Cold spraying

Last updated
Particle temperature and velocity for different thermal spraying processes Comparison of thermal spray processes.png
Particle temperature and velocity for different thermal spraying processes
Schematics of cold spraying Cold spray schematics.png
Schematics of cold spraying
SEM image of a cold sprayed titanium particle bonded to steel surface TH33ARM.TIF
SEM image of a cold sprayed titanium particle bonded to steel surface

Gas dynamic cold spraying or cold spraying (CS) is a coating deposition method. Solid powders (1 to 50 micrometers in diameter) are accelerated in a supersonic gas jet to velocities up to ca. 1200 m/s. During impact with the substrate, particles undergo plastic deformation and adhere to the surface. To achieve a uniform thickness the spraying nozzle is scanned along the substrate. Metals, polymers, ceramics, composite materials and nanocrystalline powders can be deposited using cold spraying. [2] [3] The kinetic energy of the particles, supplied by the expansion of the gas, is converted to plastic deformation energy during bonding. Unlike thermal spraying techniques, e.g., plasma spraying, arc spraying, flame spraying, or high velocity oxygen fuel (HVOF), the powders are not melted during the spraying process. [1] [4]

Contents

History

Cold spraying was developed by Russian scientists in the 1990s. While experimenting with the particle erosion of the target, which was exposed to a two-phase high-velocity flow of fine powder in a wind tunnel, scientists observed accidental rapid formation of coatings. This coating technique was commercialized in the 1990s. [1]

Types

There are two types of CS. High pressure cold spraying (HPCS) in which the working gas is nitrogen or helium at pressures above 1.5 MPa, [5] a flow rate of more than 2 m3/min, heating power of 18 kW. It is used for spraying pure metal powders with the sizes of 5–50 μm. In low-pressure cold spraying (LPCS), the working gas is a compressed gas with pressure 0.5–1.0 MPa, flow rate 0.5–2 m3/min and the heating power 3–5 kW. It is used for spraying a mechanical mixture of metal and ceramic powders. The inclusion of a ceramic component in the mixture provides high-quality coatings with relatively low energy consumption. [6]

Basic principles

The most prevailing bonding theory in cold spraying is attributed to "adiabatic shear instability" which occurs at the particle substrate interface at or beyond a certain velocity called critical velocity. When a spherical particle travelling at critical velocity impacts a substrate, a strong pressure field propagates spherically into the particle and substrate from the point of contact. As a result of this pressure field, a shear load is generated which accelerates the material laterally and causes localized shear straining. The shear loading under critical conditions leads to adiabatic shear instability where thermal softening is locally dominant over work strain and strain rate hardening, which leads to a discontinuous jump in strain and temperature and breakdown of flow stresses. This adiabatic shear instability phenomena results in viscous flow of material at an outward flowing direction with temperatures close to melting temperature of the material. This material jetting is also a known phenomenon in explosive welding of materials. [7] [8] [9]

Key parameters in cold spraying

There are several factors that can affect the quality of cold-sprayed coatings and the deposition efficiency. Main influential factors are:

Cold spray parameters are selected with respect to the desired coating characteristics and economic considerations. This can be done by considering correlations between process parameters and final coating properties. [11] There are also software packages available for this purpose.

Advantages and disadvantages

CS has many advantages that make the technology potentially very competitive. Being a cold process, the initial physical and chemical particle properties are retained and the heating of the substrate is minimal, resulting in cold-worked microstructure of coatings where no melting and solidification happen. Dynamic recrystallization with refined grains has been observed between particle and particle bonding region. [12] [13] Furthermore, the technology allows to spray thermally sensitive materials and highly dissimilar materials combinations, due to the fact that the adhesion mechanism is purely mechanical.

Other advantages are: [14]

The jet obtained is a high-density particle beam due to the small size of the nozzle (10–15 mm2) and the short stand-off distance (25 mm). This results in high focus of the jet and precise control over the deposition area. Finally, inducing compressive stresses allows to obtain dense uniform and ultra-thick (20 μm – 50 mm) coatings.

On the other side, some difficulties can be found. For instance, it is difficult to spray hard and brittle materials because, in this case, mechanical adhesion through plastic deformation could be not as effective as it is for ductile particles. Other problems could include: [14]

Applications

Coatings

The ability for CS to deposit materials that are phase-sensitive or temperature-sensitive has positioned the technique to prepare coatings not possible with other thermal spray techniques. CS can generally be used to produce coatings of a wide variety of metals, alloys, and metal-based composites, including those materials that have an exceptionally high melting temperatures (e.g. tantalum, niobium, superalloys). The process is also valuable for depositing materials that are extremely sensitive to the presence of oxygen and will readily oxidize at modest elevated temperatures – a result which is deleterious to the performance of these materials. Some examples of oxygen sensitive coatings that are commonly produced with CS are aluminum, copper, titanium, and carbide composites (e.g. tungsten carbide), [15] as well as coatings made from amorphous alloys. [16]

Additional developments in CS are related to the deposition of ceramic materials on metals, notably titanium dioxide for photocatalytic effects, [17] and the use of CS in additive manufacturing. [18]

Repair

Cold spraying is now used to repair machine parts in a matter of minutes. Metal (nickel alloys) particles travel in a blend of nitrogen and helium gas and gradually stack up on the damaged part to recreate the desired surface. A robot controls the movement of the sprayer. The U.S. Army uses the technology to repair a component in Blackhawk helicopters. General Electric is adapting the technology for civilian applications. [19] The US Navy has adopted cold spray welding across its global operations on an experimental basis. [20]

Manufacturing

Additive manufacturing using cold spray technology can be used to develop parts and components rapidly with deposition rates as high as 45 kg/hour – much faster than other additive manufacturing methods.

Unlike other additive manufacturing methods such as selective laser melting or electron beam additive manufacturing, cold spraying does not melt metals. This means that metals are not affected by heat-related distortion, and parts do not need to be manufactured in an inert gas or vacuum sealed environment, allowing the creation of much larger structures. The world's largest and fastest metal 3D printer has a build envelope of 9×3×1.5 m and utilizes gas dynamic cold spray. Manufacturing with cold spray technology provides advantages such as the ability to create shapes with no shape or size constraints, more efficient buy-to-fly ratio when compared to machining, and capable of fusing dissimilar metals to create hybrid metal parts – materials such as titanium alloys, copper, zinc, stainless steel, aluminium, nickel, even hastelloy and inconel can be sprayed together. [21]

Related Research Articles

<span class="mw-page-title-main">Chemical vapor deposition</span> Method used to apply surface coatings

Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films.

<span class="mw-page-title-main">Metallurgy</span> Field of science that studies the physical and chemical behavior of metals

Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys.

In materials science, a metal matrix composite (MMC) is a composite material with fibers or particles dispersed in a metallic matrix, such as copper, aluminum, or steel. The secondary phase is typically a ceramic or another metal. They are typically classified according to the type of reinforcement: short discontinuous fibers (whiskers), continuous fibers, or particulates. There is some overlap between MMCs and cermets, with the latter typically consisting of less than 20% metal by volume. When at least three materials are present, it is called a hybrid composite. MMCs can have much higher strength-to-weight ratios, stiffness, and ductility than traditional materials, so they are often used in demanding applications. MMCs typically have lower thermal and electrical conductivity and poor resistance to radiation, limiting their use in the very harshest environments.

<span class="mw-page-title-main">Powder metallurgy</span> Process of sintering metal powders

Powder metallurgy (PM) is a term covering a wide range of ways in which materials or components are made from metal powders. PM processes can reduce or eliminate the need for subtractive processes in manufacturing, lowering material losses and reducing the cost of the final product.

A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films is a fundamental step in many applications. A familiar example is the household mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as sputtering. Advances in thin film deposition techniques during the 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media, electronic semiconductor devices, integrated passive devices, LEDs, optical coatings, hard coatings on cutting tools, and for both energy generation and storage. It is also being applied to pharmaceuticals, via thin-film drug delivery. A stack of thin films is called a multilayer.

<span class="mw-page-title-main">Titanium nitride</span> Ceramic material

Titanium nitride is an extremely hard ceramic material, often used as a physical vapor deposition (PVD) coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface properties.

A coating is a covering that is applied to the surface of an object, or substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. Powder coatings.

<span class="mw-page-title-main">Superalloy</span> Alloy with higher durability than normal metals

A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Key characteristics of a superalloy include mechanical strength, thermal creep deformation resistance, surface stability, and corrosion and oxidation resistance.

<span class="mw-page-title-main">Plasma electrolytic oxidation</span>

Plasma electrolytic oxidation (PEO), also known as electrolytic plasma oxidation (EPO) or microarc oxidation (MAO), is an electrochemical surface treatment process for generating oxide coatings on metals. It is similar to anodizing, but it employs higher potentials, so that discharges occur and the resulting plasma modifies the structure of the oxide layer. This process can be used to grow thick, largely crystalline, oxide coatings on metals such as aluminium, magnesium and titanium. Because they can present high hardness and a continuous barrier, these coatings can offer protection against wear, corrosion or heat as well as electrical insulation.

Titanium powder metallurgy (P/M) offers the possibility of creating net shape or near net shape parts without the material loss and cost associated with having to machine intricate components from wrought billet. Powders can be produced by the blended elemental technique or by pre-alloying and then consolidated by metal injection moulding, hot isostatic pressing, direct powder rolling or laser engineered net shaping.

Spray forming, also known as spray casting, spray deposition and in-situ compaction, is a method of casting near net shape metal components with homogeneous microstructures via the deposition of semi-solid sprayed droplets onto a shaped substrate. In spray forming an alloy is melted, normally in an induction furnace, then the molten metal is slowly poured through a conical tundish into a small-bore ceramic nozzle. The molten metal exits the furnace as a thin free-falling stream and is broken up into droplets by an annular array of gas jets, and these droplets then proceed downwards, accelerated by the gas jets to impact onto a substrate. The process is arranged such that the droplets strike the substrate whilst in the semi-solid condition, this provides sufficient liquid fraction to 'stick' the solid fraction together. Deposition continues, gradually building up a spray formed billet of metal on the substrate.

<span class="mw-page-title-main">Thermal spraying</span> Coating process for applying heated materials to a surface

Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface. The "feedstock" is heated by electrical or chemical means.

<span class="mw-page-title-main">Thermal barrier coating</span> Form of exhaust heat management

Thermal barrier coatings (TBCs) are advanced materials systems usually applied to metallic surfaces on parts operating at elevated temperatures, such as gas turbine combustors and turbines, and in automotive exhaust heat management. These 100 μm to 2 mm thick coatings of thermally insulating materials serve to insulate components from large and prolonged heat loads and can sustain an appreciable temperature difference between the load-bearing alloys and the coating surface. In doing so, these coatings can allow for higher operating temperatures while limiting the thermal exposure of structural components, extending part life by reducing oxidation and thermal fatigue. In conjunction with active film cooling, TBCs permit working fluid temperatures higher than the melting point of the metal airfoil in some turbine applications. Due to increasing demand for more efficient engines running at higher temperatures with better durability/lifetime and thinner coatings to reduce parasitic mass for rotating/moving components, there is significant motivation to develop new and advanced TBCs. The material requirements of TBCs are similar to those of heat shields, although in the latter application emissivity tends to be of greater importance.

<span class="mw-page-title-main">Sputter deposition</span> Method of thin film application

Sputter deposition is a physical vapor deposition (PVD) method of thin film deposition by the phenomenon of sputtering. This involves ejecting material from a "target" that is a source onto a "substrate" such as a silicon wafer. Resputtering is re-emission of the deposited material during the deposition process by ion or atom bombardment. Sputtered atoms ejected from the target have a wide energy distribution, typically up to tens of eV. The sputtered ions can ballistically fly from the target in straight lines and impact energetically on the substrates or vacuum chamber. Alternatively, at higher gas pressures, the ions collide with the gas atoms that act as a moderator and move diffusively, reaching the substrates or vacuum chamber wall and condensing after undergoing a random walk. The entire range from high-energy ballistic impact to low-energy thermalized motion is accessible by changing the background gas pressure. The sputtering gas is often an inert gas such as argon. For efficient momentum transfer, the atomic weight of the sputtering gas should be close to the atomic weight of the target, so for sputtering light elements neon is preferable, while for heavy elements krypton or xenon are used. Reactive gases can also be used to sputter compounds. The compound can be formed on the target surface, in-flight or on the substrate depending on the process parameters. The availability of many parameters that control sputter deposition make it a complex process, but also allow experts a large degree of control over the growth and microstructure of the film.

Electron-beam additive manufacturing, or electron-beam melting (EBM) is a type of additive manufacturing, or 3D printing, for metal parts. The raw material is placed under a vacuum and fused together from heating by an electron beam. This technique is distinct from selective laser sintering as the raw material fuses having completely melted.

<span class="mw-page-title-main">Ultrasonic nozzle</span> Type of spray nozzle

Ultrasonic nozzles are a type of spray nozzle that use high frequency vibrations produced by piezoelectric transducers acting upon the nozzle tip that create capillary waves in a liquid film. Once the amplitude of the capillary waves reaches a critical height, they become too tall to support themselves and tiny droplets fall off the tip of each wave resulting in atomization.

Titanium adhesive bonding is an engineering process used in the aerospace industry, medical-device manufacture and elsewhere. Titanium alloy is often used in medical and military applications because of its strength, weight, and corrosion resistance characteristics. In implantable medical devices, titanium is used because of its biocompatibility and its passive, stable oxide layer. Also, titanium allergies are rare and in those cases mitigations like Parylene coating are used. In the aerospace industry titanium is often bonded to save cost, touch times, and the need for mechanical fasteners. In the past, Russian submarines' hulls were completely made of titanium because the non-magnetic nature of the material went undetected by the defense technology at that time. Bonding adhesive to titanium requires preparing the surface beforehand, and there is not a single solution for all applications. For example, etchant and chemical methods are not biocompatible and cannot be employed when the device will come into contact with blood and tissue. Mechanical surface roughness techniques like sanding and laser roughening may make the surface brittle and create micro-hardness regions that would not be suitable for cyclic loading found in military applications. Air oxidation at high temperatures will produce a crystalline oxide layer at a lower investment cost, but the increased temperatures can deform precision parts. The type of adhesive, thermosetting or thermoplastic, and curing methods are also factors in titanium bonding because of the adhesive's interaction with the treated oxide layer. Surface treatments can also be combined. For example, a grit blast process can be followed by a chemical etch and a primer application.

<span class="mw-page-title-main">Detonation spraying</span> Method of thermal spraying

Detonation spraying is one of the many forms of thermal spraying techniques that are used to apply a protective coating at supersonic velocities to a material in order to change its surface characteristics. This is primarily to improve the durability of a component. It was first invented in 1955 by H.B. Sargent, R.M. Poorman and H. Lamprey and is applied to a component using a specifically designed detonation gun (D-gun). The component being sprayed must be prepared correctly by removing all surface oils, greases, debris and roughing up the surface in order to achieve a strongly bonded detonation spray coating. This process involves the highest velocities and temperatures (≈4000 °C) of coating materials compared to all other forms of thermal spraying techniques. Which means detonation spraying is able to apply low porous and low oxygen content protective coatings that protect against corrosion, abrasion and adhesion under low load.

Cold spray additive manufacturing (CSAM) is a particular application of cold spraying, able to fabricate freestanding parts or to build features on existing components. During the process, fine powder particles are accelerated in a high-velocity compressed gas stream, and upon the impact on a substrate or backing plate, deform and bond together creating a layer. Moving the nozzle over a substrate repeatedly, a deposit is building up layer-by-layer, to form a part or component. If an industrial robot or computer controlled manipulator controls the spray gun movements, complex shapes can be created. To achieve a 3D shape, there are two different approaches. First, to fix the substrate and move the cold spray gun/nozzle using a robotic arm; the second one is to move the substrate with a robotic arm, and keep the spray-gun nozzle fixed. There is also a possibility to combine these two approaches either using two robotic arms or other manipulators. The process always requires a substrate and uses only powder as raw material.

Laser metal deposition (LMD) is an additive manufacturing process in which a feedstock material is melted with a laser and then deposited onto a substrate. A variety of pure metals and alloys can be used as the feedstock, as well as composite materials such as metal matrix composites. Laser sources with a wide variety of intensities, wavelengths, and optical configurations can be used. While LMD is typically a melt-based process, this is not a requirement, as discussed below. Melt-based processes typically have a strength advantage, due to achieving a full metallurgical fusion.

References

  1. 1 2 3 4 Kuroda, Seiji; Kawakita, Jin; Watanabe, Makoto; Katanoda, Hiroshi (2008). "Warm spraying—a novel coating process based on high-velocity impact of solid particles". Sci. Technol. Adv. Mater. 9 (3): 033002. doi:10.1088/1468-6996/9/3/033002. PMC   5099653 . PMID   27877996.
  2. ↑ Moridi, A.; Hassani-Gangaraj, S. M.; Guagliano, M.; Dao, M. (2014). "Cold spray coating: review of material systems and future perspectives". Surface Engineering. 30 (6): 369–395. doi:10.1179/1743294414Y.0000000270. hdl: 11311/968457 . S2CID   987439.
  3. ↑ Raoelison, R.N.; Xie, Y.; Sapanathan, T.; Planche, M.P.; Kromer, R.; Costil, S.; Langlade, C. (2018). "Cold gas dynamic spray technology: A comprehensive review of processing conditions for various technological developments till to date". Additive Manufacturing. 19: 134–159. doi:10.1016/j.addma.2017.07.001.
  4. ↑ Daroonparvar, Mohammadreza; Bakhsheshi-Rad, Hamid Reza; Saberi, Abbas; Razzaghi, Mahmood; Kasar, Ashish K; Ramakrishna, Seeram; Menezes, Pradeep L.; Misra, Manoranjan; Ismail, Ahmad Fauzi; Sharif, Safian; Berto, Filippo (August 2022). "Surface modification of magnesium alloys using thermal and solid-state cold spray processes: Challenges and latest progresses". Journal of Magnesium and Alloys. 10 (8): 2025–2061. doi:10.1016/j.jma.2022.07.012.
  5. ↑ Faizan-Ur-Rab, M.; Zahiri, S.H.; Masood, S.H.; Phan, T.D.; Jahedi, M.; Nagarajah, R. (2016). "Application of a holistic 3D model to estimate state of cold spray titanium particles". Materials & Design. 89: 1227–1241. doi:10.1016/j.matdes.2015.10.075.
  6. ↑ Irissou, Eric; Legoux, Jean-Gabriel; Ryabinin, Anatoly N.; Jodoin, Bertrand; Moreau, Christian (December 2008). "Review on Cold Spray Process and Technology: Part I—Intellectual Property". Journal of Thermal Spray Technology. 17 (4): 495–516. Bibcode:2008JTST...17..495I. doi:10.1007/s11666-008-9203-3.
  7. ↑ Hussain, T.; McCartney, D. G.; Shipway, P. H.; Zhang, D. (2009). "Bonding Mechanisms in Cold Spraying: The Contributions of Metallurgical and Mechanical Components". Journal of Thermal Spray Technology . 18 (3): 364–379. Bibcode:2009JTST...18..364H. doi:10.1007/s11666-009-9298-1. S2CID   135893433.
  8. ↑ Assadi, Hamid; Gärtner, Frank; Stoltenhoff, Thorsten; Kreye, Heinrich (2003). "Bonding mechanism in cold gas spraying". Acta Materialia. 51 (15): 4379–4394. Bibcode:2003AcMat..51.4379A. doi:10.1016/S1359-6454(03)00274-X.
  9. ↑ Schmidt, Tobias; Gärtner, Frank; Assadi, Hamid; Kreye, Heinrich (2006). "Development of a generalized parameter window for cold spray deposition". Acta Materialia. 54 (3): 729–742. Bibcode:2006AcMat..54..729S. doi:10.1016/j.actamat.2005.10.005.
  10. ↑ Zahiri, Saden H.; Antonio, Christian I.; Jahedi, Mahnaz (2009). "Elimination of porosity in directly fabricated titanium via cold gas dynamic spraying". Int. J. Journal of Materials Processing Technology. 209 (2): 922–929. doi:10.1016/j.jmatprotec.2008.03.005.
  11. ↑ Assadi, H.; Schmidt, T.; Richter, H.; Kliemann, J.-O.; Binder, K.; Gärtner, F.; Klassen, T.; Kreye, H. (2011). "On Parameter Selection in Cold Spraying". Journal of Thermal Spray Technology. 20 (6): 1161. Bibcode:2011JTST...20.1161A. doi: 10.1007/s11666-011-9662-9 .
  12. ↑ Zou, Yu; Qin, Wen; Irissou, Eric; Legoux, Jean-Gabriel; Yue, Stephen; Szpunar, Jerzy A. (2009). "Dynamic recrystallization in the particle/particle interfacial region of cold-sprayed nickel coating: Electron backscatter diffraction characterization". Scripta Materialia. 61 (9): 899. doi:10.1016/j.scriptamat.2009.07.020.
  13. ↑ Zou, Yu; Goldbaum, Dina; Szpunar, Jerzy A.; Yue, Stephen (2010). "Microstructure and nanohardness of cold-sprayed coatings: Electron backscattered diffraction and nanoindentation studies". Scripta Materialia. 62 (6): 395. doi:10.1016/j.scriptamat.2009.11.034.
  14. 1 2 Champagne, Victor K. (2007). The cold spray materials deposition process. Woodhead Publishing. pp. 63–70. ISBN   9781845691813.
  15. ↑ Karthikeyan, J. (December, 2004). "Cold Spray Technology: international status and USA efforts". ASB Industries.
  16. ↑ Wang, A.P. (January 2006) "Ni-based fully amorphous metallic coating with high corrosion resistance". Shenyang National Laboratory for Materials Science, Institute of Metal Research.
  17. ↑ Kliemann, J. -O.; Gutzmann, H.; Gärtner, F.; Hübner, H.; Borchers, C.; Klassen, T. (2010). "Formation of Cold-Sprayed Ceramic Titanium Dioxide Layers on Metal Surfaces". Journal of Thermal Spray Technology. 20 (1–2): 292–298. doi: 10.1007/s11666-010-9563-3 .
  18. ↑ Gabel, Howard; Tapphorn, Ralph (August 1997). "Solid-state spray forming of aluminum near-net shapes". JOM. 49 (8): 31–33. Bibcode:1997JOM....49h..31G. doi:10.1007/BF02914398.
  19. ↑ McFarland, Matt. (2013-11-22) Repairing an airplane engine on a tight budget might become a lot easier. The Washington Post. Retrieved on 2016-11-26.
  20. ↑ Fuentes, Gidget. "Navy Expanding 'Cold Spray' Welding Alternative in Fleet Repair". news.usni.org. USNI. Retrieved 17 September 2023.
  21. ↑ "Cold spray for melt-less direct manufacturing". csiro.au.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.