What working gas is used for cold spraying

       The selection of gas or gas source first considers its acceleration effect, that is, whether the combination of a certain material particle and a certain material substrate can reach a critical speed and achieve effective deposition. On this basis, the cost, safety and activity of the gas are also important. factor.



For different gases, the larger the specific heat [capacity] ratio γ, the smaller the relative molecular mass, which can accelerate the gas flow more significantly. Therefore, the spraying effect of using monatomic gas He is better than that of diatomic N2. Under the conditions of normal pressure and 15 ℃, the speed of sound in several commonly used gases, that is, the acceleration effect is in ascending order: argon 319m/s, air 343m/s, nitrogen 349m/s, helium 989m/s, hydrogen 1303m/s. Among them, although hydrogen has the best acceleration effect, it is a flammable and explosive gas, and its storage, handling and use are greatly restricted, and the price is high; argon has poor acceleration effect and high price; air is cheap and has a general acceleration effect And the oxygen contained will cause oxidation of the coating material when used at high temperature; nitrogen is inexpensive, has a good acceleration effect, and remains inert to most materials at high temperatures, but may react with Ti and its alloys to form nitrides at high temperatures ; Helium acceleration is good but expensive. It can be seen that nitrogen is commonly used in practice, followed by helium and a mixture of helium and nitrogen. The selection should be made according to the characteristics of the coating material and spraying requirements.