Tailoring the EB-PVD columnar microstructure to mitigate the infiltration of CMAS in 7YSZ thermal barrier coatings

Abstract

The CMAS associated degradation of 7YSZ TBC layers is one of the serious problems in the aero enginesthat operate in dusty environments. CMAS infiltrates into TBC at high temperatures and stiffens the TBCwhich ultimately loses its strain tolerance and gets delaminated. The EB-PVD technique is used to coatTBCs exhibiting a columnar microstructure on parts such as blades and on vanes. By varying the EB-PVDprocess parameters, columnar morphology and porosity of the 7YSZ coating is changed and its effect onthe CMAS infiltration behaviour is studied in detail. Two different TBC pore geometries were created andinfiltration experiments were carried out at 1250◦C and 1225◦C for different time intervals. The 7YSZcoating with more ‘feathery’ features has resulted in higher CMAS resistance by at least by a factor of 2than its less ‘feathery’ counterpart. These results are explained on the basis of a proposed physical model.