Cold Spray Deposition Research Articles

Air-based cold spray: An advanced additive manufacturing technique for functional and structural applications

Abstract Cold spray (CS) is a solid-state deposition process that accelerates particles in a gas to create parts or coatings. Deformation is central to the mechanical and metallurgical bonds that facilitate particle cohesion and deposit formation. Most research works focus on high-pressure inert gas CS (HPCS), neglecting the potential of air-based CS which is often overlooked because of its poorer deposit qualities. Despite this, air-based CS presents advantages in terms of cost and energy savings and has recently gained attention as a promising new CS additive manufacturing method. This review contrasts HPCS and air-based CS, identifying key differences and bonding modes. Then, state-of-the-art air-based CS research is captured and reviewed revealing a diverse range of application areas including functional coatings, medical, machine tool manufacture, and metal-to-ceramic interfacing. Additionally, research efforts to improve air-based CS quality and bonding, which mainly centre around feed-stock morphology optimisation, print pathing, and post-treatment techniques, are captured. Literature is grouped into three main research categories: metal feed-stocks, metal matrix composites and powder mixes, and novel applications. Accompanying tabulated summaries are presented, detailing CS system parameters, such as gas pressures and temperatures, feed-stock and substrate materials, and application area. Future research directions in air-based CS are also discussed in the context of technology promotion, key strengths and applications, and methods for enhancing CS systems and deposit qualities.

Development of an epoxy-metallic powder sublayer for the cold spray metallization of carbon-fiber reinforced thermoset composites

This paper investigates the development of a composite sublayer for the cold spray metallization of carbon-fiber reinforced thermoset composites. The hybrid sublayer/carbon-fiber reinforced structure is prepared using a vacuum assisted infusion process. The sublayer consists of a mixture of epoxy with micron-sized metallic powder particles and is directly embedded onto the carbon-fiber reinforced structure during the infusion process. During the cold spray metallization, the erosion of this biphasic sublayer has the capability to produce a metal-to-metal bonding between the cold sprayed powder particles and the sublayer powder particles. The mechanical response of the sublayer due to the high-speed collision of the cold spray powder is investigated using a computational analysis. A decohesion at the epoxy/metallic particle interface within the sublayer, along with the fragmentation of the epoxy matrix upon impact, eases an erosion that prevents the coating formation onto the sublayer. The erosion/coating formation strongly depends on the mechanical property of the spray powder compared to the powder of the sublayer. In the case of a sublayer made of soft metal particles, the plastic deformation during the high-speed collision is better absorbed by such a biphasic sublayer. This circumstance is conducive to an adhesion of the sprayed particles onto the sublayer despite an occurrence of an erosion. Thus, the cold spray deposition of Cu powder onto a biphasic epoxy/Al sublayer results in deposit formation, with Cu particles bonding to Al particles and anchoring to the epoxy matrix.

Exploring the bonding mechanism in cold spray deposition of engineered graphene nanoplates-Ni nanocomposite powder

Exploring the bonding mechanism in cold spray deposition of engineered graphene nanoplates-Ni nanocomposite powder

Numerical optimization of cold gas dynamic spray process parameters through response surface methodology

ABSTRACT Copper-Zinc and its alloys are extensively used for the corrosion protection of the metal substrate surfaces like steel. Cold gas dynamic spraying (CGDS) is a material coating technique in which metal particles directly adhere to the substrate surface at a relatively low temperature. Numerical simulation (CFD) is a better alternative to understanding CGDS as compared to experimental data due to less expenditure and less energy consumption in CFD. Optimisation of CGDS can be done either by varying the process parameters or by improving the design of the de-Laval nozzle. In this study, the Response Surface Methodology (Central Composite Design) was used to optimise cold spray deposition efficiency by using a 2-D axisymmetric model by varying the process parameters such as carrier gas temperature, stand-off distance, and particle size. Various models were used to predict the critical velocity and erosion velocity. All the process parameters under consideration were found significant in analysing the model by ANOVA. Copper-Zinc Alloy (C93200) particle size is varied from 2.96 µm to 87.04 µm and carrier gas temperature is varied from 287.78K to 708.22K. With the increase in carrier gas temperature and particle size diameter, critical velocity decreases resulting in improved deposition efficiency.

Understanding Electrochemical Behavior and Localized Corrosion Susceptibility in Cold Sprayed Al-Mg Binary Deposits with Varying Mg Contents

This paper elucidates electrochemical behavior and localized corrosion susceptibility in cold sprayed Al-Mg binary deposits with varying Mg content. Cold spray (CS) deposition is a solid-state deposition process, being investigated as protective layers and repair applications. Nevertheless, a lack of understanding of corrosion mechanisms in CS deposits is prevalent due to its complex microstructure-driven mechanisms different from wrought counterparts. Analytical electrochemistry techniques, including potentiodynamic polarization and Mott-Schottky testing showed that corrosion resistance increased with increased Mg content in CS Al-Mg binary deposits. However, immersion tests (50 h) demonstrated that the effect of Mg content on localized corrosion damage was insignificant compared to that of prior particle boundaries that primarily governed localized corrosion initiation and propagation.

Subsurface Weave Pattern Influences on Polymer Cold Spray Deposits onto Woven Fiber-Reinforced Composites

AbstractThe polymer cold spray (CS) process has recently been demonstrated as a promising coating and repair technique for fiber-reinforced polymer composites (FRPs). However, a noticeable variation in coating thickness (herein referred to as checkerboard pattern) often occurs in the initial pass of low-pressure CS deposition. The checkerboard pattern occurs due to the periodic variations in matrix thickness and volume above the subsurface fiber weave pattern. When the initial pass exhibits the so-called checkerboard pattern, the CS deposition for subsequent passes may be negatively affected in terms of deposition efficiency, porosity, adhesion, surface roughness, and thickness consistency. The present work compares results of both numerical simulations and experimental studies performed to reveal the governing mechanisms for and elimination of checkerboarding. Single particle impact numerical simulations are conducted to observe thermomechanical behavior of particles during CS impact on the FRP surface at different regions of the composite material. Complementary experimental CS studies of exemplar powders onto FRPs with various surface interlayer thicknesses are also presented and discussed. Experimental analyses of deposits include microstructural observations to compare against the simulations while also providing practical strategies for the elimination of checkerboarding effects. It is demonstrated that the thickness and volume of the matrix region underneath the impact area are the main contributing factors that govern the CS deposition variations on CFRP substrates. As such, increasing the surface epoxy layer thickness beyond a critical value can reduce the effect of substrate stiffness effects imposed by the subsurface fiber tows, thereby effectively eliminating the checkerboard patterns.

Microstructure and mechanical performance of cold spray Cr coatings

Cold spray deposition has emerged as a promising method for applying protective coatings in the nuclear industry, particularly for enhancing the accident tolerance of fuel assemblies. In this process, helium gas is often used to propel solid powder particles towards the target substrate, however, nitrogen gas is also considered due to its significantly lower cost. In this study, we investigate the influence of nitrogen and helium gas as propellants on the properties and microstructure of pure chromium (Cr) coatings on zirconium (Zr) alloy cladding tubes. Employing Scanning Electron Microscopy (SEM) and electron and x-ray diffraction techniques (EBSD, XRD), we explore the structural characteristics of the coatings. Additionally, in-situ SEM tensile testing at room temperature, coupled with Digital Image Correlation (DIC), is utilized to assess the coating cracking behaviour. Our findings reveal distinct differences in coating morphology and residual stress between nitrogen and helium propelled Cr coatings. The nitrogen-propelled coating exhibits a more porous structure with smoother coating/substrate interfaces and lower compressive residual stress compared to the helium-propelled one. This results in earlier strain-induced crack initiation and higher crack density at lower strains (0.5–2%). However, at higher strains (2–5%), both coatings demonstrate identical crack saturation densities (saturated number of cracks per unit length), accompanied by similar crack toughening mechanisms and evidence of shear strain bands at intercrack regions, indicative of plasticity onset.

Evaluating fracture toughness of cold sprayed IN625 coatings: Micro-scratching method

Cold spray deposition of metals and alloys has gained considerable attention due to its advanced applications across various industries. This technique offers numerous advantages, including the absence of phase changes and oxidation. However, the process presents challenges due to its inherent complexities. Plastic deformation is crucial for the successful deposition of powder particles during cold spray. Therefore, achieving an optimal level of plastic deformation is essential. Fracture toughness is one of the important properties that can help understand the degree of plastic deformation in cold-sprayed coatings. Yet, measuring fracture toughness in these coatings is challenging because most evaluation methods are destructive and require large sample sizes. This study investigates the feasibility of predicting the fracture toughness of cold-sprayed coatings. Specifically, the micro-scratching method is employed to predict the fracture toughness of cold-sprayed IN625 coatings. IN625 is selected because of its high-end applications in sectors such as nuclear, marine, and aerospace component manufacturing. In addition to evaluating fracture toughness, the deposited coatings undergo rigorous testing and characterization to establish the microstructure-process-property relationship. The scaling of frictional force and fracture toughness confirms the validity of using scratch data for fracture toughness calculations. Hence, fracture toughness of the resulting coatings was successfully evaluated.

High-performance porous 3D Ni skeleton electrodes for the oxygen evolution reaction

A key component of green hydrogen production technologies is the fabrication of large-scale porous transport layer (PTL) for use in anion electrolyte membrane water electrolysers (AEMWEs). One strategy to achieve that goal is to manufacture Ni-based 3D electrode skeletons that can be further catalyzed to achieve high current densities at low overpotentials. In the present work, shock-wave induced spray (SWIS) and cold spray (CS) deposition techniques were used to prepare 20 cm2 Ni-based electrode skeletons. In our experimental conditions, the porosity of coatings prepared using the SWIS deposition system and Ni powders with particle sizes D50 = 32 and 75 μm never exceeded 28%. Higher porosity could only be achieved using the CS deposition system and a spheroidal Ni–Al powder, whose particles consist of an aluminum core encapsulated in a nickel shell. After Al leaching in an alkaline solution, the resulting electrodes showed good mechanical and structural integrity with up to 41% porosity. The electrochemical active surface area of the most porous electrodes is a factor of 2100 larger than a polished Ni plate, and it has superaerophobic properties with a captive air bubble contact angle of 151°. During 1 h of electrolysis, the overpotential at 100 mA cm−2 of the most active leached Ni–Al cold spray deposited electrode was 330 mV, compared to 380 mV for a Ni foam electrode.

Towards Strength–Ductility Synergy in Cold Spray for Manufacturing and Repair Application: A Review

Cold spray is a solid-state additive manufacturing technology and has significant potential in component fabrication and structural repair. However, the unfavourable strength–ductility synergy in cold spray due to the high work hardening, porosity and insufficient bonding strength makes it an obstacle for real application. In recent years, several methods have been proposed to improve the quality of the cold-sprayed deposits, and to achieve a balance between strength and ductility. According to the mechanism of how these methods work to enhance metallurgical bonding, decrease porosity and reduce dislocation densities, they can be divided into four groups: (i) thermal methods, (ii) mechanical methods, (iii) thermal–mechanical methods and (iv) optimisation of microstructure morphology. A comprehensive review of the strengthening mechanism, microstructure and mechanical properties of cold-sprayed deposits by these methods is conducted. The challenges towards strength–ductility synergy of cold-sprayed deposits are summarised. The possible research directions based on authors’ research experience are also proposed. This review article aims to help researchers and engineers understand the strengths and weaknesses of existing methods and provide pointers to develop new technologies that are easily adopted to improve the strength–ductility synergy of cold-sprayed deposits for real application.

Combinatorial synthesis of AlNi alloys by low-pressure cold spray deposition and post-laser alloying process

Aluminum-Nickel (AlNi) alloys are of great interest due to their exceptional high-temperature wear and corrosion resistance, making them valuable in transport, energy, and materials processing applications. However, challenges in the production and shaping of these alloys, particularly as thick coatings, remain significant. This study introduces an innovative method for the high-throughput synthesis of AlNi coatings, utilizing a two-step process: low-pressure cold spray deposition followed by laser surface alloying. The combination of these two techniques not only improves the synthesis process but also opens avenues for exploring new material compositions with specific application requirements. This approach holds significant potential for accelerating the development and optimization of advanced coatings and multiphase compounds in applications such as repair and additive manufacturing.Aluminum and nickel powders were co-sprayed to create coatings with controlled compositions ranging from 50Al50Ni to 10Al90Ni (wt%). Subsequent laser treatment induced in-situ alloying and homogenization, resulting in dense, uniform AlNi coatings. The microstructure and chemical composition were characterized using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS), while X-ray Diffraction (XRD) identified the formation of various phases, including Al3Ni and AlNi3 phases. The process demonstrated effective alloying and microstructural homogeneity, with residual alumina present at the surface. Despite the presence of some microstructural defects, such as cracking, this method provides a robust foundation for further refinement and opens new possibilities for tailoring alloy properties through combinatorial cold spray and laser alloying techniques.

Effect of Nonessential Alloying Elements and Solution pH on Corrosion Behavior of Al-Mg Alloys Fabricated by Cold Spray Deposition

This paper highlights the difference in corrosion behavior of cold spray (CS) deposited AA5083 and Al-5.0 wt% Mg alloys with an emphasis on the effect of nonessential alloying elements and solution pH. CS process is an emerging technology for repairing damaged structures via solid-state deposition. While recent works have focused on CS Al alloys, less attention has been paid to CS Al binary alloys in comparison to Al engineering alloys, which have important implications for the integrity of structural components repaired by the CS process. Herein, the microstructure of CS AA5083 and Al-5.0 wt% Mg binary alloy was analyzed using various microstructure characterization techniques. Corrosion behavior was assessed using electrochemical and immersion tests in 0.6 M NaCl (pH 8.3 and 11.5) solution. Intermetallic phases, such as Fe- and Si-containing phases, in CS AA5083 decreased corrosion resistance by increasing cathodic kinetics in a near-neutral solution. In addition, immersion tests demonstrated lower corrosion resistance in CS AA5083 than in CS Al-5.0 wt% Mg, whereas an alkaline environment showed the presence of a secondary passive layer on CS AA5083, providing higher corrosion resistance compared to CS Al-5.0 wt% Mg.

In Situ Measurement of Track Shape in Cold Spray Deposits

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

Laser assisted cold spray of aluminum alloy 6061: Experimental results

Laser-assisted cold spray (LACS) is investigated for its potential to improve the mechanical properties of cold spray deposits made by using nitrogen as the gas that carries the powder. High strength cold spray deposits are typically achieved by using the more expensive and resource limited helium. In this work, a laser collocated with the spray spot was used in nitrogen CS operations and the porosity, adhesion strength, tensile strength, and fatigue performance of aluminum alloy 6061 (Al6061) were examined. Using the laser improved all the performance metrics. By increasing the spray spot temperature from 180°C to 455°C, the porosity of the deposit reduced to 0.24 % from 1.73 %. The adhesion strength was increased from 18.4 MPa to 76.6 MPa. The tensile strength was increased from 34.3 MPa to 167.6 MPa, and the elongation was increased from 0.07 % to 15.58 %. It was shown that using laser heating during deposition increases the residual stress in the deposit, but its effects can be counteracted by using a hotplate beneath the substrate. Fatigue testing showed that fatigue performance was largely driven by tensile strength. These results are discussed in the context of in-situ temperature data and metallographic analysis. Analysis indicates these improvements are due to the combined effects of material softening, improved bonding between particles, and various heat treatment modalities.

Influence of powder heat treatment and particle size on the corrosion performance of cold-sprayed nickel-aluminum bronze (NAB) for repair applications

Nickel-Aluminum-Bronze powder was heat-treated to reduce martensite and segregated into three sizes for Cold Spray deposition. Heat treatment (HT) significantly increased deposition efficiency (DE) from 20 % to nearly 100 %. Mechanical properties (hardness, scratch) and electrochemical corrosion tests were conducted to evaluate inter-splat bonding. Performance tests revealed that as-received (AR) powder deposit exhibited superior properties, albeit with a low DE. Among HT powders, the coarser size exhibited better inter-splat bonding due to particle size and surface oxide of the powder. The AR powder's enhanced performance is linked to a novel densification mechanism.

A comprehensive review on the analysis of adhesion strength of cold spray deposits

Cold spray (CS) is a new kind of coating that has many potential uses, including functionalizing surfaces, doing localized repairs, and mass production. Its fast deposition rate and diverse feedstocks have led to its growing popularity as an additive manufacturing method, which has been driven by improvements in lateral resolution. CS materials have several uses in the transportation industry, and some of the most frequent ones include nickel super-alloys, titanium alloys, copper, aluminum and metal-ceramic composites. Nevertheless, the mechanical properties depend upon number of parameters involved during spraying process. Therefore, there is an immediate need for researchers and businesses to understand the various parameters affecting the adhesion strength of CS deposits. The current research presents an analysis of the adhesion behavior of coatings that have been deposited by CS methodology.

Effect of SiC content on the microstructure and wear behavior of cold-sprayed Al-SiC coatings deposited on AZ31 alloy substrate

As a promising and recently developed deposition technique, cold spray deposition method is among the most recently implemented approaches to enhance the poor hardness and wear resistance of AZ31B magnesium alloy. This study investigated the effect of SiC content on the microstructural characteristics, microhardness, and wear behavior of cold-sprayed Al-(16, 28, and 38 wt%) SiC composite coatings. The incorporation of SiC particles into the Al-matrix coating led to the development of a mechanical interlocking mechanism and improved coating-substrate interfacial bonding. The microhardness of the Al-38 wt% SiC coating was approximately 80 % higher than that of the bare substrate due to reduced porosity and a uniform distribution of SiC particles. For coatings with higher SiC content, the dominant wear mechanism transitioned from adhesive to abrasive wear, as evidenced by the friction coefficient (COF) values and wear track micromorphology. The Al-16 wt% SiC coating exhibited the lowest COF and wear rate values, indicating superior wear resistance among the specimens.

Scanning Acoustic Microscopy Characterization of Cold-Sprayed Coatings Deposited on Grooved Substrates

AbstractThe effect of non-planar substrate surface on homogeneity and quality of cold-sprayed (CS) deposits was studied by scanning acoustic microscopy (SAM). Fe coatings were cold-sprayed onto Al substrates containing artificially introduced grooves of square- and trapezoid-shaped geometries, with flat or cylindrical bottoms. The Al substrates were either wrought or cold-sprayed, to comprehend their prospective influence on the Fe coatings buildup. SAM was then used to assess morphological properties of the materials from the cross-view and top-view directions. The microstructure below the surface of the studied samples was visualized by measuring the amplitudes of the reflection echoes and the velocity of the ultrasonic waves. The SAM analysis revealed that the regions of coating imperfections around the grooves are larger than what is suggested by standard scanning electron microscopy (SEM) observations. Furthermore, we found that the seemingly non-influenced coating regions that appear perfectly homogeneous and dense in SEM do, in fact, possess heterogeneous microstructure associated with the individual CS nozzle passes.

Cold Spray Deposition of MoS2- and WS2-Based Solid Lubricant Coatings

The cold spray deposition technique has been used to produce a new class of solid lubricant coatings using powder feedstocks of the metal disulfides WS2 or MoS2, either pure or mixed with Cu and Ni metal powders. Friction and cycle lives were obtained using ball-on-flat reciprocating tribometry of coated 304 SS flats in dry nitrogen and vacuum at higher Hertzian contact stresses (Smax = 1386 MPa (201 ksi)). The measured friction and thickness of the coatings were much lower than for previous studies (COF = 0.03 ± 0.01 and ≤1 µm, respectively), which is due to their high metal disulfide:metal ratios. Cu-containing metal sulfide coatings exhibited somewhat higher cycle lifetimes than the pure metal sulfide coatings, even though the Cu content was only ~1 wt%. Profiling of wear tracks for coatings tested to 3000 cycles (i.e., pre-failure) yielded specific wear rates in the range 3–7 × 10−6 mm3N−1m−1, similar to other solid lubricant coatings. When compared to other coating techniques, the cold spray method represents a niche that has heretofore been vacant. In particular, it will be useful in many precision ball-bearing applications that require higher throughput and lower costs than sputter-deposited MoS2-based coatings.

Multi-parameter coupled optimization of Al6061 coating porosity based on the response surface method

The objective of this study is to study the multi-particle deposition process of cold spray through numerical simulation methods and to use multi-factor coupling to optimize the porosity of Al6061 coating to more accurately characterize the real cold spray deposition process. This study aimed to predict and optimize the porosity of Al6061 coatings using numerical simulation methods. The tasks to be solved are: to nest the multi-particle model established by the Python script in the CEL deposition model to simulate the cold spray deposition process. A multi-parameter function with particle temperature, substrate temperature, and particle velocity as independent variables and Al6061 coating porosity as dependent variables was established. The response surface analysis method was used to predict the optimal spraying parameters and coating porosity of Al6061 coating. The methods used are as follows: optimize the porosity of the coating through multi-factor coupling through response surface analysis; use a multi-particle model established through a Python script to be nested in the CEL deposition model to simulate the deposition process of cold-sprayed Al6061 multi-particles. To characterize the coating porosity more accurately, the average value of multiple groups of samples was taken as the final coating porosity value. Conclusions. the porosity value of Al6061 coating obtained by the prediction model is 1.969%; Under the influence of multi-factor coupling, particle velocity has the greatest impact on the porosity of the Al6061 coating, and the substrate temperature has the least impact. Optimum spraying parameters: particle temperature 649.692K, substrate temperature 536.437K, and particle velocity 672.385m/s. Under the optimal spraying parameters, the porosity value of the Al6061 coating is 1.91875%; The error between the predicted value and the actual value obtained by numerical simulation is only 2.55%.