Cold Spray System Research Articles

Effect of post-deposition heat treatment on microstructure and mechanical properties of NASA HR-1 cold spray coatings

The primary goal of this work was to examine the impact of heat treatment on the evolution of microstructure and mechanical properties of NASA HR-1 cold spray coatings. Coatings were produced employing a high-pressure cold spray system using N2 and He process gases and the effect of process gas and deposition temperature on the microstructure and mechanical properties of the coatings was examined. Microstructural characterization was performed using optical microscopy, scanning electron microscopy, micro X-ray computed tomography, and electron backscatter diffraction. NASA HR-1 coatings produced with He process gas exhibited improved plastic deformation and resulted in the lowest porosity compared to those deposited with N2 process gas. All coatings showed brittle failure with limited ductility in the as-deposited condition. Heat treatment of the NASA HR-1 cold spray coatings was performed at 550 °C and 950 °C for 1 h to improve the mechanical strength of the coatings. Heat treatment improved the particle bonding and enhanced the mechanical properties of the cold spray coatings. Heat treatment performed at 550 °C resulted in higher mechanical strength of coatings, whereas the heat treatment performed at 950 °C resulted in recrystallized microstructure and improved ductility of the coatings. However, heat treatment at 950 °C resulted in forming the Eta (η) phase and Ni-Ti intermetallics in all the NASA HR-1 cold spray coatings. The overall results suggest that using He as process gas contributed to reduced porosity and enhanced mechanical properties of the cold spray coatings.

Polymer Metallization by Cold Spray Deposition of Polyamide-Copper Composite Coatings

Cold spray metallization of polymers is a promising surface engineering technique that enables the deposition of metal coatings onto polymer substrates at low process temperatures, resulting in improved surface properties, thus enhanced functionality of the polymeric material. However, deposition of well-adhering metallic coatings without causing surface damage to the polymer substrate is still a challenge. In this work, copper-polyamide composite coatings with different copper concentrations between 30 and 75 vol.% in the starting powders were deposited on polyamide substrates using a low-pressure cold spray system with two nozzle geometries of short and long diverging sections. The spray parameters were first developed for the deposition of polyamide powder (at gas temperature of 260 °C and gas pressures ranging from 0.41 to 1.37 MPa), and then used to spray the composite powder mixtures where the polyamide particles were acting as a binder for copper particles. Inflight and impact particle characteristics (velocity and temperature) of the polyamide powder were simulated to better understand the deposition properties. Considering that the selected conditions were suboptimal for the deposition of copper particles, no surface damage was caused as no penetration of the copper particles into the polymer substrate occurred. The results show that increasing the copper content in the powder mixtures significantly improved the resulting coating uniformity and the retained copper content. In addition, the coating deposited by spraying the powder mixture with a higher copper content of 75 vol.% and using the longer nozzle yielded the highest cohesion strength. To further improve coatings cohesion, two post-spray processing methods of furnace heating and hot pressing were used, and the effect of each process on coatings properties was investigated.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Given name: [Kintak Raymond] Last name [Yu]. Also, kindly confirm the details in the metadata are correct.The author names are now correct: Kintak Raymond given name and Yu last nameAll other details are corrects

Effect of heat treatment on the gas-atomized nickel‑aluminum bronze feedstock powders for cold spray

Due to the high strength of the nickel‑aluminum bronze (NAB), the cold spray deposition efficiency of the NAB powders was less than satisfactory. To improve the deformation behavior of powder, different heat treatment strategies were adopted for gas atomized NAB powders and then the heat-treated powders were deposited on NAB substrates using a high-pressure cold spray system. For various powders and their corresponding deposits, a series of related characterizations were performed. The results indicate that the microstructure of the gas-atomized powder was mainly composed of martensitic β′ and bainite α with high hardness, resulting in low deposition efficiency and poor bonding between particles and particles in the prepared deposits. An effective technique of heat treatment can eliminate the non-equilibrium structure in the gas atomized powder, reduce the hardness of the powder, and significantly improve the deposition efficiency and enhance particle interface bonding.

Analysis of spray particles entrance of Right-angle cold spray nozzle based on CFD

Cold spray technology is a solid-state deposition technology, and the nozzle is an important part of the cold spray system. This article proposes a right-angle nozzle. The characteristic of this nozzle is that it can change the flow direction of the gas flow inside the nozzle to realize spraying on the surface of special parts; the acceleration of particles by the right-angle nozzle with different particle entrances is studied. The results show that the outlet center velocity of the right-angle nozzle with a circular throat section is greater, the viscous boundary layer effect is better, and the effective circulation area is larger; the maximum airflow velocity near the outlet of the right-angle nozzle at the particle entrance A is 663.4m/s; it can also effectively avoid the deposition of particles inside the right-angle nozzle, thereby reducing the loss of kinetic energy during the acceleration of particles in the right-angle nozzle; the research on the structure of the new right-angle cold spray nozzle can provide reference for the nozzle of cold spray technology Opinion.

Preferential Corrosion in Cold Sprayed Cu Induced by Oxide Inclusions

Cold spray (CS) deposition is a solid-state deposition technique that finds applications in additive manufacturing, coating, and repairing damaged components. During the cold spray deposition process, feedstock particles are accelerated by compressed gas and impinged onto the substrate at high velocity. Bonding between particles and the surface being coated is established by the high kinetic energy released during collision rather than by added thermal energy. As the particles remain in the solid state during spraying, oxidation is minimized. Despite the partial removal of the native air-formed oxides by the jetting effect, residual oxide debris often remains along the particle boundaries within the sprayed objects as inclusions [1]. The oxide inclusions have attracted attention concerning their influence on the inter-particle bonding strength in the deposit [2]. However, little is known about whether they affect the material’s corrosion behavior.In this work, we report a preferential corrosion phenomenon observed in a CS Cu-diluted HNO3 system that is caused by the remaining oxide inclusions. A mechanism that integrates Cu-NO3 – catalytic corrosion cycles with confined geometry resulting from the dissolution of the oxide inclusions is proposed. Furthermore, we find that this corrosion phenomenon may be mitigated through microstructure engineering. Annealing the CS Cu at 600 °C consolidated the oxide inclusions with their distribution changed from continuous thin films to isolated spherical particles [3]. The propagation of the preferential corrosion is hence interrupted by the lack of interconnected pathways. Counterintuitively, Cl– can function as an inhibitor for this preferential corrosion. Preferential corrosion did not initiate when 1 mM Cl– was initially present in the solution and slowed down when Cl– was added after the preferential corrosion occurred. Reference [1] S. Yin, X. Wang, W. Li, H. Liao, H. Jie, Deformation behavior of the oxide film on the surface of cold sprayed powder particle, Applied Surface Science, 259 (2012) 294-300.[2] Y. Ichikawa, R. Tokoro, M. Tanno, K. Ogawa, Elucidation of cold-spray deposition mechanism by auger electron spectroscopic evaluation of bonding interface oxide film, Acta Materialia, 164 (2019) 39-49.[3] J. Tam, B. Yu, W. Li, D. Poirier, J.-G. Legoux, J.D. Giallonardo, J. Howe, U. Erb, The effect of annealing on trapped copper oxides in particle-particle interfaces of cold-sprayed Cu coatings, Scripta Materialia, 208 (2022) 114333.

A continuous toolpath strategy from offset contours for robotic additive manufacturing

Toolpath planning is an essential component of robotic additive manufacturing. An efficient toolpath strategy allows parts to be made that are geometrically accurate, free of defects, have good mechanical properties and have low residual stress. Toolpaths for cold spray additive manufacturing have some technical constraints that need to be considered compared to their counterpart designed for conventional 3D printing machines. This study presents an automated toolpath planning method based on offset contours. The generated toolpath is globally continuous, layer-wise setting, making it suitable for robotic cold spray additive manufacturing. The toolpath algorithm was tested on a variety of geometries to demonstrate its robustness. One model was selected for printing using a commercial high-pressure cold spray system. The experimental results show that our method is applicable to cold spray robotic additive manufacturing for near-net shape construction. The method is particularly good for web-rib structures.

Enhanced wear and corrosion resistances of Al coated Mg alloy using high pressure cold sprayed commercially pure-zirconium coating

Commercially pure (CP) Zr coating with high microhardness (387 ± 26 HV0.025) was produced on CP-Al coated Mg alloy by a high pressure cold spray (HPCS) system. Substantial densification of Al layers, beneath deposited Zr coating, was observed because of shot-peening influence by Zr particles. The electrochemical impedance spectroscopy after 24 h of immersion in 3.5 wt% NaCl electrolyte revealed highest charge transfer resistance (Rct), polarization resistance (Rpol), and corrosion resistance (|Z|f=0.01Hz) for the Zr/Al coated Mg alloy. Also, wear rate for the Zr/Al coating was lowest which could be attributed to its higher hardness caused by smaller crystallite size and higher dislocation density.

The effect of process temperature and powder composition on microstructure and mechanical characteristics of low-pressure cold spraying aluminum-based coatings

The effect of operating gas temperature and powder type on microstructure and mechanical characteristics of cold spraying coatings deposited on EZ33A-T5 magnesium alloy was studied. Three aluminum-based cold spraying powder mixtures Al + Zn, Al + Al2O3 and Al + Zn + Al2O3 were used for the investigation. Deposition was performed using D423 low-pressure cold spray system at operating gas pressure of 1.0 MPa and different temperatures –300 °C, 450 °C, and 600 °C. The coatings microstructure was investigated with optical and scanning electron microscopy. Mechanical properties of the coatings were characterized through standard test methods for adhesion and cohesion strength, and standard test methods for Vickers hardness of thermal spray coatings. The results demonstrate that with increasing initial gas temperature at spraying nozzle inlet from 300 °C to 600 °C, an increase in the porosity of the coatings of all investigated powder mixtures can be observed. Microstructure characterization showed an increase in porosity from 2.3% to 4.1% for Al + Zn powder mixture, from 2.1% to 3.5% for Al + Al2O3 powder mixture, and from 2.5% to 5.6% for Al + Zn + Al2O3 powder mixture. The minimum porosity was obtained at 450 °C for all investigated powder mixtures. Adhesion and cohesion strength and microhardness of coatings were reach their maximum value at 450 °C. The best performance was obtained for Al + Al2O3 powder mixture: coating adhesion—31.9 MPa (was limited by the bonding strength of the glue), cohesion—93.5 MPa, microhardness—81 HV0.15. The influence of Al2O3 particles in the powder mixture on the above-mentioned parameters was also established. The results show that the presence of ceramic particles in powder mixtures can positively effect porosity level and mechanical characteristics.

HIGH-TEMPERATURE DRY SLIDING WEAR BEHAVIOR OF COLD-SPRAYED INCONEL 738 COATING

This paper deals with the dry sliding wear behavior of cold-sprayed Inconel 738 (IN 738) coating up to 600∘ C. The coating was deposited by a high-pressure cold spray system using helium as the propellant on T11 low-carbon steel substrate. The dry sliding wear behavior of uncoated specimens is compared with IN 738 coating using pin-on-disk tribometer (ASTM G99). SEM, EDX, and XRD analyses provide better insights on the worn surface morphology, changes in oxide scales, and phase transformation. At 400∘C, the tribo-layer developed at the interface contains NiO, which is a lubricious oxide, which reduces the wear rate of the coating. With further increase in temperature up to 600∘C, there is a formation of a protective layer, which results in the enhancement of high-temperature dry sliding wear resistance of the coating. At 600∘C, sliding wear resistance offered by the coating is approximately four times higher than T11 low-carbon steel. Therefore, the developed cold-sprayed IN 738 has high potential for usage at elevated-temperature dry sliding applications.

Measurement methods for quantifying powder flowability and velocity in cold spray systems

Four powders with varying bulk densities, Al, Al2O3, Sn, and Cu, were used to determine quantifiable relationships between powder flowability, mass flow rate, and powder velocity with particle morphology and particle distribution in a cold spray system. High particle density results in good powder flowability, specifically when the powders are spherical relative to irregular morphology. Particle velocity during cold spray, measured with a double disk rotary system, increases non-linearly with an increase of inlet pressure. The increase in mass flow rate from the hopper and the resulting mass output of the cold spray system shows a consequence of good powder flowability. Conversely, a high mass flow rate decreases the particle velocity during the cold spray process, with better flowability leading to decreases on the order of 10% in particle velocity in the cold spray system. The described methods, proposed tools, and findings can be easily made with cost-effective and on-the-spot measurements.

Portable cold spray technology

VRC Metal Systems explains the technology behind its new portable cold spray system.

Application and assessment of the improved delayed detached eddy simulation model to the cold spray process: Toward high fidelity computation fluid dynamics simulations

Despite many years of research about the comprehension of fluid-dynamic related phenomena and improvements in the performance of cold spray systems, ensuring high fidelity simulations of gas and particle flow remains a challenge. In this work, a detailed high fidelity modeling, namely, improved delayed detached eddy simulation, in axisymmetric geometries was proposed and compared with a more usual numerical framework, the Reynolds averaged Navier–Stokes model. After its validation against literature data in three different nozzle configurations, the new model could demonstrate more accurate predictions of phenomena such as oblique shocks, bow shock, and particle–gas flow coupling. Finally, thanks to the high fidelity numerical framework, a new nozzle geometry with a narrower extension of the particle jet was proposed and assessed.

Cold Spray-Based Additive Manufacturing of Thermosets

This research proposes an approach of utilizing thermosetting polymer powders for additive manufacturing via a customized low-pressure cold spray system. To reveal the underlying deposition mechanisms during the polymer powder-impacting process, the microstructure, thermal and mechanical properties of deposited samples are examined and compared with those of the as-received and fully cured materials. It is found that severe plastic deformation, partial melting, and curing reaction (including latent curing agent decomposition and cross-link reaction) occur simultaneously to form the bonding. However, due to the insufficient heat generation for complete cross-linking reaction, a post-heat treatment is needed to improve the mechanical properties of the fabricated objects, where a low heating rate is necessary to maintain the sample geometry.

Current Implementation Status of Cold Spray Technology: A Short Review.

In recent years, cold spray technology has attracted more and more attentions. After more than 30 years of rapid development, research focus of cold spray technology is gradually shifting from fundamental and theoretical studies to application developments, some of which have been industrialized and mass-produced. In this paper, the characteristics of cold spray technology, cold spray materials perspectives and cold spray system developments were briefly introduced. Besides, the recent developments of cold spray applications in different fields including aerospace, biomedical, energy, electronics, semiconductor fields were discussed. Although cold spray technology is in the early stages of implementation, it has demonstrated a great potential to reduce costs and improve performance. World-wide awareness of ongoing and planned cold spray programs is critical to expand its applications and benefits.

Effect of Gas Propellant Temperature on the Microstructure, Friction, and Wear Resistance of High-Pressure Cold Sprayed Zr702 Coatings on Al6061 Alloy

For the first time, Zr702 coatings were deposited onto an Al6061 alloy using a high-pressure cold spray (HPCS) system. In this work, five different N2 process gas temperatures between 700 and 1100 °C were employed to understand the formation of cold sprayed (CS) Zr coatings and their feasibility for enhanced wear resistance. Results indicated that the N2 processing gas temperature of about 1100 °C enabled a higher degree of particle thermal softening, which created a dense, robust, oxide- and defect-free Zr coating. Across all CS Zr coatings, there was a refinement of crystallinity, which was attributed to the severe localized plastic deformation of the powder particles. The enhanced thermal boost up zone at the inter-particle boundaries and decreased recoverable elastic strain were accountable for the inter-particle bonding of the coatings at higher process gas temperatures. The flattening ratio (ε) increased as a function of temperature, implying that there was a greater degree of plastic deformation at higher N2 gas temperatures. The microhardness readings and wear volume of the coatings were also improved as a function of process gas temperature. In this work, the wear of the Al6061 alloy substrate was mainly plowing-based, whereas the Zr CS substrates demonstrated a gradual change of abrasive to adhesive wear. From our findings, the preparation of CS Zr coatings was a feasible method of enhancing the wear resistance of Al-based alloys.

Inconel 713C Coating by Cold Spray for Surface Enhancement of Inconel 718

Inconel 713C is a nickel-based superalloy usually considered as a material of poor weldability due to its susceptibility to hot cracking in the heat-affected zones. Cold spray, a solid-state deposition technology that does not involve melting, can be proposed as a methodology to deposit Inconel 713C for surface enhancement of other target components. In this study, Inconel 713C coating was deposited on Inconel 718 substrate with a high-pressure cold spray system. The coating was characterized in terms of microstructure, hardness, and wear properties. The cold-sprayed Inconel 713C coating has a low porosity level and refined grain structures. Microhardness of the Inconel 713C coating was much higher than the Inconel 718 substrate. The sliding wear tests showed that the wear resistance of the cold-sprayed Inconel 713C coating is three times higher than the Inconel 718 substrate, making the coating a suitable protective layer. The main wear mechanisms of the coating include oxidation, tribo-film formation, and adhesive wear.

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.

Towards optimization of thickness, hardness, and porosity of low-pressure cold sprayed WC-Ni coatings

In this study, a 33 full factorial design methodology was used to analyze the effects of spray parameters on the thickness, hardness, and surface porosity of low-pressure cold-sprayed WC-17Ni coatings. Three levels were selected for the spray parameters included in the design which were the powder feed rate (17.1 g/min, 21.1 g/min, and 23.7 g/min), gas temperature (475°C, 500°C, and 525°C), and the nozzle to substrate stand-off distance (3 mm, 5 mm, and 10 mm). It was found that the feed rate was the most significant parameter that affected the coating thickness. The surface porosity was most significantly affected by stand-off distance. The coating hardness was most influenced by the interaction between the feed rate and stand-off distance. An optimization study was then performed to maximize the coating thickness and hardness while minimizing the surface porosity. The optimal spray parameters (OSP) were found to be at a feed rate of 23.7 g/min, 500°C for the carrier gas temperature, and 10 mm for the stand-off distance. The OSP yielded a coating that was 1.22 ± 0.06 mm thick, with a hardness of 364.5 ± 8.5 HV and porosity of 6.8 ± 0.6%. With a multi-parameter process, the system response is affected by both the variation in the individual parameters and the interaction of the parameters with each other. It was also concluded that the interaction between the parameters significantly affected the coating hardness. These results suggest that variation of the selected parameters produce statistically significant effects on the coating quality of WC-17Ni coatings using a low-pressure cold spray system.

Metallization of polymers by cold spraying with low melting point powders

Polymers and polymer composites have been increasingly used due to their low density and high specific strength; however, their low electrical conductivity has limited their further application. Cold spray has recently been proven to be a feasible approach to metallize polymers. Previous results have shown that tin can be cold sprayed onto polymeric substrates when spraying with a low-pressure cold spray system at gas temperatures close to the melting point of tin. The successful deposition of tin was partly attributed to the tin reaching its incipient melting point. In this work, three low melting point metal powders, namely, Sn, Sn-Zn alloy, and Sn-Bi alloy, were cold sprayed onto five widely used engineering polymers . Different combinations of gas temperature and gas pressure were assessed. Results show that decreasing the melting points of the feedstock powders can improve their deposition efficiency on polymeric substrates, due to a higher degree of particle melting. Among the five polymers, the high-toughness ultra high molecular weight polyethylene and polycarbonate were relatively difficult to metallize. • SnZn and SnBi powders with lower melting points than Sn were cold sprayed on polymeric substrates. • Five common engineering thermoplastic polymers (ABS, Nylon, PC, PE, and PP) were metallized using low melting point powders. • Particle melting facilitated the deposition and inter-particle bonding, resulting in high deposition efficiency. • SnBi coatings exhibit higher adhesion to ABS than Sn when spraying at 300°C and 60 psi.

A framework for a knowledge based cold spray repairing system

Restoring damaged components is a very promising and high-value project, which enable to save a lot of production time and cost, and thus has already attracted wide attention, especially in the aviation industry. In the past few years, cold spray (CS) had been widely adopted in restoration and repair applications due to its unique advantages, such as no thermal influence, high efficiency, flexibility, etc. Nowadays, speeding up the product lifecycle as well as improving the accuracy and reliability of CS based repairing require an advance strategy with higher efficiency and more agility. To respond to this need, in this article, a concept on the development of a knowledge based intelligent CS repairing framework is presented. The framework includes a 3D scanning system for providing the information needed on the partially damaged part to repair, a dynamic defect repairing knowledge base for providing related standard defect geometry repairing strategy, including matching the standardized defect geometry, machining pre-treatment, CS toolpath, CS parameter setting, etc., and a CS additive repair system involving robotic repair trajectory programming, simulation and material deposition. Based on the proposed framework, the design of intelligent CS additive repair system and its flow are explained. The novel repair strategy and method proposed in this article can become a model for the metal repair industry in the future.