Overview and Research Progress of Cold Spray Technology

Cold spraying ( Cold Spray ), also known as cold gas dynamic spraying ( Cold Gas Dynamic Spray , abbreviated as CGDS ), which is based on aerodynamics and uses a high-pressure gas source to accelerate solid particles to extremely high velocities, causing them to impact the substrate and deposit a coating.

Cold spraying is an effective technique for achieving multifunctional surface treatments of materials. Its principle involves using compressed gas as an accelerating airflow to propel... 5-45 mu m powder particles, at low temperature (room temperature) -600 ℃) Supersonic particles impact the substrate in a fully solid state, causing intense plastic deformation of the particles and resulting in their deposition to form a built-up layer, thereby completing the fabrication of three-dimensional parts. This technology boasts characteristics such as high efficiency, density, and corrosion resistance, making it ideally suited for flexible and complex printing environments. Currently, cold spray technology has been widely adopted in military and aerospace applications, while also demonstrating broad application potential in fields such as aviation, energy, and healthcare.

Depending on the different gas pressures used to propel the particles, cold spraying is primarily categorized into high-pressure (above...). 1MPa ) and low pressure (below 1MPa ) Two major categories of cold spraying. In high-pressure cold spraying, (a) During the process, the compressed gas is split into two streams: one part passes through the heater, while the other part goes through the powder-feeding channel. After the two gas streams are mixed, they enter... de-Laval The nozzle expands to form an ultrasonic gas-powder stream, and the powder is rapidly impacted onto the substrate, depositing to form a thick coating. Low-pressure cold spraying. (b) The process is simpler, and the required equipment is portable. A compressed gas that has been heated is directly fed into the nozzle, where it converges to spray the introduced powder onto the substrate. However, due to the low spraying pressure, carrier gas flow rate, and preheating temperature in low-pressure cold spraying, the coatings produced often suffer from poor density and weak interfacial bonding. As a result, its applications are greatly limited and it is suitable only for a restricted range of materials, such as... With you 、 Al in the field surface strengthening and repair of metallic components and their alloys. Therefore, in most cases, " Cold spray " The term refers to " High-pressure cold spray "。

Schematic diagram of cold spray technology

Advantages of Cold Spray Technology

1 — Versatility with multiple materials: It can be used to spray a variety of materials, including metals, plastics, ceramics, and more, demonstrating strong versatility.

2 Durability and Protection: The resulting coating typically exhibits excellent corrosion resistance and wear resistance, effectively protecting the substrate and extending its service life.

3 Cold spraying causes virtually no environmental pollution, and the powder sprayed and splashed during the process can be recycled and reused.

4 The cold-spray coating has low residual stress and is under compressive stress, which is favorable for preparing thicker coatings.

5 The chemical composition and microstructural features of the coating can remain consistent with those of the raw material, and phenomena such as oxidation, burn-off of alloying elements, and grain growth are essentially absent. This allows for the spraying of thermally sensitive materials, reactive metals, and polymeric materials, making it suitable for the preparation of amorphous and nanocrystalline coatings.

Factors Affecting the Quality of Cold-Spray Coatings

The factors affecting the performance of cold-spray deposited coatings can be categorized into three types: (1) Process parameters: such as gas conditions, nozzle design, and spray dynamics; (2) Powder characteristics; (3) Spraying parameters.

( 1 Process parameters: Cold spraying is primarily studied from a fluid dynamics perspective, focusing on the impact of process parameters on deposition efficiency and the quality of the final formed part. It is well known that the deposited material depends mainly on the particle impact conditions—specifically, the particle impact velocity, the particle impact temperature, and the surface temperature of the substrate (or the already existing substrate). Consequently, most current research focuses on the relationships between cold-spray process parameters and these three key factors.

( 2 ) Powder characteristics: In the cold spray process, the physical properties of powder materials—such as particle size, morphology, and oxygen content—have a certain impact on the quality of the formed parts. The commonly used particle size range for cold spray processes is: 5-45 mu m By the way, the particle size distribution of powder materials affects both particle velocity and critical velocity. Typically, the critical velocity decreases as the size of powder particles increases—larger particles are harder to accelerate and have a greater thermal capacity. Therefore, if you aim to improve deposition efficiency, you might consider using finer powders. Given these complex influencing factors, the final powder particle size ultimately depends on a variety of parameters, including spraying conditions, nozzle specifications, and spraying distance. Second, the morphology of powder particles is another crucial factor: under low-energy spraying conditions, irregular shapes such as dendritic structures tend to reduce porosity; whereas under high-energy spraying conditions, spherical powders yield more pronounced effects. Finally, the oxygen content of metal powders also has a certain impact on deposition efficiency. Powders with lower oxygen content are easier to deposit, and the thin oxide film formed on the particle surface promotes stronger bonding. The size and morphology of powder particles determine the free surface area per unit volume; the larger the surface area, the faster the oxidation rate, which can negatively affect coating quality. Thus, it’s essential to properly seal and store powders to prevent oxidation.

( 3 ) Spraying parameters: Traditionally, the critical velocity has been used as a metric to evaluate the spraying performance of various materials. However, many cold-spray characteristics depend not only on the critical velocity but also on the impact velocity of the particles. Therefore, it is more appropriate to discuss spraying performance in terms of velocity ratios or energy parameters. It is important to note that when the temperature of the spraying gas rises, certain low-melting-point materials and nickel-based alloys tend to adhere to the nozzle throat, causing nozzle blockage, reducing spraying efficiency, and impairing deposition performance. In such cases, selecting an appropriate nozzle material and adopting water-cooling methods can help address the issue of nozzle clogging. In the process control of cold spraying as well as in the optimization of microstructure and properties, one can enhance the driving force for plastic deformation by increasing particle velocity—for example, by raising the pressure of the accelerating gas, reducing powder particle size, or substituting helium for nitrogen. However, these approaches may increase production costs, and reducing powder particle size can also lead to poorer flowability of the powder particles. Alternatively, one might consider raising the particle temperature to reduce the resistance to plastic deformation—for instance, by preheating the powder particles or increasing the temperature of the accelerating gas. Finally, factors such as nozzle velocity and angle, spraying distance, powder feed rate, and gas pressure also significantly influence the quality of cold-spray coatings.

Typical Cold Spray Materials, Coating Characteristics, and Applications

Typical cold spray materials

1. Aluminum and Aluminum Alloy Coatings: Aluminum and its alloys exhibit characteristics such as low density, high ductility, excellent corrosion resistance, and superior thermal and electrical conductivity, making them widely used in both industrial and everyday applications. Cold-spray coatings of aluminum and its alloys can be employed to repair industrial components made from aluminum alloys, attracting considerable attention from both academic and industrial communities. Although aluminum and its alloys have relatively low strength and melting points, they display excellent plasticity, high deformability, and a low critical spraying velocity during cold spraying, making them theoretically easy to spray. However, due to aluminum’s low density, the motion of particles in flight is easily influenced by bow shock waves generated near the substrate. Moreover, the surface of aluminum powder is prone to oxidation; overcoming the effects of the oxide layer and producing high-density deposits remain significant challenges. In addition to pure aluminum, cold-spray aluminum alloys also demonstrate outstanding performance. Aluminum-silicon alloys possess high strength, low thermal expansion, and excellent anti-friction properties. Studies have shown that during cold spraying of aluminum-silicon alloys, the high-temperature gas-induced thermal effects result in the formation of aluminum-silicon alloy coatings that not only exhibit... alpha -Al The phase is present, and there are also fine silicon particle-reinforced phases, thereby resulting in increased strength. Al-Sn Binary alloys exhibit excellent anti-sticking properties and low modulus, and are often used as sliding bearing materials in the automotive industry. Cold spraying Al-Sn Binary alloy coatings feature low porosity, high deposition rates, and excellent mechanical properties. In addition, in... Al-Cu Different alloying elements are added to the alloy (such as Mg 、 Fe 、 Ag 、 You ), which can form different intermetallic compounds (such as Al2Cu、Al2CuMg、Al9FeNi ), further enhance mechanical strength, high strength Al-Cu Alloys are widely used in the aerospace and automotive industries.

Example image of a cold spray coating

(2) Copper and Copper Alloys: Copper and its alloys exhibit excellent thermal conductivity, electrical conductivity, ductility, corrosion resistance, and wear resistance. , Widely used in fields such as power, electronics, energy, and mechanical engineering, it is one of the easiest materials to spray using cold spraying technology. Cold-sprayed copper coatings exhibit excellent physical properties and performance. The cold-sprayed copper coating is highly dense with virtually no porosity, and its electrical conductivity in the sprayed state can approach that of the bulk material itself. 100% Copper in AA5052、AA6063 and 316L The adhesion strength on the substrate all exceeds 200MPa However, the higher the yield strength of the substrate, the greater the particle velocity required for effective bonding. As the particle velocity increases, it becomes possible to produce copper coatings with high adhesion strength on a variety of substrate materials.

Cold-spray components with complex structures and thin coatings

( a) A thick copper coating is deposited inside the pressure ring of the food processor. b ) Axially symmetric bulk ( Ti6Al4V )

( c ) Conical structure ( d Copper Coating for Power Electronics Heat Sinks

(3) Titanium and Titanium Alloy Coatings: Due to their characteristics—low density, high strength, excellent corrosion resistance, and good biocompatibility—titanium and titanium alloys are widely used in fields such as aerospace, aviation, petroleum, chemical engineering, medical care, and automotive industries. In cold spraying... , The critical velocity required for the deposition of titanium and titanium alloys is relatively high; therefore, to obtain a dense coating of titanium and titanium alloys, , High-pressure cold spraying equipment and higher process parameters are required. ( For example : Nitrogen as a carrier gas, gas temperature 800~1100 ℃, gas pressure 4~5 MPa) Additionally , Using helium as a carrier gas can accelerate titanium and titanium alloy particles to higher velocities, thereby inducing more intense plastic deformation and stronger bonding strength in these particles. Consequently, using helium enables titanium and titanium alloy coatings to achieve exceptional density. According to relevant studies, compared with single-spray deposition... You or Ti6Al4V In comparison, using mixed ingredients (Ti + Ti6Al4V) Helps form a relatively dense composite coating (approximately 1.5% Porosity). This observation indicates that hard particles are generated during the cold spray process. / The soft-impact interface is beneficial and can lead to improved coating performance. By customizing process parameters, titanium and its alloys can be coated with varying porosity levels: porous coatings are suitable for biomedical applications, while dense coatings are ideal for the repair and remanufacturing of aerospace components.

(4) Nickel-based high-temperature alloy coating: Inconel 718 It is a nickel-based superalloy, and its alloying elements include: You 、 Cr 、 My 、 Nb 、 You and Al By forming γ ' and γ " Reinforced phase and fine particles / Stable carbides, Inconel 718 It exhibits high strength at elevated temperatures as well as excellent oxidation resistance and resistance to gas corrosion, making it widely used in aerospace components operating at higher temperatures. Compared to pure nickel, which is easy to spray-coat, Inconel 718 It has a high yield strength, poor ductility, and a high strain-hardening rate, making it difficult to cold spray. Similar to titanium alloys, Inconel 718 The critical velocity required for cold spray deposition is also very high.

As evidenced by the material systems listed above, cold spray technology now encompasses a wide range of materials—including metals, alloys, ceramics, polymers, and advanced functional materials (such as composites, nanomaterials, and metal-ceramic composites). Among these, the preparation of advanced functional materials represents a new trend in cold spray technology. In recent years, cold spray has also been successfully employed to fabricate high-strength metallic glass materials. Metals and alloys possess excellent processing properties; although they have been extensively studied over the past decade or so, given the future potential of cold spray as an important additive manufacturing and repair technique, the application scale of metallic materials or metal-based composites is expected to expand steadily.

Main applications of cold spraying

1. In the electronics sector, the electronics industry leverages cold spray technology to rapidly deposit silver coatings onto target substrates. Cold spray direct-forming of targets boasts high production efficiency, high relative density, and excellent bonding with the substrate. The grain structure within the target is uniform and fine, free of defects, and exhibits relatively high deposition efficiency. Currently, large-scale metal sputtering targets fabricated directly via cold spray are widely used in the electronics and information industries. , Such as integrated circuits, information storage, liquid crystal displays, laser memory devices, electronic control components, and glass coatings.

Cold Spray Rotating Silver Target Material

2. In the aerospace field, cold spray technology can be used to treat aircraft components such as aircraft engines, landing gear, and wings, forming protective coatings with high density, excellent electrical and thermal conductivity, and strong adhesion on their surfaces. These coatings effectively reduce aircraft energy consumption and enhance the corrosion resistance of components.

Cold Spray Fabrication of Large Aerospace Components

(3) In the shipbuilding industry, cold spray technology can form a protective coating on ship surfaces that exhibits excellent antioxidant properties and high corrosion resistance, effectively reducing the degree of corrosion caused by prolonged immersion in seawater or freshwater and thereby extending the service life of ships.

(4) In the automotive manufacturing sector, cold spray technology can reduce corrosion and wear on automotive components, effectively extending their service life and thereby enhancing overall vehicle performance and prolonging the vehicle’s lifespan.

Cold Spray Technology for Repairing Components

5. Maintenance Field: Repairing anti-corrosion coatings on civil aircraft, civilian ships, energy equipment, and large-scale mechanical equipment, and addressing the loss of magnesium-aluminum substrates caused by environmental corrosion and wear.

U.S. forces are using cold spray technology to repair in-service aircraft.

Future Development Directions of Cold Spray Technology

1 Diversification of Materials: The types of cold-spray powders cover metals, ceramics, polymers, and composite powders. Research on cold spraying of metal powders was among the earliest to begin, primarily focusing on stable materials such as copper, aluminum, silver, titanium, magnesium, zinc, tin, tantalum, iron-based alloys, nickel-based alloys, titanium-based alloys, magnesium-based alloys, and zinc-based alloys. Currently, research is shifting toward metastable materials such as amorphous, quasi-crystalline, and high-entropy alloys. This further expands the range of available materials to meet the needs of various industries and applications.

2 — Technological integration: As material systems become increasingly diverse, the original process conditions can no longer meet the deposition requirements for specialized materials. Consequently, the development of hybrid cold-spray technologies has become a current research priority. The Institute of Welding and Coating at Xi'an Jiaotong University has developed a micro-forging-assisted cold-spray technology, while the Laser Processing Technology Engineering Research Center at the University of Cambridge and Zhejiang University of Technology have independently developed laser-assisted cold-spray technologies.

3 — Application in High-End Fields: Currently, cold spray technology is primarily used in military and aerospace equipment. Commercial applications of cold spray technology mainly involve rotating targets, such as cold-sprayed rotating titanium-aluminum, zinc-aluminum, zinc-tin, titanium, tantalum, silver, copper, nickel-chromium alloys, and others. These applications span fields including semiconductors, flat-panel displays, magnetic storage, glass coating, and decorative plating.

4 Sustainability and Environmental Protection: Develop more environmentally friendly materials and printing methods, reduce resource consumption, and promote sustainable manufacturing.

Conclusion and Outlook

Cold spray technology is of paramount importance for expanding and complementing thermal spray technology. It can bring greater economic benefits in industrial applications and open up new avenues for the use of surface engineering technologies. As an emerging solid-state additive manufacturing process, cold spray technology holds tremendous application potential across various industrial sectors due to its unique advantages over traditional fusion-based additive manufacturing processes. With the continuous advancement and iteration of cold spray technology, related theoretical research is increasingly being applied to practical production, gradually shifting from laboratory studies toward industrial-scale applications. Consequently, its range of applications continues to expand.