A Plasma Torch Designed for Low Pressure Plasma Spraying and Formation of Yttria Stabilized Zirconia Coatings

摘要

To enhance deposit efficiency and improve quality of the yttria stabilized zirconia (YSZ) coatings used for thermal barrier coatings, two kinds of plasma torches with different nozzle sizes using an internal powder feedstock were designed respectively according to the plasma spray characteristic in the low pressure environment. The properties of the plasma jet with or without powder injection were analyzed by optical emission spectroscopy. Optical Microscope and Field Emission Scanning Electron Microscope were applied to analyze the microstructure of the feedstock powders and coatings. The micro-hardness was measured by the HM-6 test. The results indicated that the feedstock powder of YSZ could be partially vaporized in plasma jets, and equiaxed microstructure YSZ coatings were first successfully deposited by using the both of plasma torches. The Kundsen number is lower in the plasma jet with along anode nozzle, so the long anode nozzle could improve the melting of the powders. With the increase of the spraying distance, fine equiaxed grains and unmelted agglomerated particles appear in the coatings, and the micro-hardness value of the coatings decreased.