Effect of CMAS Deposits on MOCVD Coatings in the System Y 2 O 3 – ZrO 2 : Phase Relationships

Three metal‐organic chemical vapor deposition ( MOCVD ) coatings ( ZrO 2 , Y 2 O 3 · ZrO 2 , Y 2 O 3 ) were studied in contact with model CMAS to investigate the microstructural evolution and phase formation. The MOCVD coatings were covered with CMAS powder deposits and annealed for 1 h at 1250°C, respectively. The ZrO 2 coating was completely infiltrated by CMAS , whereas the yttria containing coatings show a higher resistance against CMAS infiltration. This is explained by the formation of a continuous oxyapatite layer in the reaction zone of the coating and the CMAS deposit. The Y 2 O 3 · ZrO 2 coating shows the best infiltration resistance despite the fact that the Y 2 O 3 – CMAS sample is the only completely crystallized. As crystallization products, oxyapatite, melilite, anorthite as well as new garnets bearing all available cations were formed. The garnet phase was confirmed by XRD and TEM . EDS measurements were used to calculate structural formula A 3 B 2 T 3 O 12 (A = Ca , Y , Zr ; B = Mg , Al ; T = Al , Si ).