating coatings for temperature control in steel pipes was investigated. A data-intensive model was developed to compare fabrication, installation, operation, and maintenance expenditures with those of conventional heating cables. The multi-layered coating consists of flame-sprayed Al 2 O 3 and NiCr layers and cold-sprayed copper. Scalability factors were incorporated in the model to estimate the total projected costs for fabricating the coatings as opposed to installing heat tracing. Although material costs for the coating and heat tracing were approximately the same, the cost of fabrication for the coating was higher due mainly to labor expenses. However, the coating-based system was found to be more energy efficient than heat tracing due to the good adhesion and reduced thermal contact resistance between the heating elements and pipe.

In this study, copper coatings are deposited on polyacetal substrates by low-power microwave plasma spraying and the coating formation mechanism is investigated. In the initial formation of the coating, molten copper particles are embedded on the substrate, creating conditions for excellent bonding as confirmed by adhesion strength measurements exceeding 40 MPa. The study also shows that adding hydrogen to the argon working gas improves oxide reduction, resulting in copper coatings with volume resistivity as low as 0.049 µΩm.