Infiltration‐Inhibiting Reaction of Gadolinium Zirconate Thermal Barrier Coatings with CMAS Melts

The thermochemical interaction between a Gd 2 Zr 2 O 7 thermal barrier coating synthesized by electron‐beam physical vapor deposition and a model 33CaO–9MgO–13AlO 3/2 –45SiO 2 (CMAS) melt with a melting point of ∼1240°C was investigated. A dense, fine‐grained, ∼6‐μm thick reaction layer formed after 4 h of isothermal exposure to 1300°C. It consisted primarily of an apatite phase based on Gd 8 Ca 2 (SiO 4 ) 6 O 2 and fluorite ZrO 2 with Gd and Ca in a solid solution. Remarkably, melt infiltration into the intercolumnar gaps was largely suppressed, with penetration rarely exceeding ∼30 μm below the original surface. The microstructural evidence suggests a mechanism in which CMAS infiltration is arrested by rapid filling of the gaps with crystalline reaction products, followed by slow attack of the column tips.