First, the main advantages of low pressure plasma spraying are as follows:
1. Due to the effect of vacuum, the navigation resistance of the plasma jet in the vacuum chamber is greatly reduced, thus extending the length of the plasma jet beam from 4cm-5em to 40cm-50cm under normal pressure. The residence time of the powder particles in the arc beam is significantly increased, which is conducive to the full heating and melting of the powder particles. The spray paint particles have a high heat energy.
2. Due to the low pressure of the vacuum chamber, the plasma flow speed can be increased to 3Ma~4Ma. Moreover, the navigation resistance of the powder particles in the low-pressure chamber is greatly reduced, so the flight speed and kinetic energy of the powder particles are high.
3.Almost no oxidation of metal particles The oxygen content of the vacuum chamber is low, especially after being filled with high-purity rare gases, the oxygen content is very low. The coating in the low-pressure room basically does not contain oxides, the coating is clean, and the bonding strength between the coating particles is greatly improved, and the coating is dense. Therefore, low pressure plasma spraying is suitable for spraying heat-resistant alloys containing easily oxidized components (such as MCrAIY), easily combustible metals (Mg, Ti, Li, Na and Zr, etc.), toxic metals (such as Be and its alloys) and easily oxidized cementte cermets.
4. Due to the dual role of vacuum and rare gas protection, the workpiece matrix can allow higher preheating temperatures without deformation or organizational changes. In this way, one can reduce the temperature difference between the coating particles and the substrate, reduce the cooling rate of the coating, and then reduce the thermal stress, so that the coating is not easy to crack; Second, when the molten particles are sprayed to the surface of the workpiece, the terrain can be completely changed, wetting and dispersing, eliminating gas, producing a dense coating, so that the coating porosity is less than 1%; Third, the increase of preheating temperature of the substrate makes the surface of the substrate in a better active state, which is conducive to improving the bonding strength of the coating and the substrate.
5. Self-purifying surface pretreatment can be carried out before low-pressure plasma spraying, and the transfer arc starting is selected by the automatic control system, that is, the workpiece matrix is connected to the negative electrode of the power supply when the arc starting, so that the electrons escape from the surface of the workpiece and produce a clean and active surface. Make the workpiece and spray paint droplets to achieve good combination performance, no need for mechanical coarsening or sandblasting process.
6. The paint distance has little influence on the coating performance, because the low-pressure plasma spraying beam is long and the sailing particles are in a state of high thermal energy and high kinetic energy, so the spraying distance between the nozzle and the substrate has little influence on the coating performance, making the low-pressure plasma spraying very suitable for painting complex shapes and curved workpieces, such as painting gas turbine blades, and obtaining uniform high-quality coating.
7. The quality of the high and low pressure plasma spraying layer can be compared with the electron beam-material * phase deposition (EB-PVD) and the coating, and its deposition speed is fast
Two to three orders of magnitude. For example, the deposition rate of low-pressure plasma CoCrAIY coating sprayed on 25.6cm2. Low pressure plasma can reach 260μm/min, and the deposition rate of physical phase deposition is 4μm/min~50μm/min
8. Low pressure plasma spraying coating has high bonding strength, very dense coating, very low porosity, no oxide mixing, small coating stress, high hardness, good toughness, and excellent overall performance.
9. Vacuum chamber painting operating conditions are good, isolation of high noise, sealing dust, good operating conditions.
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