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A variety of metallic powders were mixed with tin in 10:90 weight ratios and cold sprayed onto thermosetting epoxy carbon fiber-reinforced polymers (CFRPs) substrates with varying surface finishes, and onto a thermoplastic polyether-ether-ketone (PEEK)-CFRP. Where previous studies focused on understanding the impact of the secondary component (SC) on the deposition efficiency (DE) of tin, this study aims to explore the pull-off strength and electrical conductivity of the deposited coatings. An extensive study on fractured surfaces highlighted that better adhesion usually arose from increased potential to mechanically interlock with a feature at the surface such as carbon fibers or surfacing elements. The polymeric nature of the composite resin was observed to affect the pull-off strengths as the ductile thermoplastic PEEK seems to absorb more of the impinging particle energy. The pull-off strengths were then related to the SC properties, and it was observed that the better coating strengths were obtained with SC that were previously reported to be detrimental to pure Sn deposition. Finally, four-point resistivity/conductivity measurements were carried out and results were generally better than those previously reported in the literature (50-80% the conductivity of bulk tin), with variations being associated with differing bonding quality within the coatings.

Cold gas spray (CGS) technology has allowed the development of biofunctional coatings composed of 45S5 and polyetheretherketone (PEEK). The combination of a bioactive glass material embedded in a polymeric matrix makes this composite an interesting material for orthopedic applications since this composite meets the biomechanical and biological requirements of an implant. In the present study, blends of bioactive glass 45S5 and PEEK powder with different granulometry and 45S5/PEEK ratio have been prepared. These mixtures of powders have been deposited onto PEEK substrates by CGS with the goal of incorporating a bioactive additive to the biocompatible polymer, which can improve the bone-implant interaction of PEEK. The deposition efficiency (DE) of the coatings has been evaluated, and from the results obtained, it was possible to conclude that DE is significantly affected by the granulometry and by the 45S5/PEEK ratio of the blends. By scanning electron microscopy (SEM) inspection, it was observed that the use of blends with high 45S5/PEEK ratio lead to the deposition of coatings with high content of 45S5. Finally, the friction behavior of the coatings was analyzed performing ball-on-disk tests and these experiments showed that the presence of glass particles has a beneficial role in the wear resistance.

Graphical Abstract Antibacterial properties of copper against planktonic bacteria population are affected by surface microstructure and topography. However, copper interactions with bacteria in a biofilm state are less studied. This work aims at better understanding the difference in biofilm inhibition of bulk, cold-sprayed, and shot-peened copper surfaces and gaining further insights on the underlying mechanisms using optical and scanning electron microscopy to investigate the topography and microstructure of the surfaces. The biofilm inhibition ability is reported for all surfaces. Results show that the biofilm inhibition performance of cold sprayed copper, while initially better, decreases with time and results in an almost identical performance than as-received copper after 18h incubation time. The shot-peened samples with a rough and ultrafine microstructure demonstrated an enhanced biofilm control, especially at 18 hr. The biofilm control mechanisms were explained by the diffusion rates and concentration of copper ions and the interaction between these ions and the biofilm, while surface topography plays a role in the bacteria attachment at the early planktonic state. Furthermore, the data suggest that surface topography plays a key role in antiviral activity of the materials tested, with a smooth surface being the most efficient.

With regards to cold spraying, wear resistant metal coatings reinforced with boron nitride nanotubes (BNNTs) have remained unexplored when compared to carbon nanotube-based composites. Using commercially pure aluminum powder, 1-3 μm B4C powder, and BNNTs, multiple reinforced metal matrix composite powders were fabricated via high energy ball milling (HEBM). The powder compositions included an Al control, a 4 vol.% B4C composition, a 4 vol.% BNNT composition, and a 2 vol.% B4C with 2 vol.% BNNT composition. The compositions were sprayed onto AZ31 substrates using helium. The coatings were evaluated using nanoindentation, micro-indentation hardness, adhesion, and tensile tests. The coatings were then qualitatively evaluated under an optical microscope and scanning electron microscopes. Good dispersion of the ceramic reinforcements throughout the Al matrix was achieved via HEBM. A 14.1% increase and a 20.8% increase in micro-indentation hardness over the control were achieved for the Al/BNNT and the Al/B4C/BNNT compositions, respectively. Adhesion testing led to the Al/B4C/BNNT composition failing cohesively and the control failing adhesively at approximately the same force. The Al/B4C adhesion tests experienced a combination of the two failure modes at a 31.2% increase in force over the control. Stress vs. strain curves from tensile testing demonstrated that the load is partially supported by the cold spray coating until the coating ruptures. Office of Naval Research (ONR) Outstanding Thesis Lieutenant, United States Navy Approved for public release. Distribution is unlimited.

Quantitative percussion diagnostics (QPD) is a non-destructive evaluation method that has been used successfully in a number of applications. This technique involves a rod that is actuated to impact a specimen with a given amount of kinetic energy and the resulting mechanical response of the specimen as a function of time is measured using a piezoelectric force sensor. The mechanical energy returned to the rod is then analyzed. Because contact with the specimen is on the order of a few hundred microseconds, QPD can be used in situations and for specimen conditions (e.g. high temperature) that are not feasible for other nondestructive testing methods. The objective of the present study was to evaluate the use of QPD for characterization of defects in specimens fabricated using two additive manufacturing methods, i.e. cold spray deposition and laser powder directed energy deposition (LPDED). Cold spray specimens were produced using commercially pure nickel with varied process conditions including gas type (i.e. helium and nitrogen) and deposition rate. In addition, a Ti–6Al–4V specimen was manufactured using LPDED with varying porosity content. All specimens were characterized using both QPD and destructive methods (i.e. cross-sectional metallography) to compare results for observed defect characteristics. Cold spray specimens exhibited a lower energy return when they contained more porosity and/or surface roughness. Microscopic plastic deformation at highly porous surfaces was indicated during percussion testing that reached a saturation level after repeated percussion. Overall, the results showed that QPD can effectively evaluate cold spray and LPDED specimens for porosity and surface roughness.

Additive manufacturing (AM) has seen remarkable development in recent years due to relatively high efficiency of the process. Cold spraying (CS) is a particular method of AM, in which titanium and titanium alloy powders are used. CS is a very competitive technology enabling the deposition of coatings, repairing machine parts, and manufacturing new components. For specific applications, the surface of cold-sprayed materials may require further processing. This paper reports an attempt to employ laser surface treatment (LST) of cold-sprayed coatings on an aluminium alloy substrate. The influence of laser beam interaction time on the coatings’ properties was analysed. The microstructure was investigated and observed employing scanning electron microscopy (SEM). To evaluate residual stress after CS and LST, the sin2ψ technique was used. Investigations were also performed on Vickers hardness, contact angle, and surface roughness. Significant changes in the surface morphology of the coatings and elevated residual stress levels dependent on the laser beam interaction time were observed. Increased Vickers hardness was recorded for titanium alloy Ti6Al4V. LST also led to increased surface hydrophilicity of the modified materials Ti and Ti6Al4V.

Aluminum-based metal matrix composites (Al-MMCs) have shown enhanced strength, hardness, and wear properties. Hence, Al-MMCs are gaining momentum in the aerospace, automotive, defense and marine industries as a protective wear layer and for battlefield repairs. Recently, Al-MMC coatings were fabricated through cold spray (CS), a form of additive manufacturing (AM). The CS process has shown advantages of minimal oxidation, no phase transformation, and good metallurgical bonding when applied to a substrate. However, drawbacks such as porosity and low ductility limits its practical application. Heat treatments to CS coatings were successful in overcoming the drawbacks but sacrificed hardness for ductility. In a recent study, four variations of Al-MMCs CS coatings were fabricated using nano-sized aluminum and dual ceramic nanoparticle (NP) reinforcements, where the CS feedstock was synthesized through cryo-milling and high-energy ball milling. The study showed that the use of ceramic reinforcements of nano-boron carbide and boron nitride nanoplatelets at various combinations up to 2 vol% showed improvements in the hardness of the coating. Further research into controlling the properties of NP-reinforced Al-MMC CS coatings can further its application. This study examines the effect of heat treatments and the addition of up to two ceramic nanoparticles on the mechanical and tribological properties of an Al-MMCs coating fabricated by CS. Office of Naval Research Major, Singapore Army Approved for public release. Distribution is unlimited.

Surface treatments on polymer-based materials are frequently used to enhance mechanical and physical properties. Cold spray is a metallisation technique that provides a viable solution to overcome ...

In previous studies at McGill University, tin has successfully been cold sprayed onto carbon fiber reinforced polymers (CFRPs) and, with the idea of improving the coating conductivity, other metal powders (aluminum, copper and zinc) were added to tin and also sprayed. Results indicated that addition of any of the aforementioned secondary components (SCs) provided a noticeable increase in deposition efficiency (DE); it was hypothesized that a tamping mechanism might explain the improvement. In this study, aluminum and several aluminum alloys (5083, 6061, 7075) were mixed with tin powders to understand how the hardness of secondary components with similar densities may affect the deposition of tin on CFRPs. The top-surface and cross section of the coatings were examined, and DE and coating thicknesses were measured. Profilometric data were acquired on some coating top surfaces, as well as directly on some substrates after coatings peeled off. Mixing tin with other metallic powders is discussed and a refined “crack filling” mechanism related to SC hardness is explored as an improvement mechanism in the cold spraying of mixed powders on CFRPs.

This study explores the individual and combined reinforcement effects of graphene nanoplatelets (GNP) and micro-boron carbide (µB4C) in cold-sprayed Al matrix composite coatings. High energy ball milling was used to create compositions of 2 vol.% GNP, 2 vol.% µB4C, and one of 1 vol.% GNP with 1 vol.% µB4C. All reinforced compositions consisted of a total of 2 vol.% reinforcement to compare the effectiveness of single and dual reinforcement and not the amount of total reinforcement. Coatings were heat treated for 1 h at 400◦C to improve coating densification. Each coating was evaluated using microhardness tests, nanoindentation, dry-sliding wear tests, and adhesion tests. The coatings were also qualitatively evaluated using optical and scanning electron microscopy. All three reinforced coatings experienced a greater than 47% increase in microhardness after heat treatment than the control Al coating. Adhesion testing revealed that 2 vol.% µB4C and the dual-particle coatings had a 40% and 29% increase in adhesion strength, respectively. Most notably, nanoindentation showed that the dual-particle coating experienced a 17% increase in hardness and a 13% increase in elastic modulus compared to the unreinforced coating. The singly reinforced coatings either had the same or lower hardness and elastic modulus than the unreinforced coating. ONR, Washington DC, 22217 Outstanding Thesis Ensign, United States Navy Approved for public release. Distribution is unlimited.

INCONEL 718 superalloy (IN 718) is frequently used in highly aggressive environments, such as aerospace and gas turbine engines, where excellent mechanical properties, creep-, fatigue- and oxidation-resistance performance at high and cryogenic temperatures are required. Recent studies have successfully cold sprayed IN 718, showing great potential mainly in maintenance and repairing fields. However, due to the low plastic deformation, the manufacture of IN 718 cold sprayed coatings often requires the use of expensive propulsive gases or high working parameters to enhance deposition efficiency, with a significant increase in production costs. This paper investigates for the first time the addition of Ni to IN 718 powders in order to increase plastic deformation and interparticle bonding strength. Four composite coatings were deposited via a high-pressure cold spray process using nitrogen as propulsive gas, considering different IN 718 mass fractions in the feedstock: C1 (0 wt%), C2 (25 wt%), C3 (50 wt%), C4 (75 wt%). The coatings are examined in terms of microstructural characteristics and tribological performance. The addition of IN 718 particles significantly improves the mechanical properties of the coatings, despite an increase in porosity, which however does not exceed 1%. The tribological performance of the four coatings is investigated using a pin-on-disk test, demonstrating that the coating wear resistance behaviour improved as the IN 718 content increased. Analysis of the wear mechanism shows that C4 coating has a different wear behaviour than the other coatings, thus achieving the best wear-resistance performance.

Owing to low-temperature deposition conditions and high deposition rate, cold spray offers unique advantages in manufacturing a wide variety of metallic and composite coatings including metal matrix composites produced from physically blended powders. One of the challenges of producing composite coatings using cold spray is the deviation of coatings composition from the blended feedstock powder composition. This is of utmost importance as it affects the composition and phase evolution of intermetallic forming coatings during post spray heat treatment. In this work, cold spray of composite Ni-Ti coatings and formation of intermetallics from post spray heat treatment were investigated as a first step to examine the potential of producing equiatomic bulk Ni-Ti by cold spray. Three different physically blended Ni and Ti powders mixtures were sprayed on titanium substrates to address the coating composition variation from the blended feedstock powder and study its influence on phase evolution during post spray heat treatment. High-density and well-dispersed composite coatings were achieved for each case. EDS analysis revealed as-sprayed coatings with 10.5, 35.9 and 56.9 at.% Ni (and with balanced Ti ratios) from the three powder mixtures. Annealing treatments were conducted at 400, 500 and 900 °C for 1 and 2 h and comparative studies of the intermetallic compound formations were carried out. Microstructural investigation showed that all three equilibrium intermetallics phases of binary Ni-Ti phase diagram (Ni3Ti, Ti2Ni and NiTi) formed in the two Ni-rich composite coatings with NiTi phase being maximum in the coating with the closest composition to equiatomic ratio while only Ti2Ni phase formed in the Ti-rich coating after annealing. Thermal etching analysis of coatings showed that NiTi phase forms with a gradient microstructure from Ti splats boundary toward the center of splats, which is attributed to the grain refinement of CS samples at splat boundary and intermetallic nucleation mechanism.

This article contextualizes how the antimicrobial properties and antipathogenic contact killing/inactivating performance of copper cold spray surfaces and coatings and can be extended to the COVID-19 pandemic as a preventative measure. Specifically, literature is reviewed in terms of how copper cold spray coatings can be applied to high-touch surfaces in biomedical as well as healthcare settings to prevent fomite transmission of SARS-CoV-2 through rapidly inactivating SARS-CoV-2 virions after contaminating a surface. The relevant literature on copper-based antipathogenic coatings and surfaces are then detailed. Particular attention is then given to the unique microstructurally-mediated pathway of copper ion diffusion associated with copper cold spray coatings that enable fomite inactivation.

International audience; Polymer coating by cold-spray presents interesting features such as the possibility to protect metallic substrates or to add functionalities to a structure. However, it is characterized by a low deposition efficiency and a weak interface between the substrate and the coating. In this study, we performed fluoropolymer coatings by the cold-spray process. Analysis of the particle deposition during cold-spray highlighted the importance of the particle size, substrate temperature, and inlet gas temperature and pressure on the adhesion polymer/substrate. The addition of hydrophobized fumed nano-ceramics (FNC) to the polymer feedstock enhances the deposition efficiency and polymer adhesion on the substrate. The addition of fumed nano-alumina (FNA) to the polymer feedstock tends to give better results than fumed nano-silica in terms of deposition efficiency thanks to (i) the difference of surface charge leading to the attractive force between the polymer and the FNA during the powder preparation stage, and (ii) a homogeneous repartition of the FNA on the polymer particle surface. In addition, the hydrophobization of the FNC maintains and enhances the hydrophobicity and water repellency properties of the fluoropolymer coating.

In this work, solid-state mechanical alloying (MA) and cold spraying (CS) processes were applied to fabricate powder AlNiCoFeCrTi high-entropy alloy (HEA) and then to produce HE coatings on steel substrate. Shot-time MA for 3 h has been employed to synthesize nanostructured equiatomic AlNiCoFeCrTi HEA of metastable supersaturated substitutional solid solution with bcc crystal structure. Although alloying is not complete at this shot milling time, it goes to completion during thermal annealing to achieve the alloy formation. XRD study on mechanically alloyed high-entropy AlNiCoFeCrTi alloy after thermal annealing at 1200 °C for 1 h revealed the formation of a three-phase structure consisting of ordered bcc phase with fine precipitates of intermetallic σ-phase (FeCr) and titanium carbide TiC. The powder agglomerates resulted from annealing were grinded in a ball mill for 1 h. Nanostructured disordered bcc solid solution, TiC and σ-phases are noticed after milling. Coatings of 450 μm in mean thickness were deposited by the CS process using an air like a working gas, temperature and pressure of 450 °C and 0.9 MPa, respectively. The experimental results confirm that CS process can be used to produce HE coatings with low porosity. As a low-temperature deposition process, CS completely retained the HEA phase composition and nanostructure in the coating without any phase transformation. The AlFeNiCoCrTi HE coatings exhibit 10.3 ± 0.3 GPa in Vickers hardness.

HA composite coatings added reinforcement phases could improve the mechanical properties and bonding strength of the coatings. Cold spraying is a feasible surface technology for preparing HA composite coatings. In order to investigate the influence of cold spraying parameters on the deposition behavior of a single HA/Ti composite particle, numerical and experimental investigation of gas-particle two-phase flow in cold spraying nanostructured HA/Ti composite particle were investigated in this study. The results show that the influence of different temperatures and pressures on static pressure was not significant. The effects of gas pressure on the static temperature were tiny under the same inlet temperature and different pressure conditions; however, the static temperature in the entire spray gun cavity increased as the inlet temperature increased under the same pressure and different inlet temperature conditions. There is little effect of gas pressure on the axial velocity of gas flow in the spray gun cavity; however, the axial velocity of gas flow increased with the increase in gas temperature. Meanwhile, the axial velocity of gas flow gradually increases throughout the spraying process. At a gas temperature of 573 K and 973 K, the maximum axial velocities of a gas flow at gas pressure of 2.2 MPa were 778 m/s and 942 m/s, respectively. There is little effect of gas pressure on the axial velocity of HA/30 wt.% Ti particles under the same gas temperature. The axial velocity of HA/30 wt.% Ti particles increased with the increase in gas temperature under the same gas pressure condition. The axial velocity of composite particles decreased with the increase in the particle size under the same gas pressure and gas temperature. At a gas temperature of 573 K and 973 K, the minimum axial velocity of HA/30 wt.% Ti particles with a particle size of 30 μm at a gas pressure of 2.2 MPa was 435 m/s and 467 m/s, respectively. A certain deformation of splats occurred after impacting the substrate, and the splats adhered to the surface of the Ti6Al4Vsubstrate, clearly presenting a flat shape with a central hump surrounded by a ringy band. At a gas temperature of 973 K, particles generated more severe deformation with more cracks and ejecta phenomenon. The splats attached to the substrate were increased as the gas temperature increased.

The surface roughness of additively manufactured (AM) components can have deleterious effects on the properties of the final part, such as corrosion resistance and fatigue life. Modification of the surface finish or parts produced by AM processes, such as cold spray, through methods such as mass finishing, can help to mitigate some of these issues. In this work, the surface evolution of as-produced copper cold sprayed material consolidations was studied through mass finishing. Three different copper powders attained by different production methods and of different sizes were used as feedstock. The surface topography of the cold spray deposits was measured as a function of the mass finishing time for the three copper cold spray samples and analyzed in terms of relative area and complexity, revealing an inverse correlation relating material removal rate and hardness/strength of the cold sprayed deposits. The material removal rate was also affected by the quality of the cold spray deposition, as defined by deposition efficiency (DE). Large initial drops in relative area and complexity are also likely due to the removal of loosely bonded powders at the start of mass finishing. Based on this study, the cold spray parameters that affect the rate of mass finishing have been explored.

Surface metallization is amongst the recent trends in the polymer and polymer matrix composites (PMCs) research industries to improve the electrical and thermal properties and exploit the subsequent utilization in the aerospace sector. Specifically, polymer matrix composites have been subjected to the limitations in form of high temperature exposure and substrate deterioration. The present study encompasses a new strategy in the manufacturing and metallization process. The first stage in the manufacturing of hybrid thermoplastic-thermoset composite was the hot compaction which comprised of primary preform preparation enabling the partial impregnation of the thermoplastic resin through the fabric reinforcement layer. The subsequent stage entailed the preform vacuum bagging and conducting catalyzed thermoset resin impregnation. The vacuum resin infusion step included a cocuring cycle to generate a fiber reinforced composite comprising of thermoplastic and impregnated thermoset resin with improved adhesion. Resin flow front movement was analyzed during the resin infusion process. Composite metallization was achieved through cold spray (CS). CS process parameters influence on the coating quality and characterization of laminates through microstructural analysis and results have been reported. The hybrid composite with thermoset resin through thickness and in-plane impregnation was achieved with the intact adherent thermoplastic layer after the curing cycle. In the CS metallization, the effective operative window of stand-off distances (SoD) and temperature has been determined.

Cold spray (CS) is a low-temperature process that can be used for the metallization of temperature-sensitive materials, such as polymers or polymer matrix composites, so coupling the lightweight of polymers with the wear resistance, physical properties and hardness of metals. The study of the cold spray of metal particles applied to polymers is still in its early stage and the deposition mechanisms underlying the process are not thoroughly understood yet. Moreover, numerical studies of cold spray of metal-to-polymer are almost completely absent in literature. Therefore, aiming to fulfill this gap of knowledge, the scope of this work is to develop a numerical FE model capable of predicting the impact and the adhesion of a micron size metallic particle onto a polymeric substrate. The results from the model were compared with the experimental outcomes found in literature to establish the effectiveness of the model that was used as a powerful tool to better understand the bonding mechanisms and all the related phenomena ruling the CS process of metal-to-polymer.

At present, the common protection technology of power-transmission and transformation equipment is mainly coating protection and hot-dip zinc protection. However, due to the low adhesion of epoxy zinc-rich coating, and the poor compatibility with top paint, environmental pollution, complex processing, high energy consumption and other defects of the hot-dip zinc process, its development is limited. In view of the above deficiencies, new anti-corrosion coating materials and processes were investigated in this study. Zinc coatings and Al-Zn coatings were prepared on the C45 steel matrix by hot-spraying and cold-spraying processes. The macro appearance, micromorphology and phase composition analysis of the coatings were evaluated. The adhesion of the coating to the substrate after the salt-spray test was tested. The results showed that the hot dip zinc coating and hot spray zinc coating had obvious cracking after the salt-spray test. The surface structure of cold-sprayed Al-Zn coating was relatively dense after the salt-spray test. The critical load of the cold-sprayed Al-Zn coating after the salt-spray test was higher than that of the other two coatings. The corrosion resistance to salt spray of cold-sprayed Al-Zn coating was demonstrated to be better than the hot-dip zinc coating, and thus has great application prospects.

One of the open questions in cold spraying on fibre reinforced composites is the optimal thickness of the top layer to provide a suitable base for successful deposition of the metallic particles and at the same time to hinder the probable damage of the fibres. In this study, a detailed finite element model is developed to study the deformation of a single Cu particle deposition on to polyether ether ketone (PEEK) substrate reinforced with carbon fibres. A PEEK layer with 30, 40 or 60 μm thickness was considered on the top surface of the composite. The particle impact velocity was varied in the range of 300-600 m/s to analyse its effects on the induced deformations as well as the structural integrity of the critical carbon fibres. It is believed that the proposed model can provide a helpful tool for predicting the optimal conditions in the metallization of polymers using the cold spray technique.

The aluminum cold spray feedstock powder was single- and dual-reinforced with no greater than 2 vol% boron nitride nanoplatelets (BNNP) and/or nanometric boron carbide (nB4C). These powders were cold sprayed onto Al-6061 substrates and then heat-treated in an argon environment. In addition, micro- and nano-indentation hardness and wear testing were performed on the heat-treated samples. Further microscopy and optical profilometry were used to characterize the microstructure and wear track volumes. Minimal changes to the splat structure were observed after heat treatment. However, when compared to the pure Al coating, microhardness improved with reinforcement after treatment at 500 °C, while nanohardness improved only in the dual-reinforced coatings, again after treatment at 500 °C. The elastic modulus generally decreased for the reinforced coatings after treatment; however, indentation test results were mixed. The wear testing done on samples heat treated at 500 °C for one hour showed increases in the specific wear rate for single-reinforced coatings but decreases in the dual-reinforced coatings. These results indicate that both dual-reinforcement and heat treatment are required for improvements in the mechanical and tribological properties of Al nanocomposites.

Fe/Al composite coatings with compositions of Fe-25 wt.% Al, Fe-50 wt.% Al and Fe-75 wt.% Al were deposited on pure Al and P91 steel plates by a cold spray, respectively. The microstructure of the cross-section of the fabricated coatings was characterized by SEM and EDX. The bonding strength between the coatings and substrates was measured and analyzed. The effects of the Fe/Al ratios and substrate hardness on the deposition behavior were investigated. It was interesting to find fragmented zones in all fabricated coatings, which were composed of large integrated Al particles and small fragmented Al particles. Meanwhile, the fraction of fragmented zones varied with the fraction of the actual Fe/Al ratio. An Fe/Al ratio of 50/50 appeared to be an optimized ratio for the higher bonding strength of coatings. The in situ hammer effect caused by larger and harder Fe particles played an important role in the cold spray process. The substrate with the higher hardness strengthened the in situ hammer effect and further improved the bonding strength.

This thesis provides an overview of how a successful method for structuring cold spray deposition was developed, allowing the creation of defined surfaces from a previously uncontrolled deposition profile. When considering both additive and traditional manufacturing techniques, there remains a gap in the market for a high build rate, low-cost manufacturing system, capable of building net shape structures with good material properties from a range of difficult to work with engineering materials. A cold spray system had the potential to meet these requirements, and to provide additional benefits from being a solid-state fusion process, but the technique lacked the structural control capabilities required. The aim of this body of work was to develop methods for controlling the shape of depositing material, allowing the creation of three-dimensional structures, and determining an approach which would allow the creation of flexible manufacturing platform. A limited number of attempts had been previously made to control the deposition shape. These methods met with limited success, did not offer real control over the shape of the deposit during operation, and presented issues of accuracy, reliability, and repeatability. In this work, a series of concepts for shaping the deposition of the material were tested for the creation of flat vertical surfaces. Copper was used as the deposition powder as it readily deposits with cold spray under easily manageable conditions. The samples were investigated for shape conformity, surface roughness, porosity and build height, using optical microscopy and a white light interferometer. Successful shaping was delivered using masks, wide flow impeding backstops and thinner flow separating tools, provided the non-adhering powder had sufficient room to be cleared from the deposition zone. The thinner tool was further developed, as it allowed better positioning in smaller spaces for future systems. Computational fluid dynamics models were created to assist with the understanding of some inconsistencies in deposit quality. The results of these simulations showed minimal alteration to the particle trajectory was caused by the alteration of gas dynamics from the introduction of obstacles. The developed thin tool deposition concept was then successfully tested for robustness with deposition of further materials, and with the inclusion of laser irradiation of the substrate. It was demonstrated that the density, deposition efficiency and build heights are comparable with those expected from typical cold spray/supersonic laser deposition deposits. Following this, a range of building block structures were created, to further advance the shaping capabilities of the system, and demonstrate the freedom of deposition profile. Flat surfaces, thin walls, corners, curves, rings and overhangs were all shown to build efficiently without further complication. It is concluded that it is both possible to control the shape of the depositing material during cold spray, and possible to do so without adversely affecting the deposit characteristics that give cold spray manufacturing its specific advantages over other manufacturing methods. The next steps for this process are to create a more flexible system, automating the placement of the shaping tool and using a 5 or 6 axis bed and nozzle positioning setup. Further to that, precise control over the powder dosage, and the development of a known parameter space for select materials would progress the system to an additive capable platform.

Cold spray is a developing additive-manufacturing technology well suited as a preventive and corrective measure for metallic materials. The key challenge lies in formulating the optimal multifaceted spray parameters to achieve a functional coating on a substrate. Copper-nickel (Cu-Ni) alloy is particularly suited for study, due to its feasibility as both coating and repair material to be deposited onto a substrate through cold spray technology and its well-established characteristics for corrosion protection and mechanical strength. This thesis studied the change in mechanical behavior due to annealing of cold-sprayed Cu-Ni coating. In order to do so, the subject Cu-Ni powder's behavior and coating quality were characterized through the variation of certain spray parameters and examined by the mechanical behavior of multiple passes of Cu-Ni coatings through tensile testing, adhesion testing and nanoindentation testing. The as-sprayed coating exhibited brittleness and had weak mechanical interlocking adhesion with the substrate. Annealing mitigates and delays the mechanical deficiencies associated with porosity in the coating, which showed signs of the stronger metallurgical bonding with the substrate. Annealed cold spray coating itself can bear significant load and strengthen the substrate. Thus, cold spray coating with appropriate post-processing treatment can potentially reinforce and even repair the component to achieve robust mechanical behavior. Outstanding Thesis Military Expert 5, Republic of Singapore Air Force Approved for public release. Distribution is unlimited.

In order to provide a basis for future optimization and control of the cold spray process, we experimentally studied the impact of various factors on the ductility (% elongation) of copper coatings. For the current application, cold-sprayed copper is employed as a corrosion barrier on carbon steel, while in addition to this, sufficient ductility is required for mechanical integrity. Results show that the cold-sprayed copper coating ductility increases with annealing temperature. A corresponding linear relationship is also derived with ductility and hardness. The current investigation further shows that there can be significant variability in ductility when the feedstock powder characteristics (e.g., chemical composition) are changed while keeping the spray and heat treatment conditions constant. Configuration/substrate dimensions are also considered as factors affecting the ductility of the copper during the cold spray process. The main findings that were observed include: (1) an increase in ductility from ~ 9 to ~ 29% when heat treating the samples from 320 to 600 °C; (2) a variation in ductility from ~ 8 to ~ 39% upon changing powder characteristics; and (3) a decrease in ductility from ~ 27 to ~ 15%, upon increasing the size of the substrate and by changing its geometry.

The cold spray deposition process has gained interest as a promising technique for producing metallic coatings on polymers and composite materials thank to its low working temperatures. However, poor adhesion of metallic particles on polymeric substrates and the brittle nature of these materials lead to generation of cracks under the impact of the sprayed particles, limiting its application to polymeric matrix composite. The interposition of an intermediate metallic layer over the thermoset composite to be coated has been claimed to improve the adhesion of the sprayed particles and the formation of a stable link between the metal coating and the underlying polymer panel. The present work discusses a methodology that integrates the manufacturing of glass reinforced epoxy panels having functionalized surface and the subsequent production of a dense metallic layer by cold spray. Pure copper and titanium metallic powders, having spherical and irregular shape respectively, were placed on the top of the stack of dry glass fiber fabrics. Resin infusion process was then applied to impregnate the glass fabrics providing the simultaneous functionalization of the composite panel. In order to assess the effectiveness of the produced substrate, and of the proposed procedure, metallic coatings have been finally deposited on manufactured composite panels by means of a low-pressure cold spray facility. Regardless the spraying condition (namely gas temperature, stand-off distance, sprayed particles), copper samples showed a remarkable erosion of functionalized layer after cold spray process with pronounced damages of the composite substrate. On the other hand, effective depositions have been observed on titanium samples under specific combination of process parameters.

Cold spray (CS) is an emerging coating technology that makes use of a converging/diverging nozzle, a high pressure and a heated gas source to create a high‐velocity gas flow. Coating deposition occurs at relatively low temperatures compared to other spray technologies, therefore the sprayed particles remaining in the solid-state. The process can produce dense coatings when the process parameters are optimized. Despite the incredible advantages of CS and the established knowledge of CS considering metal substrates, some questions like the bonding mechanism and the adhesion/cohesion strength of the coating with polymeric substrates remain an open research topic. In this paper, a metal coating (AlSi10Mg) was deposited on a plate in polypropylene by cold spray in order to increase the properties of the surface. Metallic particles, in the range of 20-40 µm, were injected into gas flow and propelled to supersonic velocities. Polymers require a deposition technique in which the substrate remains at relatively low temperatures during the whole process in order to avoid plastic deformation or degradation. Determination of the mechanical properties of thin films on substrates by indentation has always been difficult because of the influence of the substrate on the measured properties. In order to evaluate the local properties of the deposited coating, microindentation tests and DMA were carried out. In particular hardness values by microindentation tests and values of elastic modulus by DMA were calculated.

With the global trend towards electrification of transport, the interest for various configurations of electric motors is growing. Unfortunately, the low versatility of the motor magnet fabrication technologies limits the development of new motor geometries. Cold spray additive manufacturing was used for shaping permanent magnets for the direct fabrication of electric motor parts without the need for additional assembly steps. This novel technique allows an increase in the design flexibility of electrical machine geometries targeting improved performance. The permanent magnets were deposited from a NdFeB-Al composite powder mix featuring high raw theoretical remanence and coercivity. The role of the process parameters such as powder mix composition, binder granulometry and gas temperature on the magnetic volume fraction and the resulting magnetic properties will be investigated and compared with data from the literature. The use of complex robot toolpath programming necessary to spray on motor parts will be illustrated through an example of the fabrication of a complex shape rotor. The obtained magnetic properties demonstrate the feasibility of using cold spray additive manufacturing as an effective technology to fabricate motor parts without additional assembly steps.

© 2019 The cold spray process and laser-induced projectile impact test (LIPIT) are used to deposit Ti powder particles on sintered polycrystalline Al 2 O 3 . Whereas LIPIT allows real-time observations of single particle impact and measurement of particle impact velocity, cold spray rapidly and simultaneously deposits particles with a wide range of deposition velocities and sizes. By use of these two techniques, the effect of particle velocity and substrate morphology on adhesion strength of single splats is investigated. The critical velocity for deposition is identified to be approximately 580 m/s for the Ti/Al 2 O 3 system when using LIPIT and particles of 10 μm. Above the critical velocity, flattening ratio (FR) is also evaluated and observed to be linearly dependent on the particle impact velocity. Splat adhesion testing is performed on LIPIT-deposited as well as on cold spray-deposited powder particles to measure adhesion strength. This analysis shows that adhesion strength is highly affected by local substrate surface morphology, where particles bond more weakly to relatively smooth portions of the substrate. Therefore, mechanical bonding plays a significant role in adhesion. Also, adhesion strength decreases with an increase in FR and therefore velocity. This decrease can be associated with fracture of the ceramic substrate and rebound forces.

Cold Spray additive manufacturing (CSAM) is an emerging technique to fabricate freestanding objects by depositing solid-state layers of materials. Thanks to its remarkable deposition rate and maneuverability, it can be tailored to manufacturing intricate geometries in aerospace industries. In comparison to other additive manufacturing techniques, it is the processing speed, solid-state deposition, and the cost that make CSAM unique. In this study, CSAM process was modeled for a system comprised of a high-pressure cold spray gun with axial powder injection. To represent the flow structure around the already built objects and the deposited layers of CSAM, three walls with different profiles are placed on a flat substrate. In this work, the gas-particle behaviors are studied at the vicinity of these non-axisymmetric objects that can be generalized to more complex geometries and the applications of CSAM. The model is 3D and aluminum and copper powders were used for the feedstock. The particles’ conditions upon impact, such as particles’ footprint and normal impact velocities are studied. The numerical results show that the deviation of particles which is caused by the supersonic flow inside the nozzle and the shock waves outside the nozzle defines the accuracy of the deposition. Furthermore, the results manifest the particle’s material and size have a significant influence on the acquired velocities and trajectories of the particles, and consequently on the resolution of the process. It is found that the profile of the deposited layers has some effects on the gas flow near the substrate which plays a role in the dispersion of fine particles.

This paper addresses the potential use of high-pressure cold spray (HP-CS) technology to produce a film of friction material onto a low-carbon steel substrate to allow its use as potential composite material for the stators and rotors of aircraft brake units. Namely, WC-Cr3C2-Ni, WC-Ni, WC-Co-Cr, Cr3C2-NiCr and WC-Co coatings were deposited by using HP-CS, for the purpose of creating high friction and wear resistance composite coatings onto a low-carbon steel substrate. Tribological (friction coefficient and wear rate) and thermal properties as well as coating hardness and adhesion to the low-carbon steel substrate were evaluated to assess the potential use of the coatings as brake surface materials. The tribological and adhesion properties were evaluated by using a pin-on-disk high-temperature tribometer at 450 °C and a scratch test, respectively, whereas coatings hardness was evaluated with a Rockwell C hardness tester. Results obtained show that all coatings exhibit high friction coefficients and low wear rates compared to the low-carbon steel substrate, good adhesion, and elevated microhardness. Furthermore, the WC-Co coating shows better microhardness and thermal properties, while the WC-Co-Cr coating exhibited a better friction coefficient. Unfortunately, it was not possible to quantify the wear resistance due to the elevated roughness of the coatings, but from the analysis carried out on the alumina counterpart of the tribometer, it can be concluded that all the coatings exhibited a very low wear rate. In fact, after the tribological tests, it emerged that the alumina counterpart was more abraded than the investigated coatings.

The influence of the laser treatment on the corrosion resistance of the Cr3C2-25(Ni20Cr) cermet coating on the Al7075 (EN, AW-7075) substrate (Cr3C2-25(Ni20Cr)/Al7075) was investigated. The coating was produced by the cold sprayed (CS) method. The tested coatings were irradiated with a laser spot speed of 600 mm/min, 800 mm/min, and 1000 mm/min. The mechanical properties of the Cr3C2-25(Ni20Cr)/Al7075 were characterized by microhardness (HV) measurements. The surface and microstructure of the specimens were observed by ascanning electron microscope (SEM) and other assistive techniques. The corrosion test of materials wascarried out by using the electrochemical method in the acidic chloride solution. Cermet coatings perfectly protect the Al7075 substrate against contact with an aggressive corrosion environment. The laser remelting process of the Cr3C2-25(Ni20Cr) layer caused the homogenization of the structure cermet coatings. The irradiation with the laser beam eliminates microcracks and pores on the Cr3C2-25(Ni20Cr) surface. However, the best effect of improving the anti-corrosion properties of cermet coating was obtained for the lowest laser spot speed (i.e., 600 mm/min). It was found that the corrosion rate of the Cr3C2-25(Ni20Cr) cermet coating was reduced by more than two times compared to the highest speed of the laser spot.

The selection of materials in the cold spraying process has a significant impact in corrosion resistance. Recognition of this could provide the opportunity to adapt a wide range of coating deposits for different applications for repair in protection against corrosion. Cold sprayed coatings of pure aluminum and alumina reinforced aluminum were deposited to understand the role of composition on corrosion. Coatings were sprayed with thicknesses varying from 100 µm to ~3 mm in order to understand the role of coating thickness on corrosion. A salt fog chamber test helps mimic an austere marine condition for 1000 hours and 2000 hours of continuous exposure. Dimensional changes and mass gain were measured periodically throughout the salt fog exposure testing. The corrosion test revealed that reinforced aluminum is better for protection than pure aluminum having unresolved galvanic vulnerabilities within the coating and delaminating from the substrate. The alumina reinforced coating exhibited greater roughness in thicker coatings, which resulted in higher initial corrosion rates. With additional testing, cold spray could be used for coating protection of parts that are exposed to austere environments. Lieutenant, United States Navy Approved for public release. Distribution is unlimited.

Cold spray technology has the potential to greatly reduce the effects of corrosion on susceptible materials. Lack of adhesion strength is one of the limitations currently preventing cold spray from becoming a dominant resource. Adhesion strength is the strength of the bond between the cold-sprayed coating and the substrate. Without good adhesion, the coating provides minimal protection against corrosion and could potentially make corrosion worse. In order to determine how to increase cold spray adhesion, the feedstock powder and substrate were manipulated to analyze their effects on adhesion. The main areas of focus for this project were the effects of the following characteristics on adhesion strength: i) the surface condition of the substrate, ii) the hardness of the substrate, and iii) the size of the cold spray particles. Samples within each area of focus were sprayed using cold spray and then a pull-off adhesion test was performed. The surface condition of the substrate was further studied to determine its effect on Mg AZ31 alloy’s corrosion rate by placing a smooth, roughened, and polished sample within a salt fog chamber for 672 hrs. The results from the adhesion tests showed that softer substrates and smoother surface condition produce higher adhesive strength. The corrosion experiments found that the samples with the higher roughness value saw the highest corrosion rates and formed the thickest oxide layer. Outstanding Thesis Lieutenant, United States Navy Approved for public release. distribution is unlimited

Gas-atomized powders are frequently used in metal additive manufacturing (MAM) processes. During consolidation, certain properties and microstructural features of the feedstock can be retained. Such features include porosity, secondary phases, and oxides. Of particular importance to alloys such as Al 6061, secondary phases found in the feedstock powder can be directly related to those of the final consolidated form, especially for solid-state additive manufacturing. Al 6061 is a heat-treatable alloy that is commonly available in powder form. While heat treatments of 6061 have been widely studied in wrought form, little work has been performed to study the process in powders. This work investigates the evolution of the Fe-containing precipitates in gas-atomized Al 6061 powder through the use of scanning and transmission electron microscopy (SEM and TEM) and energy dispersive X-ray spectroscopy (EDS). The use of coupled EDS and thermodynamic modeling suggests that the as-atomized powders contain Al13Fe4 at the microstructure boundaries in addition to Mg2Si. After one hour of thermal treatment at 530 °C, it appears that the dissolution of Mg2Si and Al13Fe4 occurs concurrently with the formation of Al15Si2M4, as suggested by thermodynamic models.

In this work, the influence of thermal pre-processing upon the microstructure and hardness of Al 6061 feedstock powder is considered through the lens of cold spray processing and additive manufacturing. Since solid-state cold spray processes refine and retain microstructural constituents following impact-driven and high-strain rate severe plastic deformation and bonding, thermal pre-processing enables application-driven tuning of the resultant consolidation achieved via microstructural and, therefore, mechanical manipulation of the feedstock prior to use. Microstructural analysis was achieved via X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, energy dispersive spectroscopy, and differential thermal calorimetry. On the other hand, nanoindentation testing and analysis were relied upon to quantify pre-processing effects and microstructural evolution influences on the resultant hardness as a function of time at 540 °C. In the case of the as-atomized powder, β-Mg2Si-, Al-Fe-, and Mg-Si-type phases were observed along polycrystalline grain boundaries. Furthermore, after a 60 min hold time at 540 °C, Al-Fe-Si-Cr-Mn- and Mg-Si-type intermetallic phases were also observed along grain boundaries. Furthermore, the as-atomized hardness at 250 nm of indentation depth was 1.26 GPa and continuously decreased as a function of hold time until reaching 0.88 GPa after 240 min at 540 °C. Finally, contextualization of the observations with tuning cold spray additive manufacturing part performance via powder pre-processing is presented for through-process and application-minded design.

This study aims to enhance the corrosion performance of cold-sprayed titanium/baghdadite (Ti/BAG) bio-composite coatings. Laser post processing was performed to reduce porosity and improve mechanical properties. The process parameters for laser treatment of cold-sprayed coatings were verified experimentally using scanning electron microscopy (SEM) and a thermal imaging camera. The laser-treated coatings are analyzed with SEM, energy-dispersive spectroscopy (EDS), ImageJ software, and X-ray diffraction (XRD). Furthermore, electrochemical analysis of the laser-treated and as-sprayed coatings was conducted in Ringer’s solution. The results of this study revealed that laser treatment helps significantly in enhancing resistance to corrosion for Ti/BAG composite coatings in a Ringer’s solution. The reduction in porosity and surface roughness is ascribed as the reason for their superior performance relative to as-sprayed coatings.

WC-Co cermet materials serving as protective coatings are widely used in many fields. Conventional WC-17Co coatings were formed in high-velocity oxygen-fuel (HVOF), warm spraying (WS), and cold spraying (CS), respectively. Deposition behavior of a single WC-17Co particle, as well as the microstructure, microhardness, fracture toughness, and abrasive wear of WC-17Co coatings formed in various spraying ways were investigated. The results show that the deposition behavior of a single WC-17Co particle was different after it was deposited onto a Q235 steel substrate in various spraying ways. The WC-17Co splat deposited by HVOF showed a center hump and some molten areas, as well as some radial splashes presented at the edge of the splat. The WC-17Co splat deposited by WS presented a flattened morphology with no molten areas. However, the WC-17Co splat deposited by CS remained nearly spherical in shape and embedded into the substrate to a certain depth. All the WC-17Co coatings had the same phase compositions with that of feedstock. The microstructure of all the WC-17Co coatings was dense with no cracks or abscission phenomena between the coatings and substrate. Moreover, fine WC particles were formed in the coatings due to the fracture of coarse WC particles, and the content of fine WC particles in the cold-sprayed coating was significantly more than the other coatings. A stripe structure was formed by the slippage of fine WC particles with a plastic flow of Co binder in the warm-sprayed and cold-sprayed coatings. More fine WC particles, as well as the stripe structure, in the coatings were conducive to improve the microhardness and fracture toughness of the coating. The microhardness and fracture toughness of the cold-sprayed WC-17Co coating were the highest among the coatings. The main wear mechanism of all coatings was the groove and some peel-offs. The cold-sprayed WC-17Co coating with the lowest wear loss presented the highest wear resistance among the coatings.

Cold spray is an emerging additive manufacturing process that allows particles to be coated onto the surface of a base material without melting. It is suitable to repair components made from temperature-sensitive materials, such as grey cast iron, which cannot be easily restored using conventional methods like welding or thermal spray. In this study, the nickel-based alloy Inconel 625 was successfully coated onto a grey cast iron (GJL250) using a cold spray process, and extensive experiments were carried out to study the effects of diffusion between the coating and the substrate after heat treatment at 400, 600, 850 and 1050◦ C for 3 and 6 hours durations. The coatings in all conditions were dense (0.25% to 3%) and had defect-free interfaces. Under heat treatment, the diffusion layer increased in thickness with increasing temperature and duration due to atomic diffusion. The Inconel 625 coating is also shown to be effective against oxide growth as compared to grey cast iron. The hardness of the coatings is also stable at high temperatures. The heat-treated coatings at 600◦ C achieved a peak hardness of around 500 HV, which is 30% and 60% higher than the as-sprayed coating and grey cast iron substrate, respectively, because of the possible formation of recrystallized nanostructured grains and strengthening precipitates. These findings demonstrate the potential application of using cold spray on nickel-based alloy coatings for restoration and surface enhancement of grey cast iron components, such as engine blocks and pump housings.

Cold spray is emerging as an additive manufacturing technique, particularly advantageous when high production rate and large build sizes are in demand. To further accelerate technology’s industrial maturity, the problem of geometric control must be improved, and a neural network model has emerged to predict additively manufactured geometry. However, limited data on the effect of deposition conditions on geometry growth is often problematic. Therefore, this study presents data-efficient neural network modelling of a single-track profile in cold spray additive manufacturing. Two modelling techniques harnessing prior knowledge or existing model were proposed, and both were found to be effective in achieving the data-efficient development of a neural network model. We also showed that the proposed data-efficient neural network model provided better predictive performance than the previously proposed Gaussian function model and purely data-driven neural network. The results indicate that a neural network model can outperform a widely used mathematical model with data-efficient modelling techniques and be better suited to improving geometric control in cold spray additive manufacturing.

17 USC 105 interim-entered record; under review. The article of record as published may be found at https://doi.org/10.1080/02726351.2021.1876192 Properties, such as morphology, particle size, and hardness affect the ability of a powder to flow and bond to a surface in additive manufacturing (AM) applications. The effects of high energy ball milling on spherical copper and stainless steel powders were evaluated. Morphology of both stainless steel and copper powders, quantifiable by aspect ratio, showed larger changes due to ball-to-powder ratio (BPR, 2:1–1:10) compared to the total milling time (2–60min). Hardness of copper increased from 53 HV0.01 in the as-received condition to 96 HV0.01 after milling for 60min with a BPR of 1:1 or 2:1. Hardness of steel increased from 336 HV0.01 in the as-received condition to 523 HV0.01 after milling for 60min with a BPR of 2:1. Hardness of both powders was insensitive to milling times at low BPR (1:10). At high BPR (2:1), hardness of steel increases after just 2min of milling, while Cu changed significantly only after 60min. Hardness was influenced more by BPR than by milling time. It is shown that a broad range of milling parameters exist where metallic powders can be processed with minimal changes to their morphology, while controlling for hardness. The Hartnell College and California State University at Monterey Bay for supporting and organizing the Hartnell Community College Catalyst (3C) programs which enabled T. Hanneman and A. Gonzalez-Perez to conduct research at NPS during the summer of 2019. NPS Foundation SEED program NPS Research Initiation Program

As a form of additive manufacturing, the use of cold spray has made significant strides since different-sized particles were explored in the process. There is proof that micron-sized particles down to nanoparticles enhance the mechanical material properties of a substrate in wear resistance. Micron- and submicron-sized particles are beneficial, but due to their low relative surface areas, they tend to exhibit pull out more often and do not adhere to a substrate as well as a nanoparticle. Using nanoparticle metal and dual ceramic matrix reinforcements, six composites were fabricated through cryomilling and then applied to an aluminum substrate as a cold sprayed coating. Using nano-boron carbide (nB4C) and boron nitride nanoplatelets (BNNP) at various combinations up to 2 vol%, an increase of 11.59% in hardness from the control was achieved. Wear testing of each coating was performed, but most of the tests drove through the coatings into the substrate, indicating more refinement of the testing parameters is required. Additionally, corrosion testing was performed on cold sprayed samples for 500- and 2,000-hr trials in a salt fog chamber, revealing underlying pitting corrosion and galvanic corrosion vulnerabilities of the coatings. In the right application, the U.S. Navy could potentially use these coating materials in parts that are subjected to austere marine environments. Outstanding Thesis Lieutenant, United States Navy Approved for public release. distribution is unlimited

In this work, the manufacturing through cold gas dynamic spray (cold spray or CS) of metallic composite coatings of Al-Al2O3 on organic composite substrates with thermoplastic PLA matrix and hemp fibers was studied. Alumina powders, with a mean diameter of 50 μm, were used blended with aluminum powders in three different weight concentration percentages (0, 15, 20, and 45%) as feedstock material in order to highlight and discuss the variations of the coating surface properties depending on the alumina percentage. The coatings were produced by using a low-pressure cold spray equipment. A detailed experimental campaign, including microstructural observations and confocal microscopy, was carried out to study the structure of the coatings. Moreover, the tribological behavior of the coatings was studied through both scratch test and pin-on-disk test. The experiments showed that a small addition of alumina improves the compactness of the coating and its resistance to scratch and wear behavior.

Cold spraying is a novel technology for preparing solid-state coatings. Single Ni-coated Al particles were deposited onto different substrates by cold spraying at different accelerating gas temperatures, as well as preparing for the coatings. The influence of the accelerating gas temperature and substrate microhardness on the particle deposition deformation, microstructure, and microhardness of Ni-coated Al coatings were investigated. The results show that the embedding depth of Ni-coated Al particles into the Al substrate increased with increasing the accelerating gas temperature. However, the cold-sprayed Ni-coated Al particles did not embed into the Q235 steel substrate, and the degree of plastic deformation of the Ni-coated Al particles increased with increasing the accelerating gas temperature. Moreover, the morphology of the Ni-coated Al splat deposited onto the Q235 steel substrate at an accelerating gas temperature of 400 °C presented a flattened morphology, which was different from the nearly spherical or ellipsoidal morphology of the Ni-coated Al feedstock. Ni-coated Al coatings exhibited the same phase compositions as the feedstock powders, and the Ni and Al phases in the coatings incurred a certain plastic deformation. Compared with the Q235 steel substrate, an Al substrate with a lower microhardness is beneficial for forming the first layer coating, as well as for the formation of an intermixing structure between the Ni-coated Al coating and Al substrate. The porosity of Ni-coated Al coatings decreased and the thickness increased when increasing the gas temperature; in particular, the coating deposited onto Al substrate had the lowest porosity and the largest thickness at an accelerating gas temperature of 400 °C. Meanwhile, the microhardness of the coating deposited onto the Al substrate was higher than that deposited onto the Q235 steel substrate under the same cold spraying conditions.

The Cold Gas Dynamic Spray technology, generally referred as Cold Spray, is a relatively new additive manufacturing technique able to produce fully dense coatings through the deposition of particles on a substrate. Fine powders are accelerated to high velocity and projected onto a substrate, upon impact with the target surface, conversion of kinetic energy to plastic deformation occurs and the solid particles deform and bond together. During the cold spray deposition process, the particles remain in a solid state during the deposition, resulting in high-quality coatings with low residual stresses and oxide inclusions. The relative lower process temperatures allow the cold spray to manufacture coatings on high temperature-sensitive materials. It could also be a valid method for deposition of a wide variety of materials, from metallic alloys up to ceramics and composites. Depending on the materials employed as substrate and coating, different bonding mechanisms can occur during the deposition. The present review aims to summarise the main bonding theories proposed up to now for the cold spray, focusing on both the particle deformation behaviour during the contact with the surface and the interfacial bonding mechanisms. The available theories for different substrate/coating configurations will be discussed and compared. The effects of deposition parameters, the substrate’s surface and microstructure of feedstock powders on the bonding mechanism will also be discussed.

The deposition behavior of cold-sprayed metallic glass particles onto different metallic substrates was studied by numerical analysis and simulation using the ABAQUS/Explicit software. The mechanical response of a Vitreloy-1 particle was modeled accounting for the non-Newtonian and Newtonian regime of metallic glasses in the undercooled liquid state. The spreading, viscous dissipation and stress distribution of the metallic glass particle at impact showed a strong dependence on the substrate properties. By describing the rheological behavior of metallic glass particles according to the dynamics of viscous fluids, defining the impact Reynolds (Re) number, the Weissenberg (Wi) number and the Elasticity (El) number, the simulation results prove that shear thinning is the main deformation mechanism of metallic glass particles during impact, regardless of the substrate used. Specifically, a threshold value of Re exists, above which the MG particles undergo homogeneous flow, regardless of the substrate material. The generality of this finding is confirmed by its independence of the mathematical model used to describe substrate plasticity. However, the mechanical and thermal properties of the substrate have a strong influence on the shear thinning level experienced by particles impinging at Re values above the threshold. In this manner, the present study considers various aspects of relevant importance to build up metallic glass coatings by cold spray onto different metallic substrates.

The cold spray technique may be used to fabricate metal matrix composites and to metallize ceramics. Both applications involve the creation of metal/ceramic interfaces, which are well researched for other processes but not nearly as much for cold spray. Here, the effect of ceramic substrate composition and surface roughness on adhesion strength of metallic splats is investigated. Splat adhesion testing was performed on Ti splats deposited on Al2O3 substrates with varying average reduced peak height roughness (Rpk) values. Ti splats sprayed onto Al2O3 with the lowest surface roughness had a higher bond strength (305 ± 87 MPa) than splats deposited on the higher surface roughness Al2O3 (237 ± 47 MPa). Failed interfaces revealed that the bonding mechanism for substrates with higher surface roughness is predominantly mechanical interlocking. Adhesion to the Al2O3 substrate with low surface roughness is predominantly along the periphery of the particle where jetting occurs. Splat adhesion testing was also performed on Ti splats deposited on SiC. Ti splats had a significantly higher bond strength to all Al2O3 substrates than to SiC. Posttest observations of SiC substrates showed little evidence of bonding. Several rebounded or detached splats left traces of Ti along the periphery of the impacted particle.

Cold spray is a solid-state coating deposition technology which has recently been applied as an additive manufacturing process to fabricate individual components and to repair damaged components. In comparison with fusion-based high-temperature additive manufacturing processes, cold spray additive manufacturing (CSAM) has been shown to retain the original properties of the feedstock, to produce oxide-free deposits, and to not adversely influence underlying substrate materials during manufacture. Therefore, CSAM is attracting considerable attention from both scientific and industrial communities. Although CSAM is an emerging additive manufacturing technology, a body of work has been carried out by various research groups and the technology has been applied across a range of manufacturing areas. The purpose of this paper is to systematically summarize and review the CSAM-related work to date.