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Continuous monitoring of spray velocity during the cold spray process would be desirable to support quality control, as spray velocity is the key process parameter determining the deposit quality. This study explores the feasibility of utilising Airborne Acoustic Emission (AAE) for real-time monitoring of spray velocity. Six spray tests were conducted, varying pressure and temperature to achieve different velocities. Optical means were used to measure velocity; while, the signal from the AAE was captured during deposition via a microphone. Features demonstrating a strong correlation with velocity were extracted from the acoustic signals. Both rule-based and machine learning models were employed to identify the moments where the nozzle was engaged with the substrate and diagnose the velocity. The results indicate that monitoring the spray velocity of the cold spray process using AAE is feasible. [ABSTRACT FROM AUTHOR]

Cold spray is a dynamic additive manufacturing process which results in a unique microstructure and mechanical properties. This work investigates cold spray deposited material under high strain-rate dynamic loading, and specifically the influence of post-build heat treatment on the material strength when subjected to incipient spallation. As-deposited and heat-treated samples were characterized and subjected to shock loading with a plate impact apparatus; the free-surface velocity was measured during the experiment, and the samples were recovered for postmortem analysis. The test results show that the as-deposited material has little to no strength under high strain-rate tensile loading and breaks into pieces. After a short heat treatment, the material recovers some of its tensile strength (compared to wrought copper) but does not exhibit the expected damage morphology and void distribution. When the heat treatment time is extended to several hours and the temperature is increased, the material exhibits ramp-like shock rise and damage formation that is widely distributed within the sample. This work contributes to a better understanding of the influence of heat treatment on the microstructure and subsequent material strength properties under high strain-rate loading, which is crucial for applications where cold spray is a technique of interest. [ABSTRACT FROM AUTHOR]

This study explores the potential of cold spray technology for repairing high-strength Al7075 alloy components, particularly in the aerospace industry. The gas-atomized powder contains a dendritic cell structure with solutes segregated at the dendritic cell boundaries. Thus, direct aging of atomized powder fails to induce the formation of strengthened precipitates. Therefore, the effect of different powder pre-treatments on the deposition efficiency, microstructure, and aging behavior of the coatings was investigated. Cold spray coatings were deposited using as-received powder, solutionized, and solutionized + aged powders, revealing a significant improvement in thickness for coatings obtained using solutionized (110%) and solutionized + aged (80%) powders compared to the coating from the as-received atomized powder. Further, coatings deposited using as-received, solutionized, and solutionized + aged powders, were aged at 120 °C for various durations and the aging response of different coatings were studied. Microstructural studies revealed that gas-atomized powders exhibited dendritic structures with segregated solutes. Solutionizing eliminated the dendritic features, promoting deposition efficiency upon cold spraying. Aging of the coating from the solutionized powder led to the formation of ultrafine η' precipitates (29 ± 8 nm length, 2 ± 1 nm diameter) at peak-aged condition (after 8 h). These findings demonstrate the effectiveness of powder pre-treatment in tailoring the microstructure and deposition behavior of cold-sprayed Al7075 coatings, offering a promising approach for repair applications. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer composites are prominent structural components in various industries such as aerospace, automotive, and wind energy. These materials are considered due to their high strength-to-weight ratio and relative ease of fabrication. However, fiber composites possess low electrical and thermal conductivities and are prone to impact-induced damage. Metallization of fiber-reinforced polymer composites has become an area of interest as a means to prevent abrasive and corrosive damage while also improving other physical properties including thermal and electrical conductivity. The possibility of using cold spray as a novel composite metallization approach has been investigated in this work. The significance of cold spray for metallization is due to relatively low process temperatures which effectively protect the underlaid substrate from potential temperature degradation. As a practical approach to further reduce the possibility of cold spray-induced damage, the present study explores the impact and failure mechanics of metal particles coated with a thin polymeric shell, hence the term polymer-coated metal particle. The thorough model-based analyses presented herein indicate that the so-called polymer-coated metal particles can be cold spray deposited without imposing significant damage to the composite substrate mainly due to the 'cushioning' effect of the thin polymer shell. The results discussed here also provide guidelines for the surface metallization of high-performance fiber-reinforced thermoplastic composites in practice. [ABSTRACT FROM AUTHOR]

In this study, the effect of an in situ shot peening and cold spraying process for depositing niobium using nitrogen gas was studied and compared to that of traditional niobium sprayed using helium gas. The samples were evaluated using Vickers hardness indentation and defect analysis to compare the mechanical properties and microstructure of the shot-peened samples with that of the helium-sprayed samples. During this study, a mathematical model was proposed to effectively predict the amount of shot peening required to achieve a specific increase in sample hardness. A novel means of using two cold spray systems was also proposed to obtain a better level of control during the shot-peening process. It was found during this study that in situ shot peening can be used to increase the as-sprayed hardness and density of nitrogen-sprayed niobium cold spray deposits to levels comparable to niobium cold sprayed using helium gas. This offers a potential means to transition away from the use of helium gas without sacrificing material properties. [ABSTRACT FROM AUTHOR]

PEEK surface copper metallization is widely used in fields such as power, electronics, and new energy. To enhance the mechanical and electrical characteristics of copper coating on PEEK surface further, this study employed a cold spraying deposition technology of graphene-reinforced copper composite coatings. The investigation focused on the properties comparison between composite coatings and pure copper coatings, and systematically studied the influence of nozzle speed within the range of 50–200 mm/s on the structure and properties of composite coatings. Results show that the mechanical and electrical properties of composite coatings are far superior to those of pure copper coatings. And results indicate that at a nozzle speed of 100 mm/s, the composite coating exhibits the densest structure, with a porosity of 0.31% and minimal graphene aggregation, resulting in superior mechanical and electrical properties. Specifically, the friction coefficient is reduced by 46.81% compared to pure copper coating, measuring 0.4046. Additionally, the Vickers hardness of the composite coating reaches 105.96 HV, and its wear rate is 70.59% lower than that of pure copper coating, at 4.32·10−4 mm3/N·m. Furthermore, the conductivity peaks at 1.295·105 S/cm, representing a 38.77%, increase over pure copper coating. [ABSTRACT FROM AUTHOR]

The present study focused on optimizing the cold spray (CS) process parameters for depositing Fe20Cr20Mn20Ni20Co20 (Cantor alloy) coatings using mechanically alloyed (MA) powder. A two-step design of experiments approach was employed, beginning with the initial screening of input variables using the L8 Taguchi method, followed by the refinement of process parameters through the Box–Behnken design of experiments. Key performance indicators included deposition efficiency (DE), coating thickness per pass, and microstructural parameters including porosity, cracks, and interfacial defects/delamination. The study identified process gas temperature as the primary factor influencing both DE and thickness per pass. Higher gas temperature and pressure, combined with increased scanning speed, resulted in higher DE. The DE of the MA Cantor alloy powder peaked at around 14-15%, with a deposit density greater than 99% achieved at the highest process gas temperature and pressure (1000 °C and 60 bar, respectively). The average hardness of the optimal CS coating deposited using MA powder was found to be 679 ± 17 HV0.1, which is approximately 90% greater than the average hardness reported for CS coatings deposited using atomized powder. [ABSTRACT FROM AUTHOR]

This study investigates the feasibility of using cold spray for repair of Inconel 718 (IN718) components. The effect of cold spray parameters on the particle velocity, splat morphology, deposition efficiency (DE), thickness, and porosity was evaluated. Thick coatings of approximately 4 mm were deposited onto ground and polished IN718 substrates using N2 gas heated to 1000 °C with gas pressure of 5 and 7 MPa. The coatings were subjected to standard double aging (DA) and a combination of solutionizing and double aging (STDA) heat treatment. The microstructure, hardness, porosity, tensile strength, and adhesive strength of as-sprayed and heat-treated coatings were evaluated. Additionally, the tensile properties of the coating–substrate combination (sandwich samples) were also evaluated. It was observed that higher gas pressure led to increased particle velocity, decreased porosity, enhanced hardness, and improved adhesion/tensile strength. The splat size increased with higher particle velocity, indicating greater particle deformation. The DE decreased with increase in number of deposited layers and increased with increase in gas pressure. The AS coating microstructure exhibited a deformed powder microstructure having fine dendritic/cellular structure. Following the DA treatment, the dendritic features were preserved, accompanied by the precipitation of γ′, γ′′, and δ phases. After STDA treatment, a homogeneous microstructure with the presence of γ′, γ′′, and Nb and Ti carbides without any δ phase was observed. The most favorable outcomes were achieved with the 7 MPa STDA sample, yielding a minimal porosity level of 0.4 ± 0.1% and a tensile strength of 1325 ± 10 MPa with a failure strain of 6.1 ± 0.6%. The tensile strength of 7 MPa sandwich sample was found better (1049 ± 8.5 MPa) compared to stand-alone coating (965 ± 24 MPa) after DA treatment. [ABSTRACT FROM AUTHOR]

Cold spray is a material deposition technology with a high deposition rate and attractive material properties that has great interest for additive manufacturing (AM). Successfully cold spraying free-form parts that are close to their intended shape, however, requires knowing the fundamental shape of the sprayed track, so that a spray path can be planned that builds up a part from a progressively overlaid sequence of tracks. Several studies have measured track shape using ex situ or quasi-in situ approaches, but an in situ measurement approach has, to the authors' knowledge, not yet been reported. Furthermore, most studies characterize the track cross section as a symmetric Gaussian probability density function (PDF) with fixed shape parameters. The present study implements a novel in situ track shape measurement technique using a custom-built nozzle-tracking laser profilometry system. The shape of the track is recorded throughout the duration of a spray, allowing a comprehensive investigation of how the track shape evolves as the deposit is built up. A skewed track shape is observed—likely due to the side-injection design of the applicator used—and a skewed Gaussian PDF—a more generalized version of the standard Gaussian PDF—is fit to the track profile. The skewed Gaussian fit parameters are studied across two principal nozzle path parameters: nozzle traverse speed and step size. Empirical relationships between the fit parameters and the nozzle path parameters are derived, and a physics-based inverse relationship between nozzle speed and powder mass deposition rate is obtained. One of the fit parameters is shown to be an effective means of monitoring deposition efficiency during spraying. Overall, the approach presents a promising means of measuring track shape, in situ, as well as modeling it using a more general shape function. [ABSTRACT FROM AUTHOR]

The grain structure evolution and nanomechanical behavior of cold-sprayed Al coating on Ti substrate with friction stir spot processing (FSSP) were studied by the electron backscatter diffraction and nanoindentation methods. The low-angle boundaries (LAGBs) fraction and the density of the geometrically necessary dislocations (GNDs) decreased from the base zone (BZ) to the stir zone (SZ). The average grain size, the LAGBs fraction and the density of the GNDs were various in different locations of the SZ, which can be attributed to the variety of local shear strain and temperature gradient during FSSP. The B/ B - component, the C component, and the A*1/ A*2 component were mainly developed in the SZ. The highest intensity of the B/ B - component appeared in the 3/8D of the SZ, indicating that the plasticized materials flowed downward experienced the highest shear strain. The materials in the heat affected zone (HAZ) underwent static recrystallization, while the continuous dynamic recrystallization (CDRX) and the geometric dynamic recrystallization (GDRX) occurred in the thermo-mechanically affected zone (TMAZ) and SZ. The nano-hardness and elastic modulus of the cold-sprayed Al coating after FSSP were comparable to those of pure Al bulk. The grain size and dislocation density were the main factors affecting the nano-hardness in the SZ. [ABSTRACT FROM AUTHOR]

7-Series aluminum (Al) alloys have been widely used in aircraft and high-speed train manufacturing owing to its excellent mechanical properties and fracture toughness. However, surface problems of corrosion, wear and fatigue failure of Al alloy parts seriously affect the service life. In the present study, the noncontact laser shock peening (LSP) was applied to improve the fatigue life of the substrate before the coating deposited by cold spraying (CS). The effect of LSP on the interfacial bonding behavior between CS Al with 50 vol.% Al2O3 composite coatings and 7075 Al alloy substrate was comprehensively investigated. Results showed that after LSP treatment, the tensile strength is reduced from 47 to 34 MPa and 32 MPa when the laser shock energy was 2 and 3 J, respectively. Under the condition of shear strength, it decreases from 41.5 to 30 MPa and 26 MPa, respectively. In addition, numerical simulations were conducted on LSP and CS processes, and the results showed that with the increase of laser shock energy, the plastic deformation dissipation energy of Al particles increases gradually, while the plastic deformation dissipation energy of the matrix decreased. Therefore, the surface hardening caused by LSP treatment is the main reason for the decrease of interfacial bonding strength. [ABSTRACT FROM AUTHOR]

This study investigated the effect of powder pre-oxidation on the microstructures and mechanical properties of cold-sprayed nickel coatings. The artificially pre-oxidized nickel powders at 200, 300 and 400 °C for 5 h show the resulting oxygen contents of 0.27, 0.36 and 0.41 wt.%, as compared to 0.21 wt.% in the feedstock powder. Microstructurally, the higher oxygen contents of the impact particles significantly increased in both the number and size of the pores in the as-sprayed coatings by using the pe-oxidized powders, as a result of the porosities of 0.7, 1.5 and 3.3% compared to 0.4% by using the as-atomized powder (natural oxidation condition). Mechanically, the increased oxygen contents of powders result in the reduced properties for the as-sprayed Ni coatings, as the microhardness of 263.2 HV0.1, 245.3 HV0.1 and 236.3 HV0.1 and the tensile strength of 94, 76 and 61 MPa by using oxidized powders compared to those of 289.2 HV0.1 and 208 MPa by using natural oxidation powder. In addition, post-spray heat treatment at 800 °C for 2 h effectively reduces the small-sized pores and nonbonded particle-particle boundaries within the coatings, which is attributed to a combination effect of annealing twins and dislocation slip during heat treatment. As a result, the microhardness significantly decreased to 135.3 HV0.1, 126.7 HV0.1, 124.5 HV0.1 and 114.7 HV0.1, while the tensile strength is increased to 210, 166, 133 and 117 MPa, respectively. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive set of characterization techniques are employed to demonstrate that the cold spray deposition process can result in a significant increase in martensite in austenitic stainless steel. The lack of consensus in the literature on the formation of strain-induced martensite in cold spray can be attributed to the diverse processing conditions and measurement techniques used in different studies. In this work, EBSD, neutron diffraction, TEM imaging, and precession electron diffraction were used in combination to examine whether strain-induced martensite is formed during cold spray deposition of 304L stainless steel powder and to give further insight into possible mechanisms controlling this phenomenon. Cold spray was performed at both 350 °C and room temperature (25 °C) to investigate the effects of spray temperature on the martensite transformation. It is shown that the strain-induced martensite formation is significantly suppressed compared to that which would be expected for comparable levels of plastic strain at quasi-static strain rates. Additionally, the spray gas temperature is shown to directly impact the microstructure formed at the prior particle interface and the formation of dynamically recrystallized regions. [ABSTRACT FROM AUTHOR]

A computational framework is proposed for modelling particle bonding in cold spray. The model is based on the commonly-held view that bonding is a consequence of jetting, namely, the large plastic strains occurring at extreme rates upon particle impact. The model incorporates a bonding criterion at contacting boundaries by introducing a novel strain-like history variable referred to as the bonding parameter conjugate to a rate-dependent evolution law. In doing so, an analogy is made with classic damage mechanics where bonding is viewed as a similar but opposite process to fracture. Two new material constants are introduced, namely, the bonding toughness and the bonding toughness rate. Furthermore, a numerical implementation of the model in the Material Point Method (MPM) is presented which, thanks to a proposed regularization technique, is free of non-physical dependence on discretization parameters. The mesh-free nature of the MPM allows avoiding the numerical issues in conventional Lagrangian and Eulerian methods such as mesh distortion and artificial dissipation. The model is calibrated numerically for aluminum-aluminum material pair using an in-house computer program. Several numerical results are presented to demonstrate that the model can accurately capture material jetting and directly relate it to bonding within the simulation. [ABSTRACT FROM AUTHOR]

This study establishes a machine learning (ML) model utilizing the expectation-maximization approach to predict maximum residual stresses, encompassing both tensile and compressive states, in the cold spraying process across various substrates. The main feature of the ML algorithm lies in its two-step iterative process, where the Expectation (E step) refines latent variable estimates, and the Maximization (M step) optimizes the model's parameters, aligning them with the data. Based on the results, regression analysis highlighted the predictive capabilities of the proposed model for tensile and compressive residual stresses, exhibiting root mean square error values of 8.8 and 3.5%, along with determination coefficient values of 0.915 and 0.968, respectively, indicating higher prediction performance in the compression mode. This suggests higher predictability for residual stress within the depth of material's body. Moreover, analyzing low residual stress levels underscored the significant impact of substrate and particle mechanical strength on prediction performance, whereas higher residual stress levels highlighted the strong influence of thermal conductivity. This correlation suggests that high stresses during the cold spray process generate more heat, thereby emphasizing the crucial role of thermal conductivity in predicting resultant residual stresses. Furthermore, a notable trend emerges as tensile stress increases, spotlighting the augmented influence of processing parameters in the prediction process. Conversely, at elevated compressive stresses, material properties' weight factors assume a vital role in predictions. These findings offer insights into the intricate interplay between processing parameters and materials properties in determining resultant residual stresses during cold spraying. [ABSTRACT FROM AUTHOR]

With the widespread use of nuclear energy, the storage of surplus spent fuel has emerged as a critical issue that needs to be solved, especially for the efficient absorption of neutron radiation and secondary γ-rays generated by spent fuel produced when 10B absorbs neutrons. In this work, B4C/Al and W/B4C/Al coating were prepared on 316 L stainless steel by cold spraying. The microstructure and tensile properties of the coatings were investigated. The performance of the thermal neutron and secondary γ-rays absorption of the two coatings were simulated using the Monte Carlo approach. The results indicated that, compared to the B4C/Al coating, the W/B4C/Al coating exhibited better mechanical properties due to the tamping effect of the W particles. In addition, the secondary γ-rays absorption property was improved due to the addition of W. [ABSTRACT FROM AUTHOR]

This paper offers a concise critical review of finite element studies of the jetting phenomenon in cold spray (CS). CS is a deposition technique wherein solid particles impact a substrate at high velocities, inducing severe plastic deformation and material deposition. These high-velocity particle impacts lead to the ejection of material in a jet-like shape at the periphery of the particle/substrate interface, a phenomenon known as "jetting". Jetting has been the subject of numerous studies over recent decades and remains a point of debate. Two main mechanisms, Adiabatic Shear Instability (ASI) and Hydrodynamic Pressure-Release (HPR), have been proposed to explain the jetting phenomenon. These mechanisms are mainly elucidated through finite element method (FEM) simulations, a numerical technique rooted in continuum mechanics. However, it is important to emphasize that FEM is limited by the equations established for analysis, and as such, its predictive capabilities are confined to those principles clearly defined within these equations. The choice of employed equations and approaches significantly influence the outcomes and predictions in FEM. While recognizing FEM's capabilities, this study reviews the ASI and HPR mechanisms within the context of CS. Additionally, this paper reviews FEM's algorithms and the core principles that govern FEM in calculating plastic deformation, which can lead to the formation of jetting. [ABSTRACT FROM AUTHOR]

Cold spray is an additive manufacturing and coating process in which powder particles are accelerated to supersonic speeds without melting them and then deposit on a surface to form a layer of a coating. Process parameters and materials affect the characteristics of manufactured parts and therefore must be chosen with care. Machine learning (ML) techniques have been specifically applied in additive manufacturing for tasks such as predicting and characterizing porosity. Machine learning algorithms can learn how a variation in the input spray parameters affects annotated output data, such as experimentally measured part properties. In this work, a dataset was developed from experiments reported in published academic papers, to train ML algorithms for the porosity prediction of cold spray manufactured parts. Data cleaning steps, such as null value replacement and categorical feature handling, were applied to prepare the dataset for the training of different ML models. The dataset was split into training and testing portions, and floating feature selection and hyperparameter optimization were performed using parts of the training set. A final evaluation of all trained models, using the test portion of the dataset, showed that a prediction accuracy with an average deviation of 0-2% porosity of the predicted values compared to the true values can be achieved. [ABSTRACT FROM AUTHOR]

With multiple merits compared with thermal spray, cold spray technology is widely applied for various application fields. As part of an intelligent cold spray repair system, an approach for three-dimensional (3D) damage region contour extraction is proposed, which is without nominal Computer-Aided Design models and prior knowledge of damaged workpieces. Moreover, due to partially image processing based, the computation load of the proposed method is lower caused by partially avoiding the 3D point cloud processing. According to the results, it is capable to handle the uneven, sparse and unorganized point cloud to precisely extract 3D contour of damage region. The effectiveness of the proposed approach is highlight. Furthermore, the proposed methods on 3D cloud point to grayscale conversion, two-dimensional (2D) edge detection on images, 3D contour reconstruction from 2D edge are also promising for point cloud processing in other application fields. [ABSTRACT FROM AUTHOR]

The main objective of this work is to investigate the microstructure, mechanical and corrosion properties of 304 stainless steel-H13 composites produced using high pressure cold spray process. 304 stainless steel powders with varying amount of H13 tool steel powders (0, 25, 50 and 75 wt.%) were pre-mixed and cold spray deposited using nitrogen process gas to produce metal-metal composites. H13 tool steel addition improved plastic deformation, reduced porosity, increased microhardness, and tensile properties of 304 cold spray coatings. The tensile properties increased with the increase in H13 tool steel content and with post deposition heat treatment. Post deposition heat treatment at 900 °C significantly improved the tensile strengths and ductility of the composite coatings. However, the wear rate and corrosion susceptibility increased with the tool steel addition in the as-deposited condition, but improved when heat treated to 900 °C. The overall results suggest that the addition of H13 in 304 cold sprayed coatings deposited with nitrogen process gas could be used as a cheaper alternative to helium as well as improve both the microstructure and mechanical properties over pure 304 cold spray coatings. [ABSTRACT FROM AUTHOR]

In this study, a method is demonstrated for predicting defect-laden areas within deposits produced by cold spray additive manufacturing that are caused by substrate geometry and robot tool path. Leading edge shapes were used as the test bed for this method, and porosity was selected as the metric by which defects are quantified. A porosity model was developed based on the observation that porosity is significantly influenced by particle impact velocity normal to the surface and is therefore highly correlated to particle impact angle. The model outputs deposit shape and a probability map of porosity based on initial substrate geometry and robot tool path as inputs. The model was calibrated by experimental deposits formed at varying impact angles. To validate the method, the model was applied to three airfoil leading edge geometries and was shown to qualitatively estimate the density of pores in the deposit. The study also revealed that robotics alignment is an important factor in causing defects within highly curved geometries. The mathematical construct of the model is applicable to other applications outside of leading edges and deposit properties beyond porosity, but other applications and properties are not evaluated in this study. [ABSTRACT FROM AUTHOR]

Cold spray metallization of polymers is a promising surface engineering technique that enables the deposition of metal coatings onto polymer substrates at low process temperatures, resulting in improved surface properties, thus enhanced functionality of the polymeric material. However, deposition of well-adhering metallic coatings without causing surface damage to the polymer substrate is still a challenge. In this work, copper-polyamide composite coatings with different copper concentrations between 30 and 75 vol.% in the starting powders were deposited on polyamide substrates using a low-pressure cold spray system with two nozzle geometries of short and long diverging sections. The spray parameters were first developed for the deposition of polyamide powder (at gas temperature of 260 °C and gas pressures ranging from 0.41 to 1.37 MPa), and then used to spray the composite powder mixtures where the polyamide particles were acting as a binder for copper particles. Inflight and impact particle characteristics (velocity and temperature) of the polyamide powder were simulated to better understand the deposition properties. Considering that the selected conditions were suboptimal for the deposition of copper particles, no surface damage was caused as no penetration of the copper particles into the polymer substrate occurred. The results show that increasing the copper content in the powder mixtures significantly improved the resulting coating uniformity and the retained copper content. In addition, the coating deposited by spraying the powder mixture with a higher copper content of 75 vol.% and using the longer nozzle yielded the highest cohesion strength. To further improve coatings cohesion, two post-spray processing methods of furnace heating and hot pressing were used, and the effect of each process on coatings properties was investigated.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Given name: [Kintak Raymond] Last name [Yu]. Also, kindly confirm the details in the metadata are correct.The author names are now correct: Kintak Raymond given name and Yu last name All other details are corrects [ABSTRACT FROM AUTHOR]

In this study, the role of feedstock powder in influencing the characteristics of cold spray deposition is explored. Four distinct types of Cu feedstock powders, derived through electrolysis and employing varied gas atomization methods, are applied to a Cu substrate via low-pressure cold spray coating. We investigated the impact of feedstock powder on the resultant coatings' microstructure and mechanical properties. A comprehensive statistical model is developed, considering the cold spray parameters, weight change, coating thickness, and discerning their significance and interactions. Optimal conditions for carrier gas temperature and pressure are identified at approximately 400 °C and 1.99 MPa, respectively, consistent across all Cu powders. Velocity analysis reveals particle velocities ranging from 373 to 564 m/s under these optimal conditions. Coatings deposited using satellite-free gas-atomized powder, characterized by enhanced sphericity, exhibit superior characteristics, including minimal porosity (0.66 ± 0.35%), high flattening ratio (3.57 ± 1.51), elevated microhardness (107 ± 3 HV) and high bonding strength (20.7 ± 2.3 MPa). In contrast, coatings deposited with gas-atomized powder featuring microsatellite particles and electrolytic powder with irregular shapes display distinct properties. The observed trends are attributed to lower oxygen content and reduced oxide levels near the surface of the more spherical, satellite-free powder. This powder also demonstrates heightened plastic deformation during deposition. The increased peening effect of satellite-free gas-atomized powder during cold spray results in elevated dynamic recrystallization near the substrate surface, leading to smaller grains at the interface. Microstructural evolution analysis, utilizing electron backscatter diffraction, further elucidates the heterogeneous deformation and grain refinement occurring in Cu splats during cold spray coating. [ABSTRACT FROM AUTHOR]

Polymers have proven to be challenging to cold spray, particularly with high efficiency and quality when using inexpensive nitrogen (N2) and air propellants. Helium (He), when used as a process propellant, can improve spray deposit properties but is often undesirable due to its limited availability and high cost. In this study, additives of multiple particle sizes and materials were mixed with polymer powder in an effort to improve the performance of polymer sprays using mainly N2 as a process propellant. The effects of hard-phase additives on deposit microstructure were investigated by precise ion beam polishing of deposit cross sections and subsequent electron microscope imaging. Additional metrics including the density and post-spray composition of deposits were investigated to quantify the peening effect and the amount of embedded additive. Additives, regardless of size, were observed to embed in the spray deposits. Additionally, hard-phase additives demonstrated nozzle cleaning properties that continually remove polymer fouling on the nozzle walls. Inversely, sprays with polymer powder and no additives tended to clog the nozzle throat and diverging section because of continual fouling. [ABSTRACT FROM AUTHOR]

The promising structural properties of fiber-reinforced polymer composites make them widely popular in the energy, automotive, defense, and aerospace industries. One of the most challenging limitations associated with the application of composites is their maintenance and repair. In this study, a polymer cold spray approach is introduced as an efficient alternative for the structural repair of fiber-reinforced polymer composites, without the use of additional repair media. Damage in the form of circular tapered holes is created in glass fiber-reinforced polymer (GFRP) composite substrates using conventional drilling. This damage is repaired by cold spray with thermoplastic (nylon 6) and thermosetting (polyester epoxy resin) materials. The fundamental adhesion mechanisms near the repair surface are investigated through microstructural observations and highlight the role of adiabatic shear instability due to the occurrence of severe plastic deformation in the particle impact zone. Microstructural examinations also suggest that no significant fiber damage or surface degradation occurs due to the repair by cold spray. Mechanical tests performed on neat, damaged, and repaired composites reveal the partial recovery of structural performance and load-bearing capacity after cold spray repair. Additionally, the cold spray-repaired GFRP samples are compared with conventional epoxy resin repair methods. Results obtained in this work highlight cold spray as a promising and rapid technique for the on-site repair of composite structures with minimal pre-/post-processing requirements. [ABSTRACT FROM AUTHOR]

High-performance polymers such as poly(ether ether ketone) (PEEK) are appealing as composite components for a wide variety of industrial and medical applications due to their excellent thermomechanical properties. However, conventional PEEK metallization methods can often lead to poor quality control, low deposition rate, and high cost. Cold spray is a promising potential alternative to produce polymer–metal composites rapidly and inexpensively due to its relatively mild operating conditions and high throughput. In this study, we investigated the deposition characteristics of metal–polymer composite feedstock, composed of PEEK powder and copper flake in varying ratios, onto a PEEK substrate. Copper-PEEK powder blends were prepared by both hand-mixing and cryogenic milling (cryomilling), which predominantly creates composite particles with micron-scale copper domains coating PEEK particle surfaces. This process non-monotonically affects the relative dominance and length scales of the multiple contributing deposition mechanisms present in mixed-material cold spray. In low-pressure cold spray, deposits showed significant changes in deposition efficiency and composition as a result of milling, with improvements in these characteristics most dramatic at lower Cu fractions. Deposits of a cryomilled blend of nominally 30 vol.% copper in PEEK exhibited minimal porosity under scanning electron microscopy, complete retention of powder composition, and the highest deposition efficiency among all samples tested. Notably, neither neat PEEK nor neat Cu meaningfully deposited at the same mild conditions as this 30 vol.% Cu blend, indicating a synergistic departure from linear mixing rules driven by the relative balance of local deposition interactions (e.g., hard–soft, soft–soft, etc.). Intentional powder and process design toward optimizing this balance may facilitate cold spray metallization applications. [ABSTRACT FROM AUTHOR]

Cold spray (CS) is a solid-state process for depositing thick layers of material via the successive high-velocity impact of powder particles onto a solid surface, which leads to high rates of deformation, interparticle bonding, and coating build-up. Although CS is finding commercial utilization in non-load-bearing repair and coating applications, clear nondestructive characterization procedures are necessary to realize its potential in load-bearing structural applications. In this study, the viability of electrical conductivity and through thickness ultrasound wave velocity measurement methods was studied to serve as a means for nondestructive quantitative measurement for quality control in CS and potentially other additive manufacturing (AM) methods. Eddy current, ultrasound, porosity, hardness, and uniaxial tensile strength tests were conducted on CS deposited layers of aluminum alloy 6061 and copper on aluminum alloy 6061 and commercially pure copper substrates, respectively. CS gas dynamic parameters were intentionally and systematically varied to result in corresponding discrete differences in mechanical properties of deposits. Ultrasound measurements of longitudinal wave velocity and eddy current electrical conductivity measurements showed good correlation with process conditions, microstructural characterization results, and destructive mechanical tests (hardness, tensile). The results of this work show that ultrasound wave velocity and electrical conductivity correlate well with increased particle impact velocity in CS deposited aluminum and copper blocks, which evidently show an incremental decrease in porosity, increase in hardness, and increase in tensile strength. The outlined ultrasound and eddy current nondestructive testing methods present effective means for quantitative assessment of cold spray deposited structures while intact with the substrate. [ABSTRACT FROM AUTHOR]

A previous study on the pull-off testing of metallized carbon fiber-reinforced polymers (CFRPs) via cold spray showed that better adhesion strengths could be obtained when features such as carbon fibers or surfacing elements were present, by providing potential mechanical interlocking features. In this work, a first approach to determining the effect of the fiber orientation on the deposition and bonding of the metallic coating to the thermoplastic composite substrate is explored. Pure Sn powder was cold sprayed onto two thermoplastic Polyether–Ether–Ketone (PEEK) CFRP substrates, containing carbon fibers with different orientations: one had fibers in the plane of the substrate (unidirectional tape), while the other had fibers mostly perpendicular to the substrate (ZRT film). Characterization of the coatings was performed via scanning electron microscopy (SEM) and confocal microscopy, and some aspects of mechanical testing (namely wear and scratch testing) were carried out to assess the effect of the substrate on the properties of the coatings. A slight improvement of the coating deposition was observed on the sample with the ZRT film, and this was associated with deeper penetration of tin into the substrate, around the carbon fibers, for improved mechanical interlocking. Wear testing did not seem to reveal any differences between both samples. Finally, scratch adhesion tests were performed to qualitatively assess the bonding mechanism at the coating-substrate interface, and while adhesive failure seems to be the main failure mechanism, the coating of the Z sample seems to co-deform with the substrate during testing, which could highlight better adhesion strength. [ABSTRACT FROM AUTHOR]

Cold spraying (CS) of high-strength materials, e.g., Inconel®625 is still challenging due to the limited material deformability and thus high critical velocities for achieving bonding. Further fine-tuning and optimization of cold spray process parameters are required, to reach higher particle impact velocities and temperatures, while avoiding nozzle clogging. Only then, sufficiently high amounts of well-bonded particle–substrate and particle–particle interfaces can be achieved, assuring high cohesive strength and minimum amounts of porosities. In this study, Inconel®625 powder was cold sprayed on carbon steel substrates, using N2 as propellant gas under different spray parameter sets and different powder sizes for a systematic evaluation. Coating microstructure, porosity, electrical conductivity, hardness, cohesive strength, and residual stress were characterized in as-sprayed condition. Increasing the process gas temperature or pressure leads to low coating porosity of less than 1% and higher electrical conductivity. The as-sprayed coatings show microstructures with highly deformed particles. X-ray diffraction reveals that powder and deposits are present as γ-solid-solution phase without any precipitations. The deposits show high microhardness and compressive residual stresses, which is attributed to work hardening and peening effects. The optimized deposits reach almost bulk material properties and are thus well suited for industrial applications. [ABSTRACT FROM AUTHOR]

The use of process–microstructure–property relationships for cold spray can significantly reduce application development cost and time compared to legacy trial and error strategies. However, due to the heterogeneous microstructure of a cold spray deposit, with (prior) particle boundaries outlining consolidated splats (deformed particles) in the as-spray condition, the use of automated analysis methods is challenging. In this work, we demonstrate the utility of quantitative data developed from a convolutional neural network (CNN) for feature extraction of cold spray microstructures. Specifically, the power of CNN is harnessed to automatically segment the deformed particles, which is hardly accessible at scale with traditional image processing techniques. Deposits produced with various processing conditions are evaluated with metallography. Parameters related to particle morphology such as flattening ratio are also quantified and correlated to strength. [ABSTRACT FROM AUTHOR]

Cold spray additive manufacturing is an emerging solid-state deposition process that enables large-scale components to be manufactured at high-production rates. Control over geometry is important for reducing the development and growth of defects during the 3D build process and improving the final dimensional accuracy and quality of components. To this end, a machine learning approach has recently gained interest in modeling additively manufactured geometry; however, such a data-driven modeling framework lacks the explicit consideration of a depositing surface and domain knowledge in cold spray additive manufacturing. Therefore, this study presents surface-aware data-driven modeling of an overlapping-track profile using a Gaussian Process Regression model. The proposed Gaussian Process modeling framework explicitly incorporated two relevant geometric features (i.e., surface type and polar length from the nozzle exit to the surface) and a widely adopted Gaussian superposing model as prior domain knowledge in the form of an explicit mean function. It was shown that the proposed model could provide better predictive performance than the Gaussian superposing model alone and the purely data-driven Gaussian Process model, providing consistent overlapping-track profile predictions at all overlapping ratios. By combining accurate prediction of track geometry with toolpath planning, it is anticipated that improved geometric control and product quality can be achieved in cold spray additive manufacturing. [ABSTRACT FROM AUTHOR]

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

Cold spraying has emerged as a promising technique for the repair of metallic components. Manipulating the cold spray gun by industrial robots, referred to as robot-guided cold spraying, enables flexible and controlled material deposition. This work proposes a concept for automated planning of robotic cold spray paths and trajectories, enabling effective and efficient material deposition at specified repair locations. The concept incorporates predefined cold spray parameterizations and boundary conditions to provide the best possible material deposition for the individual repair application. The concept begins with the extraction of the volume to be filled. This volume is then sliced into suitable adaptively curved layers and converted into point clouds for path planning. Subsequently, the cold spray path is converted into a trajectory by adding a calculated spray velocity profile to produce the required locally varying layer thicknesses. In addition, simulation of the material deposition and a kinematic analysis of the simulated trajectory are performed. These are utilized as performance indicators for assessing deposit quality and material efficiency, enabling the validation and improvement of the parameterized trajectory. Finally, the implementation of the entire concept is demonstrated by representative use cases. The results demonstrate successful automated path and trajectory planning by the proposed concept, contributing to the overall goal of automated repair of damaged components by cold spraying. [ABSTRACT FROM AUTHOR]

In this study, the effect of particle size on the microstructure and mechanical properties of cold-sprayed nickel coatings was investigated using three particle size ranges of pure nickel powders. The experimental results show that the mechanical properties of the coating fabricated by the fine powder with a D50 of 25 μm are lower (microhardness and tensile strength of 257.5 HV0.1 and 126 MPa, respectively) compared to those from the coarser particle sizes (D50 = 45 μm and 67 μm) because of the higher yield strength of powder, which makes it difficult to generate sufficient plastic deformation during the spraying process. The powder with the largest particle size, D50 of 67 μm, has a low impact velocity, which does not allow for a high-quality coating due to less plastic deformation, and the porosity is higher up to 0.7%. When the mean particle size of the powder is 45 μm, the coating shows the highest degree of densification, the porosity is 0.4%, and the mechanical properties of the coating are better with the microhardness and tensile strength of 289.2 HV0.1 and 208 MPa, respectively. [ABSTRACT FROM AUTHOR]

In the cold spray additive manufacturing (CSAM) process, layer-by-layer stacking is an efficient method to achieve materials additive manufacturing (AM). Unlike other AM processes, such as selective laser cladding, which can quickly achieve trajectory planning by using commercial software, there is currently no general methodology for spray trajectory planning in the CSAM process. Accurate and fast generation of trajectories for each layer of the manufactured workpiece is a challenge. When a component with multiple features is manufactured, the spray paths between features cannot be created easily due to the "one-stroke" character. That is, the powder feeding cannot be interrupted during the entire spraying process. This means that for the deposition of multi-featured components, the planning of the path of the nozzle transfer from one feature to another is a challenge. If the transfer path goes directly across the area of the deposited feature, it can significantly change the shape of the deposit and cause undesired deposition results. Additionally, the spray gun or the substrate held by the robot usually needs to be deflected by a certain angle to compensate for the loss of deposit along the edges. An accurate and efficient spray trajectory planning is the most critical part of the CSAM process. Thus, this article proposes a general manufacturing methodology for complex structural components in the CSAM process. The simulation and experimental results revealed that the methodology can efficiently generate the necessary spray trajectory to fabricate the desired deposit. It makes CSAM truly possible in the manufacture of workpieces with complex geometries. [ABSTRACT FROM AUTHOR]

Al-x%Al2O3 composite protective coatings were prepared on the surface of LA43M Mg-Li alloy substrate by cold-spraying technology. The microstructure, corrosion resistance, tribological properties of the coatings were investigated in detail. The results showed that the addition of hard Al2O3 particles was conducive to the deposition of Al-based coating, and the bonding mode between Al-x%Al2O3 coating and substrate was metallurgical bonding and mechanical interlocking. Moreover, the addition of Al2O3 particles was beneficial for increasing the density of the coating, and significantly improving the corrosion resistance, hardness and tribological properties of composite coatings. Respecting the corrosion resistance of Al-x%Al2O3 composite coatings, the electrode potential of coatings increased significantly and stabilized to about − 1.0 V when the additive amount of Al2O3 increased to 10-25%, while the corrosion current density decreased to about 10-8 A/cm2, which was four orders of magnitude lower than that of LA43M Mg-Li alloy substrate. On the other hand, the tribological properties of Al- x%Al2O3 composite coatings were improved with the additive amount of Al2O3 phase increased. When the additive amount of Al2O3 increased to 15-25%, the coefficient of friction was stable at about 0.45 and the wear rate decreased. [ABSTRACT FROM AUTHOR]

The residual stress state in cold spray coatings, which is typically compressive in nature, can be crucial for the coating integrity at high levels or for thick coatings. As an alternative, the analysis using the curvature measurement was applied in this study. The stress measurement during cold spray deposition was made by using an in situ coating property sensor (ICP sensor), which is relatively widely used in thermal spray and enables a fast comparison of several process parameters. The results were then compared to post-deposition curvature measurements. It could be revealed that the usage of a very slow robot traverse speed can lead to tensile residual stresses in cold-sprayed coatings. This finding was explained by the high local temperature during deposition and the formation of tensile stresses during cooling of the deposited material to the average substrate temperature. The increase in the powder feed rate can increase this effect. Preheating did not influence the final stress state. An analytical model is presented which can at least semi-quantitatively explain the observed findings. As an outcome of the research work, it is now possible to adjust the residual stress state in cold spray coatings from tensile to compressive and vice versa with the opportunity of a zero stress state. [ABSTRACT FROM AUTHOR]

This paper investigates customized AA5083 and Al-Mg binary powders produced by gas atomization and assesses cold spray (CS) deposition of these materials with the evaluation of interface quality, deposition efficiency, porosity, and microhardness. While there has been extensive research progress on CS deposition of AA2024, AA6061, and AA7075, less attention has been given to CS 5xxx-series (Al-Mg) aluminum alloys. For the development and investigation of CS Al-Mg series alloys, AA5083 and customized Al-Mg binary powders were fabricated using a close-coupled inert gas atomizer, and those powders were sprayed using a high-pressure cold spray system to produce CS Al-Mg deposits. The microstructural characteristics of the powders, such as lattice constant and the formation of intermetallic networks, were affected by the Mg content of as-atomized powders. Selected CS parameters were able to produce highly dense CS deposits over a range of 1.7-5 wt.% Mg. The Mg content of as-atomized powders also influenced the hardness of the deposits and the DE while having no effect on porosity. The influence of Mg content on powder properties, CS process, and CS Al-Mg deposits has been discussed. [ABSTRACT FROM AUTHOR]

The inter-particle bonding (IPB) mechanism of cold-sprayed titanium alloy during heat treatment (HT) is not clear. The interfacial microstructure and bonding characteristics at the interface of cold-sprayed Ti6Al4V after HT were studied at the micro- and nano-scale. As a result, the nanocrystallization at IPB during cold spray (CS) cannot cause obvious metallurgical bonding between Ti6Al4V particles. The average Young's modulus of CS Ti6Al4V is 57% higher than that of powder, but the average Young's modulus of HT sample decreases by 16%. The internal stress and dislocation distribution of interfacial microstructure can lead to various microstructure features and non-uniform rates of microstructure growth at deformed transition layer and IPB during HT. The nanograins at the IPB grow into micron-equiaxed grains. On the contrary, the micron martensitic laths at deformed transition layer adjacent to IPB show the characteristics of equiaxed nanograins transformation under the action of grain boundary bulges induced by dislocation entanglement. [ABSTRACT FROM AUTHOR]

Residual stress is an important factor that affects the properties of cold spray coatings. The study performed 2D single-, 3D single-, and 3D multiple-particle finite element simulations based on the Eulerian method, and hole drilling measurements to study residual stress in cold-sprayed copper coatings. The study examined how the basic modeling parameters affect residual stress in the 2D system. It found that the mesh size, substrate dimension, and simulation duration change the residual stress; while material failure does not have much effect because failure is localized. It also found that thermal softening, which occurs when the initial temperature and/or plastic deformation increase, helps to reduce the residual stress. In addition, the residual stress along the axisymmetric axis of the particle changes from being compressive at first to being compressive-tensile-compressive along the through-depth thickness direction with the interfacial stress being tensile that mainly originates from friction shear of the interfacial layers. For the 3D single-particle simulations, the average residual stress to the through-depth thickness shows tension to compression transition and is similar to the 2D cases. For the 3D multiple-particle simulations, the residual stresses in the coatings/substrate are all compressive because of the repeated and strong impact of the particles, which agree with the experimental measurements. The study also found that the compressive stresses decrease when the coating thickness increases because of more plastic deformation-induced thermal softening. This paper clarifies the effects of Eulerian-based finite element parameters on simulating residual stress in cold spray and will serve as a valuable reference for future studies. [ABSTRACT FROM AUTHOR]

Hybrid bond layers (BLs) were designed, fabricated, and evaluated for cold spray metallization of CFRP. The bond layers consisted of metal mesh embedded in a polymer film adhesive co-cured to the CFRP. Efforts were devoted to identifying the critical opening ratio—i.e., the ratio of mesh opening size to powder diameter, for deposition of an adherent coating. Analysis of powder deposited at mesh openings show a transition from erosion (at a mesh opening ratio of 6.4) to mechanical interlocking and formation of a continuous coating with decreasing opening ratio. Selection of opening ratio yielded either (a) a grid of consolidated thin-walled deposits atop mesh wires separated by microchannel openings, or (b) densified coatings of cold-sprayed Ti. The effective opening ratio increased with increasing diameter ratio—i.e., the ratio of wire diameter to powder size, a consequence of eroded wire peripheries at shallow impact angles. These findings inform the design of future hybrid BLs, in concert with the selection of powder size, for cold spray metallization of CFRP. [ABSTRACT FROM AUTHOR]

This study presents a bibliometric analysis of cold spray research publications from the Scopus database from 1994 to 2022 period. This study aimed to: (a) examine the evolution and dissemination of cold spray research; (b) identify the key topics discussed in cold spray research; and (c) identify the research power of this research area and its collaborations. The study retrieved 1944 documents for further analysis using various tools based on the keywords used in the article title that are related to cold spray. This study employed Microsoft Excel for frequency analysis, VOSviewer for data visualization, and Harzing's Publish or Perish for citation metrics and analysis. Standard bibliometric indicators such as the growth of publications, authorship patterns, collaboration, and prolific authors, country contribution, most active institutions, and most cited articles are used to report the findings of this study. According to our study, there has been a steady increase in publications on cold spray research for almost three (3) decades. The results of the bibliometric analysis illustrate the positive trend in cold spray research around the world, highlighting the advancement of cold spray technology, applications, and fabrications. Indirectly, it would also affect manufacturers all over the world since the promising results of research into cold spray would eventually lead to a rise in demand for cold spray. The study contributes significantly to expanding the accessibility and global reach of cold sprays. [ABSTRACT FROM AUTHOR]

In high-pressure cold spray, it has been demonstrated that the enthalpy of the particle carrier gas has a significant effect on the propellant gas conditions and resulting particle impact velocities and temperatures. Through modeling and experimentation, this study demonstrates that in low-pressure cold spray, the enthalpy of the particle carrier gas has a minimal effect on the particle velocity; therefore, particle temperature can be controlled independently from particle velocity. This is a unique feature of downstream injection and a valuable tool when dealing with temperature sensitive substrates and particles. In this study, particle preheating was used to inject pure aluminum particles up to temperatures of 500 °C, about 80% of their melting temperature. This particle preheating was accomplished without clogging because of a novel particle preheater which eliminated the particles exposure to hot metal surfaces. It was found that even after substantial spray time, there was no evidence of wear or clogging. The preheating resulted in a DE increase of 3.6 times when compared to the injection of room temperature particles. [ABSTRACT FROM AUTHOR]

There is an increasing need for ice protection systems that do not require complex manufacturing considerations or are energy intensive. Fluorinated polymer coatings are potential candidates for such systems although conventional manufacturing processes can be costly, limited in the achievable coating thickness or can degrade the coating's material mechanical properties during deposition. The current work aims to offer an alternative approach by using cold spray as the mean of coating production. Computational and experimental approaches are used to design a new cold spray nozzle for the efficient deposition of adhesive perfluoroalkoxy alkane. The icephobicity of as-sprayed coatings are evaluated using threefold characterization, one for each stage of the icing process. First, the surface's wetting behavior is established using single droplet analysis, followed by a time-lapse study of water droplets to observe their freezing process, and finally ice adhesion is evaluated with both macro- and micro-ice adhesion tests. While the as-sprayed coatings exhibited superhydrophobic properties that should be sought in icephobic coatings, their behavior changed when exposed to frost formation. Ice adhesion testing revealed that surface frosting leads to degraded wetting behaviors resulting in much higher ice adhesion, which demonstrates the importance of this phenomena when studying icephobic coatings. [ABSTRACT FROM AUTHOR]

Cold spray (CS) is a thermal spray method that deposits solid particles at high velocity at about room temperature using gases such as nitrogen or helium. Despite of CS's unique advantages, it is expensive to operate due to its high gas consumption and the need for small particle sizes for deposition. To enhance cost-effectiveness, liquid cold spray (LCS) has been developed with the capability of depositing large particles with a wider size cut by using water as a propellant. Though LCS has demonstrated success in manufacturing copper coatings, it raises questions about how wetting of particles and/or substrate surfaces can affect adhesion. This paper addresses these concerns using a finite element method based on elastic–plastic theory. Results demonstrate that wetting the deposited particle reduces both particle and substrate deformation. Water film wetting the particle primarily affects the bonding area due to its presence in the interfacial area between the particle and substrate. In order to avoid interfacial water, this paper investigates the effect of four parameters as follows: particle velocity, particle size, water film thickness, and water temperature. The results demonstrate that the volume of interfacial water is reduced by increasing particle impact velocity and particle size and decreasing water film thickness. A rise in water temperature does not affect the amount of interfacial water; however, evaporation of interfacial water can increase. [ABSTRACT FROM AUTHOR]

The objective of this study was to prepare a copper-coated rubber surface using cold spray technology with improved virucidal and antimicrobial properties to fight against highly transmissible viruses and bacteria. A successful cold spray coating was produced using irregular-shaped pure Cu powder on an escalator handrail rubber. The powder particles and the deposited coatings (single and double pass) were characterized in terms of particle morphology and size distribution, coating surface and coat/substrate cross-section properties. The bonding between powder and rubber surfaces was purely mechanical interlocking. The Cu powder penetration depth within the rubber surface increases with a number of depositions pass. The virucidal properties of the coated surface were tested utilizing surrogates for SARS-CoV-2: HCoV-229E, a seasonal human coronavirus, and baculovirus, a high-titer enveloped insect cell virus. A double-pass coated surface showed significant baculovirus inactivation relative to a bare rubber control surface after 2-h (approximately 1.7-log) and 4-h (approximately 6.2-log), while a 4-h exposure reduced HCoV-229E titer to below the limit of detection. A similar microbial test was performed using E. coli, showing a 4-log microbial reduction after 2-h exposure relative to the bare rubber. These promising results open a new application for cold spray in the health sector. [ABSTRACT FROM AUTHOR]

As a new member of the additive manufacturing family, cold spray provides various benefits such as a limited oxidation during deposition. Titanium alloys, being oxidation-sensitive materials, could thus benefit from this processing route. However, the high strength of these alloys implies that dense deposition is a significant challenge. Two pathways were explored to reduce porosity. The sensitivity to the different deposition parameters was first investigated. Further improvements were then obtained using in situ shot peening. Another major issue regarding the material performance is the presence of residual stresses. Usually, cold spray induces compressive residual stresses in the resulting deposits because of the shot peening effect of the solid-state particles. In contrast, the prevailing stresses are in tension in cold sprayed Ti-6Al-4V. An improved understanding of this feature, which stems from the contribution of different physical phenomena to the final stress state, would provide insights into a reduction of residual stress. This is crucial to maintain structural integrity and, in turn, consider cold spray as a viable additive manufacturing process. The in situ coating properties device allowed to measure the evolution of the residual stresses during and after deposition and to identify most influent operating parameters. The purpose of this study is to provide guidelines to control porosity and residual stresses in order to produce dense and thick Ti-6Al-4V coatings with good structural integrity. [ABSTRACT FROM AUTHOR]

In a solid-state deposition technique such as cold spray (CS) or high-velocity air-fuel (HVAF), particle and substrate initial conditions play a crucial role in particle deformation and its adhesion strength to the substrate. In these thermal spray techniques, the deposited particle and the substrate are required to deform plastically; hence, both components are usually metallic. An oxide layer at the surface of these metallic components may avoid producing a metallurgical bonding and strong adhesion between them. To better understand the effect of particle and substrate initial conditions, e.g., particle velocity, particle temperature, and substrate temperature, on the formation of metallurgical bonding, it is necessary to examine particle and substrate oxide layer failure. In this work, the effect of a 20 µm Ti-6Al-4V particle and a Ti-6Al-4V substrate initial conditions on the failure of their oxide layer during impact has been studied. The results show that the presence of an oxide layer increases the required critical velocity for particle adhesion on the substrate. Furthermore, regardless of the chosen initial conditions, the particle oxide layer would fail in the adiabatic shear instability region because of the severe deformation that the particle experiences upon impact. This study shows that a stronger bonding between the deposited particle and the substrate can be achieved by increasing the particle velocity and substrate temperature, as they increase the extent of the failed oxide layer region of the substrate. Rising particle temperature increases particle deformation and has no significant effect on the adhesion between the particle and substrate. [ABSTRACT FROM AUTHOR]

This study deals with WC-12Co coatings deposited by cold spraying on 13Cr4Ni steel hydraulic turbine blades. The coatings were deposited under different pressure conditions such as 25, 30, 40 bar at 800 °C, and 50 bar at 900 °C. The microstructural evolution under different pressure conditions and the effect of temperature variation were investigated using a scanning electron microscope (SEM) equipped with energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction analysis (XRD). In addition, the microhardness analysis of the coatings showed that the WC-12Co coating deposited at 40 bar 800 °C had the highest (270 HV) hardness which was a good attribute for anti-wear applications in hydraulic turbine blades according to most tribological theories. [ABSTRACT FROM AUTHOR]

To metallize non-metallic surfaces by cold spray, bond layers (BLs) are often used to achieve a degree of compatibility between the substrate and the deposit and generally to mitigate the disparate properties of substrate and deposit. The objective of the present work is to design hybrid (Al-epoxy) BLs for metallization of epoxy-based carbon fiber-reinforced polymers (CFRPs) and to determine parametric effects on adhesion and deposition yield. The few studies that have focused on metal deposition onto thermoset composites have highlighted risks of erosion of the thermoset matrix and of fiber fracture. To address these problems, a BL is introduced to reduce erosion of CFRP and to provide surfaces for impinging powder to cold-weld onto and interlock. Effort is devoted to engineer a BL compatible with cold spray and to develop understanding of the quantitative effects of BL microstructure on adhesion. The BL microstructure strongly affected the adhesion of the deposit, which relied on BL-CFRP, powder-BL, and powder-powder bonding. Analysis of initial stages of deposition revealed matrix erosion and subsequent compaction, both contributing to mechanical interlocking. The findings indicate a pathway for CS deposition onto CFRP through judicious design of BLs. [ABSTRACT FROM AUTHOR]