Silicate-based environmental barrier coatings: Reflections on chemical composition and layered architectures

Silicate-based environmental barrier coatings (EBCs) are the present choice to protect ceramic matrix composites (CMC) components used in existing and future turbine engines from the combustion environment produced during operation. Atmospheric plasma spray (APS) is a common means of depositing these materials in the form of coatings. The coatings produced in this way are characterized, depending on the processing conditions, for having an amorphous character and shift from the original chemical composition. In the present work are discussed the distinct characteristics of coatings obtained with different RE-Silicates (RE=Y,Yb,YYb) deposited by APS on SiC substrates. The benefits of the inherent shift of chemical composition caused by the plasma are also raised and presented as an in-situ process of producing layered architectures with graded thermomechanical and chemical properties. For this purpose, a comprehensive study of crystalline phase evolution and thermomechanical analysis of the different coating compositions is presented and correlated with microstructural appraisals.