Cold Spray Additive Manufacturing Research Articles

Cermet Systems: Synthesis, Properties, and Applications

Cermet is an advanced class of material consisting of a hard ceramic phase along with a metallic binding phase with the combined advantages of both the ceramic and the metal phase. The superior properties of this class of materials are particularly useful in high-temperature, tribological, and machining applications. This review paper seeks to provide a comprehensive overview of the various cermet systems. More specifically, the most commonly used cermet systems based on tungsten carbide (WC), titanium carbide (TiC), titanium carbonitride (TiCN), and aluminum oxide (Al2O3) are discussed based on their development, properties, and applications. The effect of different metallic binders and their composition on the tribological and mechanical properties of these cermet systems is elaborated. The most common processing techniques for cermet systems, such as powder metallurgy (PM), reaction synthesis (RS), thermal spray (TS), cold spray (CS), and laser-based additive manufacturing techniques are discussed. The influence of the processing parameters in each case is evaluated. Finally, the applications and challenges of cermet systems are summarized.

Residual stress investigation in the metallic coating approach of micro-sized particles on the substrate: cold spray additive manufacturing

ABSTRACT Recently, copper and its alloys have been widely used as coating materials due to their high applications in industries and the medical sector. Meanwhile, it is necessary to investigate several stresses induced in such coatings, especially residual stress (RS). Furthermore, this RS can influence the integrity of a coating or repair. The RS is favourable for fatigue life, fatigue strength and resistance to crack under environmental assistance. Meanwhile, the cold spray additive manufacturing approach (CSAM) has been widely adopted for successful metallic coating. The deposition phenomenon is due to the high-velocity impact with a high strain rate that introduces different stresses in the coating and substrate. In this study, both experimental and numerical approaches were adopted to investigate the RS in coating. A finite element approach called Abaqus/Explicit has been used to validate the residual stress under high-velocity impact. The experimental techniques, i.e. X-ray diffraction, scanning electron microscopy, Debye-Scherrer μ-X360n analyser have used to investigate the deposition of cold spray. Numerical output gives minute deviation of RS from the experimental one. It has been found that sufficient RS is induced to enhance the coating life used for several engineering and medical aspects along with improved fatigue life and strength.

High-Speed Micro-Particle Motion Monitoring Based on Continuous Single-Frame Multi-Exposure Technology.

The impact phenomena of solid micro-particles have gathered increasing interest across a wide range of fields, including space debris protection and cold-spray additive manufacturing of large, complicated structures. Effective motion monitoring is essential to understanding the impact behaviors of micro-particles. Consequently, a convenient and efficient micro-particle motion monitoring solution is proposed based on continuous single-frame multiple-exposure imaging technology. This method adopts a camera with excellent low-light performance coupled with high-frequency light-emitting diode (LED) flashes to generate short interval illumination. This technology can, in theory, achieve 1 million effective frames per second (fps) and monitor particles as small as 10 microns with speeds up to 12 km/s. The capabilities of the proposed method were validated by a series of micro-particle motion monitoring experiments with different particles sizes and materials under varying camera configurations. The study provides a feasible and economical solution for the velocity measurement and motion monitoring of high-speed micro-particles.

Electrochemical Deposition of Pure-Nickel Microstructures with Controllable Size.

Pure nickel microstructures have been widely used in MEMS and have great application potential as a sacrificial mandrel for fabricating terahertz micro-cavity components. The performance of MEMS and terahertz micro-cavity components can be significantly improved through the use of high-quality pure nickel microstructures. Up to now, microfabrication techniques, such as laser micromachining, wire electrical-discharge machining, and cold-spray additive manufacturing, have been used to machine various types of such microstructures. However, huge challenges are involved in using these micromachining techniques to fabricate pure-nickel microstructures with controllable size and good dimensional accuracy, surface roughness, and edge radius. In this paper, taking the example of a pure-nickel rectangular mandrel that corresponds to the size of the end face of a 1.7-THz rectangular waveguide cavity, the machining processes for the electrochemical deposition of pure-nickel microstructures with controllable size, high dimensional accuracy, and good surface roughness and edge radius are discussed systematically. This proposed method can be used to manufacture various types of high-quality pure-nickel microstructures.

High Modulus Steel Produced by Cold Spray Additive Manufacturing

High Modulus Steel Produced by Cold Spray Additive Manufacturing

Cold Spray Additive Manufacturing of CoCrFeNiMn High-Entropy Alloy: Process Development, Microstructure, and Mechanical Properties

Cold Spray Additive Manufacturing of CoCrFeNiMn High-Entropy Alloy: Process Development, Microstructure, and Mechanical Properties

Microstructure and Mechanical Properties of Ti–Ta Composites Prepared Through Cold Spray Additive Manufacturing

Microstructure and Mechanical Properties of Ti–Ta Composites Prepared Through Cold Spray Additive Manufacturing

Study of Low-Pressure Cold Spray Additive Manufacturing: Investigation of Kinematic Spray Parameters on Deposition and Properties.

Low-pressure cold spray (LPCS) has broadened the application field of cold spray owing to its portability and low cost. For additive manufacturing (AM) based on LPCS (LPCSAM), it is important to investigate the effects of parameters such as temperature and pressure of the gas, stand-off distance, gun traverse speed, and the number of scanning passes of the gun on the deposition and properties. This study aims to determine the optimal kinematic spray parameters for spraying Cu+Al2O3 powder onto an aluminum substrate through LPCS, so as to prepare for the next AM work. The deposition mass, deposition rate, microhardness, and roughness under different spraying conditions were studied. The best spraying effect, with a high deposition rate and without nozzle clogging, was obtained at a nitrogen pressure of 0.9 MPa and a temperature of 400°C.

Cold Spray Additive Manufacturing of Ti6Al4V: Special Nozzle Design Using Numerical Simulation and Experimental Validation

Cold spray additive manufacturing (CSAM) shows great potential in titanium-alloy production as it is a solid-state process. However, data published so far have demonstrated the difficulty of producing dense and high-strength Ti alloy parts. Our previous studies have shown that nozzle design together with high-cost helium propulsive gas plays a crucial role in particle acceleration. In this work, special nozzles for Ti alloy were designed and validated experimentally with commercially available Ti6Al4V powder. Simulation results show that particle impact temperature increases remarkably for a long convergent length, while particle kinetic energy slightly increases, which is validated by experiments. The relationship between the particle impact temperature and practice diameter shows the first increase and then decrease. The experimental results show that as the nozzle convergent section becomes longer, the edges of the single-pass deposits become smoother, and the width, density, deposition efficiency, and microhardness of the single-pass deposits increase.

A sustainable ecofriendly additive manufacturing approach of repairing and coating on the substrate: cold spray

ABSTRACT In this study, surface modification and deformation behaviour of different engineering materials were microscopically examined by an approach called cold spray additive manufacturing (CSAM). The CSAM is a layer-by-layer deposition technique for repairing and coating the deteriorated or dimensionally unstable surface. Furthermore, in this study, both the experimental and numerical investigation have been carried to understand the surface modification approach. In the experimental procedure, the de Laval nozzle accelerates the microsize particle at a high velocity on the substrate to obtain the uniform surface coating. Engineering materials like copper, aluminium, titanium and mild steel were probed with different ranges of velocities. Additionally, an explicit/Abaqus finite element approach was used to investigate the bonding between particle and substrate by using the high velocity of particles. At the interface, refining meshing size reduces the beginning velocity for adiabatic shear instability (ASI). For the different combinations of particles and substrates like copper/copper, aluminium/aluminium, titanium/aluminium, aluminium/ titanium, and copper/mild steel at perpendicular impact, the adiabatic shear instability was numerically estimated. Deformation behaviour for multi-impact has also been seen with different particle diameter sizes to determine coating phenomenon. Furthermore, the characterisation technique called scanning electron microscopy (SEM) also showed the uniform coating on the substrate.

Fundamental Study on the Effect of Nozzle Cross-Sectional Geometry on Molding Patterns of Copper in Cold Spray Additive Manufacturing

Cold spray (CS) is a coating deposition process in which material particles in a solid state are impacted onto a substrate. Cold spray additive manufacturing (CSAM) is attracting attention as a new method for additive manufacturing, an additive manufacturing technology that takes advantage of the features of CS. Compared to other metal AM processes, the advantages of CSAM include reduced manufacturing time, unlimited product size, flexibility to adapt to complex geometries, and suitability for damaged component repair. On the other hand, the coating profile deposited by CS becomes triangular due to the decrease in particle velocity near the nozzle tube wall caused by tube friction and the decrease in the number of particles from the center of the nozzle to the edge of the nozzle. Therefore, the cross-section of the CSAM modeling object becomes sharply triangular as coatings are laminated. In this experiment, the rectangular nozzle, which is effective in flattening the spray pattern, is traversed in the short side direction for molding. The behavior of the working gas and copper particles on the molding pattern of the molding object at each nozzle was investigated and discussed using Computational Fluid Dynamics (CFD) analysis. As a result, the molding pattern obtained by traversing the rectangular nozzle in the short side direction was relatively flatter.

Effect of carrier gas species on the microstructure and compressive deformation behaviors of ultra-strong pure copper manufactured by cold spray additive manufacturing

Cold spray (CS) which has recently become a promising additive manufacturing (AM) technology, was used to fabricate ultra-strong pure copper. In addition, the effects of carrier gas species on the microstructural characteristics, mechanical properties and deformation mechanisms were systemically explored. The CSAM copper manufactured with N2 carrier gas reveals a heterogeneous bimodal microstructure consisting of ultra-fine grains at the particle interface and relatively coarse grains in inner particles. With He carrier gas, a homogeneous grain structure consisting of ultra-fine grains in most areas was obtained. Compressive tests showed that N2 and He carrier gasses enabled ultra-high yield strengths of 340 and 415 MPa, respectively. These values are comparable to severely plastic deformed copper, which has extremely low ductility and shape fidelity. On the other hand, both samples showed a strain-softening phenomenon that does not commonly occur at room temperature. The deformation microstructures revealed that dynamic recovery (DRV) and dynamic recrystallization (DRX) phenomena were generated despite being deformed at room temperature. Based on the above findings, the overall deformation mechanisms according to the carrier gas species in the CSAM copper manufacturing process were discussed. Furthermore, the work hardening and softening behaviors of CSAM Cu are predicted by using a constitutive equation .

Crystal plasticity finite element investigation of deformation of single crystal copper during cold spray

Over the past decade, cold spray (CS) process quickly emerges as an attractive additive manufacturing technology to fabricate individual components along with repairing damaged components. In comparison with fusion-based high-temperature additive manufacturing processes, the feedstock remains solid throughout the deposition process with low oxidation, minimal microstructural and chemical degradation in the final component. Considering the small size of cold spray particles (10–50 µm), the dependence of plastic behaviour on the crystalline orientation at high-velocity impacts needs to be investigated. In this work, we present a crystal-viscoplasticity model with Johnson-Cook type strain-rate and temperature dependence developed for metals with low stacking fault energy (SFE). Through the numerical study, a dependence of the dominating bonding mechanism on the crystal orientation was observed. Some orientations showed higher localized plastic deformation than others. For instance, for FCC copper particle, [ 1 ̅ 11 ] orientation often exhibited better bonding characteristics than [ 100 ] and [ 110 ] orientations. Additionally, the effect of substrate crystallographic orientations on particle bonding was also clarified in this work. The incorporation of the explicit microscopic information in the present study provides important insights into the role of crystal-scale micro-mechanics in the deformation behaviour during cold spray additive manufacturing. • A crystal plasticity model with Johnson–Cook-type hardening behaviour has been implemented. • A dependence of particle and substrate crystallographic orientation on particle bonding was observed. • Explicit microscopic information is important for modeling particle deformation during cold spray process.

Bonding behavior of Bi-metal-deposits produced by hybrid cold spray additive manufacturing

Cold spraying (CS) is one of the most recently used additive manufacturing (AM) processes that allow forming large 3D objects efficiently without severe thermal effects. However, due to some limitations of the CSAM process, it is difficult to achieve the desired geometry with high precision. As a potential solution to this issue, CSAM process coupled machining, that is, hybrid addition and subtraction manufacturing, is proposed to achieve desired accuracy and reliable shape. Therefore, it is necessary to assess the mechanical reliability of multilayer deposits deposited by CSAM + machining processes before that. In this work, different bi-deposits were obtained via hybrid CSAM. The adhesion performance at the bonding interface of bi-deposits was assessed by mechanical measurements including tensile and shear failure tests. The morphology of fracture surfaces was observed by scanning electron microscope. The results showed that CSAM bi-deposits with different materials and different interface states had different adhesion effects: the adhesion effect of soft/soft bi-deposits was the best, followed by hard/hard bi-deposits, and hard/soft bi-deposits were the worst. This is due to the fact that hard CS deposits are difficult to deform, making it difficult to embed with particles and build a good bonding; The bonding interface without any treatment had the best adhesion effect, followed by the milling + grit-blasting surfaces, and the milling surfaces performed the worst. The interface’s roughness is the major influencing factor. Roughening of bonding interface promotes more embedding and interlocking effect, which improves bonding strength.

Toolpath planning for cold spray additively manufactured titanium walls and corners: Effect on geometry and porosity

Cold spray additive manufacturing (CSAM) is a solid-state deposition process well-suited to titanium that has the potential to make large, near-net-shape parts at high productivity. However, further research is required to truly accomplish the freedom of design expected from CSAM and, in particular, to address how to manufacture a specific 3D object with minimal porosity. Therefore, this paper focuses on understanding how tool path planning strategy and robot kinematics affect the geometry and porosity distribution in a 3D object. Square titanium frames were manufactured layer-by-layer using a continuous tool path planning strategy in which the contour spray angle, traverse speed and corner smoothing radius were varied selectively. The sample geometry was analysed by 3D laser scanning, and the capacity to produce straight, vertical walls and square corners were demonstrated. The total porosity in the manufactured objects was measured using the Archimedes’ principle, further investigated by metallographic cross-section analysis, and then validated by X-ray computed tomography on selected samples. Porosity was distributed layer by layer, creating a fishbone structure in the cross-section with higher porosity between the layers and near the edges of the walls and corners. The influence of robot kinematics and toolpath planning on forming underbuilt and overbuilt structures and how they influenced porosity development are also discussed. The knowledge generated from this research can significantly influence the development of tool path planning strategies in CSAM, providing the means to produce improved near-net-shapes with controlled porosity formation.

Polymer metallization via cold spray additive manufacturing: A review of process control, coating qualities, and prospective applications

Polymer metallization via cold spray additive manufacturing is an emerging thermal spray approach for deposition of thick metallic coatings on polymers and fiber-reinforced composites that promises high productivity, ecofriendliness, and scalability of the coating process. In polymer metallization via cold spray, solid metallic powder is accelerated by a supersonic stream of preheated gas and propelled toward a polymer substrate, where it is built layer-by-layer via impact-induced heating and particle deformation. Since the pioneering study at Cambridge in 2006, nearly 50 experimental reports on polymer metallization via cold spray have been published, half of which have appeared within the past three years. This review distinguishes cold spray from other thermal spray methods, analyzes the peculiarities of cold spraying on polymers and fiber-reinforced composites, outlines the historical establishment of the field, and summarizes the available literature on polymer metallization via cold spray. The major focus here is on the influence of the cold spray process parameters on the deposition efficiency, adhesion strength, electrical conductivity and other properties of metallic coatings formed on polymers and fiber-reinforced composites. The promising applications of cold spray additive manufacturing in lightning strike protection, electroplating, osseointegration, antifouling, antivirus, e.g. anti-Covid-19 surfaces, and other surface functionalizations have been reviewed. Finally, recommendations were given on how to enhance the data reuse in future studies on polymer metallization via cold spray.

A convolution-based approach to cold spray additive manufacturing

Cold Spray Additive Manufacturing (CSAM) is a well-established technology that has recently attracted interest for forming 3D shapes in a fast and scalable fashion. Nonetheless, the resulting surface of cold sprayed parts normally requires post-deposition machining to achieve the desired surface finish. In this work, a convolution-based digital framework for CSAM yield and surface finish prediction able to calculate the optimal interline distance to reduce surface waviness was developed. The aim is to minimise post-deposition treatments, thereby reducing production time, material waste and costs. This method is applicable beyond CSAM and can be of interest for other additive manufacturing techniques.

Study of microstructural and mechanical anisotropy of 7075 Al deposits fabricated by cold spray additive manufacturing

In this work, microstructural and mechanical anisotropy in cold spray additively manufactured (CSAMed) 7075 Al deposits were studied in detail. For clarity, spray gun traverse direction, pass interval direction and deposition direction were defined as the X, Y and Z, respectively. Tensile tests for two different groups of samples were carried out in different orientations to study the in-plane and three-dimensional anisotropy of CSAMed 7075 Al deposits. Fracture morphology of the specimens was studied by optical microscopy (OM) and scanning electron microscopy (SEM). Transmission electron microscopy (TEM) was employed to examine particle–particle interface bonding. The results revealed that there exists a strong microstructural and mechanical anisotropy in the CSAMed deposits. The ultimate tensile strength (UTS) gradually decreased as the tensile direction changed from X/Y to Z direction. Further, crack propagation behavior was uniform in XY plane but a strong anisotropy was resulted in the planes that were perpendicular to XY plane. The underlying reason and possible mechanism related to this anisotropy was discussed in detail.

Cold Spray Additive Manufacturing: Microstructure Evolution and Bonding Features

ConspectusMost metal additive manufacturing (AM) methods involve the melting or sintering of feedstock powder or wire using an energy source (laser, electron beam, or electric arc). Solid-state AM, sometimes also known as non-beam-based AM, is a process in which the deposited material does not melt and is built up layer-by-layer, typically through severe plastic deformation. Initially considered to be a coating technique, by virtue of its high deposition rate, cold spray additive manufacturing (CSAM) is attractive as a solid-state AM technology. In the CSAM process, metal powder particles are impacted onto a substrate at a supersonic velocity and relatively low temperature. The CSAM process reduces or eliminates many problems associated with melting or beam-based AM methods, making the CSAM technically attractive for a wide range of applications, such as in the aerospace, automobile, marine, biomedical, machinery, and energy sectors.In this Account, the author briefly reviews the setup of a cold spray system and discusses the strengths and drawbacks of CSAM compared with thermal sprays and beam-based AM processes, as well as applications in relevant industries. The author summarizes the bonding mechanisms proposed for the cold spray process. The focus of this Account is to review the microstructure evolution of several typical model metals (copper, nickel, aluminum, and titanium) during the cold spray process. The author shows a large variety of microstructure characteristics (recrystallized grains, annealing twins, shear bands, submicron-sized grains, deformation twins, and nanometer-sized grains) in cold-sprayed copper, dynamic recrystallization of cold-sprayed nickel, and the formation of refined grains even below 10 nm in size in cold-sprayed aluminum. The magnitude of the stacking fault energy of as-sprayed materials considerably influences the microstructure after cold spray and postprocessing. Due to the relatively low thermal conductivity and ductility of titanium, cold spraying of titanium shows both a high deposition efficiency and relatively high porosity of as-sprayed parts, as well as a heterogeneous microstructure. Moreover, the Account introduces the postprocessing heat treatment and nanoindentation characterization of cold-sprayed materials. A fundamental understanding of microstructure evolution during and after the cold spray process is essential for optimal mechanical properties. Lastly, the author provides a perspective on applying old lessons and taking advantage of new techniques and materials, including powder characterization, hybrid additive manufacturing, machine learning for searching process windows, nanomechanical testing, and emerging alloys (high-entropy alloys, nanocrystalline alloys, and quasicrystals), to advance the research and applications of CSAM.

Cold spray deformation and deposition of blended feedstock powders not necessarily obey the rule of mixture

Cold spray additive manufacturing has the potential to be used in repair and manufacturing of a wide variety of parts and coatings including composite coatings . Understanding materials' fundamental behaviour during deposition is essential for the process development which was not addressed enough for mixed powders. One objective of this study is to explore the process-structure relation of mixed Ni-Ti powders in cold spray to provide a methodology to achieve a coating with the composition of interest. Single/multi-particle impact experiments and FEM modelling were employed to investigate the particle deformation and microstructure evolution using SEM, EBSD and EDS. The sprays of mixed powders were performed using a wide process parameter window and the deposition characteristics and composition variation as a function of process parameters were explored. The experiments and modelling showed that splats in dissimilar multi-particle impacts experience more deformation than those of similar materials, which in microstructural scale translates to variation of deformation mechanism from single-component coatings. This results in higher degree of grain refinement, specifically for Ti in the composite coating with an average grain size of 500 nm. Experiments showed that the DE of mixed powder deviates from the rule of mixture, which means the critical velocity of Ni-Ti powder is different from the single-component Ni and Ti coatings due to material interactions. Findings showed there is a process parameter criteria for which relative DEs of components, and thereby composition of composite coatings, remain at almost constant ratios. η (impact velocity/critical velocity ratio) is used as a measure to predict qualitative composition variation as a function of spraying parameters and powder characteristics. • Process-structure relation of cold sprayed mixed powders is explored experimentally & numerically. • Process criteria are proposed to predict composition variation using V and V cr . • A methodology is proposed to achieve a composite with the composition of interest. • Materials interaction & intrinsic materials properties result in change of V cr & DE deviation from mixing rule.