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.

Fluorinated polymer coatings are potential candidates for ice protection systems. The current work aims to develop such coatings using cold spray as a production method. A computational approach is used to design a new cold spray nozzle for the efficient deposition of adhesive perfluoroalkoxy alkane. The icephobicity of as-sprayed coatings are evaluated using three-fold characterization: surface’s wetting behavior, time-lapse study of water droplets freezing, and ice adhesion at both macro and microscopic levels. While the as-sprayed coatings exhibited sought superhydrophobic properties, their behavior changed when exposed to frost formation resulting in degraded wetting behaviors and much larger ice adhesion strength. This demonstrates the importance of frost formation when studying icephobic coatings.

The development of efficient ice mitigation systems for surfaces exposed to atmospheric ice has been in progress for decades. The need for passive anti-icing systems is essential as current ice mitigation systems require a substantial amount of energy and their implementation involves complex manufacturing considerations. Fluorinated polymer coatings are among the candidates for passive anti-icing systems. While many processes have been investigated to produce them, these methods can be costly, time consuming and can cause thermal damage to the substrate. The current work aims to explore a green and cheap alternative approach by using cold spray. Furthermore, the cold spray process offers advantages such as being a portable easy to perform solid-state coating process for eventual repairs. This work uses computational and experimental approaches to design and test a new dedicated nozzle for the efficient deposition of adhesive perfluoroalkoxy alkane. Computational results reveal that for the same operating conditions, the use of the new nozzle design increases particle impact temperature, improving the deposition of the feedstock material, as confirmed experimentally. The wetting behaviour, ice nucleation time and ice adhesion strength were compared for 6 different surface types, including bare aluminum, various polymer materials and the cold spray perfluoroalkoxy alkane coating on aluminium substrate. Results indicate that the as-sprayed coating performs as both a superhydrophobic and icephobic surface.

The cold spray process is sensitive to variations in feedstock and requires consistent powder properties, particularly flowability, to produce uniform structures. Poor powder flow causes a cascade of effects arising from erratic feeding including deposits with void spaces and inconsistent geometries. These issues result in deposits which are not suitable for testing and prevent sample replication, hindering experimental evaluation of deposits. Powder flowability is largely affected by the material preconditioning and storage conditions; with flowability directly affecting the deposit properties of deposition efficiency (DE), porosity, and surface finish. In this study, the flowability and deposit quality of a fluoropolymer-based powder was evaluated with changing pretreatment conditions. Powder flowability was analyzed by mass flowrate (g/s), the Carr angle of repose, and the Hausner ratio. Flowability was evaluated for powders as received, after sieving (45-100 μm), with drying at elevated temperature (80 °C), with inert gas vacuum purging, and after 72 hrs. of exposure to high relative humidity (95% RH). Powders exposed to humid conditions were also dried under inert gas vacuum purging to determine the effectiveness of the process as a reconditioning method. Preconditioned powders with the highest flowability according to these tests were sealed in metal containers, stored under 95% RH for one week, and reevaluated to determine the ability of this preconditioning and storage method to protect materials from exposure to undesirable conditions. Next, the effect of preconditioning on cold spray deposit quality was evaluated for the fluoropolymer-based powder with the best and worst flowability. The choice of spray conditions was informed by simulation of particle velocity and temperature distribution at impact using one-dimensional compressible flow modeling, couple with thermal analysis of the powder. The DE was determined gravimetrically, surface roughness was evaluated using a profilometer, and microstructure was evaluated using a scanning electron microscope (SEM). The ability to manipulate powder flowability through simple preconditioning methods and quickly evaluate the properties of the feedstock before use in the manufacturing process, coupled with straightforward and rapid evaluation the resultant deposit; will save time and money, and accelerate research efforts, compared to evaluating powder suitability by trial and error.

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.

Fluoropolymer and other polymer materials are extremely difficult to coat using solid-state deposition techniques such as cold spraying. In this study, fluoroethylene propylene (FEP) is cold sprayed onto a metallic substrate in order to investigate the effect of powder size, gas temperature and pressure, and substrate surface treatments. A powder modification technique that uses fumed nanoceramic particles as an additive to the feedstock is evaluated as well. The results show that the deposition efficiency of FEP is affected by particle size, gas temperature, and traverse speed as well as the added nanoceramic which, in this case, is either silica or alumina. It is also shown that the hydrophobic properties of the fluoropolymer are retained in the coatings and that adhesion between the coating and substrate plays a critical role.

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.

In this study, high pressure cold spray (HPCS) process was used to metallize the surface of polymeric substrates to improve their mechanical performance, such as erosion, wear, and strength. Thermoplastic polymer materials (PEEK, PEI, and ABS) were used as substrate. Commercially pure (CP) Al and 7075 Al were cold sprayed onto the polymeric substrates. Good quality defect-free coatings were achieved in all combinations except with ABS substrates, which suffered from distortion during CS process due to stored thermal energy. 7075Al coatings showed high adhesion strength but low thickness (low deposition efficiency (DE)), whereas CP Al coatings revealed high thickness (high DE) but poor adhesion strength. Based on the obtained results, the DE and bonding strength are not only highly sensitive to properties of the substrate, but also to the applied process parameters as well as powder morphology. It is concluded that two separate sets of spray parameters should be applied for 7075 Al and CP Al deposition otherwise, either more damage or less bonding is achieved to the substrate. Also, for each one of these powders, the first layer of metal/polymer should be deposited with a separate recipe than the subsequent metal/metal layers. Coefficient of thermal expansion and hardness difference between the coating material and the substrate were also found to be key factors to developing continuous coatings on the polymeric substrates with the HPCS process.

In this study, ball-milled Al 2 O 3 powder was used as a feedstock material for vacuum kinetic spray to deposit hard ceramic Al 2 O 3 coating on a relatively soft polycarbonate substrate. Microstructural and X-ray diffraction analysis of powders and coatings were performed. The results shows that the ball-milled powder has more unstable state than the primary powder. Compared to primary Al 2 O 3 coating the crystallite size and coating thickness of ball-milled Al 2 O 3 coating are smaller and thicker, respectively. Since the ball-milled Al 2 O 3 particles are more easily fragmented during the VKS coating process, it is possible to deposit hard Al 2 O 3 coating on the soft polycarbonate substrate.

Recent advances has made possible to obtain Ultra High Molecular Weight Polyethylene (UHMWPE) coatings by cold spray technique with nano-ceramic additives with the feedstock. However, the exact role of nano particles is largely not understood. In this work, isolated depositions of UHMWPE particles with 0%, 2%, 4%, 10% of fumed nano alumina (FNA) on Al surface were performed at different gas/particle temperatures. Particle velocities and particle temperatures were controlled by varying the carrier gas pressure and temperature. The impact behavior of UHMWPE was analyzed using SEM, FIB and high-speed camera. Increase in gas temperature and percentage of FNA showed a significant variation in the deposition volume. FIB analysis showed that successful depositions were influenced by degree of deformation of particle. Further, addition of FNA helped in deposition of particles that have required a lesser degree of deformation. Finally, high speed camera showed that particles are moving at an incidence velocity of 180-200m/s and rebound velocity of 40-50m/s. This suggests that particles lose a significant amount of their kinetic energy during the impact.

This paper presents the results of research, testing, and comparison of polyamide (nylon) 11 coatings made by flame spraying and electrostatic spraying followed by oven or induction heating. It discusses the advantages and disadvantages of each process and the coating properties that can be achieved.

In this work, two agglomerated hydroxyapatite (HA) powders, with and without heat treatment, were cold sprayed using various spraying parameters on metallic (Ti-6Al-4V) and polymeric (PVA) substrates. The structure of the agglomerated powders and corresponding features of the coatings were examined. For both types of substrates, it was shown that submicron HA powders produce homogenous layers with submicron HA grains. In the case of non-heat treated particles, thick layers could be obtained due to the binding action of residual by-products. HA layers were also found to be adherent after immersion in water, which could potentially lead to the fabrication of ceramic coated hydrogels.

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.

Numerous automotive and aircraft/aerospace applications involve metallic coating of organic matrix composite materials, e.g. for aesthetic, electric, or engineering functions. In the thermal spray process family, cold spray is very attractive for the achievement of metallization of low-temperature resistant materials such as organic composites, due to its “cold” characteristic. However, despite the current (and justified) craze for cold spray, little is still known about the potential of this process for this type of application. The work demonstrated the feasibility of cold spray for satisfactory metallization of PA66-matrix composites with Al. This paves the way for using cold spray as an advantageous substitute process for the industrial protection of polymer-based composites.

Cold spray deposition of polycarbonate on the various substrates has been investigated. The polycarbonate particles are sieved and accelerated at elevated temperature in air through a DeLaval type nozzle, and are deposited on the metallic and ceramic substrates. The influences of the particle size, the gas temperature, the thermal conductivity and surface roughness of substrate on the deposition process are studied. As a result, the continuous deposits are formed on the metallic substrate. The powder sieved below 300 μm shows better deposition efficiency. Thin film of melted polycarbonate has been formed on the surface of substrate to act as a bonding layer, and its crystalline structure is changed to be amorphous, which is the more stable state for the polycarbonate. The coating seems to be better when the thermal conductivity of metallic substrate is low. For the ceramic substrates, there is no deposition whatever was the thermal conductivity.

In this investigation, flame spraying is used to deposit polyether ether ketone (PEEK) layers on stainless steel substrates and CO 2 and Nd:YAG laser remelting treatments are performed to densify the deposited material. Microstructural analysis of the as-sprayed and remelted coatings shows that both lasers are suitable for densifying PEEK polymer layers on stainless steel and that the resulting crystalline structure depends on laser processing parameters. Hardness measurements and tribological and scratch tests are also carried out and the results are correlated with microstructure.

In this study, single splats of polyether ether ketone were plasma sprayed onto aluminum substrates that had been boiled, etched, or polished and then thermally treated, except for one etched substrate, to remove water from the surface. Splat morphology was viewed in a scanning electron microscope and splat-substrate interfaces were examined using TEM and focused ion beam imaging. The results show that PEEK splats have a poor level of contact on aluminum substrates that were boiled and those that were etched but not thermally treated. In contrast, specimens that had undergone thermal treatment to minimize the presence of water on the substrate surface exhibited high levels of contact at the splat-substrate interface with significantly less porosity.

Abradable coatings are widely used in aerospace turbine engines to improve seal performance between rotating and stationary parts and thus the engine efficiency. As they are elaborated by thermal spraying of composite powders, these materials are highly heterogeneous. Their behaviour in working conditions is quite complex and not fully understood. This study contributes to a better knowledge of the mechanical behaviour of a range of abradable coatings. Finite Element calculations were derived from the analysis of micrographs and allowed to estimate the coefficients of an anisotropic elastic law of behaviour. Several models were investigated in the case of an AlSi-PE (Polyester) coating. As the PE % appeared to be a determinant factor, its influence was quantified ranging from 0% to 100%, using virtual micrographs deduced from the original ones. The computed Young's moduli Ex (in coating longitudinal direction) were quite consistent, considering the hypotheses made. An empirical relationship giving the variation law of Ex versus the PE % was suggested and applied to predict the modulus Ex of a real coating, which was close to the measured value.

Abradable seals are used in aerospace applications to control the overtip leakages between the blades of an engine rotor and its static parts. To achieve the combination of properties required, these seals have been developed with thermally sprayed coatings and are generally elaborated from a range of two or three phase powder mixtures. In the present study, the thermal conductivity of thermally sprayed AlSi/Polyester abradable coatings produced with Metco 601 NS and Durabrade 1605 powders was measured and investigated using finite element and finite difference methods based on two-dimensional structures obtained from micrographs. The computed values were compared to the experimental results.

In this paper, submicron α-Fe/nylon-12 microwave absorbing composite coatings were deposited by a Low Temperature High Velocity Air Fuel (LTHVAF) spraying technique. The microstructure and the electromagnetic parameters of coatings and powders were tested. The coatings are dense and have low porosity. The microwave reflectivity coefficient of the coatings was calculated with permeability and permittivity of the powders. It shows that there is a relationship between the mass fraction of composite powders and microwave absorption ability of coatings. At the threshold value, the composite coatings can absorb microwave strongly. When the coatings thickness increases, the minimal reflectivity coefficient moves to the low microwave frequency. There exists an appropriate coatings thickness in order to optimize the absorption of the microwave energy. The mass fraction and the thickness can affect the performance of composite absorber coatings.