The Accelerating Effect of CaSO 4 Within CMAS ( CaO – MgO – Al 2 O 3 – SiO 2 ) and Its Effect on the Infiltration Behavior in EB ‐ PVD 7 YSZ

Infiltration and deposition of Ca SO 4 in thermal barrier coatings ( TBC ) in addition to the CMAS deposits was found in many occasions on real aviation engines. The source and role of Ca SO 4 on the degradation of TBC is not well understood. Ca SO 4 containing CMAS was synthesized and a systematic study of its role on the CMAS infiltration behavior in EB ‐ PVD 7 YSZ is presented in this work. Its influence on the melting and crystallization behavior of CMAS was studied with the help of differential scanning calorimetry. The decomposition of Ca SO 4 into CaO and SO 3 was observed at 1050°C in laboratory air under the presence of CMAS using mass spectroscopy and in situ high‐temperature XRD . The same amount of CaO is brought into the CMAS system by means of adding Ca CO 3 , which will eventually decompose into CaO and CO 2 at 700°C. CMAS infiltration tests were carried out at different temperatures with and without Ca SO 4 /Ca CO 3 and the results demonstrate that the sulfur has no direct effect on the aggressiveness of the anhydrite containing CMAS with regard to its infiltration behavior in EB ‐ PVD 7 YSZ at high temperatures. The extra amount of calcia added to CMAS that is introduced by the evaporating species is responsible for enhanced infiltration of the deposits into the TBC .