Non-uniform thermal gradient evolution in thermally cycled ytterbium silicate-silicon environmental barrier coatings

The primary purpose of barrier coating materials is to protect underlying media from harsh temperatures and/or environmental conditions that pose to undermine the performance of a system. Thus, materials with high thermomechanical stability and low thermal conductivity are choice candidates as thermal/environmental barrier coating top coats. Systems that implement a ytterbium-disilicate have shown to be promising candidates for next generation gas turbine engines. However, a robust examination of the microscale structural and thermal effects has yet to be performed over a range of cycling conditions. Considering the multi-phase, anisotropic constituents of such systems, a robust understanding of these mechanisms is necessary. In this work, we examine the microstructural and thermal evolution in ytterbium silicate-silicon environmental barrier coatings. The coating system cannot be defined by a single thermal conductivity, as local variations in thermal conductivity arise due to these multi-phase, anisotropic systems. Understanding the evolution and distribution of the thermal gradients associated with high-temperature steam-cycling is necessary for the continued development of these materials as hot-section components in gas-turbine engines.