Protectiveness of Pt and Gd₂Zr₂O₇ layers on EB-PVD YSZ thermal barrier coatings against calcium–magnesium–alumina–silicate (CMAS) attack

Thermal barrier coatings (TBCs) are susceptible to degradation caused by environmental deposits mainly composed of calcium–magnesium–aluminum–silicon (CMAS). In this work, the degradation of electron beam physical vapour deposition (EB-PVD) yttria stabilized zirconia (YSZ) TBC due to CMAS attack was investigated. To protect the YSZ coating, a Pt film and a Gd₂Zr₂O₇ (GZO) layer were deposited onto the YSZ coating surface by electroplating and EB-PVD, respectively. The coatings were heat treated at 1250 °C for 4 h with CMAS deposits, and their microstructure and chemical composition after CMAS attack were investigated. Electroplating a dense and defect-free Pt film on YSZ coating could provide effective protection from CMAS attack, but EB-PVD GZO coating was unable to prevent molten CMAS infiltration, mainly due to the large inter-columnar gaps. The associated mechanisms were discussed in detail.