A review and progress of multiphase flows in atmospheric and low pressure plasma spray advanced coating

Arc plasma sprayed thin films and coatings exhibit excellent mechanical properties for anti-corrosion, anti-wear, anti-radiation, thermal isolation, and heat conduction applications. These coatings have been used in metallic parts of aircraft engines, automobile engines, gas turbine engines, diesel engines, nuclear power equipment, and oil refining equipment. The microstructures and properties of the deposited coatings change with plasma spray processing parameters. In general, depositing of coatings through plasma spraying involves different types of material flow and atomization. Under constant feed rates of metallic or ceramic powders, various spraying distances are employed to deposit the coating. Therefore, the heating history, motion, and phase transformation of the powder in the plasma jet during plasma spraying have been extensively studied. This paper reviews the current state of plasma spray technology for the production of coatings and presents multiphase flows and heat transfer mechanisms from powders to the coating. Progresses in novel atmospheric micro plasma spraying and long laminar plasma spraying technology are shown, low-pressure supersonic plasma-induced physical vapor deposition of quasi-columnar ceramic coatings is also presented. The shadowing effect, flash vaporization, breakup, and atomization of in-flight droplets at a chamber pressure of 200 Pa, and maximum distance of 2200 mm were clarified. Finally, the remaining unresolved issues are discussed, and a future outlook on plasma spraying technology is presented.