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

Abstract Yttrium‐silicates (Y 2 Si 2 O 7 and Y 2 SiO 5 ) 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, Na 2 SO 4 ‐induced hot corrosion mechanisms are less understood. Free‐standing atmospheric plasma sprayed Y 2 Si 2 O 7 and Y 2 SiO 5 coupons were exposed to 2.5 mg/cm 2 of Na 2 SO 4 at 825°C in 0.1% SO 2 ‐O 2 (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 Na 2 SO 4 , causing significant damage to the yttrium‐silicate EBCs materials.