High Pressure Cold Spray Research Articles

ПЕРСПЕКТИВЫ ПРИМЕНЕНИЯ ТЕХНОЛОГИИ ХОЛОДНОГО ГАЗОДИНАМИЧЕСКОГО НАПЫЛЕНИЯ ДЛЯ ЗАЩИТЫ И ВОССТАНОВЛЕНИЯ ДЕТАЛЕЙ ИЗ МАГНИЕВЫХ СПЛАВОВ

Magnesium alloys are widely used in modern technology, especially in the aviation and automotive industries, primarily due to low density, which allows reducing the weight of products and structures significantly. However, one of the main disadvantages of magnesium alloys is low corrosion resistance, which limits the possibilities of their wide application. A large number of magnesium parts of helicopters are prone to corrosion in places of contact with parts made of other metals forming a galvanic couple. Moreover, magnesium alloys are also susceptible to surface damage due to impact, which often occurs in the manufacture, repair and maintenance of aviation equipment. Scratches and damage can lead to local corrosion. It is shown that energy- and resource-saving cold spraying technology is effective and advanced technology for repairing and recovering of magnesium parts against corrosion. The cold gas-dynamic spraying technology is a relatively new industry among the processes of thermal spraying. The cold spray process is based on accelerating the metal powder particles with a supersonic gas stream in the Laval nozzle followed by an impact on the substrate and the formation of a coating. The process is characterized in that the powder material used in the spraying process does not melt and therefore the oxidation of the coating decreases; there are no phase changes in the material and no considerable heating of the substrate. The results of the analysis of the current state of cold spraying of protective and restorative coatings as well as the analysis of the aviation engines magnesium parts manufactured by «MOTOR SICH», their damages, in particular corrosion, causes of occurrence and current protection methods are accomplished. The works aimed to deposition of cold spray corrosion-resistant coatings and its application for restoration and protection of magnesium parts against corrosion are analyzed. The previous work in the field of cold spraying of anticorrosive coatings was mainly aimed to achieving maximum density of coatings, since the absence of through porosity provides reliable protection of the base material. Coatings with a minimum porosity were obtained using the high-pressure cold spray systems. The analysis showed that the issue of using low-pressure cold-spray equipment remains open and confirms the urgency of further research

Structural Search for High Pressure CS2 and Xe–Cl Compounds

The recent successful implementation of several methodologies for the prediction of crystal structures based on the first-principles electronic structure have ushered in a new area of computational chemistry. In this study, the two most popular methods, namely genetic evolution and particle swarm optimization, were applied to the investigation of stable crystalline polymorphs of solid carbon disulfide and xenon halides at high pressure. It was found that both methods have their own merits. However, there are subtleties that need to be considered for the proper execution of the methods. We found a two-dimensional (2D) layered structure that may be responsible for the superconductivity in CS2. Except for XeCl2, no thermodynamically stable crystalline Xe halides were found under 60 GPa in the halide-rich region of the phase diagram.

Fatigue behavior of freestanding AA2024 and AA7075 cold spray deposits

This paper examines the fatigue properties of freestanding AA7075 and AA2024 Cold Spray (CS) deposits. In this study, high pressure cold spray was used to make deposits large enough to machine mechanical test specimens free from the substrate. To quantify the mechanical performance, monotonic tensile and stress-controlled fatigue experiments were carried out on the freestanding CS and wrought AA7075 and AA2024 specimens. The experimental fatigue results revealed a reduction in the stress-life behavior of the CS deposits compared to the corresponding wrought material. However, when normalized by their ultimate tensile strengths, the CS specimens compared very well with the wrought materials, especially for the CS AA7075. Post-mortem analysis of the CS specimens revealed that fatigue cracks typically initiated from layer interface defects and subsequent crack propagation was influenced by the CS prior-particle boundaries. The results from this study indicate that refining the layer interface bonding may increase the fatigue resistance of freestanding aluminum alloy CS deposits.

Deposition characteristics of cold sprayed Inconel 718 particles on Inconel 718 substrates with different surface conditions

This article examined the coating/substrate interface characteristics of IN718 coatings deposited on IN718 substrates using a high pressure cold spray technique. The study was aimed at a greater insight into the coating/substrate bonding mechanism under varying substrate conditions, namely surface roughness and surface preheating, from both experimental data and simulations. The coating/substrate interface microstructure and bonding strength were systematically investigated. The coating/substrate strengths were measured by using tensile and shear tests. A finite-element model on the single particle impact was used to explain and validate the experimental data and analyze the particle bonding behavior with the substrate at different preheating temperatures. The analysis of the coating/substrate interface revealed that a polished IN718 substrate surface could promote adiabatic shear instability as well as the formation of material jetting and thus resulting in a high interface bonding strength. In addition, the preheating of the substrates could increase the metallurgical bonding and promote the coating/substrate adhesion strength.

Structural repair using cold spray technology for enhanced sustainability of high value assets

Cold spray technology has been in significant development since the early 1990s, however, not until recently has it begun to approach near wrought like properties for metals and alloys of aluminum, copper, nickel, titanium, as well as steels, stainless steels, superalloys, and refractory metals like niobium and tantalum. These advancements have come through the use of high pressure cold spray equipment and a greater fundamental understanding of the process variables. As a result, numerous applications have been developed for repairing high cost and long lead time parts for the aerospace and defense market, as well as a broad range of commercial markets such as oil & gas, transportation, and heavy industry. In particular, parts with lead times in excess of 12 months have been successfully repaired and re-introduced into service. This saves not only the direct cost of the part, but also returns the system to service much sooner. Cold spray is an additive manufacturing technology that uses heated high-pressure inert gas to accelerate metal powders through a converging-diverging de Laval nozzle above the critical velocity for deposition onto a substrate. The process produces only mild heating of the substrate compared to most conventional metal deposition or welding technologies, hence the nomenclature of “cold” in cold spray, even though there is heating of the gas in almost all cases. There are also no toxic fumes or other harmful emissions from cold spray because the accelerant gases are: 1) inert (helium, nitrogen, or air), and 2) the heating source is electric and is controlled at temperatures below the melting temperature of the material being sprayed. Furthermore, because parts are being repaired and refurbished rather than replaced, there is tremendous cost, energy, and overall environmental benefit, making cold spray a very “green” technology and an excellent technology for enhancing the long-term sustainability of high value assets.

Influence of feedstock powder and cold spray processing parameters on microstructure and mechanical properties of Ti-6Al-4V cold spray depositions

A high pressure cold spray system was used to deposit three Ti-6Al-4V feedstock powders (i.e., hydride de-hydride, plasma atomized, and gas atomized) on Ti-6Al-4V substrates while varying gas temperature and nozzle length. Particle impact temperature and particle velocity were calculated using a 1-D axial model. The microstructure of the feedstock powders and the cold spray depositions were characterized via optical and scanning electron microscopy. The hardness of the as-received powders was determined using nanoindentation. To assess deposition quality, coatings were characterized in terms of porosity, microhardness, and adhesion strength. Results showed that hydride de-hydride powders were characterized by an equiaxed alpha grain structure with intergranular beta phase regions while atomized powders were characterized by martensitic α phase structures. Cold sprayed coatings revealed two distinct microstructures. Regions that experienced low/moderate plastic strain retained the as-received powder microstructure while regions that experienced significant plastic strain were characterized either by a featureless microstructure (atomized coatings) or the presence of fine, elongated beta precipitates (hydride de-hydride coatings). Depositions performed using a long nozzle resulted in the best deposition quality, with porosity as low as 0.3% and adhesion strengths >69MPa. While atomized powders resulted in comparatively higher quality coatings for all process conditions, hydride de-hydride coatings of excellent quality (average porosity≈0.6%, adhesion strength >65MPa) were achieved under optimal conditions. Thus, hydride de-hydride powders may hold promise as a cost effective alternative to atomized powders for Ti-6Al-4V cold spray depositions.

Influence of Powder Injection Parameters in High-Pressure Cold Spray

High-pressure cold spray systems are becoming widely accepted for use in the structural repair of surface defects of expensive machinery parts used in industrial and military equipment. The deposition quality of cold spray repairs is typically validated using coupon testing and through destructive analysis of mock-ups or first articles for a defined set of parameters. In order to provide a reliable repair, it is important to not only maintain the same processing parameters, but also to have optimum fixed parameters, such as the particle injection location. This study is intended to provide insight into the sensitivity of the way that the powder is injected upstream of supersonic nozzles in high-pressure cold spray systems and the effects of variations in injection parameters on the nature of the powder particle kinetics. Experimentally validated three-dimensional computational fluid dynamics (3D CFD) models are implemented to study the particle impact conditions for varying powder feeder tube size, powder feeder tube axial misalignment, and radial powder feeder injection location on the particle velocity and the deposition shape of aluminum alloy 6061. Outputs of the models are statistically analyzed to explore the shape of the spray plume distribution and resulting coating buildup.

Adhesion, tribological and corrosion properties of cold-sprayed CoCrMo and Ti6Al4V coatings on 6061-T651 Al alloy

In this study, CoCrMo and Ti6Al4V coatings were deposited on 6061-T651 aluminum alloy substrates via a high pressure cold spray process. Adhesion, tribological and corrosion properties of the CoCrMo and Ti6Al4V coatings were systematically investigated. The CoCrMo and Ti6Al4V coatings had good quality with low porosity levels and high hardnesses. X-ray diffraction patterns showed that there were no phase change and oxidation for the CoCrMo and Ti6Al4V coatings with reference to the CoCrMo and Ti6Al4V powder feedstocks. The shear bonding tests indicated good adhesion quality between the coatings and substrates. The tribological results showed that the CoCrMo coatings significantly enhanced the wear resistance of the Al alloy substrates. The corrosion results showed that the CoCrMo and Ti6Al4V coatings had higher anti-corrosion performances compared to the bare Al alloy substrates in a 3.5wt% NaCl solution as the corrosion current densities for the CoCrMo and Ti6Al4V coated samples were substantially reduced.

Wear and Corrosion Resistance of Thick Ti-6Al-4V Coating Deposited on Ti-6Al-4V Substrate via High-Pressure Cold Spray

Ti-6Al-4V (Ti64) coating with a thickness of about 9 mm was deposited on commercial Ti64 substrate via a high-pressure cold spray process. The microstructure, hardness, and wear and corrosion resistance of the Ti64 coating were systematically investigated. The hardness of the Ti64 coating was higher than that of the Ti64 substrate due to the cold-worked microstructure of the coating. The tribological results showed that there was no significant difference in the surface wear rates of the Ti64 coating measured on its different layers while the surface wear resistance of the Ti64 coating was lower than its cross-sectional wear resistance. The corrosion results showed that the Ti64 coating did not effectively prevent its underlying Ti64 substrate from corrosion due to the occurrence of pores in the coating microstructure. It could be concluded that the hardness and wear resistance of the Ti64 coating were comparable to those of the commercial Ti64 substrate.

Review of Relationship Between Particle Deformation, Coating Microstructure, and Properties in High-Pressure Cold Spray

In the cold spray (CS) process, deposits are produced by depositing powder particles at high velocity onto a substrate. Powders deposited by CS do not undergo melting before or upon impacting the substrate. This feature makes CS suitable for deposition of a wide variety of materials, most commonly metallic alloys, but also ceramics and composites. During processing, the particles undergo severe plastic deformation and create a more mechanical and less metallurgical bond with the underlying material. The deformation behavior of an individual particle depends on multiple material and process parameters that are classified into three major groups—powder characteristics, geometric parameters, and processing parameters, each with their own subcategories. Changing any of these parameters leads to evolution of a different microstructure and consequently changes the mechanical properties in the deposit. While cold spray technology has matured during the last decade, the process is inherently complex, and thus, the effects of deposition parameters on particle deformation, deposit microstructure, and mechanical properties remain unclear. The purpose of this paper is to review the parameters that have been investigated up to now with an emphasis on the existent relationships between particle deformation behavior, microstructure, and mechanical properties of various cold spray deposits.

Tribological and Corrosion Characteristics of Ti6Al4V Coatings Cold Sprayed with Nitrogen and Helium Propellant Gases

The tribological and corrosion characteristics of Ti6Al4V coatings on Ti6Al4V substrates with nitrogen (N2) and helium (He) propellant gases cold sprayed via a high pressure cold spray process were investigated because different masses of the N2 and He working gases could affect the velocities of Ti6Al4V particles during the cold spraying and consequently the properties of the coatings. The more uniform and denser structure of the Ti6Al4V coatings with a lower porosity level was achieved with He working gas. As a result, the Ti6Al4V coatings deposited with the He working gas had a higher hardness than those deposited with the N2 working gas. The tribological results showed that the use of He gas during the cold spraying produced the more wear resistant Ti6Al4V coatings associated with their higher hardness. The denser Ti6Al4V coatings deposited with the He gas had a lower anodic current density in a NaCl solution than those deposited with the N2 working gas. It is clear that the wear and corrosion resistances of the Ti6Al4V coatings were significantly influenced by the propellant gases during the cold spray deposition.

Cold spraying of WC-Co-Ni coatings using porous WC-17Co powders: Formation mechanism, microstructure characterization and tribological performance

WC-Co metal matrix composite is frequently applied in the form of coating to prevent the underlying base materials from serious wear. Cold spray has been successfully used to produce WC-Co coatings in recent years, showing great potential. However, due to the lack of sufficient Co matrix phase for plastic deformation, the fabrication of cold sprayed WC-Co coating naturally requires expensive propulsive gas or very high working parameters, significantly increasing the manufacturing difficulty and cost. This paper aims to use conventional high pressure cold spray to fabricate WC-Co-Ni wear-resistance coatings under moderate working parameters, and to clarify the coating formation mechanism. To achieve this objective, mechanically mixed porous WC-17Co and dense Ni powders were selected as the feedstock with different WC mass fractions, F1 (41.5 wt%), F2 (64.5 wt%) and F3 (74.7 wt%). Working parameters were set at a moderate level (nitrogen, 3.0MPa and 350°C). Experimental results show that the WC reinforcements had no phase transformation and were completely retained in the WC-Co-Ni coatings as compared with in the feedstock. Fracture of the porous WC-Co particles during the deposition process was found to be the reason for such high WC retainability, dominating the coating formation mechanism. Tribological performance test shows that the coating hardness, toughness and wear-resistance performance improved as the WC content increased from the F1 to F3 coating. Wear mechanism analysis demonstrates that the F3 coating exhibited a completely different wear mechanism from the F1 and F2 coatings, thus the F3 coating had the best wear-resistance performance.

Effect of substrate surface condition on fatigue behavior of cold sprayed Ti6Al4V coatings

Ti6Al4V coatings were deposited on Ti6Al4V substrates by using a high pressure cold spray system. Before deposition, the substrate surfaces were prepared with four different surface preparation methods, namely, grinding, milling, sand blasting and water-jet cutting. The fatigue behavior of the coated specimens was studied with three point-bending-fatigue test. The fracture characteristics of the specimens were observed by using scanning electron microscopy. The surface roughness and its effect on the crack initiation and propagation in the coatings were also investigated. The results indicated that the fracture mode of the coated samples was interface cracking. At two different stress levels such as 420 and 360MPa, the samples with the coatings deposited on the ground surfaces survived the longest fatigue life before failure, while the samples with the coatings deposited on the water-jet cut surfaces survived the shortest fatigue life. It was clearly shown that the fatigue strength of the cold sprayed Ti6Al4V coatings was strongly affected by the both spraying and substrate surface preparation conditions.

The effects of heat treatment on 7075 Al cold spray deposits

High-pressure cold spray was used to deposit 7075 aluminum powder onto 7075-T6 substrates. We investigated the effects of post deposition heat treatments on the microstructure and mechanical properties of the deposits. For this purpose, both low-temperature and high-temperature treatments were carried out on specimens excised from the deposits. Microstructures of the as-deposited and heat treated samples were characterized via different microscopy techniques and mechanical properties were evaluated by microtensile and hardness tests. The results were then correlated with the observed microstructures in different conditions. The strength and ductility of the cold sprayed 7075 deposits increased after both low- and high-temperature treatments, which resulted in precipitation of strengthening phases and increased inter-particle bonding. Because of a change in bonding mechanism, heat treatment at high temperature yielded markedly greater ductility than all other conditions. Diffusion and microstructural sintering at the particle-particle interfaces were proposed to cause the change in bonding mechanism from mechanical interlocking to metallurgical bonding and lead to the ductile characteristics of these samples. The understanding gained from this research should lead to optimization of and pre- and post-processing treatments for cold spray deposits.

Flow boiling heat transfer of R1234yf on a microparticle coated copper surface

This article investigates the flow boiling heat transfer of the low global warming potential refrigerant R1234yf on a microparticle coated surface obtained via high-pressure cold spray, a simple and nonexpensive technique. The sample was obtained by depositing pure copper particles with average size of 20 μm obtaining a 0.1 mm thick coating on a smooth copper plate 10 mm wide and 200 mm long. The experimental measurements were carried out at constant saturation temperature of 30°C, by varying the heat flux from 50 to 100 kW m−2, the refrigerant mass flux from 30 to 200 kg m−2 s−1, and the vapor quality from 0.2 to 0.99. The coating was found to be hydrophilic, leading to hysteresis on the heat transfer behavior, which is discussed in detail. Furthermore, the experimental results are compared against similar measurements obtained during R1234yf flow boiling over a plain copper surface.

Effect of Heat Treatment Temperature on Microstructure and Mechanical and Tribological Properties of Cold Sprayed Ti-6Al-4V Coatings

ABSTRACTIn this study, Ti-6Al-4V (Ti-64) coatings were prepared on commercial Ti-64 substrates via a high-pressure cold spray process. The coatings were heat treated at different temperatures of 400–1000°C to investigate the effect of heat treatment temperature on their microstructure and mechanical and tribological properties. The increased heat treatment temperature from 400 to 600°C promoted diffusion between sprayed Ti-64 particles. Recrystallization of the sprayed particles was found at the heat treatment temperature of 800°C and grain growth was found in the microstructure of the coating heat treated at 1000°C. The highest and lowest hardnesses of the heat-treated coatings were found at heat treatment temperatures of 400 and 800°C, respectively. Therefore, the lowest and highest specific wear rates of the coatings were consistently found at 400 and 800°C due to their highest and lowest abrasive wear resistances associated with their highest and lowest surface hardnesses, respectively. The coating heat treated at 400°C showed the highest surface hardness of 470.1 Hv and lowest specific wear rate of 69.6 × 10−14 m3/Nm. It could be concluded that the microstructure and mechanical and tribological properties of the Ti-64 coatings were significantly influenced by heat treatment temperature.

Retraction Note to: Structure and Mechanical Properties of Thick Copper Coating Made by Cold Spray

The main purpose of this study was to form cold-sprayed copper coatings on A 516 low carbon steel, which is considered a prospective material for manufacturing used nuclear fuel containers. The 3 mm-thick Cu coatings were formed using the high pressure cold spray method with Nitrogen as the propellant gas. The deformation of copper particles during the deposition process was studied. The obtained SEM images of the Cu layer-A 516 low carbon steel substrate interface cross sections demonstrated that the Cu layer at the substrate interface had a dense microstructure with localized jet-metallic mixing areas. The Cu particles were deformed considerably more severely in this layer than in the consequently deposited upper layers. The steel substrate underwent severe deformation due to the impact of Cu particles. The mutual severe deformation of Cu particles and steel substrate resulted in a considerable increase of adhesion strength up to 120 MPa. The structure of coatings and coating-substrate interface was studied.

707 高圧コールドスプレーにおける矩形断面ノズルの形状の最適化 : ノズル末広部と平行部の長さの比の影響(GS3-2 材料加工)

707 高圧コールドスプレーにおける矩形断面ノズルの形状の最適化 : ノズル末広部と平行部の長さの比の影響(GS3-2 材料加工)

高圧コールドスプレーにおける矩形断面ノズルの形状の最適化

In the cold spray process, cross-sectional shape of the nozzle has a significant effect on spray pattern of coatings. Spray pattern of the rectangular spray nozzle is wider than that of the circular spray nozzle. Accordingly, rectangular nozzle is better efficiency than circular nozzle at spray a constant width. The goal of this investigation is to establish a design for the cold spray gun nozzle in order to gain a flatter the spray pattern of coatings. We have investigated the effect of expansion ratio of rectangular nozzle on spray pattern of copper coatings in cold spraying by the computational fluid dynamics (CFD) and experiments. And the particle velocity and deposition efficiency of the copper coatings were dependent on the expansion ratio and geometry of the rectangular nozzle. In this study, CFD and experiments investigated the influence of length of divergent and parallel section of the converging-diverging parallel-shaped rectangular cross-section (C-D-Para-Re) nozzle on behaviours of the gas and copper particles (20μm) in high-pressure cold spray, and C-D-Re nozzle, too. As the results, it found that there is an optimal ratio of the length of the diverging section and the parallel section for C-D-Para-Re nozzle.

Application of High-Pressure Cold Spray for an Internal Bore Repair of a Navy Valve Actuator

Cold spray is a reduced temperature, supersonic thermal spray process that is increasingly being used to perform repairs on high-value components. In this case, a valve actuator internal bore sealing surface was repaired on an aluminum 6061 hydraulic valve body using high-pressure cold spray. Corrosion damage to non-critical surfaces was also repaired, allowing the part to be returned to service. A high-pressure cold spray system was used to deposit gas-atomized 6061 aluminum powder using helium. The internal bore surfaces were approximately 100 mm in diameter with a depth of nearly 200 mm, and were sprayed using a 45° nozzle 65 mm in length. Modeling predictions validated the approach, and were used to identify a favorable nozzle geometry and process window combination. The minimum required adhesion strength on critical surfaces was 69 MPa. The average adhesion strength was 71.4 MPa, with glue failures on ASTM C633 bond test specimens. The actuator subsequently passed all bench top service related testing, was qualified as an approved repair, and is now in service. This was a first of its kind repair for cold spray, and demonstrates that it is a viable repair technology and is ready for broader implementation.