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Principle of Cold Spray Technology
Release time:
2020-08-28 12:12
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Principle of Cold Spray Technology
Cold Spray (CS) technology, also known as gas-dynamic spraying, refers to a coating deposition method in which high-speed solid particles with a certain degree of plasticity, upon impacting a substrate, undergo intense plastic deformation and thereby deposit to form a coating. Under normal conditions, the conventional understanding is that when solid particles collide with a substrate, they exert an erosive effect on the substrate.
Simply put, cold spray technology differs from traditional thermal spraying techniques—such as high-velocity flame spraying, plasma spraying, and detonation spraying—because it does not require melting the metal particles to be sprayed. In cold spray, compressed air is used to accelerate metal particles to a critical velocity, after which they are ejected through a nozzle. Upon impact with the substrate surface, these metal particles undergo physical deformation. The metal particles flatten upon striking the substrate and adhere firmly to its surface. Throughout the entire process, the metal particles remain unmelted, and the temperature generated on the substrate surface never exceeds 150°C (the NRC technology developed by the Canadian Materials Research Centre does not exceed 200°C). The principle of cold spray is illustrated in the figure below.
During cold spraying, whether the high-speed particles form a coating upon impacting the substrate, induce shot peening or erosion on the substrate, or even cause pitting damage to the substrate depends on the velocity of the particles before they strike the substrate. For a given material, there exists a critical velocity Vc: when the particle velocity exceeds Vc, the particles will deposit onto the substrate surface after impact; whereas when the particle velocity is below Vc, erosion will occur (resulting in damage to the substrate surface and the detachment of metal particles). The critical velocity Vc varies depending on the type of powder used; typically, it ranges from about 500 to 700 m/s, as detailed in Table 1. Therefore, to increase the velocity of the gas flow—and thus enhance the particle velocity—cold-spray technology can preheat the accelerating gas before it is fed into the spray gun; generally, the preheating temperature is kept below 600 ℃. Meanwhile, to achieve high particle velocities and deposition efficiency, the powder particles must have a narrow size distribution and small particle size, usually ranging from 1 to 50 μm.
Critical velocity (m/s) of different metal particles
| Materials |
Copper |
Nickel |
Iron |
Aluminum |
| Critical speed |
560~580 |
620~640 |
620~640 |
680~700 |
Cold spray technology, depending on the pressure of the compressed air used, is divided into high-pressure cold spraying and low-pressure cold spraying. High-pressure cold spraying employs compressed air at a pressure of 15 atmospheres (psi) or higher, while low-pressure cold spraying uses compressed air at a pressure of 10 atmospheres (psi) or lower. Compared to traditional thermal spray technologies, both high-pressure and low-pressure cold spraying share the following common advantages:
① It can be used to spray a variety of materials with certain plasticity, enabling the formation of coatings with properties such as electrical conductivity, thermal conductivity, corrosion resistance, and wear resistance. Examples include pure metals like zinc, aluminum, copper, iron, nickel, and titanium; alloys such as stainless steel and bronze; and even high-temperature alloys based on Ni-Cr.
② Cold-spray particles are at low temperature yet high velocity, which can prevent physicochemical reactions that might occur during particle acceleration and heating. This makes cold spraying suitable for coating materials that are sensitive to temperature (such as nanomaterials and amorphous materials), sensitive to oxidation (such as Cu and Ti), and sensitive to phase transformations (such as metal-ceramics).
③ Minimal thermal impact on the substrate. The surface temperature of the substrate being coated does not exceed 150°C instantaneously, and the perceived temperature is around 70°C (the specific temperature depends on the velocity of the coating particles and the speed at which the spray gun is moved). This helps prevent thermal deformation of the substrate and damage to the material’s microstructure.
④ Can be sprayed onto any metal, glass, ceramic, and rock surfaces.
⑤ The coating exhibits excellent densification and boasts a substantial coating thickness, easily reaching over 10 mm. Since the high-speed particles undergo intense plastic deformation during deposition, the coating microstructure becomes highly dense, and significant compressive stresses are generated within the coating, enabling the fabrication of thick coatings.
⑥ Metal particles can be recycled. Since they do not undergo significant thermal processing, their microstructure remains largely unchanged, and the undeposited particles can be recovered and reused.
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The complete set of plasma-sprayed equipment has been shipped to the customer’s site in Thailand.
Core spraying equipment: SX-80 plasma spray main unit, with a 15,000℃ flame suitable for multiple materials including zirconia and silicon carbide; powder feeding accuracy of ±1%, and coating thickness tolerance ≤ ±5 μm. Environmental protection support system: Customized soundproof booth + pulse dust collector—effectively addressing spray noise pollution while achieving highly efficient dust recovery, compliant with Thai environmental standards. Automated equipment: 6-axis industrial robot + intelligent spray cart, enabling precise spraying of complex workpieces and automated loading/unloading, boosting production efficiency by 40%.
On-site engineers provide hands-on training, focusing on the core operations of plasma spraying equipment such as the SX-80. Sanxin has customized a complete solution for its customers, including an automated spraying robotic arm, a soundproof booth, and a dust removal system—ensuring both high spraying efficiency and compliance with environmental standards.
Guangzhou Sanxin Thermal Spraying Turntable Shipment
Guangzhou Sanxin Company manufactures single-station and multi-station thermal spray turntables, which can be paired with plasma equipment, supersonic equipment, and arc equipment. We offer rapid, customized production tailored to customer requirements and product dimensions. A thermal spray turntable is a high-precision rotary worktable specifically designed for thermal spraying processes—including flame spraying, plasma spraying, and arc spraying. By providing controllable rotational speed and exceptional stability, it ensures uniform coating thickness on the workpiece surface, thereby enhancing spraying efficiency and quality.
SX-80 plasma equipment is being used at a customer site in Russia.
SX-80 plasma equipment is being used at a customer site in Russia.
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