Thermal spraying technology is one of the key technologies in the field of material science

            As one of the key technologies in the field of material science, Thermal spraying technology is an important part of advanced manufacturing technology. The technical principle is to use gas combustion or discharge to heat raw material particles to a molten or semi molten state, and then spray them onto the substrate through a flame jet or compressed air. The particles Z eventually flatten and solidify into stacked fragments, forming a coating. Thermal spraying coating is widely used in aerospace, automobile, ship, petrochemical and other fields because of its functional characteristics such as wear resistance, friction reduction, heat insulation, insulation, high temperature resistance, oxidation resistance, and microwave radiation resistance, as well as its advantages in repairing the size reduction of parts caused by wear and corrosion, which can achieve the purpose of saving materials and energy.

          Thermal spraying technology is a Thermal spraying technology developed in the 1970s. Compared with the traditional high-pressure oxygen fuel spraying and arc spraying technology, Thermal spraying technology shows higher efficiency. Thermal spraying can provide excellent bonding with the substrate and compact structure, variable thickness and low thermal strain, especially suitable for the formation of amorphous coatings. With the improvement of the requirements of service environment on coating performance and the innovation of spraying technology, Thermal spraying technology has obtained new development, such as supersonic Thermal spraying, low-pressure Thermal spraying, etc. The characteristics and research status of low pressure Thermal spraying technology are reviewed.

          Thermal spraying technology is a method that uses the DC driven plasma arc as the heat source to heat ceramics, alloys, metals and other materials to the molten or semi molten state, and spray them to the pretreated substrate surface at a high speed, so as to form a solid coating. Its principle is shown in. Apply a high voltage between the gun electrode (cathode) and the nozzle (anode) and excite it with a high-frequency oscillator. The Thermal spraying electrode ionizes the gas (argon, nitrogen, hydrogen, etc.) to form an arc.

         When passing through a nozzle with a special hole type, the arc is subjected to mechanical compression, resulting in a decrease in the cross-sectional area of the arc. At the same time, it is cooled by the continuous cold air flow from the outside and the wall of the cold nozzle with good thermal conductivity. The surrounding gas of the arc column is strongly cooled, resulting in a decrease in temperature and a reduction in the conductive cross-section, resulting in a thermal shrinkage effect. The arc is further compressed, causing the arc current to only pass through the center of the arc column, and the arc current density increases sharply, Forming a high compression, high-speed plasma jet. The spraying powder is loaded into the plasma flame stream by the powder gas (two methods: external powder feeding and internal powder feeding), causing the powder to quickly melt or semi melt, and high-speed spraying forms a dense flake coating on the surface of the workpiece.