Comprehensive understanding of coupled stress characteristics in ytterbium disilicate environmental barrier coatings undergoing corrosion transformation and thermal cycling

Abstract

Ytterbium disilicate (Yb2Si2O7, YbDS), with good thermal matching ability, is a promising candidate for environmental barrier coatings (EBCs). Nevertheless, cracking and delamination of the YbDS topcoat may occur in a flowing steam environment due to the corrosion transformation from YbDS to ytterbium monosilicate (Yb2SiO5, YbMS). In this work, a scanning electron microscope (SEM)-based thermo-mechanical model, involving such corrosion transformation, is established to explore the stress characteristics in EBCs under the coupling effect of YbDS corrosion and thermal cycling. The main factors resulting in EBC failure during YbDS corrosion were also investigated. The results showed that compressive stress acted on the YbDS topcoat without a water vapor attack. However, the tensile stress occurred in the corroded YbDS coating after steam cycling. A large stress led to premature cracking of the EBC, thus providing channels for corrosive medium penetration. Volume shrinkage during YbDS corrosion dominated the stress magnitude in the corrosion zone. Furthermore, the increasing porosity caused a decrease in the Young's modulus and shrinkage strain of the corrosion zone, significantly affecting the EBC stress field. These findings not only enhance the comprehensive understanding of coupled stress characteristics in YbDS-EBCs, but also provide theoretical guidance for extending the EBC lifetime.