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.

Direct cold spray deposition of Cu was not possible on carbon fiber-reinforced polymer composites (CFRPs) with thermosetting polymer as the matrix material due to substrate erosion. In a recent study, an epoxy-CFRP was successfully metallized through a hybrid coating process that involves three consecutive coating steps: (i) electroless deposition, followed by (ii) electrodeposition, and finally (iii) cold spray. In this present study, for the reduction of the coating process steps, a duplex metallic coating was developed on an epoxy-CFRPs by cold spray deposition of tin (Sn) to fabricate a continuous metallic interlayer, followed by Cu electrodeposition (i.e., SnCS-CuEP). The tensile adhesion bond strength and the electrical resistivity of the duplex coating were investigated. It was found that cold-sprayed Sn coating failed adhesively in the absence of the electrodeposited Cu coating. After the electrodeposition of Cu, cohesive failure of the cold-sprayed Sn coating took place. A “dissolution-deposition” mechanism has been established to explain the cohesive failure of the coldsprayed Sn coating after electrodeposition. The cohesive strength of the Sn coating is slightly higher than that of the previously fabricated three-step coating system. The electrical conductivity of the electrodeposited Cu coating was found to be 90% of bulk Cu. These results suggest that a duplex SnCS-CuEP coating can be fabricated on epoxy-CFRPs with relatively high electrical conductivity and slightly enhanced adhesion properties as compared to multilayered coatings fabricated using a three-step electroless deposition-electrodeposition-cold spray process.

Battery manufacturing involves a large number of individual cells arranged in modules configured within a battery pack and connected either in series and/or parallel to deliver the required power and driving range. Cells within a module are linked using a tab-to-busbar connection as the electrical interconnect. Therefore, a battery pack contains a plurality of tab-to-busbar joints, and each must provide low electrical resistivity connection to minimize losses that may reduce the effective performance of the battery. In this work, the Dual Flow Cold Spray (DFCS) process, a modification of low-pressure cold spraying, was used to form low resistivity Cu+10%Zn and Al+10% Zn tab-to-busbar interconnects. As test coupons, 0.8 mm thick copper (Cu) was used to represent the busbar while 0.3 mm thick aluminum and nickel coated copper foils represented the respective electrode tabs. Low resistivity joint interconnects (≈100 μΩ) with high adhesion strength (≈120 MPa) have been formed. The influence of busbar surface preprocessing on the resistivity of the tab-to-busbar joints has been studied.

High entropy alloys (HEAs) are classified as a new class of advanced metallic materials that have received significant attention in recent years due to their stable microstructures and promising properties. In this study, three mechanically alloyed equiatomic HEA coatings – AlCoCrFeMo, AlCoCrFeMoW, and AlCoCrFeMoV – were fabricated on stainless steel substrates using flame spray manufacturing technique. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Vicker’s microhardness were utilized to characterize the fabricated HEA coatings. Furthermore, Joule heating experiments using a modified version of a two-probe test was used to measure the electrical resistivity of the HEA coatings. To prevent short-circuiting of the metallic coatings, a thin layer of alumina was deposited as a dielectric material prior to the deposition of HEA coatings. The microstructure of the HEA coatings showed the presence of multiple oxide regions along with solid-solution phases. The porosity levels were approximately 2 to 3% for all the HEA coatings. The HEA coatings had a thickness of approximately 130 to 140 μm, whereas the alumina layer was 120 to 160 μm thick. The electrical resistivity values were higher for all the HEA coatings compared to flame-sprayed Ni-20Cr and NiCrAlY coatings and AlCoCrFeNi HEA thin film, which may be attributed to the characteristics of HEAs, such as severe lattice distortion and solute segregations. The combined interaction of high hardness and increased electrical resistivity suggests that the flame-sprayed HEA coatings can be used as multifunctional wear-resistant materials for energy generation applications.

An efficient temperature control on tool surfaces is essential in processes like injection moulding or die casting. A thermally sprayed heating coating could combine dynamic heating properties with a small assembly space as it is sprayed directly onto the cavity surface. With their intrinsically high electrical resistivity and low thermal expansion as compared with traditional alloys, High Entropy Alloys (HEA) show promising properties for the use as heating elements. Thus, the well-studied HEA Al 0.5 CoCrFeNi was used as a starting material for additional alloying with Zr and Si to force further lattice distortion in the solid solution. HEAs of differing compositions were melted and characterized. In the process, the potential of HEAs was assessed by characterizing their phase composition, thermal stability, and electrical resistivity. The characterized HEAs show a solid solution mainly consisting of fcc and bcc structure. Moreover, the composition Al 0.5 CoCrFeNiZr 0.2 Si 0.2 was determined as stable after heat treatment at 600 °C for 324 h. In addition, the electrical resistivity was raised by over 20 % relative to the starting material. As a result, a hitherto unknown HEA composition was detected to possess superior properties to traditional alloys for the application as heating coating.

In this study, NiCr alloy coatings were deposited by arc spraying using different combinations and mixtures of pressurizing gases and other process modifications. Coating properties were examined mainly by SEM, EDS, and conductivity measurements. The results show significantly reduced oxygen contents and improved coating morphologies compared to reference coatings produced using current plasma processes. Improved microstructure is shown to have a positive effect on surface quality and specific resistivity, making it possible to texture arc-sprayed coatings just as successfully as the plasma-sprayed reference layers. Moreover, the temperature coefficients and resistivities of arc-sprayed NiCr were found to be superior to those of conventionally manufactured coatings.

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.

By means of In-Mold-Metal-Spraying (IMMS), wire arc sprayed metal coatings are transferred onto plastic parts during the injection molding process for the efficient production of metallized plastic parts. One potential field of application of IMMS parts are electrical applications such as electrically conductive tracks or electromagnetic shielding. In the current study, the properties of the transferred coatings, especially the electrical resistivity, are determined. Different feedstock materials are used for the application of the coatings. In the first investigation, pressurized air is used as atomizing gas for wire arc spraying. In contrary to Zn coatings, Cu coatings applied with pressurized air have a significantly higher electrical resistivity in comparison to massive copper. One possible reason for this is the oxidation of the Cu particles during the spraying process. Therefore, N 2 and a mixture of N 2 and H 2 are used as atomizing gas to reduce the oxidation of particles. Consequently, the electrical resistivity of IMMS parts can be significantly reduced. Furthermore, spraying distance, current and pressure of the atomizing gas are varied to investigate the influence of these process parameters on the coating properties.

This work demonstrates a new single-cathode, multi-anode plasma spray process and compares it with conventional APS and HVOF spraying. Alumina feedstock powders mixed with 13, 40, and 44 wt% titania were deposited under a wide range of spraying conditions following a design of experiments approach. Deposition rate and efficiency were measured and coating characteristics, including microstructure, phase composition, hardness, Young’s modulus, electrical resistivity, and cavitation wear, are compared. The results are presented and the advantages of each process are discussed.

In this work, alumina coatings are produced by air plasma spraying (APS) using dense powders ranging in size from 3 to 36 µm and one porous powder with an average particle size of 33 µm. Two spray systems were used, one rated at 40 kW, the other at 100 kW. The powders were applied to grit-blasted Al 6061 and low-carbon steel substrates. Coatings applied to Al 6061 using the high-power sprayer and 3 µm powder peeled off, likely due to thermal shock and mismatch. For all other coatings, the microstructure was examined by cross-sectional SEM, porosity was estimated via optical microscopy, and dielectric strength and volume resistivity were measured. Coatings formed from 3 µm powder were found to be dense with a mostly γ-phase crystal structure. Surprisingly, however, their volume resistivity was lower than that of more porous coatings with high amounts of α-phase. The findings show that, in the case of resistivity, spray equipment has a bigger influence than particle size, but with coating density, the opposite is true.

The plasma spray process is used to create titanium oxide coatings under the current stoichiometry of titania and titanium suboxides. This study used feedstock powder with Magnéli phases TinO 2n-1 , slightly reduced titania TiO 2-x , and rutile. A factorial design of experiments approach was used to better understand the influence of operational parameters on coating quality, in particular, the electric resistivity and the degree of oxidation of the titanium oxide during the spraying. Firstly, arc current intensity and stand-off distance were studied; the results show strong correlations between particle temperatures and the electric resistivity of the coating. Then, different plasma compositions were used in order to understand the influence of hydrogen in the formation of titanium sub-oxides. The hardness of the most significant coatings was analyzed.

In this study, the influence of spray parameters on the electrical resistivity of thermally sprayed ceramic coatings from the system Cr 2 O 3 -TiO 2 was investigated. Fused and crushed feedstock powders with contents of 10 wt. % and 20 wt. % chromium oxide were deposited by APS and HVOF. Temperature and velocity of the particles in the spray jet as well as the coating surface temperature were analyzed during the deposition process. Impedance spectroscopy was used to investigate the electrical resistivity of the coatings and the results were correlated to coating microstructure and phase composition. It was found that phase transformations occur during the spray process. In the coatings a high temperature phase (n-phase) and rutile were observed. Though, the ratio of rutile depends on the spray methods employed for coating deposition. The electrical resistivity of coatings obtained by HVOF can be correlated to the content of chromium oxide. Furthermore, the surface temperature of the coating during deposition also shows some influence. Concerning the coatings resulting from APS, the different mixtures of the plasma gases (Ar-H 2 and Ar-N 2 ) are supposed to have the most important influence on the electric resistivity.

Copper coatings were deposited on ferrous substrates by utilizing high-velocity oxy-fuel spraying (HVOF). Three different coating process parameters have been used in order to optimise the required electrical characteristics. Microstructure and phase formation in the coatings were analyzed by scanning electron microscope (SEM), X-ray diffraction (XRD), and oxygen analyzer (ELTRA). Electrical resistivity of coatings was measured in-plane and through-thickness using the four-contact method. Results shown that dense coatings with high purity and low level of porosity are required to achieve high electrical conductivity. The coatings exhibited an anisotropic electrical resistivity due to the nature of the thermal spray coating microstructure. Microstructural evaluation shown that individual splats morphology and splats interfaces play important roles in the electrical conductivity.

Traditional fused and crushed (F&C) titania feedstock powders have relatively poor flow and are limited in the feed-rates that can be achieved before deposition efficiencies (DEs) start to decline. In addition, the coatings made with F&C powders generally have high stiffness and limited fracture toughness. Such coatings bear the risk of cracking/delaminating particularly in the case of thick coatings. To address these issues, a new agglomerated and sintered (A&S) titania feedstock powder has been developed and compared in side-by-side spray tests to the traditional F&C titania powder of comparable particle size. The spray behavior, achievable feed-rates and DEs, as well as the resulting coating characteristics were evaluated from the view point of their application as thick, electrically conductive coatings. The new A&S powder yields up to approximately 200% improvement in DE while producing coatings with more suitable microstructure, lower electrical resistivity and higher thickness. Furthermore, for a given set of process parameters, the DEs obtained with this new powder show little sensitivity to the powder feed-rates, thus allowing spraying at higher feed-rates without compromising coating DEs. This feature of the powder has significant commercial advantages for thick coatings when combined with high throughput guns such as TriplexPro-200. Preliminary results of particle diagnostics towards understanding of the fundamental principles behind these improvements are also discussed.

In this study, the deposition, microstructure, and resistivity of APS and HVOF sprayed Cr 2 O 3 -TiO 2 coatings is systematically investigated. Commercially available Cr 2 O 3 -rich feedstock powders are used along with five agglomerated and sintered experimental powders on the TiO 2 -rich side. Both processes are found to produce homogeneous, low-porosity coatings with phase compositions that can be changed by adjusting process parameters. Coating hardness and electrical resistivity are found to depend heavily on Cr 2 O 3 content.

In this work two different thermal spray techniques were used to deposit La 0.9 Sr 0.1 CrO 3 interconnect material: high velocity oxy-fuel (HVOF) using a modified nozzle and atmospheric plasma spray (APS). Two different APS torches were employed: A commercial torch that uses Ar/H 2 as plasma forming gases and a new torch design that uses CO 2 gas mixtures. A substitute powder with similar physical properties to La 0.9 Sr 0.1 CrO 3 was employed for the development and optimization of the process parameters to achieve the highest density before the deposition of the La 0.9 Sr 0.1 CrO 3 on zirconium oxide substrates. The microstructures observed by scanning electron microscopy (SEM) and the phase composition of the coatings obtained from X-ray diffraction analysis are correlated to the spraying characteristics of the different techniques employed. The electrical resistivity of the as-sprayed coatings is discussed in terms of microstructure features and the phase composition. Post-deposition heat treatments were studied in order to reduce the electrical resistivity.

Cold spraying is a novel coating method in which coating is formed by mechanical deformation of sprayed metal particles. This heavy deformation causes structures, which need recrystallization heat-treatment in order to gain back the materials natural deformability. Aluminum, copper, nickel and Ni-20%Cr were cold sprayed and heat-treated at several temperatures. Coatings were sprayed using nitrogen as process gas. Substrate material was carbon steel. Heat-treatment temperatures were chosen from near room temperature to below coating materials melting temperature. As-sprayed and heat-treated coatings were characterized in microstructure, hardness, phase structure and electrical resistivity. It was found that 200ºC was enough to increase electric conductivity to 87% of pure copper. By heat treatment ductility was able to be increased and hardness subsequently decreased.

In the present study, Cu coating was deposited by cold spraying and the electrical resistivity of the coating in both directions parallel and perpendicular to the coating surface was measured to investigate the anisotropy of the coating. Annealing treatment was applied to the coating to examine its effect on the microstructure and properties of cold-sprayed Cu coating. The examination of coating microstructure evidently revealed that the coating was constituted by flattened particles and the interfaces were clearly observed between the deposited particles. The anisotropy in microstructure and electrical resistivity was present in cold-sprayed Cu coating. The electrical resistivity of the as-sprayed coating was higher than that of Cu bulk. Moreover, the electrical resistivity along the direction parallel to the coating surface was lower than that along the perpendicular direction. On the other hand, it was found that the annealing led to the enhancement of particle interface bonding and evident recrystallization of the elongated grains and remarkable grain growth as well. The annealed coating presented an equiaxed grain structures similar to annealed Cu bulk with particle interfaces almost disappeared under certain annealing condition. The coalescence of voids or oxides in the coating was clearly observed at high annealing temperature. Moreover, the annealed coating yielded an electrical resistivity and microhardness comparable to Cu bulk.

Titanium oxide is established as an oxide material for thermally sprayed coating solutions and has received increasing interest over the last few years. Scientific and technological research focuses on electrical conductivity, solid lubrication and photocatalytic properties of titanium oxide (TiOx) coatings of differing stoichiometry. The aim of this study was to investigate the effect of oxygen loss by reduction with hydrogen occurring in the conditions of vacuum plasma spraying (VPS) from commercial titanium oxide feedstock on coating microstructure, hardness, phase composition, abrasion wear resistance and electrical resistivity. The X-ray diffraction pattern showed the presence of rutile, with peaks decreasing in intensity with increasing hydrogen content in the plasma-forming gas. The intensities of the peaks showed significant deviations from those of the standard. An increase in hydrogen flow rate did not influence the coating microstructure, hardness or abrasion wear resistance, but it caused the electrical resistivity to decrease. VPS coatings prepared from commercial fused and crushed powder show a resistivity in the range of 0.01-0.1 Ohm*cm, which corresponds exactly to the range published in the literature. Comparison with results for APS- and HVOFsprayed coatings reveals that VPS coatings yield the best combination of abrasion wear resistance and electrical resistivity when commercial titanium oxide spray powder is used.

In a fusion reactor (i.e. ITER), the use of a ceramic coating on structural material (SS3I6LN-IG) has been considered as electrical insulator. Al 2 O 3 including TiO 2 (Al 2 O 3 -TiO 2 ) is one of most promising materials as coating from a point of high electrical resistivity and so on. However, crack and peeling occur by difference of thermal expansion between substrate material and coating material. Therefore, 80Ni-20Cr was selected as the undercoating between SS316LN-IG substrate and Al 2 O 3 -TiO 2 coating. In this characterization, Al 2 O 3 -3%TiO 2 and Al 2 O 3 -13%TiO 2 were used as ceramic coating material. 80Ni-20Cr undercoating was fabricated by atmospheric plasma spray method. The thickness of 80Ni-20Cr was 50µm. Al 2 O 3 -3%TiO 2 and Al 2 O 3 -13%TiO 2 were fabricated by atmospheric plasma spray method. Thickness of these ceramic coatings are 200 and 500µm. From the results of out-of-pile test, it was clear that Al 2 O 3 -3%TiO 2 and Al 2 O 3 -13%TiO 2 coating had a good mechanical and electrical properties.