Cold spraying

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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.

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, [4] 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. [5]

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. [6] [7] [8]

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. [10] 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. [11] [12] 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: [13]

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: [13]

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), [14] as well as coatings made from amorphous alloys. [15]

Additional developments in CS are related to the deposition of ceramic materials on metals, notably titanium dioxide for photocatalytic effects, [16] and the use of CS in additive manufacturing. [17]

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. [18] The US Navy has adopted cold spray welding across its global operations on an experimental basis. [19]

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. [20]

Related Research Articles

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.

<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.

<span class="mw-page-title-main">Coating</span> Substance spread over a surface

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">Metal foam</span> Porous material made from a metal

In materials science, a metal foam is a material or structure consisting of a solid metal with gas-filled pores comprising a large portion of the volume. The pores can be sealed or interconnected. The defining characteristic of metal foams is a high porosity: typically only 5–25% of the volume is the base metal. The strength of the material is due to the square–cube law.

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.

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 have completely melted. Selective Electron Beam Melting (SEBM) emerged as a powder bed-based additive manufacturing (AM) technology and was brought to market in 1997 by Arcam AB Corporation headquartered in Sweden.

<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.

<span class="mw-page-title-main">Zirconium diboride</span> Chemical compound

Zirconium diboride (ZrB2) is a highly covalent refractory ceramic material with a hexagonal crystal structure. ZrB2 is an ultra-high temperature ceramic (UHTC) with a melting point of 3246 °C. This along with its relatively low density of ~6.09 g/cm3 (measured density may be higher due to hafnium impurities) and good high temperature strength makes it a candidate for high temperature aerospace applications such as hypersonic flight or rocket propulsion systems. It is an unusual ceramic, having relatively high thermal and electrical conductivities, properties it shares with isostructural titanium diboride and hafnium diboride.

<span class="mw-page-title-main">Selective laser melting</span> 3D printing technique

Selective laser melting (SLM) is one of many proprietary names for a metal additive manufacturing (AM) technology that uses a bed of powder with a source of heat to create metal parts. Also known as direct metal laser sintering (DMLS), the ASTM standard term is powder bed fusion (PBF). PBF is a rapid prototyping, 3D printing, or additive manufacturing technique designed to use a high power-density laser to melt and fuse metallic powders together.

Govindan Sundararajan is an Indian materials engineer, known for his contributions in the areas of Surface Engineering and Ballistics. The Government of India honoured him, in 2014, by awarding him the Padma Shri, the fourth highest civilian award, for his contributions to the fields of science and technology.

<span class="mw-page-title-main">3D printing processes</span> List of 3D printing processes

A variety of processes, equipment, and materials are used in the production of a three-dimensional object via additive manufacturing. 3D printing is also known as additive manufacturing, because the numerous available 3D printing process tend to be additive in nature, with a few key differences in the technologies and the materials used in this process.

Titanium foams exhibit high specific strength, high energy absorption, excellent corrosion resistance and biocompatibility. These materials are ideally suited for applications within the aerospace industry. An inherent resistance to corrosion allows the foam to be a desirable candidate for various filtering applications. Further, titanium's physiological inertness makes its porous form a promising candidate for biomedical implantation devices. The largest advantage in fabricating titanium foams is that the mechanical and functional properties can be adjusted through manufacturing manipulations that vary porosity and cell morphology. The high appeal of titanium foams is directly correlated to a multi-industry demand for advancement in this technology.

<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.

The Armstrong process is used to refine titanium. Its output is particle-sized dust which can be sprayed into pattern-molds. It was patented in 1999. The output of this process has a "coral-like morphology", which differs from the traditional outputs like "spherical gas-atomized powder, mechanically crushed angular particles, or the titanium sponge morphology created during the Kroll process."

References

  1. 1 2 3 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. ↑ 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.
  5. ↑ 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.
  6. ↑ 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.
  7. ↑ 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.
  8. ↑ 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.
  9. ↑ 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.
  10. ↑ 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 .
  11. ↑ 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.
  12. ↑ 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.
  13. 1 2 Champagne, Victor K. (2007). The cold spray materials deposition process. Woodhead Publishing. pp. 63–70. ISBN   9781845691813.
  14. ↑ Karthikeyan, J. (December, 2004). "Cold Spray Technology: international status and USA efforts". ASB Industries.
  15. ↑ 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.
  16. ↑ 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 .
  17. ↑ 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.
  18. ↑ 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.
  19. ↑ Fuentes, Gidget. "Navy Expanding 'Cold Spray' Welding Alternative in Fleet Repair". news.usni.org. USNI. Retrieved 17 September 2023.
  20. ↑ "Cold spray for melt-less direct manufacturing". csiro.au.
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