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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]

Thermal management is key to enabling increasingly powerful chips and heterogeneous integrated 2.5D/3-D systems. Composite materials with high thermal conductivities that can be placed at different levels of proximity to the die provide new solutions for heat dissipation. Here we report the fabrication of thick copper-diamond composite !lms using cold spray, which is a high-throughput, low-thermal-budget deposition technology. In cold spray, feedstock micro powder is accelerated in a specially designed nozzle by a heated pressurized gas and adheres to the substrate upon high-speed impingement. This process achieves higher deposition rates than other methods used in semiconductor manufacturing (such as electroplating). It also produces films that are denser and much less porous than ones produced by conventional thermal spray techniques. In this work, we first use process and thermal simulations to determine the requirements of the micro diamond powder feedstock, including the diamond core size, metal-clad thickness, core-clad interfacial resistance, and volume fraction to enable the cold spray of copper-diamond composites with thermal conductivities that are higher than copper. Subsequently, we perform a systematic characterization of the diamond powders from several suppliers, including the purity, metal oxygen content, particle morphology, and metal-clad adhesion. This characterization reveals the challenges of meeting all the specs using currently available diamond powders. Finally, we cold spray copper-diamond composite films on a variety of substrates with tunable thicknesses between 100 mm and 2 mm, achieving a thermal conductivity that is approximately 10% higher than cold-sprayed pure copper. Further improvement of the thermal properties relies on continued innovation in powder surface modification and powder storage/shipping methods. [ABSTRACT FROM AUTHOR]

Cold spray technology, as an emerging surface engineering technique, effectively prepares hard coatings by high-speed projection of powder materials onto substrates at relatively low temperatures. The principal advantage of this technology lies in its ability to rapidly deposit coatings without significantly altering the properties of the substrate or powder materials. Carbon-based materials, especially carbides and diamond, etc., are renowned for their exceptional hardness and thermal stability, which make them indispensable in industrial applications requiring materials with high wear resistance and durability at elevated temperatures. This review elucidates the fundamental principles of cold spray technology, the key components of the equipment, and the properties and applications of hard coatings. The equipment involved primarily includes spray guns, powder feeders, and gas heaters, while the properties of the coatings, such as mechanical strength, corrosion resistance, and tribological performance, are discussed in detail. Moreover, the application of this technology in preparing metal matrix composite (MMC) materials with carbon-based reinforcements, including tungsten carbide, boron carbide, titanium carbide, and diamond, are particularly emphasized, showcasing its potential to enhance the performance of tools and components. Finally, this article outlines the challenges and prospects faced by cold spray technology, highlighting the importance of material innovation and process optimization. This review provides researchers in the fields of materials science and engineering with a comprehensive perspective on the application of cold spray technology in MMC materials with carbon-based reinforcements to drive significant improvements in coating performance and broaden the scope of its industrial applications. [ABSTRACT FROM AUTHOR]

This paper presents the results of an extensive investigation into the durability of cold spray repairs to corrosion damage in AA7075-T7351 aluminium alloy specimens where, prior to powder deposition, the surface preparation involved grit blasting. In this context, it is shown that the growth of small naturally occurring cracks in cold spray repairs to simulated corrosion damage can be accurately computed using the Hartman–Schijve crack growth equation in a fashion that is consistent with the requirements delineated in USAF Structures Bulletin EZ-SB-19-01, MIL-STD-1530D, and the US Joint Services Structural Guidelines JSSG2006. The relatively large variation in the da/dN versus ΔK curves associated with low values of da/dN highlights the fact that, before any durability assessment of a cold spray repair to an operational airframe is attempted, it is first necessary to perform a sufficient number of tests so that the worst-case small crack growth curve needed to perform the mandated airworthiness certification analysis can be determined. [ABSTRACT FROM AUTHOR]

This research investigates the influence of thickness on residual stress profiles in aluminum cold spray coatings using finite element analysis (FEA). Residual stress is a critical factor that impacts coating adhesion, fatigue life, and susceptibility to delamination in thermal spray processes. Despite its acknowledged importance, predictive analysis of these stresses on a layer-by-layer basis remains relatively unexplored. This study introduces an innovative numerical methodology to analyze the progression of residual stresses across various deposition efficiencies (10%, 40%, 60%, and 100%) and layer thicknesses, thereby enhancing predictive accuracy for cold spray coatings. The findings demonstrate that the number of deposited layers significantly affects residual stress profiles in both coatings and the substrate, with compressive residual stress predominating in the coatings and deeper tensile stress predominating in the substrate. Residual stress behavior near the last deposited layer aligns with the expected peening effect. Discrepancies in substrate stress distributions may arise from variations in deposition parameters and unconsidered temperature effects. While the model generally aligns with theoretical and some empirical data, observed discrepancies underscore the need for further validation. This study lays the groundwork for informed decision-making for cold spray processes by providing insights into stress management, thereby contributing to enhancing coating integrity and performance. [ABSTRACT FROM AUTHOR]

In this research, a silicon-aluminizing diffusion coating constituted of homogenous Ti(Al, Si)3 phase was prepared on γ-TiAl alloy using cold spraying Al-40Si (wt.%) alloy coating followed by thermal diffusion treatment. The oxidation behavior of the diffusion coating was tested for 300 h at high temperatures of 900, 950 and 1000 °C. The differences in microstructure evolution at three different temperatures, as well as antioxidant properties of the coating, were investigated. The results showed that the weight gain of the coating after 300-h oxidation at 900, 950 and 1000 °C was sharply reduced to only 1.195, 1.550 and 1.925 mg cm−2, respectively. Although the alumina-based oxide scale formed on the coating became thicker with the increasing oxidation temperature, it had a good adherence to the coating even at 1000 °C. Thus, the coating can significantly improve the oxidation resistance of the γ-TiAl alloy at three temperatures because the generated oxide scale can act as a barrier to prevent the outward diffusion of Ti and the internal diffusion of O. The degradation rate of the coating also increased with the increasing oxidation temperature. Following 300 h of oxidation test at 1000 °C, the homogenous Ti(Al, Si)3 phase in the coating almost entirely degraded. However, the in situ formed Ti5Si3 diffusion layer maintained a good stability at 1000 °C, which can block the further invasion of O to a certain extent. [ABSTRACT FROM AUTHOR]

There are some important advantages presented by metal specimens coated with WIP-C1 (Ni/CrC)-type materials. However, given the coating methods and the stress under dynamic loads, there are issues that need to be taken into account, particularly in terms of the behavior at the interface between the two materials. Using standardized cylindrical 1018 steel specimens uniformly coated with WIP-C1 (Ni/CrC) by cold spraying, this study investigated the fatigue behavior of the specimen as a whole, focusing on the interface areas of the two materials. The fatigue life diagram is given, to a large extent, by the behavior of the base material. As a result, in this work, we have focused not so much on the fatigue behavior of the assembly as on the integrity of the coating material and the defects, failures, etc., that may occur at the interface after a certain number of cycles. The applied load was cyclic fatigue through alternating–symmetric cycles. Scanning optical microscopy was used to observe plastic deformations and crack propagation during the breakage process. It was found that both the base material zone and the cover material zone presented good performance when the maximum stresses were at low values. A fatigue durability curve was also plotted, showing a conventional appearance for a metallic material, slightly influenced by the destruction of the base material interface. At higher maximum stress and, consequently, to large strains, a series of destructions at the interface of the two materials, of different types, were observed and will be highlighted in the paper. [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]

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]

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]

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]

For high-level radioactive waste, the French National Radioactive Waste Management Agency is currently developing a 500 m deep geological disposal facility called Cigéo. Carbon steel containers will be used to contain the wastes in the specific conditions of the disposal. The use of a sacrificial coating was studied as an additional protection for the containers against corrosion. A previous work had shown the possibility to use Zn-Al coatings in this specific medium. To optimize the coatings' performance, the cold-spraying process was considered instead of the previously used wire arc spraying because it can increase the cohesion between the particles in the coating. Moreover, three aluminum contents, i.e., 5, 15 and 25 wt.%, were considered. The characterization of the obtained coatings revealed a strongly heterogeneous composition for the lower Al content (5 wt.%), with local Al contents from 1.3 wt.% Al to 44.5 wt.% Al. The corrosion study was carried out in a specific solution mimicking the pore solution of the surrounding cementitious material designed for disposal at a temperature of 50 °C. First, the polarization curves acquired with coated steel electrodes revealed the pseudo-passive behavior of the 25 wt.% Al coating, while for the other compositions, the coating remained active. Moreover, the higher aluminum content (25 wt.%) induced an important decrease in potential, with a possible risk of hydrogen embrittlement for the protected steel. Secondly, the sacrificial properties were investigated through 6 months of experiments using coated electrodes with cross-like defects and coated electrodes coupled with bare steel electrodes. Whatever the composition of the coating, the protection was maintained, with the 15 wt.% Al coating giving the best performance. [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]

Coatings deposited by the cold particle gas spray method have shown significant potential for enhancing the properties of metals. We investigated the wear characteristics and corrosion behavior of 52100 steel coated with a mixture of Ni/chromium carbide (Ni/CrC) particles. These coatings exhibited high density and were devoid of cracks, closely adhering to the substrate's surface. Microscratch resistance testing revealed strong resilience, with the apparent friction coefficient exhibiting multiple peaks as the displacement varied. The determination of the friction coefficient, utilizing linear and rotational sliding tests, displayed a brief transition period. This occurred as the apparent contact area expanded until it reached an equilibrium state, with the large asperities being smoothed out and the remaining particles on the sliding track acting as an abrasive material, resulting in higher friction coefficient values. Electro-corrosion tests confirmed the near-intact condition of the deposited layer. Few compounds were detected in the electrolyte solution, resulting in significantly lower oxidation in the layer compared to the base material. [ABSTRACT FROM AUTHOR]

Cold spray is a rapidly developing solid-state deposition technology in recent years. It has the characteristics of low spraying temperature and high velocity of spraying particles, hence showing a good prospect for preparing metal matrix composite (MMC) coatings and bulk materials. In particular, aluminum matrix composites have received great attention in electronics, aerospace and automobile industries due to their excellent physical and mechanical properties. In this paper, the research progress of cold-sprayed aluminum matrix composite coatings and materials was systematically introduced. Firstly, state of the art on cold sprayed coatings and materials with different reinforcing phases was presented. Then, research progress on different post-spray treatments, to improve the properties of as-sprayed deposit, was briefly discussed. Finally, the application fields and problems of cold-sprayed aluminum matrix composite coatings and materials were summarized. [ABSTRACT FROM AUTHOR]

Cold spray has become a prominent deposition technology for coating, repair, and restoration in many industries, such as the aerospace, automotive, and power generation industries. It also has the potential to be used as an alternative overlay restoration for power plant components as it has minimal thermal distortion phase changes, as compared to conventional welding and thermal spray. This article aims to bridge the gap in the scientific literature by presenting a comprehensive review of cold spray in the context of power plant components. Firstly, this review examines the challenges of cold spray and subsequently elucidates effective mitigation strategies. Secondly, the review analyses the recent development of cold spray in the field of coating application. Moving forward, it investigates the integration of cold spray technology in repair applications, focusing on practical implementation and effectiveness. Finally, the review presents the overall impact of cold spray, its current outlook, and discusses future prospects. As such, the review will provide the community with a broad understanding of cold spray applications in the power plant sector. [ABSTRACT FROM AUTHOR]

Laser processing is an effective post-treatment method for modifying the structure and improving the properties of cold-sprayed coatings. In the present work, the possibility of fabricating a hard and wear-resistant Ti-based cermet coating by cold spray followed by laser remelting was studied. A mixture of titanium and chromium carbide powders in a ratio of 60/40 wt.% was deposited by cold spray onto a titanium alloy substrate, which ensured the formation of a composite coating with a residual chromium carbide content of about 12–13 wt.%. The optimal values of laser beam power (2 kW) and scanning speed (75 mm/s) leading to the qualitative fusion of the coating with the substrate with minimal porosity and absence of defects were revealed. The microstructure and phase composition of as-sprayed and remelted coatings were examined with SEM, EDS and XRD analysis. It was shown that the phase composition of the as-sprayed coating did not change compared to the feedstock mixture, while the remelted coating was transformed into a β-Ti(Cr) solid solution with uniformly distributed nonstoichiometric TiCx particles. Due to the change in microstructure and phase composition, the remelted coating was characterized by an attractive combination of higher microhardness (437 HV0.1) and lower specific wear rate (0.25 × 10−3 mm3/N × m) under dry sliding wear conditions compared to the as-sprayed coating and substrate. Laser remelting of the coating resulted in a change in the dominant wear mechanism from oxidative–abrasive to oxidative–adhesive with delamination. [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]

Purpose: Measurement of the adhesion of a Ti coating applied by cold spraying on metal substrates with different elastic modulus. An attempt to analytically describe the experimental results, considering cold gas spray parameters such as working gas, pressure p and temperature T. Design/methodology/approach: Ti coating was sprayed on flat bars made of metal: copper, magnesium, brass, titanium, Al 7075, Al 2024 and steel with dimensions of 4x50x400 mm. All coatings were applied under the same spray conditions (p = 3.8 MPa, T = 800ºC, spray distance l = 50 mm, and spray spead V = 400 mm/s). The state of plastic deformation of coatings and substrates was examined using optical methods, and the adhesion strength was measured with the POSITEST tester. Findings: The experimental results are presented graphically. The adhesion force as a function of the relative modulus of elasticity showed a maximum. At this time, the mutual penetration depth of the coating and the substrate showed a minimum. The extremes of the relationships mentioned above occurred for points where the relative modulus of elasticity took the value one. The curve described by formula (1) was fitted to the distribution of adhesion points as a function of the relative elastic modulus. The function parameter described by formula (1) is related to the spray parameters (p, T). Research limitations/implications: To achieve a better accuracy of the analytical description of the adhesion of coatings deposited with cold gas, tests should be carried out on a larger number of substrates. The validity of the presented interpretation should be checked by applying coatings from other materials. Practical implications: In coating technologies, adhesion is a key concept. A coating with high adhesion strength is used primarily in regeneration and anti-corrosion protection processes. The analytical relationship between adhesion, relative modulus of elasticity and cold gas spray parameters will significantly speed up the selection of optimal spray parameters. Cold spray technology is a cost-intensive technology, so the economic element is not without significance. Originality/value: The article presents a method for limiting the number of variables on which the quality of the applied coatings depends. The relationship between the adhesion force, the relative elastic modulus and the selected spray parameters are indicated. [ABSTRACT FROM AUTHOR]

Design of steel structures in the construction industry uses built‐up or rolled steel sections. These are processed as steel elements and connected together at joints. Massive and complex steel nodes such as those in steel frame bridges or truss structures are still manufactured by forging or casting to avoid weld seams in highly stressed areas. Since this is a manual manufacturing process, it results in increased costs and time. Cold spray (CS) technology has recently attracted attention in aerospace and automotive engineering for producing metallic, composite coatings as well as repairing the surface damage of components in service. Additive manufacturing by cold spraying can offer significant advantages with respect to other additive manufacturing methods due to higher material deposition rates (up to 14 kg/h), lower energy consumption, and deposition in solid state. So far cold spraying has not been used for 3D‐printing of typical steel constructions. In the preliminary test campaign, structural steel‐powder was investigated to evaluate their suitability for cold spraying in civil engineering applications. Simple flat specimens were used, and a range of metallographic and mechanical tests were conducted to determine the properties of the deposited coupons, such as the coating quality, layer thickness, the degree of porosity, micro‐hardness, and micro flat tensile test. This paper presents the results of the powder characterisation and the preliminary tests on the printed specimens. [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]

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. [ABSTRACT FROM AUTHOR]

Supersonic cold spray (CS) of functional nanomaterials from atomized droplets has attracted significant attention in advanced thin-film coating as it enables particle deposition with high-adhesion strength. In CS, optimum design of the supersonic nozzle (i.e., converging-diverging nozzle) is essential for accelerating particles to desired velocities. However, research on the nozzle design for supersonically spraying of "liquid droplets" for nanocoating applications is limited. To this end, we investigate the effect of nozzle geometrical parameters, including throat diameter, exit diameter, and divergent length on droplets impact velocity by numerical modeling and experimental validation, followed by a case study on nanocoating. The discrete-phase modeling was employed to study droplets' flow behavior in continuous gas flow for various nozzle geometries. The results reveal that the nozzle expansion ratio, defined as a function of throat and exit diameters, has a significant influence on droplet velocity, followed by divergent length. Noteworthy, to correctly accelerate "low-inertia liquid microdroplets," it was found that the optimum nozzle expansion ratio for axisymmetric convergent-divergent nozzles should be in a range of 1.5-2.5, which is different and way smaller than the recommended expansion ratio (i.e., 5-9) for CS of conventional micron-scale "metal" powders. Based on the simulation results, an optimum design of supersonic nozzle is established and prototyped for the experimental studies. Particle image velocimetry (PIV) was used to experimentally investigate the spray flow field and to validate the numerical modeling results. Moreover, coating experiments using the optimized nozzle confirmed the effective supersonic spraying of droplets containing nanoparticles, thereby showing the potential for advanced nanocoating applications. [ABSTRACT FROM AUTHOR]

Cold Spray Additive Manufacturing (CSAM) is a thermal spray technique that is typically used for the repair of metallic components. One of the challenges of CSAM is to improve the geometrical accuracy of the sprayed parts, along with overcoming the inferiority of the mechanical properties of the deposits by tailoring their microstructure with different deposition strategies. For this, Cu, Al, Ti, and Ti6Al4V substrates were reconstructed by two Cold Spray (CS) methods: Traditional (T) and a novel strategy, Metal Knitting (MK). The final geometry, microstructure, and mechanical properties of the reconstructed parts by these two methods were compared. Additionally, we investigated the effects of annealing on the microstructure of sprayed components and its influence on adhesion, resistance to erosion, and abrasive wear. The results indicate that annealing effectively reduces the microstructure defects of the remanufactured parts (up to 30% porosity reduction) and improves the adhesive strength (i.e., below 30 MPa for as-sprayed deposits, and up to 160 MPa for heat-treated Ti4Al4V deposits). Notably, the abrasive and erosive resistance of the Cu and Al annealed deposits sprayed by MK gave very similar results compared to their bulk counterparts, suggesting that it is an efficient method for the reconstruction of damaged parts. [ABSTRACT FROM AUTHOR]

In cold spraying, formation and adhesion of the coating is mainly due to the kinetic impact of the powders as they impinge on the substrate, at velocities above the critical value, causing substantial plastic deformation of both the particles and substrate. Most of the research around cold spraying focuses on preheating the gas before spraying; however, this article is aimed at preheating the substrate only and evaluating its effect on the microstructure of the coating. Before deposition the substrate was preheated at different temperatures to understand its effect on the corrosion behavior. The analysis shows that the powder particle could efficiently deposit, by increasing the substrate temperature up to at least 250 °C. The corrosion current density extracted from the Tafel plot shows a decreasing trend than bare 1020 steel in 3.5 wt.% NaCl solution. However, at higher temperatures the corrosion behavior detriments due to an increase in the oxygen content of the coating during deposition. An estimation of the gas velocity shows that substrate heating is beneficial in obtaining high deposition efficiencies even with low gas velocities, much below the theoretical critical velocity for nickel. [ABSTRACT FROM AUTHOR]

Nickel-based coatings are widely used as thermal barriers in several sectors thanks to their remarkable corrosion and wear resistance and outstanding stability at high temperatures. Recently, Ni coatings, produced with thermal spraying and vacuum techniques, have been investigated for solar power energy applications. In the present manuscript, low-pressure cold spray (LPCS) was used to deposit pure Nickel onto a steel substrate. The influence of gas temperature, nozzle stand-off distance, and advancing speed on morphological and mechanical properties were studied. The optimal deposition conditions were derived by ANOVA analysis. The hardness and the adhesion strength were approximately 160 HV and 26 MPa, respectively. The highest thickness obtained under the optimised deposition with a single pass was around 900 µm. [ABSTRACT FROM AUTHOR]

The cold spray technique is expected to effectively form a metallic coating with fine crystal grains originating from the microstructure of the original powder. We previously reported that a pure iron coating with fine crystal grains can be formed by the cold spray technique by using mechanically-milled pure iron powder. In this study, the tensile strength of the pure iron coating was investigated. The as-sprayed coating showed significantly low Young's modulus, tensile strength, and ductility owing to the low cohesion strength between particles. For tensile strength improvement, the coating was subjected to spark plasma sintering (SPS) treatment. As a result, the Young's modulus was considerably improved by the SPS treatments at 740 and 786°C; moreover, the tensile strength of the SPS-treated coating was approximately four times higher than that of the bulk material. In contrast, the ductility was not improved by the SPS treatment. The low ductility was likely attributed to the presence of Fe oxides at the particleparticle interface. [ABSTRACT FROM AUTHOR]

The aim of this article is to investigate the characterizations and formation mechanisms of cold-sprayed coatings using gas-atomized and electrolytic powders. The study highlights the importance of reaching the particles' critical velocity for optimal deposition. The main findings reveal that the morphology and stacking conditions of the coatings have a significant impact on their mechanical properties. Coatings made with gas-atomized powders exhibited noticeable pores and higher plastic deformation, while electrolytic powder coatings had greater density and smoother interfaces with the substrate. Adhesion strength relied on the physical bonding resulting from the plastic deformation energy between the spraying powders and the substrate. Gas-atomized powders showed higher adhesion compared to electrolytic powders, with dendritic powders resulting in lower adhesion due to dispersed impact force. The interaction between thermal and kinetic energy during the cold spraying process facilitated plastic deformation and particle deposition by softening and eroding the substrate surface. Insufficient plastic deformation with dendritic powders led to incomplete overlap, pore formation at the interface, and the persistence of the oxide layer along powder boundaries. Overall, these findings provide valuable insights into the influence of powder properties on coating morphology, adhesion strength, and overall performance, contributing to the understanding and optimization of cold spray processes. [ABSTRACT FROM AUTHOR]

The cold spray (CS) process is the latest solid-state deposition method that has gained significant awareness for the metallization of polymer matrix composites (PMCs) materials to modify their surface properties, including electrical or thermal conductivity and electromagnetic shielding. In comparison with other coating processes, CS allows for the production of metallic coatings without the necessity to reach the melting temperature of the sprayed particles and provides a way to deposit resistant materials with improved properties onto various components to minimize wear, erosion and corrosion. For the first time in the literature, this work has the innovative goal of applying the life cycle assessment methodology to the case study of the CS production process in order to ascertain whether CS could be framed in the realm of green technologies offering interesting opportunities to improve manufacturing sustainability. In particular, the environmental impact of CS associated with the metallization process of PMCs was considered in terms of energy consumption and CO2, NOx and SO2 emissions, which are used as indicators in the life cycle assessment. When compared to different coating processes, the results suggest that CS has a large potential to reduce the environmental effects connected with the products in terms of the amount of CO2 and hazardous emissions created throughout the process. [ABSTRACT FROM AUTHOR]

Cold spraying is an attractive solid-state processing technique in which micron-sized solid particles are accelerated towards a substrate at high velocities and relatively low temperatures to produce a coating through deformation and bonding mechanisms. Metal, ceramic, and polymer powders can be deposited to form functional coatings via cold spraying. MAX phase coatings deposited via cold spraying exhibit several advantages over thermal spraying, avoiding tensile residual stresses, oxidation, undesirable chemical reactions and phase decomposition. This paper presents a review of recent progress on the cold-sprayed MAX phase coatings. Factors influencing the formation of coatings are summarized and discussions on the corresponding bonding mechanisms are provided. Current limitations and future investigations in cold-sprayed MAX coatings are also listed to facilitate the industrial application of MAX phase coatings. [ABSTRACT FROM AUTHOR]

For coating deposition and additive manufacturing by cold spray, supersonic de Laval nozzles are traditionally used. The application of other configurations of the prechamber-nozzle units allows for the expansion of the technological capabilities of cold spray. In particular, the use of an ejector nozzle allows utilizing an open-type powder feeder, which does not require maintaining high pressure inside itself. In the present paper, for the first time, the possibility of application of the ejector nozzle under high-pressure cold spray conditions was investigated. A comparative analysis of the main characteristics of copper coatings deposited on aluminum alloy substrates using both the ejector and de Laval nozzles was also performed. It was demonstrated that the coatings obtained using the ejector nozzle are characterized by lower thickness, higher porosity, and similar microhardness as compared to the coatings obtained using de Laval nozzle. This development can be in demand in cases where the use of an open-type powder feeder is necessary to ensure technological simplicity of the cold spraying process. [ABSTRACT FROM AUTHOR]

This study presents a novel approach for surface repairs of high-strength, cold-worked aluminium (Al) alloys, without negatively affecting the base material strength. Low-pressure cold spraying was used to fabricate Al–Al2O3 metal matrix composite overlays, with varying concentrations of Al2O3 deposited on an Al alloy. Friction stir processing (FSP) was employed to disperse and consolidate the overlay coating on the base material. The FSP was found to improve the Al2O3 particle distribution in the coating and reduce the mean free path between Al2O3 particles. The coating hardness increased after FSP. The post-FSPed overlays also exhibited lower wear rates compared to the as-sprayed condition. Remarkable improvement was observed in the tensile properties of the coatings, which were attributed to the improved dispersion of Al2O3 particles in the matrix, while the enhanced ductility was attributed to the possible grain refinement that occurred due to the recrystallisation of Al during FSP. [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]

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]