Abstract
In this study, an internal injection plasma torch is used to deposit nano-agglomerated YSZ feedstock powders on superalloy substrates at low ambient pressures ranging from 5000 Pa to 6000 Pa. Coatings with unique fully nano-equiaxed structures were obtained when operating the torch below 300 A. With increasing current, up to 700 A, coatings with mixed-grain and eventually large-grain structures were produced. Experimental results suggest that the equiaxed nanoscale structure derives from the original agglomerated nanoparticles that had undergone melting while inside the nozzle of the plasma torch and were subsequently solidified or sintered in the coating. Coating hardness and elastic modulus were also measured and are shown to correspond with microstructure.
