A novel model for coating design was proposed in this research, by considering both oxidation property and interdiffusion effect, corresponding to two factors of the Cr:Al activity ratio and the potential of Al, respectively. To verify this model, oxidation tests of coated superalloys were performed at 1000 ° C for up to 5000 h. The test results indicated a strong positive correlation between GPDZ and Al potential and a clear negative correlation between oxidation kinetics parameter k p and Cr:Al activity ratio. Our research opened up new ideas for the coating design.

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.

Revealed as a process for surface functionalization and repair, cold spray is currently used as a reliable additive manufacturing process thanks to its ability to fabricate dense solid-state deposits with high deposition efficiency. However, cold-sprayed deposits generally present limited mechanical and structural properties due to manufacturing defects such as microporosities and weak interfacial particle bonding. As solutions, post-processing methods such as heat treatment or hot isostatic pressing are proposed to reduce manufacturing defects and optimize final deposit properties. This paper investigates the heat treatment effect on structural and mechanical features of cold sprayed 3D Aluminium part by comparing deposits properties evolution with the additive growth in the as sprayed and heat-treated states. Thus, a study is carried out to identify the right heat treatment conditions for optimizing deposits properties.

Cold spraying has great potential for additive manufacturing, especially of oxidation-sensitive metals, because the material is not melted and significantly higher deposition rates can be achieved than with conventional additive manufacturing processes such as selective laser melting or direct metal deposition. Titanium is regarded as a high-performance engineering material due to its unique combination of properties, including good corrosion resistance, biocompatibility and high strength at comparatively low density. However, due to its high price, it appears reasonable for many applications to use material compounds in which titanium is only used on the surface of the workpiece, while less expensive materials such as aluminum are used for the remaining volume. In the present work, cold sprayed pure titanium coatings were deposited on Al substrates and then formed to defined 3-dimensional final contours by die forging and rotary swaging. Different porosities were selectively set in order to evaluate their influence on the coating adhesion and cohesion in the forming process. Pre-consolidation of the coatings and the use of Al/Ti interlayers proved to be promising strategies.

Hybrid aerosol deposition (HAD) has been proposed recently as a new coating regime to deposit homogeneous ceramic coatings via the utilization of mesoplasma and solid particle deposition. This study will discuss the implementation of HAD for the deposition of alumina (Al 2 O 3 ) coatings on 304 stainless steel and aluminum substrates, and evaluation of the hardness and Young’s modulus using a nanoindentation method to clarify the through-thickness properties. Dense and uniform coatings with a nanocrystalline structure were fabricated on both substrate materials. The fabricated HAD coatings consisted of α-Al 2 O 3 phase. The hardness and Young’s modulus distributions along the through-thickness direction showed a significant difference across the coating-substrate interface and tended to show a slight decrease by 10-15% as the measured position went close the surface. Increasing the hardness and Young’s modulus on the substrate side near the interface is presumably related to the peeing effect of the substrate as well as the increase of interface roughness during the room temperature impact consolidation (RTIC) and deformation of the hard ceramic particles on the substrate. The decrease in the coating’s mechanical properties along the through-thickness direction is considered to be related to the particle deformation tendency during the coating build-up. At the beginning stage of the deposition, initial particles are impacting on a metallic substrate which is ductile enough to facile plastic deformation and the deposited layer can have an enough hammering effect by the subsequent impacting particles. The hardness and Young’s modulus in this location are 15.6 GPa and 246 GPa, respectively, and the highest through the thickness in case of the stainless steel substrate. However, the later particles are impacting on a hard ceramic surface (initially formed HAD Al 2 O 3 layers), which hardly undergo plastic deformation or led to less particle deformation. In addition, through-thickness measurements revealed that the deposited coatings on the stainless steel substrate showed higher hardness than deposited coatings on aluminum substrates. Thus, the stainless steel enhances the degree of deformation of the deposited particles, and the resulted smaller crystallite size and strain lead to increased hardness and modulus.

Miniaturization and performance improvements of electronic devices in recent decades have significantly increased heat dissipation rates. To overcome this, researchers have developed heat sinks with miniature fluid channels to maintain small device footprints with increased heat transfer performance. These channels are often fabricated using either subtractive fabrication methods, such as etching or micro-milling, or additive methods such as direct metal laser sintering (DMLS). These methods are limited by their long processing times, low geometric accuracy, or high cost. To overcome these limitations, a novel additive manufacturing method is developed using twin wire-arc spray. Wire-arc spray was used to build complex aluminum structures with length scales varying from 0.5 mm to 74 mm. Surface structures were built on a metal plate by spraying aluminum through a 3D printed polymer mask. Internal flow passages were made by filling surface channels with a water-soluble polyvinyl alcohol (PVA) paste that was allowed to harden, spraying metal over it, and then dissolving the PVA. The influence of wire-arc spray process parameters, such as standoff distance and scanning speed, on coating solid PVA with aluminum, were also investigated.

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.

Cold spray (CS), a solid-state depositing technique, has recently demonstrated promising application in additive manufacture (AM). Compared with fusion based AM technique, cold spray can eliminate solidification defects and is appropriate to fabricate some materials that are difficult for high energy beam methods, such as Aluminium. In the cold spray process, extreme plastic deformation will occur, which triggers the severe dynamic recrystallization and result in the formation of ultrafine grain structure. For a dense CSed component, the grain structure highly influences its performance. Especially for the grain structure in the region around the impact interface, which decides the bonding of particles. However, due to the extreme processing condition of CS and complicated deformation history around the interface, it is challenging to carryout systematic study on the factors that influence the finial grain structure and make a prediction on the final grain size in this region. Here, a Monte Carlo model was built to simulate the dynamic recrystallization in the Aluminium cold spray process. The influence of impact velocity and single/multiparticle impact on the final grain structure in the interface was investigated comprehensively and independently. And the average grain size on the impact interface predicted by the modelling agreed well with reported experimental results.

In cold spray (CS) additive manufacturing process, micrometer scale particles accelerated through a supersonic nozzle are targeted on a surface with velocities in the rage of 300-1500 m/s in solid state. The impact energy of the particles leads them to deform plastically with high shear energy near the impact interface and adhere to the surface metallurgically, mechanically, and chemically. Using CS, deposition of metals, metal matrix composites, and polymers are achieved with high adhesive/cohesive strength and low porosity. Sensitivity of the CS additive manufacturing process to the variabilities in the process parameters are still being understood. Among the process parameters, particle morphology can have significant implications on drag forces, and therefore, on the particle impact velocity. This in turn affects the deposition efficiency (DE) and the quality of products. In this work, a new approach is introduced for computing DE by incorporating particle sphericity and its variation into one-dimensional numerical models. Size, sphericity, and the variability of size and sphericity of aluminum, copper, titanium, and tantalum particles are measured from static optical microscope images. The data is used for predicting impact velocity, temperature, and DE. The model results are then compared with particle velocity measurements.

In a novel approach for guiding elements of sawing machines wear resistant coatings were applied on open-porous AlSi 7 Mg substrates by means of high velocity suspension flame spraying (HVSFS). The challenge is to establish a wear resistant coating but simultaneously maintain the open-porous structure that is necessary to serve as a permeable structure for liquid cooling or lubricant media under operation. In a first approach, a water-based suspension containing a mixed Al 2 O 3 -TiO 2 powder for HVSFS was used to deposit dense and well adherent mixed-oxide coatings. As the substrates exhibit an open-porous structure and a well-defined pore size distribution, transpiration cooling through the pores is possible and even necessary in order to ensure a low thermal impact on the fragile pore structure, preserving the open-porosity of the substrate. The coatings are characterized and compared by the means of light microscopy and hardness indentation.

Metals were deposited on components made by 3-D printing with polyvinyl alcohol (PVA), a water-soluble polymer. The polymer was then dissolved, leaving a metal layer whose surface topography was the negative of that of the polymer. This is a rapid and low-cost alternative to 3D printing directly using metal, but to succeed it is essential for the sprayed metal to adhere to the polymer substrate. Tests were done in which aluminum and copper were sprayed using a twin-wire arc spray system onto 3D printed coupons, 50 mm x 50 mm in size, made from polylactic acid (PLA), PLA mixed with metal (aluminum, copper) or carbon fiber, and PVA. Adhesion depended on substrate roughness (minimum 1-2 μm) and substrate temperature (above the glass transition temperature but below the melting temperature of the polymer). It was shown that surface features could be made with high resolution on metal components using this technique.

The scanning acoustic microscopy (SAM) technique is used for studying the character and interface quality of cold sprayed Fe coatings deposited onto notched Al-based substrates. Three notch geometries were used: a rectangular notch, a trapezoidal notch with a flat bed, and a trapezoidal notch with a cylindrical bed. Scanning electron micrographs demonstrated an increased porosity and cracks at the areas where the spraying direction was not perpendicular to the surface of the substrate. The SAM measurements were then performed on thin plates cut vertically across the notches such that the scanned area included the locations of the increased porosity and their surroundings. The resulting distributions of longitudinal wave velocities and their attenuation revealed that the affected area is more complex and the mechanical response of the coatings could be limited not only at areas of the visible porosity, but also in their vicinity.

Low pressure cold spraying is an attractive technique for onsite metal coating fabrication due to its compactness and portability. However, the bonding strength of the coating prepared by low pressure cold spraying is generally low, which restricts the further applications in engineering and industrial fields. To improve the bonding strength, pre-treatment on substrate surface can be an effective procedure. In this study, a low-temperature plasma treatment was applied to a pretreatment technique, and the effect of the treatment on particle bonding was compared with that of a laser treatment. Copper coatings on aluminum and copper substrates were selected and studied as basic metal materials. The SEM observation results show that the particle adhesion rate significantly increases by the laser and plasma treatments, due to the removal of the native oxide films on the substrates. The particle bonding on the plasma-treated substrate reveals better interfacial adhesion with less gap compared with the laser-treated one. The pre-treatment by low-temperature plasma can be an attractive technique to assist the cold spraying process due to the oxide removal ability and no thermal effect which can apply a wide range of materials.

Biofouling has been persisting as a worldwide problem due to the difficulties in finding efficient environment-friendly antifouling coatings for long-term applications. Developing novel coatings with desired antifouling properties has been one of the research goals for surface coating community. Recently hydrogel coating was proposed to serve as antifouling layer, for it offers the advantages of the ease of incorporating green biocides, and resisting attachment of microorganisms by its soft surface. Yet poor adhesion of the hydrogel on steel surfaces is a big concern. In this study, porous matrix aluminum coatings were fabricated by cored wire arc spray, and the sizes of the pores in the aluminum (Al) coatings were controlled by altering the size of the cored powder of sodium chloride. Silicone hydrogel was further deposited on the porous coating. The hydrogel penetrated into the open pores of the porous Al coatings, and the porous Al structure significantly enhanced the adhesion of the hydrogel. In addition, hydrogel coating exhibited very encouraging antifouling properties.

This paper discusses the challenges of constructing mathematical models of physicochemical and heat-mass transfer processes associated with reactive heterogeneous materials used in laser additive manufacturing. The results of calculations of thermocapillary convection induced by laser heating in an aluminum melt with an admixture of nickel particles are presented. Models of interphase and chemical interactions with the formation of intermediate phases and intermetallic compounds on nickel particles added to the melt during laser alloying or cladding are proposed, which make it possible to calculate the composition of intermetallic phases in the trace of the beam after crystallization and cooling.

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.

This study focuses on the relationship between porosity and leak tightness in cold-sprayed aluminum. Aluminum coatings with 0.2-9% porosity were produced by cold spraying and evaluated via helium leak testing. Multiscale porosity was determined through SEM and TEM analyses and shows good correlation with leak test results. The mechanisms involved in the creation of porosity were investigated as well through finite element analysis of single and multi-particle impacts.

Cold spraying of automotive engine blocks requires a gun adaptation for inner diameter spraying with a very short nozzle. In this work, 316L coatings are sprayed with such a gun and the behavior of particles impacting aluminum and stainless steel surfaces is studied in order to understand the factors that affect coating adhesion and cohesion. Correlations between spraying parameters and coating properties were investigated via design of experiments and the effect of process parameters on deposition efficiency and coating thickness was optimized for mass production. Post-process honing was also employed as part of the study and smooth coatings with small pores were obtained.

This study investigates how Al and Ta diffusion affects the growth of surface oxides in NiCoCrAlYTa coatings and the interdiffusion that occurs between coatings and single-crystal substrates in high-temperature oxidation processes. HVOF-sprayed layers were tested at temperatures between 900 °C and 1100 °C and the corresponding oxidation behavior of Al and Ta was assessed. It was found that higher amounts of Al in MCrAlY coatings promote the selective oxidation of Al 2 O 3 and that the addition of Ta increases the stability of the γ’-Ni 3 (Al,Ta) phase.

This paper is the second part of a study on how Al and Ta diffusion affects the oxidation of NiCoCrAlYTa coatings. Thermodynamic and diffusion simulations of the coatings with different additions of Al and Ta predicted the development of a typical γ, γ’, ß-phase microstructure and suggested that the ß-NiAl phase was depleted as Al diffused into the substrate. The simulations also indicated that Ta could diffuse back to γ’-Ni 3 (Al,Ta) phase in the substrate with a γ’ depletion due to inward diffusion of Co and Cr from the HVOF-sprayed deposit. How this process impacts microstructure development is discussed in detail.