In the atmosphere, as soon as the plasma flame leaves the nozzle, it will inhale a large amount of air from around. When the spray distance is 100mm, the air intake can account for more than 90% of the plasma. In the process of atmospheric plasma spraying, metal powder is seriously oxidized. In addition, some toxic substances (such as beryllium and beryllium oxide) cannot be sprayed into the atmosphere. In order to solve the above problems, low pressure plasma spraying is proposed. Vacuum plasma spraying, also known as low pressure plasma spraying, is a plasma spraying (spraying technology in a controlled environment) carried out in a low vacuum confined space below atmospheric pressure. The controllable environment spraying technology makes our understanding of plasma spraying move forward. Operate the spray gun in the spray room to completely control the environment. The characteristics of the coating produced in this way are impossible to produce in the standard atmospheric environment. The environment can be changed in the range of close to vacuum (as low as 50 mbar) and increased pressure (as high as 4 bar). The selection of spraying in the spraying room can prevent the contamination of the coating and/or substrate, or because the spraying material needs to react with the added substance. The principle of controllable atmosphere plasma spraying is to place the plasma spray gun in a sealed chamber and operate it by a manipulator. Vacuum plasma spraying (VPS) is used to pump the engine room to a vacuum state. When the engine room is in a low pressure state, it becomes low pressure vacuum plasma spraying (LPPS). The atmosphere in the cabin can be inert or other protective atmosphere. Due to the low ambient pressure or controllable atmosphere, the flow of plasma flame is longer, the particles are more fully heated, the oxidation is reduced, and the coating quality is significantly improved, which can be used to prepare the deposited diamond film and superconductor oxide coating. The coating produced by this process has many advantages. The coating has good compactness, strong adhesion, no pollution, and no oxide in the metal coating. The ceramic and other non-metallic coatings sprayed in the spray chamber filled with non-reactive atmosphere have high purity. Moreover, the application of high melting point metal coatings such as tungsten is also very successful. Because the distance between the spray gun and the workpiece is not as important as under atmospheric spraying conditions, the control of the parts becomes simple. Due to the uniform profile of the plasma plume, the "focal spot diameter" can be large, so the spraying process time can be greatly shortened. In addition, the lack of atmospheric cooling of coating particles means that the coating curing process is relatively slow. The atmospheric pressure plasma coating has almost no interlayer "sheet", and the crystal structure of the coating is close to that of the casting material. In the low vacuum environment, the non-transfer plasma arc can be superimposed on the surface of the workpiece because of the rough stretching of the non-transfer plasma arc and the formation of a conductive channel. The transfer arc is used to sputter the surface of the workpiece, remove the surface oxide layer and pollution, and heat the workpiece to a higher temperature, so that the coating can combine on the smooth surface and diffuse at the interface, thus improving the adhesion strength. The thickness of the coating can also be infinite. When spraying in a closed room, the pollution of noise and dust to the environment is also solved accordingly. Compared with atmospheric pressure plasma spraying, low vacuum environment spraying has the following remarkable characteristics: 1. The velocity and temperature of plasma jet are obviously higher than that of atmospheric pressure plasma spraying. The lower the pressure, the higher the jet velocity and temperature. 2. The residence time of the powder in the high temperature zone of the plasma jet increases, the heating is more uniform, and the flight speed is faster. 3. It can greatly increase the preheating temperature of the substrate surface; The substrate can also be sputtered and cleaned by reverse transfer arc to remove oxides and dirt, so as to improve the bonding condition between the coating and the substrate. 4. The surface of powder and substrate can completely avoid oxidation, and various active metal material coatings can be prepared 。 5. Due to the above reasons, the bonding strength of the coating is greatly improved, the porosity is greatly reduced, the residual stress of the coating is reduced, and the coating quality is significantly improved. 6. Vacuum plasma spraying equipment is complex and expensive, and it is difficult to popularize and apply.