Bilayer TBC

Abstract

A two layered thermal barrier coating (TBC) system comprises a metallic substrate 4, a ceramic bottom layer 10 comprising zirconia partially stabilised with yttria or zirconia stabilised with yttria and ytterbia or zirconia stabilised with yttria and ytterbia and erbia, and a ceramic top layer 13 comprising zirconia stabilised with yttria and ytterbia or erbia or both. Preferably, the total amount of stabilisers in the ceramic top layer is at least 5% or at least 10% higher than the total amount in the ceramic bottom layer. The ceramic top layer and the ceramic bottom layer may further comprise hafnia and alumina. A NiCoCrAlY layer 7 may be applied to the metallic substrate, which is preferably a nickel or cobalt based superalloy.