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 compactness are also quantified and correlated to strength.

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 modelling additively manufactured geometry; however, such a data-driven modelling 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 modelling of an overlapping-track profile using a Gaussian Process Regression model. The proposed Gaussian Process modelling 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 is able to provide better predictive performance than the Gaussian superposing model alone and 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.

In this work, we propose a novel visual navigation method to estimate the state of mobile and fixed cold-spray material deposition systems using a stereo-camera sensor installed in the workspace. Unlike other visual localization algorithms that exploit costly onboard sensors such as LiDARs or fully rely on distinct visual cues on the robot and grid markers in the environment, our method significantly reduces the cost and complexity of the sensory setup by utilizing a cost-effective remote stereo vision system. This allows for the localization of the target system regardless of its appearance or the environment, and enables scalability for tracking and operation of multiple mobile material deposition systems at the same time. To achieve this aim, deep neural networks, kinematic constraints, and learning-aided state observers are employed to detect and estimate the location and orientation of the deposition system. A physical model of the system with bounded uncertainty and fusion with a remote visual sensing module is proposed. This accounts for frames in which depth estimation accuracy is reduced due to perceptually degraded conditions in the cold spraying context. The algorithm is evaluated on a fixed and mobile setup that demonstrate the accuracy and reliability of the proposed method.

The Cold spray (CS) is a promising solid-state additive manufacturing method. The interesting physics involved in the CS process including cold, high strain rate, adiabatic and severe plastic deformation results in a unique and complex structure of CS deposits at different length scales that directly determines the properties of the deposits. Therefore process- structure properties (performance) (PSP) linkages explorations are pivotal. Integrated computational materials engineering (ICME) methods in complement with experimental analyses are required to evaluate materials properties and behaviour in PSP links exploration. Finite element modelling is used to simulate the thermomechanical response of materials and evolution of field variables in CS, i.e stress, strain, strain rate, and temperature, at structural scales. Molecular dynamics modellings of nano-particle impact have provided useful insights into atomic-scale phenomena of individual particle impact while the modelling of microstructure evolution in micro and mesoscale has yet to be investigated. In this study, we developed and implemented a thermodynamic phase field simulation method to capture the structure evolution of CS composite Ni-Ti deposit upon post-spray heat treatment (PSHT) in microstructure scale. The external or internal stimuli such as heat and strain either generated in the system because of phase transformation or stored as internal energy upon CS process are accounted for. The interface mobility and microstructure development are calculated by minimization of Gibbs free energy of the system. The comparison of the simulated microstructure with experimental results confirms that the phase field modelling precisely predicts the microstructure evolution of the CS deposits upon PSHT.

Infection caused by bacterial contamination is a critical problem challenging the successful use of medical implants in orthopaedic and dental applications. Consequently, medical implants with antibacterial abilities are in high demand. Tantalum and silver have been previously characterized to have excellent biocompatibility and antibacterial ability, but due to their significantly different properties, it is challenging to manufacture Ta-Ag components via thermal processing methods. Herein, by taking advantage of the unique characteristics of cold spray (CS) technology, an antibacterial Ta-Ag coating was successfully fabricated for the first time. In the CS process, blended Ta-Ag powders with different Ag concentrations were used to fabricate CS Ta-Ag coatings. Their antibacterial ability was preliminary tested and deposition behaviour was systematically investigated. The coating significantly reduced the metabolic activity of S. aureus bacteria, and a better deposition efficiency was obtained by blended Ta-Ag powder. It was found that soft Ag could aggregate in the coating and hard Ta particles were prone to rebound, which induced the peening effect for Ag and mass loss of Ta in the final coating Moreover, the clue of metallurgy bonding between Ta and Ag was detected in the region that experienced severe deformation despite their immiscibility.

Cold spray (CS) is a solid-state process for depositing metal powder, accelerated by a high-velocity gas such that it bonds to the substrate metal through kinetic impact energy. Although the technology is finding applications in non-load bearing repair and coating applications, work is needed in the quality control procedures for CS for its use in load bearing structural applications. in this study, the viability of electrical conductivity and through thickness ultrasound wave velocity measurement methods are studied to serve as a means for nondestructive quantitative measurement methods 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 copper and aluminum samples that were manufactured using CS. Ultrasound measurements of longitudinal wave velocity and eddy current electrical conductivity measurements showed good correlation with process conditions that were varied to control particle velocity to intentionally produce samples with varying deposition quality. Influence of process conditions on particle velocity was confirmed via particle image velocimetry. Porosity, hardness, and tensile test results were further correlated to ultrasound wave velocity and electrical conductivity measurements. The results of this work show that nondestructive testing methods can be effectively used to quantitatively assess the cold spray products for quality control purposes.

Cold spray additive manufacturing technology (CSAM) is a progressive method of 3D print of metals and alloys. Its inherent work principles allow production of the components below the material melting points, thereby avoiding several undesired material degradation processes. Among other inherently associated phenomena, the work principles of CSAM involve extreme plastic deformation of the materials, triggering formation of several types of lattice defects. Positron annihilation spectroscopy (PAS) is an analytical technique capable of studying deformation on the atomic scale level, even in extremely deformed materials. In our study, the first historical analysis of CSAM materials by PAS was carried out. For the demonstration, four different base metals were selected (Al, Cu, Ni, Ti). For these, the character of dislocations and vacancies was observed and the respective densities were quantified. The results show that the extremely high strain rate in the cold spray process prevents recovery of vacancies by diffusion to sinks. The deformation-induced vacancies agglomerate into small vacancy clusters. Hence, metals deposited using CSAM contain not only dislocations but also vacancy clusters. Both kinds of defects were detected by positron annihilation spectroscopy.

In conventional powder processing, there has been considerable work on classifying feedstock powders based on particle size distribution, morphology, microstructure and composition, since these influence processability and final properties. Cold spray is a new application for powders and conventional characterization may be insufficient to assess powder cold sprayability. In particular, metallic powders have an oxide layer, which breaks during impact with the substrate or with another coating layer during cold spray; this fragmentation facilitates bonding. It has been suggested that the thickness of the oxide layer can influence the mechanism of fragmentation; thicker oxides are easier to remove, revealing clean metal surfaces that can metallurgically bond. Consequently, not all high-purity powders or powders that are stored in ambient conditions have the potential to give good coating properties after cold-spray. This work focuses on surface oxidation of the powders, characterizing the variation of oxide film aspects with size and composition of nominally pure copper powders using X-ray Photoelectron Spectroscopy (XPS). The results indicate the presence of Cu (I) and Cu (II) oxide species on the surface of as-received, naturally aged and heat-treated powders; their thickness is determined using the depth profiling feature.

As it has been demonstrated that the use of the observation equipment applied on the spray process helps to gain a better coating in terms of properties, non-intrusive observation equipment (Control Vision Inc's SprayCam) is used in the current work for the observations of the jet and particles during the spray process. The application of such in-situ observation techniques concerns the field of cold spraying and brings new insights into the formation process of cold sprayed coatings. The build-up of coatings operated with different parameters (copper powder, nozzle, etc.) are recorded with an extreme short unit of time and then analyzed with the help of digital techniques such as image processing. The basic theories on cold spraying were previously verified by simulation and then compared to experimental results considering the distribution of flying particles involving in the build-up of the coating. The accumulation of data collected by in situ processing techniques during the spray allows understanding the complete steps of the coating formation consequently could bring the entire cold spraying mechanism to a higher level of research.

In this study, microstructural characterization is conducted on WC-17Co coatings produced via High Velocity Oxygen Fuel (HVOF), High Velocity Air Fuel (HVAF), and Cold Spraying (CS). All coatings prepared were observed to be of good quality and with relatively low porosity content. SEM study showed important microstructural features and grain morphologies of each coating. While composition of feedstock material was approximately similar, elemental composition using EDS showed higher Co content and lower WC in the CS deposited coating. XRD experiment identified formation of more complex oxides and tungsten phases in coatings deposited technologies involving melting of powders such as HVOF and HVAF. These phases consisted mainly of cobalt oxides and brittle phases such as W 3 Co 3 C or W 2 C caused by decarburization of the tungsten carbide particles. Hardness of all coating samples were examined and CS deposited coating exhibited considerably lower hardness compared to the other two coating samples instead of having significantly lower porosity content. It could be contributed to dissociation and physical loss of hard carbide phase during high velocity impact of particles in CS process. It is in good agreement with detection of higher amount of cobalt in CS deposited coating material. It is strongly believed that results obtained from this study can be used for future investigation in thermo-mechanical properties of WC-Co coatings.

Alkaline water electrolysis is currently the most promising approach to produce hydrogen. However, a main limitation for large-scale application originates from the significant energy loss caused by the coverage of bubbles on the electrode surface. Here, pore-graded Ni electrodes with a positive and negative gradient porous structure that boosts the desorption and release of gas bubble are reported, resulting in a greatly advanced mass transference. The electrodes are obtained from a blend of Ni and Al via high-pressure cold spray. The gradient porosity is realized by varying the addition of Al and chemical etching. As-sprayed electrodes are annealed to eliminate the residual stress and strengthen the adhesion of layers, hence improving their durability. As a result, the electrode with a positive pore-graded structure exhibits a better HER/OER performance when tested with a carbon rob counter electrode. Notably, when tested with an annulus counter electrode of Nickel foam, the electrode with a negative pore-graded structure achieves minimal HER/OER overpotential, outperforming other porous electrodes. This is benefited from improved bubble removal and mass transference capability. All prepared electrodes showed an excellent stability that after 500 cycles of HER/OER test without a large potential fluctuation.

As an emerging additive manufacturing method, cold spray additive manufacturing (CSAM) has attracted more and more researchers’ attention due to its unique advantages. However, only a few researchers have studied the fabrication of complex structural components. Therefore, it is important to develop a general CSAM framework that is suitable for the fabrication of different shapes of workpieces. In particular, the choice for the optimal kinematic spraying parameters, the prediction of deposit evolution and the planning of spraying trajectory are the most basic and crucial. Different sub-modules are integrated in the proposed framework to solve these problems. In detail, the modeling methodology is used to obtain the optimal kinematic spraying parameters and to predict the deposit evolution in the simulation. Based on the feasible parameters, the trajectory planification methodology is used to generate the spraying trajectory for the workpiece being manufactured, especially the workpiece with complex structure. Finally, the simulation and experimental results of a fabrication for a workpiece with complex structure provide the developed system is reliable and effective. The framework developed in this paper can considered as a general tool for additive manufacturing of with complex structural workpieces in the CSAM.

The objective of this work is to assemble an aluminum alloy to a steel to reduce the final mass of this assembly. Doing that, cold spray is considered as an efficient solution. Surfaces are previously prepared with a texturing laser to improve the adhesion of the coating on the substrate. Deposits are slightly rough (Ra < 10 μm), porosity is less than 1% and adhesion is higher than 80 MPa for textured surfaces. These high values are also due to the high filling rates in holes (100% for steel and 65% for aluminum alloy). Shear values obtained through the combination of laser texturing and cold spray for multi-material assembly are of 90 MPa (a heat treatment of 3h at 300°C applied on the joining point improves mechanical strength and increases it by three). By analogy with linear joining methods such as Laser Welding (190 MPa), the values obtained in uniaxial tension by this assembly method are significantly lower (around 50 MPa). It can be explained by the nature of the joining bead, which is made of aluminum alloy.

Cold Spraying is an emerging additive manufacturing method that uses a high-speed collision of micrometre sized powders capable of producing a solid-state bonding. Such a principle has led to the recent development of a coating for various surface functionalization and additive manufacturing applications. This paper is the result of an experimental study on the evolution of the deposit properties (ultimate strength, and porosity) generated by the additive growth during cold spraying. The deposit characterization shows the existence of ultimate strength gradient. For samples taken from the bottom to the top of the deposit, the ultimate strength decreases but there is no significant change in porosity value. The porosity evolutions do not allow to establish a generalized law of variation. The numerical analysis of the additive growth shows that the thermomechanical response of the stacking powder during the additive growth can decrease the bonding capacity, the thermomechanical heating (due to the plastic work) and the gradient of thermal kinetics.

One of the main problems that slows down the implementation of the green hydrogen (H 2 ) economy is the cost of water electrolysis. While part of this cost is associated to the price of electricity, a significant part relies on the parts of the electrolyzers. Despite their advantages, Proton Exchange Membrane Water Electrolyzers (PEMWE) still have to overcome some drawbacks to reduce its H 2 production cost, while maintaining high efficiencies. For decades, thermal spraying has been used for the production of coatings all over the world because of its versatility in industry for machinery and tools preservation, surfaces protection and corrosion prevention. This study demonstrates the possibilities of Cold Gas Spray (CGS) for the cost-reductive production of a component of PEMWEs, the Bipolar Plates (BPPs), by metal 3D printing. In this process, the incorporation of a mask between the nozzle exit and the substrate can drastically transform the BPP production to a very fast and automatic bottom-up process where material is deposited layer by- layer for building up the three-dimensional flow field patterns from a flat surface. Microstructure and topography of 3D printed BPPs were inspected by microscopy techniques. For evaluating the fulfilment of BPPs requirements (interfacial contact resistance and corrosion resistance) the new BPPs were characterized following the Davies’ method and with potentiodynamic test in O 2 -saturated H 2 SO 4 solutions, respectively.

High-performance polymers such as poly(ether ether ketone) (PEEK) are appealing for a wide variety of industrial and medical applications due to their excellent mechanical properties. However, these applications are often limited by relatively low thermal stability and conductivity compared to metals. Many methods developed to metallize polymers, including vapor deposition and thermal spray processes, can lead to poor quality control, low deposition rate, and high cost. Thus, cold spray is a promising potential alternative to rapidly and inexpensively produce polymer-metal composites. In this study, we investigated the deposition characteristics of metalpolymer composite feedstock, composed of PEEK powder with varying volume fractions of copper (Cu) flake added, onto a PEEK substrate. We prepared the Cu-PEEK composite powder in varying compositions by two methods: hand-mixing the powders and cryogenically milling the powders. Scanning electron microscopy (SEM) of the feed mixtures shows that cryogenically milling the polymer and metal powders together created uniformly distributed micron-scale domains of Cu on PEEK particle surfaces, and vice versa, as well as consolidating much of the porous Cu flake. In lowpressure cold spray, the relatively large volume fractions of PEEK in the composite mixtures allowed for lower operating temperatures than those commonly used in PEEK metallization (300-500 °C). While the deposition efficiencies of each mixture were relatively similar in single-layer experiments, deposits formed after multiple passes showed significant changes in deposition efficiency and composition in PEEK-rich feedstock mixtures. SEM of deposit surfaces and cross-sections revealed multiple co-dominant mechanisms of deposition, which affect both the porosity and final composition of the deposit. Though present in all samples analyzed, the effects of cryogenic milling were more prevalent at lower Cu concentrations.

Cold spraying (CS) has proved as an attractive and rapidly developing solid-state material deposition process that allows for fast formation of high quality, large 3D volume objects. Low risks of undesirable heat effects lead to increased interest in CS-based rapidly additive manufacturing (AM). However, by continuous powder spraying and high-pressure gas operation, cold spray additive manufacturing (CSAM) in terms of shape building is rather sensitive to operating parameters and imposes high requirements on the control of process conditions and locally needed kinematics. Every step of the manufacturing process therefore needs to be well conceived and planned, especially with regard to the toolpath planning and implementation. This is not only essential to meet basic performance requirements, but also needed to realize the desired accuracy. In order to tackle above needs, the present study presents a new toolpath planning method for 3D volume build-up to improve manufacturing accuracy and flexibility by cold spray additive manufacturing. Applied benchmarking tests prove acceptable shape accuracy and demonstrate that the current method can enhance the capabilities of CSAM for nearnet shape construction. This implies that careful planning and manufacturing strategies should enable to overcome the challenges associated with CSAM.

Cold spray (CS) technology has proven an enormous potential in the production of composite coatings, enabling a production of materials with superior qualities such as enhanced tribological behavior. This study aims to investigate the tribological properties of CS Al-based composite coatings reinforced by quasicrystalline (QC) particles. Two different Al alloys were used as the matrix, AA 6061 and AA 2024, and mixed with Al-based QC particles (Al-Cr-Fe-Cu) at different Al/QC ratios. A room-temperature ball-on-disc test was then used to evaluate the wear resistance of the CS composite coatings in air and compared to those of the CS non-reinforced Al alloy coatings as well as cast counterparts (AA 6061-T6). We have demonstrated that CS could be employed to produce dense and thick Al-QC composites. Further, the addition of the QC particles into the structure increased the wear resistance of the matrix resistance up to 8 times.

Direct cold spray deposition of Cu was not possible on carbon fiber-reinforced polymer composites (CFRPs) with thermosetting polymer as the matrix material due to substrate erosion. In a recent study, an epoxy-CFRP was successfully metallized through a hybrid coating process that involves three consecutive coating steps: (i) electroless deposition, followed by (ii) electrodeposition, and finally (iii) cold spray. In this present study, for the reduction of the coating process steps, a duplex metallic coating was developed on an epoxy-CFRPs by cold spray deposition of tin (Sn) to fabricate a continuous metallic interlayer, followed by Cu electrodeposition (i.e., SnCS-CuEP). The tensile adhesion bond strength and the electrical resistivity of the duplex coating were investigated. It was found that cold-sprayed Sn coating failed adhesively in the absence of the electrodeposited Cu coating. After the electrodeposition of Cu, cohesive failure of the cold-sprayed Sn coating took place. A “dissolution-deposition” mechanism has been established to explain the cohesive failure of the coldsprayed Sn coating after electrodeposition. The cohesive strength of the Sn coating is slightly higher than that of the previously fabricated three-step coating system. The electrical conductivity of the electrodeposited Cu coating was found to be 90% of bulk Cu. These results suggest that a duplex SnCS-CuEP coating can be fabricated on epoxy-CFRPs with relatively high electrical conductivity and slightly enhanced adhesion properties as compared to multilayered coatings fabricated using a three-step electroless deposition-electrodeposition-cold spray process.

In high-pressure cold spray, the enthalpy of the particle carrier gas has a significant effect on the propellant gas conditions and ultimately on particle impact velocities and temperatures. Through modelling and experimentation, the current work demonstrates that in low-pressure cold spray, the particle carrier gas enthalpy has a minimal effect on the particle velocity and is rather limited to affecting the particle impact temperature. Consequently, particle impact temperature can be controlled independently from impact velocity. This is a valuable tool when dealing with temperature sensitive substrates: low propellant temperatures can be used in combination with high particle temperatures enabling particle deformation while minimizing substrate heat input. Particle preheating was used to inject pure aluminum particles in a commercial low-pressure cold spray to temperatures up to 500°C. This was accomplished without clogging because of the development of a novel particle preheater, which eliminated the particles exposure to hot metal surfaces. Even after substantial spray time, no evidence of wear or clogging was found. The particle preheating resulted in a deposition efficiency increase of 3.6 times when compared to the injection of room temperature particles.