Role of Feedstock Particle Characteristics on Phase Formation and Microstructural Development of APS-Deposited Ytterbium Disilicate EBCs

Atmospheric plasma spraying (APS) of rare-earth silicate environmental barrier coatings (EBCs) offers a scalable approach for protecting ceramic matrix composites (CMCs) in the high-temperature, water-vapor–rich environments of gas turbines. However, coating microstructure, chemical composition, and crystallization behavior are highly sensitive to feedstock characteristics, which remain insufficiently understood. This study examines how the characteristics of ytterbium disilicate (Yb₂Si₂O₇) particles affect the microstructural development and phase formation of APS-deposited EBCs. Yb₂Si₂O₇ powders with controlled physical characteristics are processed under identical plasma spray conditions to isolate feedstock-driven effects. In-flight particle behavior, splat formation, and the resulting coating microstructures are examined in relation to powder characteristics. Phase composition and crystallization behavior are assessed as a function of feedstock attributes, with particular attention to potential deviations from equilibrium phase constitution arising from the non-equilibrium thermal histories experienced during APS. The findings aim to provide practical guidelines for feedstock engineering as a tool for tailoring microstructure and performance of next-generation APS EBC systems for gas turbine applications.