Role of suspension preparation in the spray drying process to obtain nano/submicrostructured YSZ powders for atmospheric plasma spraying

Thermal barrier coatings were manufactured by atmospheric plasma spray process from YSZ powders. These powders were made by a reconstitution process which consists in a spray-drying of suspensions followed by thermal treatment of the granules.Nano- and submicron-sized YSZ particles were used as starting material. Feeding well dispersed suspension to spray-drying chamber is the first key step in the reconstitution process. With this aim, concentrated, stable YSZ suspensions were obtained by means of the optimisation of the preparation conditions. Then reconstituted granules were produced by spray-drying of the YSZ suspensions and the following thermal treatment which was optimised.The reconstituted powders were then successfully deposited on austenitic stainless steel coupons by APS. The findings in this work proved that the reconstituted powders characteristics which in turn are related to the starting suspension properties affect the final coating microstructure in terms of the amount of unmelted zones.