Surface coatings play a pivotal role in enhancing mechanical and functional properties of various materials. High Entropy Alloy (HEA) annealed coatings have garnered significant interest due to their potential to improve wear resistance and overall durability. This research presents a comprehensive study focused on the characterization of HEA annealed coatings. It focuses on evaluating their roughness and wear performance. In this research, a systematic approach is adopted to assess the effects of annealing on coating surface properties. The investigation begins with the deposition of the Al 0.1-0.5 CoCrCuFeNi and MnCoCrCuFeNi coatings using a well-established cold spray (CS) technique, followed by a controlled annealing process. The coating surface roughness is analyzed using profilometry and microscopy techniques. This offers insights into the changes induced by annealing. The wear performance of the annealed coatings is evaluated through tribological tests.

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.

The deformation behavior of particles plays a significant role in achieving adhesion during cold spray. The deformation behavior of the particles is associated with the fracture of the oxide layer and recrystallization, which are the key elements of the quality of cold spray. Studies of particle compression have been made to understand the deformation behavior of a particle. However, the deformation behavior of particle under controlled load and precise and high strain rate is yet to be studied. Here, we show the oxide layer fracture pattern and recrystallization regime under controlled load with a precise and high strain rate. We found that the cracks in the oxide layer initially appeared on the equator of the particle and propagated towards the edge of the top surface. Meanwhile, on the top surface, the circumferential crack was developed. On the other hand, the nanoindentation result showed that the compressed particle under a high strain rate has an unusual load-displacement behavior. Our results demonstrate that the oxide layer fracture behavior corresponds to the adhesion mechanism suggested by previous studies. Our study also revealed that recrystallization takes place within the particle under a high strain rate. We anticipate this finding to give a general insight into the deformation behavior of particles during cold spray. For instance, since the recrystallization behavior at a given strain rate can be predicted through this study, the resultant grain size and shape, which is associated with mechanical properties, can also be predicted. Furthermore, the amount of strain and strain rate to form optimal adhesion can be evaluated.

In this work, hot isostatic pressing (HIP) is used to reduce interior defects, adjust the microstructure, and improve the tensile properties of cold-sprayed Ti6Al4V. Optical microscope and X-ray tomography were used to characterize pore morphologies and porosity evolution. XCT reconstructions show that fully dense Ti6Al4V alloy with an equiaxed microstructure were achieved. Tensile testing shows that strength and ductility were improved as well because of enhanced diffusion and resultant metallurgical bonding.

This study employs a three-dimensional simulation to investigate the cold gas dynamic manufacturing process. During the buildup of the desired object, sharp edges, stagnation points, and corners are likely to form that can influence the trajectories of the particles. This leads to dispersion and lack of particle deposition in these areas, which can eventually reduce the precision and efficiency of the build process. A cylindrical and frustum-shaped object are numerically simulated on a substrate to represent typical additively manufactured parts. Particle trajectories and impact conditions with and without these objects are compared. The results provide useful information for understanding the limitations and challenges associated with cold gas dynamic manufacturing, which can help improve the quality and precision of the process.

In this work, a new cold-spray shot-peening process was used to achieve surface nanocrystallization on a magnesium alloy deposit. The results of various examinations and tests show that nanocrystalline layers up to 40 µm thick with an average grain size in range of 50-80 nm can be prepared on AZ91D deposits using the new process. The nanocrystalline layers also exhibit good microhardness and tribological properties.

In this work, a novel additive manufacturing process was proposed and employed in the production of stainless steel components. The underlying concept is to use selective laser melting (SLM) to fabricate a core structure onto which basic features are added by cold spraying (CS), followed by heat treatment and finish machining. The microstructure and mechanical properties of as-fabricated and heat-treated parts were studied, and interfacial bonding between the SLM core and a typical CS feature was assessed. In the as-fabricated state, it is observed that the CS material has a dendritic structure similar to the feedstock, while the SLM core is characterized by cellular subgrains confined in coarse grain structures. Following heat treatment, interparticle boundaries are less well defined, equiaxed coarse grains and twinning appear, and the extremely fine subgrains in the SLM material are enlarged. Heat treatment is also shown to improve tensile strength in the CS material and interfacial bond strength between the CS features and SLM core.

In this study, aluminum coatings were cold sprayed, with and without laser assistance, on laser-textured aluminum 6060 and Fe52 steel substrates. The results indicate that laser texturing makes for a cleaner coating interface than grit blasting and that the benefits are greatest when spraying on harder substrate materials. For the steel substrate, the optimized topography achieved through laser texturing assisted in particle deformation, leading to the formation of a much tighter coating structure. Laser-assisted cold spraying, in turn, improved deposition efficiency as well as coating density and adhesion. Separately or together, the two processes have proven to be beneficial for cold spraying.

In this study, high-strength aluminum alloy AA7055 deposits are prepared using a recently developed cold spray process that employs in-situ microforging. The in-situ hammering effect is achieved by mixing large shot-peening particles into the spray powder and is shown to enhance interparticle bonding along with the plastic deformation of deposited particles. The underlying mechanisms are discussed based on the characterization of interface microstructure and the distribution of oxide film at the interparticle interface.

This study assesses the mechanical performance of cold-sprayed aluminum 6061 coatings heat treated using focused IR radiation. The heat treatment was performed in-process with the aim of improving the ductility and strength of the coatings. The properties of the heat-treated samples are compared to those achieved using traditional annealing and as measured in as-sprayed samples. It was found that the rapid IR heat treatment increased the ultimate tensile strength of the coatings by 52% and elongation at failure by 43%.

This study investigates the feasibility of producing GaN coatings on stainless steel, aluminum, and indium tin oxide glass substrates by downstream injection low-pressure cold spraying. The formation of GaN layers on all three materials appears to be due to pseudo deformation of super agglomerated GaN particles. The deposition results showed a saturation limit to coating thickness with the number of passes. Based on XRD spectra of the coating and powder, no phase transformations took place during the spraying process.

Super wear-resistant aluminum-based metal matrix composite (MMC) coatings were produced using cold spraying. Cu-Ni coated diamond and pure diamond particles were used as reinforcing agents. Test results show that the metallic Cu-Ni shell served as a buffer layer, preventing the fracture of diamond particles upon impact as occurred with the uncoated diamond. The coated diamond particles were also found to have a higher deposition efficiency due to metallurgical bonding between the Cu shell and Al matrix. Under tribological testing, all coatings performed well, but those reinforced with the coated diamond showed higher wear resistance due to higher diamond content and involvement of Cu and Ni.

In cold spraying, oxide-free interface is an important factor for fresh metal bonding between particles and substrate, which determines the bonding strength and final coating quality. In this study, a well-designed experiment was performed to examine the deformation behaviour of the oxide film on copper alloy particle surface after deposition. The experiment results show that partial oxide film could be disrupted during the high-speed impact. However, most of the oxide films were found to remain intact after particle deposition, which limited the exposure of oxide free interface. The presence of oxide film at the interfaces between deposited particles and substrate seriously affected the metallurgical bonding. Besides, substrate material is found to have a strong influence on the deformation behaviour and final state of the oxide film. The study also demonstrated that the bonding mode between deposited particle and substrate strongly depends on the type of substrate.

The present work summarizes the most important results of a research project dealing with the comprehensive!! investigation of the bonding mechanisms between cold sprayed Al coatings and various poly- and monocrystalline ceramic substrates (Al 2 O 3 , AlN, Si 3 N 4 , SiC, MgF 2 ). Due to their exceptional combination of properties, metallized ceramics are gaining more and more importance for a wide variety of applications, especially in electronic engineering. Cold spraying provides a quick, flexible and cost-effective one-step process to apply metallic coatings on ceramic surfaces. However, since most of the existing cold spray-related publications focus on metallic substrates, only very little is known about the bonding mechanisms acting between cold sprayed metals and ceramic substrates. In this paper, the essential factors influencing the bonding strength in such composites are identified. Besides mechanical tensile strength testing, a thorough analysis of the coatings and especially the metal/ceramic interfaces was conducted by means of HRTEM, FFT, STEM, EDX, EELS, XRD and EBSD. The influence of substrate material, substrate temperature and particle size is evaluated with regard to the observed bonding behavior. The results suggest that, apart from mechanical interlocking, the adhesion of cold sprayed metallic coatings on ceramics is based on a complex interplay of different mechanisms such as quasi-adiabatic shearing, static recrystallization as well as heteroepitaxial growth.

Previous results at McGill University have shown that metallic coatings can be successfully cold sprayed onto polymeric substrates. This paper studies the cold sprayability of various metal powders on different polymeric substrates. Five different substrates were used, including carbon fibre reinforced polymer (CFRP), acrylonitrile butadiene styrene (ABS), polyether ether ketone (PEEK), polyethylenimine (PEI); mild steel was also used as a bench mark substrate. The CFRP used in this work has a thermosetting matrix, and the ABS, PEEK, and PEI are all thermoplastic polymers, with different glass transition temperatures as well as a number of distinct mechanical properties. Three metal powders, tin, copper and iron, were cold sprayed with both a low-pressure system and a high-pressure system at various conditions. In general, cold spray on the thermoplastic polymers rendered more positive results than the thermosetting polymers, due to the local thermal softening mechanism in the thermoplastics. Thick copper coatings were successfully deposited on PEEK and PEI.

This paper presents developments in the field of induction capable coatings, mainly used for induction cookware on aluminum or copper base material, based on work by OBZ Innovation GmbH. The aim was to develop a new type of “intelligent” induction coating that influences the magnetic susceptibility depending on its temperature. This not only allows to limit the maximum reachable temperature, but also supports the uniform heat distribution over the bottom of the cookware. Thus, this new type of “intelligent” induction coating regulates such important boundary conditions, independently of undesirable or even unsafe settings of an end-user. Finally, this makes cooking easier, healthier and more durable as it prevents damaged PTFE sealings and safer by reducing the danger of fire because of overheating and burning. Additionally, such coatings can be used in further applications, whenever a passively limited or uniform heat distribution is advantageous, for example when the temperatures are too high or in general an electronic control system is for technical or economical reasons not suitable.

In this study, an experimental approach to investigate basic dependencies on impact and bonding of agglomerated ceramic particles in cold spraying is presented. Single impact morphologies of ceramic particles obtained from wipe tests are correlated with data obtained from powder compression experiments with a modified nanoindenter. Different feedstock powders of agglomerated TiO 2 -nanoparticles were used and also partially heat treated. The powder shapes and sizes prior and after the compression tests were analyzed by confocal microscopy. The single particle impacts were characterized by SEM. Besides the expected influence of substrate material, substrate temperature, and spray conditions, the deformation and bonding of ceramic particles to metal substrates critically depend on the powder properties. To which degree particles fracture or contribute to layer formation upon the high-energy impact is highly correlated to their individual deformation behaviour in quasi-static compression tests.

In the cold spray process, cross-sectional shape of the nozzle has a significant effect on spray pattern of coatings. There is a rectangular and a circular cross-sectional shapes on the cold spray nozzle. It has been reported that the rectangular nozzle provide a more uniform particle velocity across the exit of the nozzle. The circular exit nozzle is parabolic in shape. So spray pattern with the rectangular nozzle is wider than that with the circular spray nozzle. The goal of this investigation is to establish a design for the cold spray gun nozzle in order to gain more uniform spray profile of coatings. We have investigated the influence of expansion ratio, nozzle total length and the ratio of nozzle length of divergent section and parallel section of rectangular nozzle on behaviours of gas and particle by the computational fluid dynamics (CFD) in high pressure cold spraying. In this study, the spray pattern and microstructure of copper coatings with the rectangular cross-section nozzle optimized by CFD analysis in high-pressure cold spraying are reported. The optimized rectangular nozzle provide a more uniform spray profile of coatings. Relatively finer powder tended to deposit on the end of the coating.

Understanding the complex mechanical behavior of stainless steel based composite coatings is important for engineering applications. The focus of this research was on gaining a fundamental understanding of the structure/property relationships that exist during structure formation of the coatings made by new low pressure cold spraying with propellant gas at the temperatures of 800-1000°C (warm spray). While composition is one of the key parameter in determining the final microstructure, the specific warm spray powder shock consolidation parameters (particle velocity and gas temperature) were found to have significant effects on the development of composite structure formation and mechanical properties. Microstructural examination and modeling results revealed that the strain localization mechanism differs from that of adiabatic shear band formation that results in large differences in the ensuing microstructure of the composite coating and its properties.

Well-known detonation thermal spraying is considered to be a good method for the preparation of WC-based coating with high adhesion. The depositing parameters, especially the oxygen-fuel ratio and spot frequency, have been observed to influence the properties of the coating. The influence of the main parameters of the detonation spraying of tungsten carbide based coatings and their mechanical properties have been investigated. Two main tasks for the development of a carbide-containing material application technology have been determined. The relationship between the phase composition of WC-based coatings and their strength, hardness and bond strength to the substrate has been identified. The technique of coating in the reductive mode has been proposed. High oxygen-fuel ratio and spot frequency decreased the decomposition of the WC-phase, which makes the WC-Ni particles harder and as a result more easily embedded in the substrate, i.e. the coating which is beneficial to enhance bonding strength.