Cold spraying technology is a coating preparation method invented by Papyrin et al. from the Institute of Theoretical and Applied Mechanics of the former Soviet Academy of Sciences in the mid-1980s. Research has found that when the powder spraying speed exceeds a certain critical value, the powder will deposit and form a coating on its surface after colliding with the substrate. As a result, they proposed the concept of cold spraying in 1990 and published a paper on cold spraying. Subsequently, cold spraying technology gradually attracted people's attention due to its advantages in preparation, and rapidly developed in the field of material surface coating preparation technology. At the same time, researchers also conducted research on the development of cold spraying equipment, coating deposition principles, coating structure and performance, which played a positive role in promoting the development and application of cold spraying technology.
Cold spraying technology is a new spraying technology based on the principles of aerodynamics, which uses compressed gas to drive powder particles to accelerate through the Laval scaling nozzle, causing supersonic powder particles to collide with the substrate and undergo plastic deformation, and deposit on the substrate surface to form a coating. According to the different spraying pressure and powder feeding methods, cold spraying equipment can mainly be divided into high-pressure (1.5-4.0MPa) and low-pressure (0.6-1.5MPa) cold spraying. The high-pressure cold spraying equipment system mainly uses N2, He or a mixture of the two gases as the gas source, and its high-pressure gas path and powder flow pipeline are independent of each other. The spraying powder enters from the front end of the scaling nozzle, mixes with the hot gas flow inside the nozzle, and is accelerated and sprayed out through the scaling nozzle. The equipment system is relatively large, and is often placed in a fixed manner; In addition, the spraying temperature of the equipment is relatively high (200-800 ℃), and the spraying powder speed can reach 300-1200 m/s; The coating has a high deposition rate and a uniform and dense structure, which can achieve rapid preparation of large-area coatings; However, there are also drawbacks such as high gas and powder consumption, high spraying economic costs, and difficulty in handling equipment.
Compared with the high-pressure cold spraying equipment system, the low-pressure cold spraying equipment system is simple and portable. The spraying powder enters from the rear section of the scaling nozzle, and the accelerated and heated gas drives the powder to spray out; Spraying equipment requires relatively low gas pressure, mostly using compressed air as the carrier gas. The spraying temperature (200-650 ℃) is relatively low, and the spraying powder speed is about 350-700m/s. The gas consumption is small, and the spraying cost is low. It can be used for coating preparation and additive repair of damaged components; However, there are also drawbacks such as low coating bonding strength and low deposition rate.