A previous study on the pull-off testing of metallized carbon fiber reinforced polymers (CFRPs) via cold spray showed that better adhesion strengths could be obtained when features such as carbon fibers or surfacing elements were present, by providing potential mechanical interlocking features. In this work, the effect of the fiber orientation on the deposition and bonding of the metallic coating to the thermoplastic composite substrate is explored. Pure Sn powder was cold sprayed onto two thermoplastic Polyether-Ether- Ketone (PEEK) CFRP substrates, containing carbon fibers with different orientations: one had fibers in the plane of the substrate (uni-directional tape), while the other had fibers mostly perpendicular to the substrate (ZRT film). Characterization of the coatings was performed via scanning electron microscopy (SEM) and confocal microscopy, and some aspects of mechanical testing (namely wear and scratch testing) were carried out to assess the effect of the substrate on the properties of the coatings.

Tin was successfully cold sprayed onto carbon fiber reinforced polymers (CFRPs) in previous studies at McGill University and a “crack-filling” mechanism was described as the mechanism that allowed deposition of the metal onto the composite counterpart. By adding other metal powders (aluminum, copper, zinc), it was possible to improve the deposition efficiency (DE) of the tin on the CFRP, as well as improve the electrical conductivity of the coating (notably with copper). While the effect of mixing powders with tin, and more notably the effect of the secondary component (SC) properties on the deposition improvement, were more thoroughly addressed in following studies, the question of the properties of these coatings remained. With the perspective of providing a metallic coating to a relatively poorly conductive composite substrate, this study aims to explore the electrical conductivity and the coating strength of cold sprayed tin with other SCs onto CFRPs. An extensive study on fractured surfaces highlighted the importance of the CFRP surface finish, and it was observed that the coating strengths improved with decreasing DE of pure tin.

In order to investigate the potentials to improve the deposition efficiency and to functionalize the polymer-based substrates, six configurations of microparticles Sn, Zn, Al, Sn+Al 2 O 3 , Al+Al 2 O 3 , Cu+Al 2 O 3 were cold sprayed on the substrate of Carbon Fiber Reinforced Polymer (CFRP) composites equipped with Cu-based sublayer or Al-based sublayer. The process conditions were kept unchanged. Microanalysis of sublayers and coatings was performed via a Scanning Electronic Microscope (SEM), the deposition mechanisms of different powders couplings on CFRP substrate were then discussed. The results indicated that although the deposition efficiencies were negative, the systems of Zn, Al and Al+Al 2 O 3 perform better among all the configurations. It was found that the addition of alumina led to a lower deposition efficiency (DE), compared to the corresponding pure coatings. For single-component Sn, Zn and Al powders, they all showed an increasing trend of DE when changing the substrate from Cu-based systems to Al-based systems. The aim of this present work is to elaborate the intrinsic causes of erosion issues and to provide a reference value for picking spraying materials and preparing functionalized CFRP substrates. According to the SEM analysis, the insufficient deformation and escape behaviours of spherical copper powders explained for the difficulty of coating formation. It was noticeable that the surfaces of Al-based systems were more uniform than those of Cu-based ones, due to their desirable deformation abilities. Besides, the significant flattened particles, material mixing and melting phenomenon were observed in Al-involved systems, which would definitely contribute to the adhesive bonding between coating and substrate.

In previous studies at McGill University, tin was successfully cold sprayed onto carbon fiber reinforced polymers (CFRPs). A “crack-filling” mechanism was described as the deposition mechanism that allowed deposition of tin onto the CFRP. Improving the coating conductivity for lightning strike protection (LSP) purposes was achieved by adding other metal powders (aluminum, copper, zinc) to tin and cold spraying on the CFRP. At the same time, it was noticed that the addition of this secondary component (SC) provided an increase in deposition efficiency (DE), tamping was initially hypothesized to explain this improvement, thus prompting a study solely on the effect of SC hardness, which is reported elsewhere in this conference. However, it is recognised that other powder characteristics may also be influencing the DE. Thus, in this study, SCs with a wider variety of particle sizes, morphologies, densities and hardness values were mixed with tin and sprayed on CFRPs. The effect of SC properties on tin deposition is discussed and an optimal combination of SC properties for cold spraying of tin is suggested.

This study assesses the feasibility of cold spraying metal onto wood for commercial applications. It was found that particle adhesion and coating build-up differ significantly from the standard case of spraying metal on metal. Phenomena such as fiber rupture and buckling, pore filling, and particle anchoring required a new approach for process development and verification. First, a microscale analysis of the unique features of wood was necessary to define the deposition surface. Next, a wide range of cold spray tests were conducted to obtain metal coatings on four species of wood. To better understand the dependency of deposition efficiency on particle state conditions, a CFD models and FEA simulations were used to investigate single and multi-particle impacts on local wood structures as observed in SEM and microtomography images. A conventional pull-off test was used to collect adhesion strength data and a numerical counterpart of the test has been developed, making it possible to compare macroscopic adhesion behavior of real and virtual interfaces.

Tin coatings have been successfully applied to polymeric substrates by means of cold spraying. In this work, three low melting point powders, including Sn, Sn-Zn, and Sn-Bi, are cold sprayed onto various polymeric substrates and different combinations of gas temperature and pressure are assessed. Based on the results, the effect of melting points on the cold sprayability of feedstock powders is discussed.

In this work, metallic powders are applied to carbon fiber reinforced polymer (CFRP) substrates by low-pressure cold spraying. The coatings as well as the coating-substrate interfaces are characterized and the deposition mechanism is determined. It is shown that gas temperatures above 300°C are required for the continuous deposition of tin. These temperatures bring about partially melting, which facilitates adhesion. Accordingly, a “crack filling” mechanism is proposed to explain the deposition.

The paper discusses a possibility of metallization of polymers using low pressure cold spray (Dymet 413). The bonding mechanism of the coating is discussed as well as the influence of the number of spraying passes on coating microstructure. Two commercial powder were used (i) tin; and (ii) aluminum to obtain coatings on PA6 polymer substrate. The substrate topography was modified with sandblasting. The adhesion strength, residual stresses, electrical resistivity, and microstructure were determined and characterized. Finally the comparison with other metallization methods was made and the application of cold spray for producing local conductive paths was assessed.

The aim of this work is to cold spray a metal coating with sound mechanical properties and good electrical and thermal conductivity on carbon fiber reinforced polymer (CFRP) substrates. Copper, aluminum, and tin were used as the coating materials and different gas pressure and preheating temperature combinations were employed during spraying. Erosion was found to be the key obstacle to develop continuous coatings, although embedded particles were observed in the residual epoxy.

Comparative studies on the intermetallic compound (IMC) formations of nano- and micro-size Sn with Ni and Cu in cold gas dynamic sprayed (CGDS, or Cold Spray) coatings were carried out. High purity pure nano (average 150 nm) and micro (under 45 μm) Sn were selected and prepared as raw materials mixture in order to be sprayed onto Ni and Cu plate-shape substrates. Nano particles of Sn were successfully coated under conventional coating parameters when they are mixed with microsize materials. And thermodynamic predictions regards to compound formation similarly worked out for both nano and micro Sn mixture. However, the kinetics of formation reaction were turned out to be different. In all case, nano particle showed more sluggish behavior. After post-annealing, microsize Sn formed larger amount of IMC with Ni than nanosize Sn although, owing to larger interfacial area, more intensive reactivities were expected. Also, there were significant differences in the size and distribution of eutectic pores as well.

Metallization of plastics by thermal spraying is studied. The possibility to obtain high adhesion of metal particles to the surface of a wide range of plastic materials is shown. Powders are sprayed with a new generation detonation gun “Dragon” designed at Lavrentyev Institute of Hydrodynamics SB RAS. The apparatus is characterized by a high-precision gas supply system and a dosed localized powder feeding system. Computer control provides a flexible programmed readjustment of the detonation gases energy impact on powder particles which is a key factor in precision control of spraying parameters for low-melting point powder materials. It is found that under certain spraying conditions molten particles of a low-melting point material not only do not provoke erosion of plastic material at their high velocity impact on the substrate but strong-bond fusion, sufficient to further form a thick coating, occurs. Aluminium, zinc and tin powders are sprayed on substrates from fibreglass, polyester, fluoroplastic and some other plastics. Load capacity of the obtained coatings reaches 100 kg/cm 2 . It is shown that on top of a thin layer from a low-melting point powder material high-melting point metals and even ceramics can be deposited.

When describing the cold spray process, one of the most widely used concepts is the critical velocity. Current models predicting critical velocities take the temperature of the sprayed particles explicitly into account but not the surface temperature (substrate or already deposited layers) on which the particle impact. This surface temperature is expected to play an important role since the deformation process leading to particle bonding and coating formation takes place both on the particle and the substrate side. The aim of this work is to investigate the effect of the substrate temperature on the coating formation process. Experiments were performed using aluminum, zinc and tin powders as coating materials. These materials have a rather large difference in critical velocities that gives the possibility to cover a broad range of deposition velocity to critical velocity ratio using commercial low pressure cold spray system. The sample surface was heated and the temperature was varied from room temperature to a high fraction of the melting point of the coating material for all three materials. The change in temperature of the substrate during the deposition process was measured by means of a high speed IR camera. The coating formation was investigated as a function of (1) the measured surface temperature of the substrate during deposition, (2) the gun transverse speed and (3) the particle velocity. Both single particle impact samples and thick coatings were produced and characterized. Both the particle-substrate and interparticle bondings were evaluated by SEM and confocal microscopy

The adhesion of splats formed by impact of molten metal droplets was studied experimentally. Tin droplets (550 µm diameter) were produced using a drop-on-demand generator. To achieve high impact velocities the stainless steel coupons used as substrates were mounted on the rim of a rotating flywheel and heated using cartridge heaters. To hit a falling droplet with the substrate and photograph its impact, a timing circuit was used to synchronize three events with the position of the substrate: ejection of a droplet, triggering of the camera and a flash to provide illumination. The impact velocity was varied from 10 – 40 m/s whereas the substrate average roughness (2.0 µm) and the droplet diameter (~550 µm) were kept constant. We measured the adhesion strength of splats by a simple pull test. A wire was attached to the upper surface of each splat using epoxy and the force required to separate the splat from the substrate was recorded. A significant increase in adhesion strength was observed as the impact velocity was increased. Coatings were produced by depositing many droplets sequentially. Substrate temperature and impact velocitiy were the main parameters varied. SEM images of cross-sections through coatings showed that increasing impact velocity and substrate temperature produced better adhesion between the coating and substrate.

The quality of thermal sprayed coatings greatly depends on the individual flattened splats. Generally they are characterized by two main factors, flattening ratio and splat profile. The flattening ratio is specified straightforward, but it is difficult what factor should be selected from the various properties for the splat profiles. Fractal geometry is introduced to the profile evaluation of the splats which are formed by the free-fall metal droplets and by the alumina coatings using plasma spraying method. The fractal dimension of each splat was measured by SIA (Slit Island Analysis) technique which measures the ratio of area to contour length of the island appeared on the horizontally sliced plane of the splat. The obtained fractal dimension was related to with Re and We numbers in a bi-linear form, which is the same characteristics as the unevenness ratio obtained previously. It was concluded that fractal dimension is an effective measure to evaluate the splat profile.

Monocrystalline lithium fluoride (LiF) windows are used in mineral physics research. Optical Pyrometric Measurements (OPM) during shock tests are done through LiF windows on which a few mm thick plates of tested materials are fixed. Current OPM requires the plates to be glued on the LiF windows. However, this glue is an undetermined source of error for OPM. This study deals with plasma spraying to deposit a tin coating directly on to the polished LiF windows as a substitute to the plate/glue/LiF system. Although seldom used for low melting point materials, plasma spraying was shown to be the appropriate technique for this original material couple and application especially for its flexibility. The study confirmed the feasibility of plasma spraying of tin on polished surfaces of LiF windows. Scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), hydrostatic weigh measurements (HWM), optical and confocal microscopy were used to characterize the coating and substrate.