Effect Of Ambient Pressure And Gas Composition On Microstructure Of Plasma Sprayed YSZ Thermal Barrier Coatings Using Nanostructure Feedstocks

In recent years, thermal spraying technology has been widely used for creating coatings which are applied in industrial fields. With the demand for increasing quality of the coatings, a new very low pressure plasma spraying technology has been widely brought into focus. Very low pressure plasma spraying technology is operated in the condition of a low pressure(50-100Pa). Plasma spray jet can reach supersonic speed due to the use of high-power plasma spaying and low pressure condition. In this way, the structure of a coating is different from atmospheric plasma spray.In this study, three different methods of plasma spraying, namely atmospheric plasma spraying, low pressure plasma spraying and very low pressure plasma spraying are used. To obtain a variety of coatings for different organization and structure, two different kinds of YSZ agglomerated powder(sintered powder and unsintered powder)are sprayed. To obtain different plasma jet, two different kinds of gas(Ar-H2 and Ar-He)are used in this experiment, which is one of the most important reasons affecting different structure of YSZ. Then the coatings deposited in different conditions are mosaiced, grinded, polished and corroded in turn. Finally the cross-sections of coatings are observed by electronic microscope, in order to analyze the characteristics of organizational structure. The experimental results show that:Porous and equiaxed thermal barrier coatings can be deposited by APS using nanoparticle powders.In low and very low pressure conditions, gas composition has a great influence on the coating microstructure. Large grains areas and larger porous exist in the coating which deposited by plasma gas Ar-H2,while the coating with uniform and fine grain can be deposited by plasma gas Ar-He,at the same time, fully nano-equiaxed-structure coating can be deposited.In low and very low pressure conditions, the plasma jet characteristics are different from that in atmosphere pressure. Fully nano-equiaxed-structure coating can be deposited by LPPS and VLPPS, and the grains deposited by VLPPS is finer.