Infiltration-inhibiting reaction of gadolinium zirconate thermal barrier coatings with CMAS melts

The thermochemical interaction between a Gd2Zr2O7 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 similar to 1240 degrees C was investigated. A dense, fine-grained, similar to 6-mu m thick reaction layer formed after 4 h of isothermal exposure to 1300 degrees C. It consisted primarily of an apatite phase based on Gd8Ca2(SiO4)(6)O-2 and fluorite ZrO2 with Gd and Ca in a solid solution. Remarkably, melt infiltration into the intercolumnar gaps was largely suppressed, with penetration rarely exceeding similar to 30 mu m 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.