Interactions of Na2SO4 and yttrium‐silicate environmental barrier coatings at 825°C

Abstract

AbstractYttrium‐silicates (Y2Si2O7 and Y2SiO5) are candidate environmental barrier coating (EBC) materials for silicon carbide ceramic matrix composites (SiC‐CMCs). These materials’ high‐temperature, high‐velocity steam, and siliceous debris resistance are well studied. However, Na2SO4‐induced hot corrosion mechanisms are less understood. Free‐standing atmospheric plasma sprayed Y2Si2O7 and Y2SiO5 coupons were exposed to 2.5 mg/cm2 of Na2SO4 at 825°C in 0.1% SO2‐O2 (g). Scanning electron microscopy, X‐ray diffraction, transmission electron microscopy, and inductively coupled plasma‐optical emission spectrometry were used to identify a previously unknown damage mechanism. Water‐soluble Y and Na‐Y sulfates and oxysulfates formed in reaction with Na2SO4, causing significant damage to the yttrium‐silicate EBCs materials.