Search Results (28)

Modern nanoindentation equipment allows for highly precise measurements of mechanical properties such as hardness and elastic modulus, generating detailed load–unload curves using advanced techniques and specialised software. In this study, titanium coatings were deposited on various metallic substrates using cold gas spraying. Before deposition, the spraying parameters (temperature, pressure, velocity, and distance) were statistically optimised using the Taguchi method, reducing the number of experiments required from 81 to 9. This approach allowed the identification of optimal spray conditions (T = 731.0 °C, p = 33.0 bar, V = 343.6 mm/s, d = 35.5 mm), which were then applied to substrates including brass, steel, titanium, Al7075, copper, magnesium, and Al2024. Mechanical characterisation included hardness (H), reduced modulus (E), coating adhesion, and dissipated energy, calculated from the area of the load–unload hysteresis loop. Each coating–substrate combination underwent 36 nanoindentation tests, and adhesion was evaluated by pull-off tests. The initial results showed a poor correlation between adhesion and conventional mechanical properties (χ² of 17.1 for hardness and 16.2 for modulus, both with R² < 0.24). In contrast, the dissipated energy showed an excellent correlation with adhesion (χ² = 0.52, R² = 0.92), suggesting that dynamic deformation mechanisms better describe bonding. This introduces a new perspective to predict and optimise cold-spray adhesion in industrial applications. Full article

Cold spraying (CS), also known as cold gas dynamic spraying or supersonic cold spraying, is a process in which particles collide with the substrate at a speed greater than the critical value and deposit layer by layer to form a coating. As an emerging coating preparation technology that has been developed rapidly in recent years, CS is characterized by a low deposition temperature, a minimal thermal effect on substrate, and a high deposition efficiency. It has received extensive attention from industry. However, the inherent high strength and low plasticity of CS coatings and the numerous defects present limit their wider application to some extent. Therefore, various post-treatment technologies are successfully applied to the CS coatings to improve their comprehensive performance. This paper reviews the latest research progress of common post-treatment techniques for CS coatings, including five categories: thermal, mechanical, thermo-mechanical, chemical, and electrochemical processing. A considerable amount of experimental research has demonstrated that post-treatment can effectively enhance the microstructure and properties of CS coatings, and this can serve as a powerful approach to expand the application scope of CS technology. In addition, the relevant post-processing parameters and corresponding results are summarized and compared systematically. Full article

A numerical study was performed to analyze the particle deposition of a cold spray process for the preparation of nickel electrocatalysts used in the Hydrogen Evolution Reaction (HER). The study focused on the creation of fin-shaped geometries with an optimal porosity on the electrode surface using a mask located between the nozzle exit and the substrate. Computational Fluid Dynamics (CFD) was performed on a three-dimensional high-pressure nozzle, with nickel powder used as the injection feedstock. The behavior of particles was effectively modeled through a two-way coupled Eulerian–Lagrangian approach. As per the parametric study, four masks of varying wire thicknesses and opening sizes were investigated. The masks were placed at 4 mm increments from the nozzle exit, with the substrate placed at standoff distances (SODs) of 10 mm and 20 mm. To capture the effects of the gas inlet operating conditions, two different nozzle inlet conditions were analyzed (2 MPa and 400 °C, 4 MPa and 800 °C). It was found that the nozzle inlet operating condition had the most significant impact, as it relates to the particle velocity and powder deposition. The high-pressure operating condition resulted in a deposition efficiency (DE) greater than 99.9% for all the test cases, with nearly all the impacted particles depositing on the substrate. For the medium-pressure operating condition, the DE increased linearly as the mask SOD was increased, due to the increase in the particle velocity upon impact. Full article

Refractory materials are used worldwide in process equipment. However, gaseous and liquid process products penetrate the surface layer and deep into the volume of refractories, destroying rather expensive constructions that are complicated to repair. To address this challenge, there is a need to develop protective coatings for refractory materials that can limit the penetration of working media and extend their operational lifespan. In this work, the application of gas-dynamic cold spraying (CGDS) to produce a coating on the refractory materials using fine titanium dioxide (TiO₂) particles is explored. These particles are accelerated within a nitrogen flow, passing through a Laval nozzle, and then sprayed onto a fireclay surface. The mechanisms of particle deposition and layer formation on porous surfaces through experiments and numerical simulations were investigated. The geometry of a typical refractory pore was determined, which was then incorporated into computational fluid dynamics (CFD) simulations to model the cold spraying process of porous substrates. As a result, the influence of the particle size on its velocity and angle of penetration into pores was established. Experimental findings demonstrate the effective closure of pores and the formation of a particle layer on the refractory surface. Furthermore, the nanoindentation tests for the refractory samples showcase capabilities for checking coating thickness for porous materials. Full article

Gas-atomization is extensively used to produce metallic feedstock powders for additive manufacturing processes, including gas dynamic cold spray processing. This work explores the potential utility of on-demand recycled titanium scrap feedstock powder as a viable substitute for virgin powder sources. Three recycled titanium powders were atomized from different battlefield scrap sources using a mobile foundry developed by MolyWorks Materials Corporation. Recycled titanium alloy powders were compared against virgin Ti-6Al-4V powder to verify there were no significant variations between the recycled and virgin materials. Powder characterization methods included chemical analysis, particle size distribution analysis, scanning electron microscopy (SEM), Karl Fischer (KF) titration moisture content analysis, X-ray diffraction (XRD) phase analysis, microparticle compression testing (MCT), and nanoindentation. Results indicate that recycled titanium powder provides a viable alternative to virgin titanium alloy powders without compromising mechanical capabilities, microstructural features, or ASTM-specified composition and impurity standards. The results of this work will be used to aid future research efforts that will focus on optimizing cold spray parameters to maximize coating density, mechanical strength, and hardness of recycled titanium feedstock powders. “Cold spray” presents opportunities to enhance the sustainability of titanium component production through the utilization of recycled feedstock powder, mitigating issues of long lead times and high waste associated with the use of conventional virgin feedstock. Full article

Coatings with high hardness were successfully obtained using low-pressure cold spray (LPCS) technology from nanocrystalline powders based on the aluminum alloy AlMg6, which were multi-reinforced with 0.3 wt.% fullerenes and 10–50 wt.% AlN. The powders were synthesized through a two-stage high-energy ball milling process, resulting in a complex mechanical mixture consisting of agglomerates and micro-sized ceramic particles of AlN. The agglomerates comprise particles of the nanocomposite material AlMg6/C₆₀ with embedded and surface-located, micro-sized ceramic particles of AlN. Scanning electron microscopy and EDS analyses demonstrated a uniform distribution of reinforcing particles throughout the coating volume. An X-ray diffraction (XRD) analysis of the coatings revealed a change in the predominant orientation of matrix alloy grains to a more chaotic state during deformation over the course of cold gas dynamic spraying. A quantitative determination of AlN content in the coating was achieved through the processing of XRD data using the reference intensity ratio (RIR) method. It was found that the proportion of transferred ceramic particles from the multi-reinforced powder to the coating did not exceed ~65%. Experimental evidence indicated that LPCS processing of mono-reinforced nanocrystalline powder composite AlMg6/C₆₀ practically did not lead to the formation of a coating on the substrate and was limited to a monolayer with a thickness of ~10 µm. The microhardness of the monolayer coating obtained from the deposition of AlMg6/C₆₀ powder was 181 ± 12 HV. Additionally, the introduction of 10 to 50 wt.% AlN into the powder mixture contributed to the enhancement of growth efficiency and an increase in coating microhardness by ~1.4–1.7 times. The obtained results demonstrate that the utilization of agglomerated multi-reinforced powders for cold gas dynamic spraying can be an effective strategy for producing coatings and bulk materials based on aluminum and its alloys with high microhardness. Full article

Vacuum cold spraying (VCS) has emerged as an environmentally sustainable method for fabricating ceramic and metal films. A high particle impact velocity is a critical factor in the deposition of metal particles during the VCS process, which can be significantly enhanced through gas preheating. This study employs Computational Fluid Dynamics (CFD) simulations to investigate the substantial impact of gas preheating temperature on particle impact velocity and temperature. Elevating the gas temperature leads to higher particle impact velocity, resulting in severe deformation and the formation of dense copper films. The experimental results indicate improvements in both film compactness and electrical properties with gas preheating. Remarkably, the electrical resistivity of the copper film deposited at a gas preheating temperature of 350 °C was measured at 4.4 × 10⁻⁸ Ω·m. This study also examines the evolution of cone-shaped pits on the surface of copper films prepared on rough substrates. VCS demonstrates a self-adaptive repair mechanism when depositing metal films onto rough ceramic substrates, making it a promising method for ceramic surface metallization. Full article

Cold gas dynamic spraying is a solid-state processing technique that is particularly attractive for surface coatings, 3D near-net shape additive manufacturing, and component repairs with an advantage of high-deposition efficiency. This technique has the sustainable potential to change the future industrial and manufacturing environment, especially in the fabrication process of complex flight-critical components that are made of aluminum. This paper investigates the microstructure of aluminum coatings generated onto a commercial Al plate called FORTAL (Al 7075-T6) via cold spraying using helium as the propellant gas. Three Al coatings (pure Al, AlSi10Mg, and Scalmalloy) are compared under a similar deposition condition. The top view of the coating revealed the highest deformation (high flattening) in the case of pure Al powders, whereas both the AlSi10Mg and Scalmalloy powders exhibit less flattening. The cross sections show fine equiaxed grains within the pure Al coating and extremely fine grains for both the AlSi10Mg coating and the Scalmalloy coating, with more extremely refined grains within the Scalmalloy coating. These results suggested an onset of recrystallization within the Al coating that is attributed to the heat generated by the strong plastic deformation. Less thermally activated recrystallization occurred within both AlSi10Mg coating and Scalmalloy coating due to their stronger mechanical properties. The structure rather resulted from the dynamic due to the high strain rate collision. The extremely fine structure is mostly at the powder/powder interface within the Scalmalloy coating and is developed towards the powder region which is also within the AlSi10Mg coating. Better plastic deformation occurred within the AlSi10Mg powder compared to the Scalmalloy powder that have a higher mechanical resistance. Together, these results evidence a limited thermally activated recrystallization within the Al alloys despite the highest deposition condition being used. The pure Al powders can also achieve a state of equiaxed fine grain due to the better plastic deformation. Full article

Cold spray (CS) is an emerging technology for repairing and 3D additive manufacturing of a variety of metallic components using deformable metal powders. In CS deposition, gas type, gas pressure, gas temperature, and powder feed rate are the four key process parameters that have been intensively studied. Spray angle, spray gun traverse speed, and standoff distance (SoD) are the other three process parameters that have been less investigated but are also important, especially when depositing on uneven substrates or building up 3D freeform structures. Herein, the effects of spray angle, traverse speed, and SoD during CS deposition have been investigated holistically on a single material system (i.e., Al2219 powders on Al2219-T6 substrate). The coatings’ mass gain, thickness, porosity, and residual stress have been characterized, and the results show that spray angle and traverse speed exercise much more effects than SoD in determining coatings’ buildup. Finite element method (FEM) modeling and computational fluid dynamic (CFD) simulation have been carried out to understand the effects of these three parameters for implementing CS as repairing and additive manufacturing using aluminum-based alloy powders. Full article

Cold gas dynamic spray (CS) is a unique technique for depositing material using high-strain-rate solid-state deformation. A major challenge for this technique is its dependence on the powder’s properties, and another is the lack of standards for assessing them between lots and manufacturers. The motivation of this research was to understand the variability in powder atomization techniques for stainless steel powders and their subsequent properties for their corresponding impacts on CS. A drastic difference (~30%) was observed in the deposition efficiencies (DEs) of unaltered, spherical and similar sized stainless steel (316) powders produced using centrifugal (C.A) and traditional gas atomization (G.A) techniques. The study highlights more the differences on a precursor level. Using recent advancements in large scale statistical measurements, such as laser diffraction shape analysis and µCT scanning; and traditional methods, such as EBSD and nanoindentation, an attempt was made to understand the powder’s properties. Insights on powder size and shape were documented. Significant differences were observed between C.A and G.A powders in terms of grain size, fraction of high-angle grain boundaries (HAGBs) and nanohardness. The outcomes of this study should be helpful for understanding the commercialization of the cold-spray process for bulk manufacturing of powder precursors. Full article

In this paper, the improvement of the characteristics of different steels that are subjected to extreme operating conditions, including the steels used in the manufacture of various military components, the AISI 52100, the manufacture of bearings, and other types of parts that are also subjected to severe operating conditions were analyzed regarding cold spraying, which uses different types of powders to increase the performance of the materials. The cold, thermal spraying technology “Cold Spray” is a method of processing particles in a solid state. Thermal spraying, based on the dynamic increase in gas acceleration up to supersonic speeds, leads to the obtainment of high kinetic energies, and the accelerated particles are deposited at values that are below their melting point. Research conducted through cold spray technology has seen a significant improvement in material properties; when processing the particles in a solid state, they adhere to the surface instead of eroding it. Cold spraying has proven to be an effective technique for improving material properties, as confirmed by its integration into different fields and industries, becoming competitive by being the only method for depositing particles below their melting point. Full article

The cold gas-dynamic spray (CGDS) technique is utilized for repairing processes of a large number of metallic components in mechanical and process engineering, such as bridges or vehicles. Fine particles impacting on the component surface can be severely deformed and penetrate into the defects, filling and coating them, resulting in possible protection against corrosion or crack propagation. This work focuses on the investigation of the impact behavior of cold sprayed particles with the wall surface having microdefects in the form of cavities. The collision of fine single particles with the substrate, both made from AISI 1045 steel, was simulated with the finite element method (FEM) using the Johnson–Cook failure model. The impact phenomena of particles on different microdefect geometries were obtained and compared with the collision on a smooth surface. The particle diameter and defect were varied to investigate the influence of the size on the deformation behaviour. The different impact scenarios result in different temperature and stress distributions in the contact zone, penetration and deformation behavior during the collision. Full article

Due to the processes solid-state nature, cold gas-dynamic spray metal additive manufacturing may be considered microstructurally and micromechanically retentive, such that properties of the feedstock material are refined and partially retained, influencing component performance. As a result, cold spray processing enables unique freedoms regarding feedstock, which can be pre-processed using chemical, thermal, and mechanical treatments to produce powder properties that achieve finely controlled consolidations with application-specific behaviors. Given such features of the cold spray process, the present review article is concerned with the through-process integration of mechanically and microstructurally characterized feedstocks for optimizable cold spray metal additive manufacturing. Therefore, in this paper, we consider how nanoindentation (dynamic, static, and quasi-static) was coupled with microstructural characterization for experimental feedstock evaluation, testing, and characterization. Atomized aluminum alloys, atomized stainless steel, and copper feedstocks, among others, were considered. Accordingly, the review validates how microparticle feedstock pre-processing and characterization in cold spray metal additive manufacturing and processing lead to controllable component performance and properties. Full article

Cold spray technique has been major improved in the last decades, for studying new properties for metals and alloys of aluminum, copper, nickel, and titanium, as well as steels, stainless steel and other types of alloys. Cold sprayed Ni/CrC coatings have the potential to provide a barrier as well as improved protection to steels. Fatigue characteristics of 52100 steel coated with Ni/Chrome-Carbide (Ni/CrC) powder mixture by using cold gas dynamic spray are investigated. Fatigue samples were subjected to symmetrically alternating, axially applied cyclic fatigue loading until failure. The test was stopped if a sample survived more than 5 × 10⁶ cycles at the applied stress. Fracture surfaces for each sample were examined to investigate the behaviour of the coating both at high stress levels and at a high number of stress cycles. Scanning electron microscopy was used to assess the damage in the interface of the two materials. Good fatigue behaviour of the coating material was observed, especially at low stresses and a high number of cycles. Details of the crack initiation region, the stable crack propagation region and the sudden crack expansion region are identified for each sample. In most of the samples, the initiation of the crack occurred on the surface of the base material and propagated into the coating material. The possible effects of coatings on the initial deterioration of the base material and the reduction of the lifespan of the coated system were also investigated. The aim of the paper was to study the interface between the base material and the coating material at the fatigue analysis for different stresses, highlighting the appearance of cracks and the number of breaking cycles required for each sample. Full article

During the process of cold spraying, the motion behavior and the arrangement of clusters, before impacting the substrate, have great influences on the coating/substrate bonding strength and the coating morphologies. In this work, the scattering and self-rotating movement of a single cluster and the different spatial positions of two clusters were taken into account to analyze the deposition characteristics between Pt clusters and Ni substrate by using the molecular dynamics method. We found that an excessively high normal velocity results in the failure of mechanical interlocking. Meanwhile, the increasing tangential velocity mainly enhances the mechanical interlocking. Moreover, the mechanical interlocking and the metallurgic bonding always are enhanced by increasing the impact torque around x-axis, but the metallurgic bonding increases only if the impact torque around z-axis is beyond a certain value. The results further show that, for the two neighboring clusters arranged horizontally, the thermal-softening effect of the first cluster impacting onto the substrate contributes more to its own metallurgic bonding and the mechanical interlocking of the latter one. In addition, for the two vertical clusters colliding with each other during their flying course, the smaller velocity difference can largely enhance the metal interlocking and the metallurgic bonding by shortening the cooling and solidifying times. Full article