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.

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.

Adhesion strength is one of the most important characteristics when discussing the reliability of a cold spray. A focused ion beam (FIB) was used to conduct ultra-micro tensile tests for micro-scale adhesive strength evaluations of high-pressure type cold-sprayed copper deposition on an aluminum substrate. It was also used to determine the essential factor of adhesion strength and the coating formation mechanism. The micro-scale local adhesion strength of cold-sprayed copper deposits on an aluminum substrate was successfully evaluated by FIB microtensile tests. The average local adhesion strength of this deposit was 223 MPa. The variations in adhesion strength between deposit and substrate were smaller than the interfacial strength of cold-sprayed deposits. This was caused by the repeated collision of these subsequent particles.

In a cold spray technique (CS), which used for making dense and thick metallic coatings, the fine solid metallic particles are impinged and deposited on a substrate at subsonic or supersonic velocity. The property and performance of a CS metallic coating significantly depends on the bonding state of particle-substrate and particle-particle interfaces. Therefore, the deposition mechanism of the CS particles has become one of the most important research targets. However, it is difficult to experimentally evaluate the deposition mechanism due to numerous impingements of very fine particles with various size and shape. In this study, in order to evaluate the deposition mechanism, a CS emulated environment was created by a single particle shot system (SPSS) in which spherical particle with 1 mm diameter is impinged on a substrate. The influence of substrate surface oxide film on deposition behavior of a spherical Al particle with 1 mm diameter was investigated. The thickness of surface oxide film on a substrate was controlled by heat treatment and estimated by X-ray photoelectron spectroscopy (XPS). Using the SPSS, Al particles were impinged on the substrates with different surface oxide film thicknesses. The critical velocity, which means the starting velocity for particle deposition, and the microstructure of deposited particle were evaluated. From the results, it was found that the surface oxide films on substrates play important roles on the deposition behavior of the Al particle.

The aim of this study is to clarify the factors that control the macroscale strength of cold spray coatings by evaluating local strength at the microscale. Using pure copper powder and high-pressure cold spray equipment, thick (15 mm) copper layers were deposited on aluminum substrates. The coatings were evaluated by SEM and EBSD analysis, then freestanding Cu specimens were fabricated in a FIB system, where in-situ micro tensile tests were carried out. The results are presented and discussed along with the role of microvoids.

This study investigates the effects of gas composition on cold-sprayed titanium coatings deposited under nine different spray conditions. Experiments show that higher levels of gas purity translate to higher particle velocities and measurable improvements in bending strength. The influence of gas temperature, pressure, and chemical composition is considered in the study along with interactions between carrier gases and sprayed particles. In addition to bending strength, the resulting coatings are assessed in terms of porosity and oxygen content.

In this study, fine aluminum powder was cold sprayed onto aluminum substrates, some of which were polished, some grit blasted, and some pretreated using a nano-pulsed Nd:YAG laser. In the latter case, the laser is coupled with the cold spray gun and the irradiation treatment occurs just prior to deposition. To better understand the interaction mechanisms involved with laser pretreating, coating-substrate interfaces were examined on thin-foil specimens and adhesion strength was determined by laser shock testing. The results show that substrate pretreatment with a nano-pulsed laser significantly improves the coating-substrate interface as well as coating adhesion.

Thermal-sprayed MCrAlY coatings are widely used for land-based gas turbine applications. The cold spray may increase the coating density owing to the high-velocity particle impacts during spraying. Many researchers have considered critical velocity to be the most important factor of the deposition mechanism of cold-sprayed coatings. However, this dominant parameter of critical deposition condition has not been completely understood. In order to understand the mechanism, two approaches were used in this study. One is the transmission electron microscope (TEM) observation of the interface between the coating and the substrate, and the other is the cross-sectional observation of the deposited particle by using the focused ion beam (FIB) cutting technique. From the TEM observations, there are no evidences of melting at the interface, and it is found that the actual bonding occurred at the nascent surfaces. Generally, there is a native oxide on the surface of the particles and substrate. After the plastic deformation of the particles and substrate, the native oxide breaks down; subsequently, a nascent surface can be created and direct contact initiates deposition. From the results of these investigations, it is thought that the dominant factor for deposition is the plastic deformation of the particles and substrates.

Cold gas dynamic spraying, namely cold spray, is an innovative coating process in which powder particles are injected in a supersonic gas flow to be accelerated above a certain critical velocity. Even though particles adhesion onto the substrate has not be yet elucidated, it appears clearly that it is influenced by particle impact velocity, which results from spraying conditions, diameter of particles and their positions from the center of the particle jet. Particle velocity can change dramatically depending on particle position from the core to the rim of the jet. In the present work, an original experimental set-up was designed to discriminate the particles as a function of the levels of velocity to investigate the influence of this parameter on adhesion. Particles at given positions in the jet could therefore be observed using SEM (Scanning Electron Microscopy), which showed different morphologies and microstructures as a function of impact velocity. High pressure and tangential velocity at the interface during impact were calculated from numerical simulations using ABAQUS. TEM (Transmission Electron Microscopy) analyses of thin foils were carried out to investigate into resulting local interface phenomena. These were correlated to particle impact velocity and corresponding adhesion strength which was obtained from LASAT testing (LAser Shock Adhesion Test).

Aluminium alloys are widely used for transportation facilities, because of light weight and high corrosion-resistance. If there are some cracks in transportation, sometimes they repair by welding. However, it is difficult to weld aluminium materials. Because, Aluminium has high specific thermal conductivity and high coefficient of thermal expansion compared with that of steel. The cold spray technique is known as a new technique not only for coating but also for thick depositions. It has many advantages, i.e. dense coating, high deposition rate and low oxidation. Therefore, it has a possibility to apply the cold spray technique instead of welding to repair the cracks. What seems to be lacking, however, is deposition mechanisms and mechanical properties of deposition produced by low pressure type cold spraying. This is a very important issue for applying the cold spray to repair some structures. In this study, elucidation of deposition mechanisms and evaluation of mechanical properties for the low pressure type cold sprayed aluminium depositions were investigated. As a result of elucidation of deposition mechanisms, it can be clear that the particle deposition needs to activate the surface by several impingements. Furthermore, as a result of evaluation of mechanical properties, the cold sprayed specimen showed higher strength than the monolithic specimen in the case of compressive loading to the coating.

Thermal-sprayed (i.e. LPPS or HVOF) MCrAlY coatings are widely used for land-based gas turbine applications against high-temperature oxidation and hot corrosion. However, due to requirement for further improvement of turbine efficiency, dense and stable coatings are necessary. The cold spray (also referred to as cold gas dynamic spray) makes it possible to increase coating density, due to high velocity particle impact during spraying. However, deposition mechanisms of cold spraying have not been elucidated yet. In this study, we investigated the deposition mechanisms focused on the behavior of interface between a coating and a substrate. The mechanisms were evaluated by the spray impact phenomena simulation tests, namely laser shock flier impact tests, and STEM-EDX elemental analyses at the interface between the substrate and the cold sprayed coating. From the results of STEM-EDX for as-sprayed coating and of SEM-EDX of the flier specimen, the bonding between the CoNiCrAlY coating and the substrate occurred at the only particular phase combination.

In waste-to-energy power generation plants, increasing the combustion temperature improves plant efficiency. However, due to problems caused by molten chloride corrosion, the combustion temperature cannot be increased. Consequently, in order to increase the temperature, it is first necessary to protect components from molten chloride corrosion. In this study, CoNiCrAlY coating is proposed as a protective film against molten chloride corrosion. Three kinds of specimens were prepared. One was standard coating made from conventional CoNiCrAlY. The others included the addition of Mo to the CoNiCrAlY by two different techniques. One technique is mechanical alloying (MA), and the other is a gas-atomizing technique. The mechanic-chemical reaction that occurs during the mechanical alloying process can be expected to create new functionality for the material. The effect of Mo content was evaluated for corrosion resistance. These specimens were coated by low pressure plasma spraying (LPPS). The specimens were exposed to NaCl-KCl for the molten chloride corrosion test. The results of the corrosion tests show that corrosion resistance improved in only MA CoNiCrAlY coatings. These results reveal that mechanically alloyed CoNiCrAlY-Mo coating has excellent corrosion resistance, and its corrosion resistance behavior is different from that of gas-atomized CoNiCrAlY-Mo.