Cold Spray Technology Research Articles

Effect of Ball-Milled Feedstock Powder on Microstructure and Mechanical Properties of Cu-Ni-Al-Al2O3 Composite Coatings by Cold Spraying

Cu, Ni and Al powders mixed in a certain stoichiometric proportion were ground via ball milling and deposited as coatings using low pressure cold spraying (LPCS) technology. The effect of particle morphology on the powder structure as well as the microstructure, composition and mechanical properties of the coatings was studied. The results revealed a core–shell structure of ball-milled powders. Compared with a mechanically mixed (MM) coating, coatings after ball milling at a rotation speed of 200 rpm exhibited the most uniform composition distribution and a lower degree of porosity (by 0.29%). Moreover, ball milling at 200 rpm was conducive to a significant increase in the deposition efficiency of the sprayed powder (by 10.89%), thereby improving the microhardness distribution uniformity. The ball milling treatment improved the adhesion of the coatings, and the adhesion of the composite coating increased to 40.29 MPa with the increase in ball milling speed. The dry sliding wear tests indicated that ball milling treatment of sprayed powder significantly improved the wear properties of the coatings. The coating after ball milling at a speed of 250 rpm showed the lowest friction coefficient and wear rate, with values of 0.41 and 2.47 × 10−12 m3/m, respectively. The wear mechanism of coatings changed from abrasive wear to adhesive wear with the increase in ball milling speed.

Effect of WC-17Co content on microstructure, mechanical properties and tribological behavior of low-pressure cold sprayed tin bronze composite coating

As an important anti-wear material, tin bronze coatings and their composites have been widely used as bimetallic bearings, sliding plates and ship propellers. In this work, the dense CuSn10/WC-17Co composite coatings were deposited by low-pressure cold spraying (LPCS) technology. The effect of WC-17Co cermet content on the microstructure, mechanical properties and tribological behavior of the LPCS CuSn10/WC-17Co coatings was investigated. The results showed that the deformation of the particles that deposited inside the coatings was enhanced by the increasing peening effect of the WC-17Co cermet in feedstock powders. During the coating deposition process, the cold spraying can effectively avoid the decomposition or oxidation of the feedstock powders. Meanwhile, in the wake of the increasing WC-17Co content in the coatings, the hardness and bonding strength of the composite coatings were improved. In addition, the evolution of the coating fracture surfaces was analyzed. It is gratifying that the wear rate of the CuSn10/WC-17Co composite coating was significantly decreased to 3.75 × 10−5 mm3/N·m. Correspondingly, the wear mechanisms of the coatings were all elucidated, respectively.

Interfacial microstructure and mechanical properties of Al/steel joints fabricated via thermo-compensated resistance brazing welding with cold spray Zn interlayer

Achieving the effective joining between Al alloy and stainless steel with a large cross-section was meaningful in the significant industry field. For this, the Al/steel dissimilar bimetal materials were manufactured by a novelty hybrid technology, named thermo-compensated resistance brazing welding. The effect of the single Zn foil and the deposited Zn coatings with cold spray technology on the bonding interface, interfacial microstructure, and mechanical properties of the final Al/steel resultant joints were systematically investigated by the relevant analysis method. The results revealed that the obvious reaction layer with main components of Al(s.s) was formed at the Al/steel joints with the single Zn foil as the interlayer. Meanwhile, the introduction of the Zn interlayer improved the temperature field of the joint, which enhanced the lap-shear load of the weld. Besides, the Zn coating was deposited at the top surface of the 304ss substrate as the interlayer to increase joint performance further. The advantage of the pre-deposition formed a better metallurgical bond between the coating and 304ss. The subsequent lap-shear load of the weld was improved with the increase of the Zn coating thickness. The maximum lap-shear load of the final joints reached 2087.6N with a Zn coating thickness of 500 μm and the interfacial structure of the joint was changed: Al alloy, reaction layer I, Al(s.s) + Al2O3, and 304ss from top to bottom. The main composition was Al(s.s) at the reaction layer I between Al alloy and coating.

High-Performance Pure Aluminum Coatings on Stainless Steels by Cold Spray

Aluminum target material is an important target material and is widely used in preparations of semiconductor films, integrated circuits, display circuits, protective films, decorative films, etc. In this study, pure aluminum coatings were deposited on stainless steel substrates by cold-spray technology as part of an overall project to produce large-size pure aluminum sputtering target materials. The results show that pure aluminum coatings exhibit high adhesive strength (~98 MPa), high deposition efficiency (~95%), and low porosity (~0.3%) on stainless steel substrates. The bonding mechanisms of pure aluminum coatings on stainless steel are a combination of metallurgical and mechanical interlocking. The evolutions of microstructure and mechanical properties of pure aluminum coatings under different heat treatments were also studied. With the increase of heat treatment temperature, it is found that cold-sprayed aluminum coatings become more homogenous in microstructure, the microhardness is reduced, and the adhesive strength seems to be slightly reduced. Overall, this study demonstrates significant advantages of cold-spray technology in depositing high-performance pure aluminum coatings on stainless steels.

Effect of high temperature exposure on microstructure, mechanical and tribological properties of cold sprayed NiCoCrAlTaY coatings

NiCoCrAlTaY coating is widely used in high temperature oxidation resistance, gas erosion protection and gas path sealing of hot-end parts of aeroengines and gas turbines. In this study, NiCoCrAlTaY coatings were prepared on cobalt-based superalloy substrates by high pressure cold spray technology. The microstructure, mechanical property and tribological behaviors of the coatings before and after thermal exposure at 1050 °C were systemically studied. The results showed that NiCoCrAlTaY coatings with very dense structure could be obtained by high-pressure cold spraying with nitrogen as carrier gas. The coating remained completely intimate with the substrate without any cracking and spalling after thermal exposure at 1050 °C for 500 h. Due to elemental diffusion at high temperatures, the coating formed a four-layer structure, including alumina film on the surface, β-NiAl phase depletion layer near the surface, intermediate layer containing β-NiAl phase and β-NiAl phase depletion layer near the substrate. With the prolongation of thermal exposure at 1050 °C, the thicknesses of β-NiAl phase depletion layers both near the surface and the substrate increased. The thickness and content of the intermediate β-NiAl phase layer decreased gradually during thermal exposure. Besides, the average hardness values of the coating rapidly decreased by about 30 % after thermal exposure at 1050 °C for 5 h. In particular, the hardness of the β-NiAl phase depletion layer near the surface substrate was lower than that of the intermediate area containing β-NiAl phase. Due to the microstructure and hardness evolution, the wear resistance of the coating decreased significantly after thermal exposure. The friction coefficient of the coating increased from 0.2 to 0.5, and the volume wear rate of the thermally exposed coating was about 4.5 times higher than that of the as-sprayed coating. The results of this study provide guidance for design and application of high-performance MCrAlY coatings.

Study on corrosion resistance of aluminium coating deposited on magnesium‐zinc‐yttrium‐calcium alloy by cold spray

AbstractPure aluminium coatings were prepared on magnesium‐zinc‐yttrium‐calcium alloy substrate via cold spraying technology with different scanning speeds and working gas temperature. The correlation between the corrosion resistance of the coatings and the different spraying process was studied. While the working gas temperature is 600 °C and the scanning speed is 1 mm/s, aluminium coating has less porosity and the coating was well combined with the substrate. Higher temperature of working gas increases the plastic deformation of particles, which lead to a dense aluminium coating. The relationship of corrosion resistance on working gas temperature and scanning speed of aluminium coatings has also been investigated by immersion corrosion test and electrochemical impedance spectroscopic techniques. The results show that the cold sprayed aluminium coatings revealed a lower porosity and higher corrosion resistance with the decreasing scanning speed and the increasing temperature of working gas. The porosity and corrosion current densities were 0.938 vol.% and 2.427 ⋅ 10−6 A/cm2. The experimental results show that the aluminium coating prepared by cold spraying has a good protective effect on magnesium alloy.

Cold Spray Coatings of Complex Concentrated Alloys: Critical Assessment of Milestones, Challenges, and Opportunities

Complex concentrated alloys (CCAs) are structural and functional materials of the future with excellent mechanical, physical, and chemical properties. Due to the equiatomic compositions of these alloys, cost can hinder scalability. Thus, the development of CCA-based coatings is critical for low-cost applications. The application of cold spray technology to CCAs is in its infancy with emphasis on transition elements of the periodic table. Current CCA-based cold spray coating systems showed better adhesion, cohesion, and mechanical properties than conventional one-principal element-based alloys. Comprehensive mechanical behavior, microstructural evolution, deformation, and cracking of cold spray CC-based coatings on the same and different substrates are reviewed. Techniques such as analytical models, finite element analysis, and molecular dynamic simulations are reviewed. The implications of the core effects (high configurational entropy and enthalpy of mixing, sluggish diffusion, severe lattice distortion, and cocktail behavior) and interfacial nanoscale oxides on the structural integrity of cold spray CCA-based coatings are discussed. The mechanisms of adiabatic heating, jetting, and mechanical interlocking, characteristics of cold spray, and areas for future research are highlighted.

Tribological properties of cold-sprayed 7075Al coatings reinforced with hybrid nano-TiB2/micro-SiC particles

In this study, strategies to strengthen 7075Al matrix by blending involving nano-sized TiB2 and micro-sized SiC particles were investigated in order to prepare advanced, highly wear-resistant Al matrix composites. Cold spray (CS) technology was used to deposit a TiB2/SiC-7075Al composite coating. For comparison purposes, three additional coatings with different powder compositions were produced using the same CS processing parameters. They were pure 7075Al, TiB2/7075Al composite and SiC-7075Al composite coatings, respectively. The mechanical properties, including hardness, modulus, adhesion strength and wear resistance, were examined. The powders and their corresponding coatings, as well as the wear tracks on the coating surfaces, were observed and analyzed by optical microscopy, scanning electron microscopy and energy-dispersive spectroscopy. Results showed that the in-situ formed TiB2 particles were uniformly distributed in the 7075Al matrix, while the ex-situ deposited SiC particles were mainly distributed at inter-particle boundaries. The hybrid reinforced TiB2/SiC-7075Al composite coating exhibited the highest hardness and modulus. The tribological tests showed that both TiB2 and SiC particles greatly influenced the wear behavior of the composite coatings, with the latter having a more significant effect. Dual reinforcement with TiB2 and SiC particles enabled the TiB2/SiC-7075Al composite coating to possess the best tribological properties.

Copper-Based Composite Coatings by Solid-State Cold Spray Deposition: A Review

Copper (Cu)-based composite coatings have been widely applied in all kinds of important industry fields due to their outstanding comprehensive properties. The preparation temperature of a composite coating is the key factor affecting the properties, so the cold spray (CS) technology is characterized by low-temperature solid-state deposition, which ensures its emergence as the most promising technology for preparing the Cu-based composite coatings. In this paper, first, the principle of CS technology and the deposition mechanism of the coatings are introduced. On this basis, the deposition mechanism of Cu-based metal/ceramic composite coatings is further explored. Secondly, the effects of key CS process parameters (particle velocity, particle morphology, and substrate state) on the quality of the Cu-based composite coatings are summarized, and the current research status of cold-sprayed Cu-based composite coatings in the fields of corrosion resistance, wear resistance, self-lubricating properties, and electrical conductivity is reviewed. Moreover, the improvement of the performance of Cu-based composite coatings by various post-process treatments of coatings, such as heat treatment (HT) and friction stir processing (FSP), is elaborated. Finally, the future development of Cu-based composite coatings and CS technology is prospected.

Improving the Usage Properties of Steel Using Cold Spray Deposition: A Review

In this paper, the improvement of the characteristics of different steels that are subjected to extreme operating conditions, including the steels used in the manufacture of various military components, the AISI 52100, the manufacture of bearings, and other types of parts that are also subjected to severe operating conditions were analyzed regarding cold spraying, which uses different types of powders to increase the performance of the materials. The cold, thermal spraying technology “Cold Spray” is a method of processing particles in a solid state. Thermal spraying, based on the dynamic increase in gas acceleration up to supersonic speeds, leads to the obtainment of high kinetic energies, and the accelerated particles are deposited at values that are below their melting point. Research conducted through cold spray technology has seen a significant improvement in material properties; when processing the particles in a solid state, they adhere to the surface instead of eroding it. Cold spraying has proven to be an effective technique for improving material properties, as confirmed by its integration into different fields and industries, becoming competitive by being the only method for depositing particles below their melting point.

Understanding cold spray technology for hydroxyapatite deposition

The standard method for applying hydroxyapatite (HAp) coatings to biomedical implants is plasma spraying. However, due to the high temperature of the plasma, these coatings frequently experience negative effects like evaporation, phase change, de-bonding, gas release, and residual stresses. This paper summarizes a revolutionary technique known as a cold spray (CS), which allows HAp coatings to be applied at temperatures well below their melting point. CS has several advantages over conventional high-temperature technologies, and it seems to be approaching parity with other older methods. When applied using the CS approach, the HAp coatings enhance bioactivity, increase corrosion resistance, and main­tain the characteristics of calcium phosphate ceramics. This study aims to give a concise and comprehensive overview of HAp-based materials, including substituted-HAp and HAp/poly­mer composites, and their applications in bone tissue engineering. To better understand the advantages of CS technology, a comparison of CS, high-velocity oxy-fuel (HVOF), and plasma spray is given at the end. The perspective and difficulties were also highlighted.

Advanced Cold-Spraying Technology

Cold-spraying technology is a solid-state, powder-based coating deposition and additive manufacturing (AM) technology, which utilises a high-pressure gas stream to accelerate micron-sized particles through a de-Laval nozzle for supersonic speed and impact on substrates and to generate dense, high-quality deposits [...]

Research Progress of Coating Preparation on Light Alloys in Aviation Field: A Review

This paper systematically introduces the application status of coating-preparation technology on light alloys in the field of aviation parts repair. Included are the advantages and disadvantages of thermal spraying technology and laser cladding technology in the application process, as well as the research status and application prospects of the emerging cold spray (CS) technology and supersonic laser deposition (SLD) technology. Compared with traditional thermal-spraying technology, CS has many advantages, such as low spraying temperature, low oxygen content of the coating, and low porosity, which can effectively avoid oxidation, burning loss, phase change, and grain length during thermal spraying. CS can prepare oxygen-sensitive, heat-sensitive, amorphous, and nanomaterial coatings that are difficult to prepare by traditional thermal-spraying technology. However, in the preparation of high-strength super-hard alloys, CS has shortcomings such as low deposition efficiency and bonding strength. SLD overcomes the shortcomings of CS while inheriting the advantages of CS. In the future, both technologies will be widely used in repairing and remanufacturing in the field of aviation. Based on the principles of CS and SLD, this paper introduces, in detail, the deposition mechanism of the coating, and the specific application examples of CS in the aviation field at the present stage are described. The research and application status of the two technologies in the fields of anti-corrosion coating, wear-resistant coating, functional coating, repair, and remanufacturing in recent years are reviewed. Finally, the application and development prospects of CS and SLD are discussed.

Nozzle Geometry and Particle Size Influence on the Behavior of Low Pressure Cold Sprayed Hydroxyapatite Particles

Low-pressure cold spray (LPCS) technology has attracted interest for the deposition of ceramic coatings due to the thermo-kinetic conditions experienced by the sprayed particles. Unlike conventional thermal spray techniques, the spraying conditions in LPCS can be controlled to avoid the formation of undesired phases. However, ceramics deposition through this process is still challenging. The present study includes a finite element analysis and simulation study of the kinetic conditions of ceramic particles in the LPCS process based on experimental data. The analysis seeks to discuss the effect of nozzle geometry on the kinetic and thermal energy of the sprayed particles at impact and elucidate how the particle travels within the high-velocity jet to be deposited onto a metallic surface. This work examines the behavior of hydroxyapatite particles as a function of particle size and nozzle geometry during LPCS deposition. Interestingly, the results from this research suggest that particle size and nozzle geometry have an influence on the deposition of hydroxyapatite particles. Inertia of large particles proved to be beneficial in keeping their trajectories, allowing them to contribute to the formation of the coatings. Nozzle geometry modifications produced changes in the jet profile and affected the homogeneity of the coatings obtained. This finding contributes to a better understanding of the deposition of hydroxyapatite particles by cold spraying.

An inclusive numerical framework to assess the role of feedstock features on the quality of cold spray deposits

Cold spray technology provides unique capabilities for coating, repair, and additive manufacturing. However experimental trial and error to optimize deposit quality indexes, that rely on powder characteristics, can be costly and tedious. In this research, multiple finite element modelling approaches were compared regarding their capability and shortcomings to analyze the role of major powder features on deposit properties. Lagrangian and CEL methods were selected as the most robust approaches for analyzing the single/multi-particle impact condition, respectively. An intricate algorithm was introduced to accurately evaluate the effect of parameters including particle size, shape, oxidation extent, and impact angle on the deposition indicators such as critical velocity, particle flattening, and deposit porosity. The results exhibited a good agreement with the reported experimental data, confirming the capacity of the proposed numerical framework to tune the deposit properties as a function of a wide range of feedstock characteristics. It was concluded that for successful deposition, the effect of various powder properties and their respective effect and contribution towards plastic deformation should be taken into account. The results indicated that for a given particle velocity, smaller particle, more irregular morphology, thicker oxide layer, and smaller impact angle will result in limited particle deformation and a lower possibility of successful adhesion.

Prediction of the Flattening Ratio and Hardness of Cold Sprayed Deposits

Cold spray technology is a solid-state deposition process where solid particles are accelerated to very high velocities by expanding a compressed gas through a supersonic nozzle. The particles impact a substrate located approximately 25 mm from the exit plane of the nozzle. Predicting the deformation and resultant properties helps in developing process parameters and tailoring coatings to get the desired properties. In this study, aluminum, copper, and nickel coatings were produced using a range of process parameters that produced different particle impact velocities. The Hollomon power law relationship and Johnson-Cook flow stress model were utilized to predict the hardness of cold spray coatings. Results showed there was good agreement between the predicted and measured hardness of the respective coatings. Additionally, a methodology was developed to measure deformation in the form of a flattening ratio of the deposited particles. There was good agreement between the predicted and measured flattening ratio, especially for the Al and Ni feedstock powders.

Insights on metallic particle bonding to thermoplastic polymeric substrates during cold spray

Metallization of polymers using cold spray technology has reached wide consideration in recent years. However, an effective modeling approach to address the deposition phenomena able to assess bonding formation in polymer metallization is still lacking. This study aims to develop a finite element model to simulate the solid-state deposition of metallic particles on thermoplastic polymeric substrates. Single copper particle impact on the Polyether Ether Ketone substrate was modeled using the coupled Lagrangian–Eulerian approach. Emphasis was given to the polymer material properties and substrate thermal history to account for the sensitivity of the physical and mechanical properties of polymers to temperature. Experimental coating depositions were performed to select an optimized set of spray parameters while single-particle impact tests were conducted for model validation. The substrate temperature was measured using an infrared thermal camera and was used to model the sub-surface temperature gradient during gas spray exposure. The proposed numerical model is shown to be capable of predicting various impact features includi mechanical interlocking and the effect of particle velocity fluctuations and temperature gradients on the extent of bonding. Substrate heating was found to have a distinct effect on the correct prediction of particle bonding. The proposed model enables tuning the appropriate processing conditions for successful copper particle adhesion on PEEK polymeric substrates.

High-Pressure Cold Spray Coatings for Aircraft Brakes Application

This paper addresses the potential use of high-pressure cold spray (HP-CS) technology to produce a film of friction material onto a low-carbon steel substrate to allow its use as potential composite material for the stators and rotors of aircraft brake units. Namely, WC-Cr3C2-Ni, WC-Ni, WC-Co-Cr, Cr3C2-NiCr and WC-Co coatings were deposited by using HP-CS, for the purpose of creating high friction and wear resistance composite coatings onto a low-carbon steel substrate. Tribological (friction coefficient and wear rate) and thermal properties as well as coating hardness and adhesion to the low-carbon steel substrate were evaluated to assess the potential use of the coatings as brake surface materials. The tribological and adhesion properties were evaluated by using a pin-on-disk high-temperature tribometer at 450 °C and a scratch test, respectively, whereas coatings hardness was evaluated with a Rockwell C hardness tester. Results obtained show that all coatings exhibit high friction coefficients and low wear rates compared to the low-carbon steel substrate, good adhesion, and elevated microhardness. Furthermore, the WC-Co coating shows better microhardness and thermal properties, while the WC-Co-Cr coating exhibited a better friction coefficient. Unfortunately, it was not possible to quantify the wear resistance due to the elevated roughness of the coatings, but from the analysis carried out on the alumina counterpart of the tribometer, it can be concluded that all the coatings exhibited a very low wear rate. In fact, after the tribological tests, it emerged that the alumina counterpart was more abraded than the investigated coatings.

Cold spraying on polymer-based composites: Understanding the single-particle adhesion

The metallization of the polymer matrix composite structures arises from the need to overcome some of the limits of the polymer-based materials, such as poor thermal and electrical conductivity. The cold spray technology has proved to be one of the most valid solutions for this scope. While the adhesion mechanisms of metal particles on metallic substrates are quite well known, the phenomena occurring when cold spraying on polymers are far to be understood. In this scenario, this paper proposes an interpretation of the phenomena leading to adhesion in cold spraying of metal particles onto polymer-based substrates, including composites. The aim is to try to unveil the phenomena ruling the adhesion by proposing a theoretical model conceived by conjecturing the phenomena occurring. The main hypothesis is that the adhesion is influenced by several energy-activated phenomena: the plastic deformation of the polymer, the plastic deformation of the particles and the loading of the fibers are conjectured to be the most influencing factors. So, the idea is to try to identify the most likely to occur phenomena based on an energy balance. A theoretical model is developed and validated through a dedicated experimental campaign to verify the effectiveness of the model to provide sufficiently reliable results. The model is applied to literature cases and the outcomes obtained are discussed to elucidate the adhesion mechanisms and the role of the fibers in fiber-reinforced polymers.

Numerical Simulation of Cold Spray Bonding for CrFeNi Medium‐Entropy Alloy

As a solid‐state deposition, cold spray maintains the intrinsic characteristics of the feedstock powder. Thus, it provides a unique opportunity for depositing high‐entropy alloys (HEAs) and medium‐entropy alloys (MEAs) that are of great interest for coatings to protect vulnerable materials from aggressive environments. However, considering the high hardness and the complexity of these powder's preparation, the choice of deposition parameters through experiments can be challenging and costly. Herein, a finite element model is presented to simulate the deposition of CrFeNi MEA using cold spray technology. A detailed approach is implemented to model the bonding of the particle to the substrate. The model is able to identify the deposition velocity window and simulate the metallurgical and mechanical interlocking. The particle adheres to the substrate at 500 m s−1 and pushes the substrate down facilitating mechanical interlocking. Furthermore, due to the strain localization induced by the particle, a notable temperature increase is observed at the substrate surface raising to its melting point in agreement with the ejecta eruption phenomenon. The developed numerical method can pave the way for successful experiments in case of costly HEAs and MEAs powders.