Spray Additive Manufacturing Research Articles

A Phase Variation-Based Smart Structure for Crack Detection on Metals Using Cold Spray Additive Manufacturing

A Phase Variation-Based Smart Structure for Crack Detection on Metals Using Cold Spray Additive Manufacturing

Printability of low-cost pre-heat-treated ball milled Al7075 powders using compressed air assisted cold spray additive manufacturing

• Cold spray printing using low-cost ball-milled powders was successfully demonstrated. • As-received powders were irregular in shape and size, significantly work-hardened, and consisted of very fine precipitates in its microstructure that affected its printability. • Annealing the powders resulted in significant reduction in hardness and coarsening of precipitates, thereby facilitating cold spray printability. • A deposition efficiency of 59% was realized with pre-treated powders using compressed air as propulsive gas, which is higher than the deposition efficiencies reported in published literature. A successful attempt at the cold spray additive manufacturing (CSAM) of low-cost ball milled Al7075 powders using air as the carrier gas is demonstrated. The irregular shape and hardness of the as-received powders are identified as a primary obstacle to the successful printability which demonstrated 0% deposition efficiency. Thus, different annealing procedures are suggested as an optimization technique to facilitate printing. These annealing procedures are compared and contrasted using differential scanning calorimetry (DSC) and the hardness/printability of the annealed powders are correlated exactly to the enthalpies in the low temperature i.e., <300 °C region. The annealing procedure of 300 °C for 4h (referred to as the C4 powder) is found to be the most optimal based on the combination of hardness, deposition efficiency, porosity and enthalpy values. On printing, the C4 powder also shows the best combination of good quality edge spraying, highest deposition efficiency of 59% and low porosity of 1.80%. Finally, while the microstructure of the C4 powder particles is retained in the microstructure of the printed part, the hardness of the printed part is higher than that of the C4 powder. This is attributed to a combination of deformation strain induced within the interparticle boundaries during the cold spray process and excellent interparticle interlocking.

Bulk-like ductility of cold spray additively manufactured copper in the as-sprayed state

• As-sprayed CSAM Cu can exhibit a simultaneous high ductility and strength. • This is triggered by a specific topology of bimodal grain size. • The deposits have a high thermal conductivity comparable to bulk. • They are perfectly gas-tight with He leakage rate of less than 1 × 10 −7 mbar•l/s. • All these were achieved with 99% efficiency using inexpensive nitrogen. In recent years, cold spray process is increasingly used for additive manufacturing of metallic components, referred to as cold spray additive manufacturing (CSAM). Unlike the fusion-based AM processes, CSAM is achieved in a solid-state, bringing several advantages such as the absence of severe oxidation or phase composition changes. At the moment, the main limitation of CSAM is the generally low ductility of the as-sprayed deposits. In this paper, using Cu as a model material, we demonstrate a way to overcome this limitation. Importantly, a high ductility of the deposits in their as-sprayed state is achieved without a trade-off in mechanical strength. Furthermore, we show that without any post-heat treatment, the properties of CSAM Cu are comparable to bulk, non-AM Cu.

Environmental impact of cold sprayed 3D-Printed aluminium metal parts

Cold spray additive manufacturing (CSAM) is a solid-state deposition process that is advantageous in depositing metal powders of heat- and oxygen-sensitive materials such as aluminium. CSAM is being considered for many applications. However, the environmental impact of CSAM of metal parts production are not well known. Therefore, the environmental impact of CSAM, in which energy consumption and CO2 emission are used as indicators in the life cycle assessment are considered in this study. We have calculated the specific energy consumption of CSAM at increasing process rate of 0.273 kg/h, 0.550 kg/h and 0.753 kg/h to be 373.0 MJ/kg, 225.1 MJ/kg, and 178.7 MJ/kg, respectively. The production of aluminium parts of different shapes was used for the cradle-to-grave life cycle analysis of machining and CSAM at different process rates. We have found that increasing process rates in CSAM of aluminium production as the route that allows less energy consumption and carbon dioxide emission compared to reducing the material used. This provides a route for optimising the layer thickness by increasing the process rate and lowering the environmental impact by reducing the number of layers required to build the parts in additive manufacturing.

SPH modeling and investigation of cold spray additive manufacturing with multi-layer multi-track powders

Cold spray (CS), as a new solid-state additive manufacturing technique, involves complex phenomena like high-speed impacting of micro-powders, large material deformations, phase change and jet generation. The CS process is difficult to be accurately simulated, and the underlying coating mechanisms, especially for multi-powders CS, have not been well understood. As a Lagrangian and particle method, the smoothed particle hydrodynamics (SPH) method has natural advantages in treating large deformations and capturing moving interfaces. In this work, we present an improved SPH approach to implement three-dimensional particle modeling and study of the multi-layer multi-track CS problem. The kernel gradient correction (KGC), adaptive smoothing length and the constitutive model are integrated in the improved SPH. The contour profile and width thickness ratio of the deformed powder obtained by the present simulation are very close to the experimental results. The bonding behaviors in a single powder CS with different materials are first explained where the critical velocities for different materials are obtained. Furthermore, coating behaviors in CS with different layers and tracks of powders are comprehensively analyzed. Some typical deformation parameters of the powders track with regard to an increasing impacting velocity are attained. With the present numerical model, a larger scale multi-layer multi-track CS is promising to be reproduced with some parameter windows predicted, which is greatly helpful to CS operations.

Numerical Study on Particle Behavior and Deposition Accuracy in Cold Spray Additive Manufacturing

Cold Spray additive manufacturing (CSAM) is an emerging technique to fabricate freestanding objects by depositing solid-state layers of materials. Thanks to its remarkable deposition rate and maneuverability, it can be tailored to manufacturing intricate geometries in aerospace industries. In comparison to other additive manufacturing techniques, it is the processing speed, solid-state deposition, and the cost that make CSAM unique. In this study, CSAM process was modeled for a system comprised of a high-pressure cold spray gun with axial powder injection. To represent the flow structure around the already built objects and the deposited layers of CSAM, three walls with different profiles are placed on a flat substrate. In this work, the gas-particle behaviors are studied at the vicinity of these non-axisymmetric objects that can be generalized to more complex geometries and the applications of CSAM. The model is 3D and aluminum and copper powders were used for the feedstock. The particles’ conditions upon impact, such as particles’ footprint and normal impact velocities are studied. The numerical results show that the deviation of particles which is caused by the supersonic flow inside the nozzle and the shock waves outside the nozzle defines the accuracy of the deposition. Furthermore, the results manifest the particle’s material and size have a significant influence on the acquired velocities and trajectories of the particles, and consequently on the resolution of the process. It is found that the profile of the deposited layers has some effects on the gas flow near the substrate which plays a role in the dispersion of fine particles.

The Study of Assessment Parameters and Performance Measurement of Cold Spray Technique: A Futuristic Approach Towards Additive Manufacturing

In recent years, high-performance additive manufacturing (AM) is being extensively investigated by the virtue of its unique benefits over traditional manufacturing processes. Complex components of Ti, Fe, Ni alloys can be manufactured with ease; however, other nonferrous alloys such as Al alloys, Mg alloys, and Cu alloys have the melting tendency during processing by laser, electron beam, or arc, hence not appropriate to be manufactured using additive manufacturing. The most useful and powerful tool recognized in AM in the last decade is the cold spray process. This paper puts forth a review of recent research innovations and the concept to build new materials in the field of AM technology. The author has highlighted the important properties including retention of original feedstock particles and oxide-free surface deposits during the entire coating process. The present research work focuses on the basic principle, bonding mechanism and impact phenomenon, and effect of nozzle parameters on mechanical properties of deposits associated with cold spray additive manufacturing. Furthermore, the concept to develop well-bonded coated deposits and its metallurgical behavior have also been studied. Various aspects of repair and maintenance against corrosion and wear along with strength and geometry restoration have also been highlighted in this paper.

Interparticle bonding and interfacial nanocrystallization mechanisms in additively manufactured bulk metallic glass fabricated by cold spray

Amorphous Zr-based bulk metallic glass deposit was produced by cold spray additive manufacturing. The bonding mechanism of metallic glass particles was systematically investigated through studying the deformation behavior of individual particles after deposition. We revealed two collective particle bonding mechanisms that contributed to the formation of metallic glass deposits, i.e., high-velocity impact induced localized metallurgical bonding at the fringe of the interface, and high particle temperature induced viscosity reduction and the resultant annular metallurgical bonding band. Moreover, the dynamic evolution mechanism of the amorphous phase into nanocrystal structures at severely deformed interfacial regions during cold spray was carefully investigated. For the first time, we observed different amorphous/nanocrystal structures in cold sprayed metallic glass deposits, which can represent different evolution stages in nanocrystallization process. Based on the observation, it is inferred that the nanocrystallization process can be divided into following three stages: composition segregation, the formation of ordered 1D and 2D transition structures, and 3D nanocrystals. The current study provides new insights into the bonding mechanisms and the mechanistic nanocrystallization origins in cold sprayed bulk metallic glass deposits.

Metal Knitting: A New Strategy for Cold Gas Spray Additive Manufacturing.

Cold Spray Additive Manufacturing (CSAM) is an emergent technique to produce parts by the additive method, and, like other technologies, it has pros and cons. Some advantages are using oxygen-sensitive materials to make parts, such as Ti alloys, with fast production due to the high deposition rate, and lower harmful residual stress levels. However, the limitation in the range of the parts’ geometries is a huge CSAM con. This work presents a new conceptual strategy for CSAM spraying. The controlled manipulation of the robot arm combined with the proper spraying parameters aims to optimize the deposition efficiency and the adhesion of particles on the part sidewalls, resulting in geometries from thin straight walls, less than 5 mm thick, up to large bulks. This new strategy, Metal Knitting, is presented regarding its fundamentals and by comparing the parts’ geometries produced by Metal Knitting with the traditional strategy. The Metal Knitting described here made parts with vertical sidewalls, in contrast to the 40 degrees of inclination obtained by the traditional strategy. Their mechanical properties, microstructures, hardness, and porosity are also compared for Cu, Ti, Ti6Al4V, 316L stainless steel, and Al.

Numerical study of multilayer cold spray additive manufacturing with oblique impacting powders using the SPH method

<p indent="0mm">As a novel solid-state additive manufacturing technique, metal powder cold spray (CS) can rapidly deposit materials and be suitable for large-scale manufacturing of metal structures. Hence, the CS technique has attracted considerable interest in engineering and science. CS involves several complex processes, such as high-velocity impacting of metal powders, large material deformations, phase change, and jetting, which are difficult to simulate accurately. This work employs an improved smoothed particle hydrodynamics (SPH) method to effectively model multilayer CS with oblique impacting powders. The deformation characteristics and bonding effects between powders and a substrate are numerically investigated. Moreover, the multilayer CS processes with multiple impacting powders are analyzed. Results showed that the bonding effects between powders and a substrate under oblique impacting conditions have several differences from that under normal impacting conditions. The separation between powders and cavities can be observed in oblique impacting CS. Furthermore, the entire CS process with the movement of the nozzle has been reproduced by the present SPH method. The geometric characteristics of the powder track in CS with different impacting angles have also been analyzed, which can help develop and improve additive manufacturing techniques.

Evaluation of a laser powder bed fusion designer Al-Mg-Zr-Si alloy for cold spray additive manufacturing

Metal additive manufacturing (AM) is a constantly developing approach utilized in many novel applications. Most metal AM techniques utilize alloys designed for traditional processing conditions, such as casting, whereas implementing alloys designed for AM may prove useful. Given the proven utility of the Al-Mg-Zr-Si Addalloy 5T® in melt-driven AM, this study investigated the use of this alloy in cold spray (CS), as minimal research has explored alloy design for use in solid-state processing. The as-atomized powder and CS samples were evaluated microstructurally and mechanically to determine suitability for CS. Premature brittle fracture were seen in the deposits, necessitating processing improvements for enhanced deposit performance. Feedstock thermal pre-processing was explored, guided by thermodynamic modeling, to improve spray-ability. Heat treatments resulted in generalized powder softening, suggesting improved processability using a CS gas-particle dynamics model. This model allowed for theoretical tuning of processing parameters, predicting improved deposition using a specific configuration with He gas. The through-process model-informed experimental approach emphasizes the potential of using Addalloy 5T® powder in CS when coupling heat treatment with processing parameter optimization. Results suggest that the CS community may benefit from alloy design specifically for solid-state processing, tailoring powder chemistry and microstructure for enhanced properties and processability.

Dynamic recrystallization of Sn coatings on carbon-fiber-reinforced plastics during cold spray additive manufacturing

The metallization of carbon-fiber-reinforced plastic (CFRP) is a promising solution for increasing the electrical conductivity of CFRP components used in airplane applications to protect them from lightning strikes. Therefore, in this study, cold spraying was used to deposit Sn coating on an epoxy-based CFRP substrate with three different pass numbers (24, 48, and 96) at a gas temperature of 473 K, and the microstructural evolution of the deposited Sn coatings was examined. The grain size of the cold-sprayed Sn coatings gradually decreased as the pass number increased, with 96-pass deposition producing relatively homogeneous, finer-grained microstructures with an average grain size of 4.5 µm. Additionally, increasing the pass number enhanced the in-grain local misorientation of the Sn coatings, which can be correlated with the geometrically necessary dislocation density. The grain refinement observed in conjunction with the formation of dislocation substructures indicated that dynamic recrystallization occurred in the Sn coatings during the multipass cold spraying process, enabling synergistic strengthening. The dynamic recrystallization fraction increased with the pass number, eventually exceeding 60% after the 96-pass deposition. Consequently, as the pass number increased, the hardness of the deposited Sn coatings increased, resulting in more homogeneous hardness distributions along the building direction. Additionally, a thermomechanical effect originating from the low melting temperature of Sn was particularly observed. The findings of this study emphasize the critical nature of cold spray additive manufacturing for the metallization of CFRP components and strengthening of deposited metals.

Microstructural and Micromechanical Characterization of Feedstock for Cold Spray Additive Manufacturing and Processing

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

Cold Sprayed Metallic Coatings on Fibre-Reinforced Composites: A Machine Learning Approach for the Optimization of the Process

Cold spray additive manufacturing (CSAM) is a promising process for producing metallic layers on different substrates, using powders as a feedstock material. The metallic powders are deposited through pressured gas that reaches supersonic velocities. Due to the low heat input required, as the powders remain in solid-state, this technology is particularly suitable to coat thermo-sensitive materials such as composites. Moreover, the absence of melting allows design freedom, allowing to build complex structures on the substrates, layer by layer. In this scenario, machine learning techniques can be crucial to improve the quality and understanding of this manufacturing process. The aim of this work is to predict the deformation and penetration of a particle upon impact using machine learning techniques in order to assess the properties of the coating. A univariate linear regression method was chosen to verify the feasibility of Theory Guided Machine Learning (TGML) techniques to predict the characteristics of the coating. The training dataset was obtained from both experimental data and computational data. It was confirmed that TGML could be a good route to pursue in order to optimize this process.

An overview of cold spray coating in additive manufacturing, component repairing and other engineering applications

AbstractCold spray process (CSP) is a thermal spray technology in which coating (10–40 µm) is formed in the solid state by the impingement of power particles with supersonic velocity (200–1,200 m/s2) on coupon employing compressed gas jet, below the melting point of coating powder. It is commonly referred as cold gas dynamic spray, high velocity powder deposition, kinetic spray and kinetic energy metallisation process. Using CSP, various engineering materials (metals, polymers and ceramics) and its composites can be deposited. It is unique and promising approach for obtaining surface coating and offers various technological benefits over thermal spray as kinetic energy is employed for deposition rather than thermal energy. This offers great benefits in additive manufacturing (AM) to develop a component denser, low oxide coating free of tensile residual stresses, and undesired chemical reactions compared to conventional AM and coating techniques. Cold spray additive manufacturing (CSAM) is the powerful and emerging technique in the field of AM to develop engineering components with improved performance covering broad range of functionalities of surface, subsurface and interfaces. There are few flaws in this technique; however, extensive research work is going in CSAM and repairing of components to meet the real-time applications. The main objective of this review article is to summarise the history, effect of process parameters on surface coating, research and development in CSP along with its implementation in AM, component repairing and biomedical, antimicrobial and electrical applications. A discussion on future trends in CSAM is also provided at the end part of this article.

Thermal Preprocessing of Rapidly Solidified Al 6061 Feedstock for Tunable Cold Spray Additive Manufacturing

In this work, the influence of thermal pre-processing upon the microstructure and hardness of Al 6061 feedstock powder is considered through the lens of cold spray processing and additive manufacturing. Since solid-state cold spray processes refine and retain microstructural constituents following impact-driven and high-strain rate severe plastic deformation and bonding, thermal pre-processing enables application-driven tuning of the resultant consolidation achieved via microstructural and, therefore, mechanical manipulation of the feedstock prior to use. Microstructural analysis was achieved via X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, energy dispersive spectroscopy, and differential thermal calorimetry. On the other hand, nanoindentation testing and analysis were relied upon to quantify pre-processing effects and microstructural evolution influences on the resultant hardness as a function of time at 540 °C. In the case of the as-atomized powder, β-Mg2Si-, Al-Fe-, and Mg-Si-type phases were observed along polycrystalline grain boundaries. Furthermore, after a 60 min hold time at 540 °C, Al-Fe-Si-Cr-Mn- and Mg-Si-type intermetallic phases were also observed along grain boundaries. Furthermore, the as-atomized hardness at 250 nm of indentation depth was 1.26 GPa and continuously decreased as a function of hold time until reaching 0.88 GPa after 240 min at 540 °C. Finally, contextualization of the observations with tuning cold spray additive manufacturing part performance via powder pre-processing is presented for through-process and application-minded design.

Parametric analysis to explore the viability of cold spray additive manufacturing to print SS316L parts for biomedical application

Parametric analysis to explore the viability of cold spray additive manufacturing to print SS316L parts for biomedical application

New insights into the effects of powder injector inner diameter and overhang length on particle accelerating behavior in cold spray additive manufacturing by numerical simulation

Application requirements, especially additive manufacturing, have forced cold spray technology to strengthen the precise control of particle behavior and optimize the spray gun for long working hours. Our recent studies show that the powder injector, as a small component inside the spray gun, greatly disturbs the stream fields and the impact parameters of particles. A model dedicated to the hydrodynamic numerical calculation was established which takes into account the influence of changed parameters of powder injector and the mixing effect between the powder feeding gas and main working gas, enabling more accurate simulations and greater insight into the particle acceleration procedure. Simulation results reveal that the particle distributions near the nozzle throat and in front of the substrate are significantly influenced by the particle diameter, the inner diameter of powder injector, and the original pressure discrepancy between the powder feeding gas and main working gas. Employing lower differential pressure and a smaller inner diameter of the powder injector can not only make the particles more concentrated near the nozzle axis, to reduce the possibility of nozzle clogging, but also improve the particle impact velocity. At the same time, for higher precision of cold spray additive manufacturing, particles with diameters of 20–40 μm should be considered. Besides, the impact velocity and temperature of particles are extremely affected by the interaction between the powder feeding gas and the main working gas, which is more sensitive to the particle diameter of 15–45 μm. In addition, the mixing state of the two gases shows significant effects on the stream fields in the upstream of the nozzle, but little influence around the nozzle exit. In the case of the powder injector extending into the nozzle throat, the flow field is greatly influenced because of the obvious disturbance of gas flow at the powder injector end.

Cold spray additive manufacturing of copper-based materials: Review and future directions

The cold gas dynamic spray process is a manufacturing process strategically designed for coatings. The conditions for the deposition of materials to form coatings have evolved over several decades. Copper and copper-based cold spray coatings are an interesting field for investigation, as it has substantial commercial demand and acceptance. Several important works have already been performed in this regard that shows the immense popularity of its applications in power industries. Cold gas dynamic spray, being an economic process, can produce coatings with superior quality and low oxidation. In this paper, a particular focus has been given to copper-based cold spray coatings along with their deposition parameters. The various mechanical, electrical, corrosion, and tribological properties of these copper-based cold spray coatings are commendable and economically lucrative. A good amount of experimental data has also been included in this review article to provide comprehensive information and future scope of research about copper-based cold spray coatings.

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.