Process and Application of Low Pressure Plasma Spraying

       (1) Evacuate the working chamber to 2.6Pa first, and then fill the working chamber with argon gas to make the indoor pressure reach 1.3X10 3Pa.



    (2) Preheating. The positive transfer arc is used, that is, the workpiece is the anode and the gun is the cathode to preheat the workpiece. This method of arc transfer heating can save 50% of the time compared to the general non-transfer arc preheating (the preheating process can be omitted for small workpieces)

    (3) Electric cleaning. The reverse transfer arc is used, that is, the workpiece is the cathode and the gun is the anode, and the surface of the workpiece is sputtered and cleaned by the arc, which can remove the oxide film and other contaminants on the surface of the workpiece, thereby generating a highly active surface, so that the coating The layer and the substrate produce a certain metallurgical combination (in practice, the combined arc has been used to connect the circuit, and then the transfer arc is used).

    (4) Preparation of coating. After electric cleaning, continue to charge argon gas into the working chamber to make the pressure reach 3.9X10 3Pa ~ 2.0 X10 4Pa. The specific value varies with the requirements of the working conditions. The pressure should be strictly controlled within ±5% of the set value, otherwise the quality of the coating will be adversely affected.

    (5) Cooling. After spraying, the studio should continue to maintain a low-pressure inert atmosphere until the workpiece is cooled to below 100 ℃, and then fill with air.

    LPPS technology is mainly used in the preparation of high-performance coatings and spray forming. In the 1980s, it replaced the PVD method and was applied to the blades of aero turbine engines. NiCrAIY series alloy coatings were sprayed as the combined bottom layer of anti-oxidation and thermal barrier coatings. ; Preparation of Ti-Ni and other anti-corrosion and anti-soaking coatings for naval high-speed ship propellers and NiAl3 anti-cavitation-erosion coatings; LPPS has also been successfully used in thermal spray forming of some high-melting-point brittle materials in recent years. In the LPPS process, the individual particles are rapidly condensed in a very short high temperature stage without being polluted, and can be made into a material with a particle size of 0.25 μm and a uniform composition, so the performance of the parts prepared by this method is better than that of the general conventional method. The 1700 ℃ high temperature resistant tungsten bushing for the inner barrel of the space shuttle crystal growth furnace has been successfully fabricated by LPPS. The process of using LPPS to prepare composite materials and functionally graded materials is under study.