Study On Preparation,Structures And Properties Of Nanostructured ZrO₂ Thick Coatings

The nanostructured ceramic thermal barrier coatings had more potential to improve the properties of TBC than conventional micro-scale coating in terms of lowing heat conduction rate. In present, The researchers overseas have had made considerable contributions in this respect(>500μm).However, few systematic investigations have been reported in China. Therefore, it is of great theoretical and practical significance in launching the project of preparing and studying thick TBCs.The nanostructured ceramic powders were agglomerated into micrometer-sized particles by spray drying process and then were subjected to thermal pretreatment. The thermal pretreatment is just helpful to improve the powders' appearance and promote the powder's sinter.Nanostructured thermal barrier coatings in three different thicknesses (0.6mm,0.8mm,1.2mm) were prepared by plasma spray. The coatings' microstructures were observed and experimental results show that the nanostructured coatings consist columnar grains as well as equiaxed grains and unmelted nanostructures which are not seen in conventional coating. There are two kinds of pores in the coatings. One is Stacking-Pore with small dimension great amount and high roundness, another one is Unmelted-Pore which is bigger,fewer and irregular. There are many micro-cracks exist on coatings' surfaces.The effects of two plasma spray parameters (spray current and spray distance) on the coatings' microstructure were studied with assistance of image analyzing system which indicated that it could decrease the pore rate and the grain size of the coatings by increasing the spray current and reducing the spray distance.The thermal insulation property and the bonding strength of the coatings were measured and their corresponding trends with the increasing thickness were analyzed. Experimental results showed that the coatings' thermal insulation property increases and the coatings' bonding strength decreases with the increasing thickness. In the same thickness, comparing with conventional coatings, the nanostructured coatings performed better in thermal insulation property but worse in bonding strength.