The difference of gas atomization and water atomization
Gas atomization and water atomization have the same theory for producing alloy powders, but the physical properties of the powders have big difference, especially the shape. The thermal capacity of gas is lower than the water, so when we use the gas atomization, the alloy is chilled to a low degree. When the medium of atomization shocks the alloy, fogging into little droplet of alloy liquid doesn’t immediately solidify, which gives time to shrink into the ball during the fall, so the alloy powder with ball shape is available. Water atomization is to the contrary, because of the chilling effect of water on the atomization into small alloy droplet, almost in a moment, it is solidified into alloy powder, which also makes the alloy powder of the alloy with smaller surface tension into potato or irregular shapes. Only the alloy with bigger surface tension, such as nickel based alloy can be produced ball shape. By adjusting atomization parameters and super heat of the alloy liquid during atomization, ball shape alloy powder can also be produced with water atomization and meet thermal spray demand. Alloy powder used for tubular shape welding wire doesn’t have special requirement about the shape, so it’s better to use water atomization.
About the alloy powder’s composition
Chemical composition of alloy powder won’t be different due to different manufacture method no matter what kind of atomization we use.
About the Micro-structure
Super cooling of alloy powder using gas atomization is much lower than that by water atomization, so metallographic structure of alloy powder using different atomization is different with the same chemical composition.
The oxygen content of the alloy powders
The oxygen content of the alloy powder is related to the oxygen sensitivity of the alloy itself and the oxygen content in the atomizing environment during atomized. If the alloy itself is very sensitive to oxygen, then it is not only necessary to take measures when it is atomized, but also better to use vacuum smelting when melting. For most alloys, it is possible to reduce the oxygen content of the alloy powder by reducing the contact with oxygen during atomized. Gas atomization usually use nitrogen as the atomization medium, then a large number of nitrogen filling with atomization area expell off the oxygen of atomization area, So it can protect the alloy droplets from oxidation during atomization and cooling .
When a furnace molten alloy liquid is atomized into metal powder, the surface area increased numerous times during atomization in a flash. In other words, its area combining with oxygen is also increased, so more metal surfaces are exposed to the atomized environment. Therefore, when using water atomization, if you do not take measures, it is impossible to avoid the oxidation of alloy droplets. In order to make the atomization environment less oxygen or without oxygen during water atomization. First of all, atomized cylinder must be sealed to insulate the atomization environment and the surrounding environment. Secondly, we need to remove the oxygen sealed in the atomized cylinder. Finally, it has to maintain such an anaerobic or hypoxic atomization environment in the process of atomization, all the alloy droplets will be solidified into alloy powder in the end of atomization.
