Liquid-phase-infiltration of EB-PVD-TBCs with ageing inhibitor

Abstract

Partially yttria stabilized zirconia (PYSZ) is the state-of-the-art material for current thermal barrier coating (TBC) applications at aircraft engines. It introduces intrinsic properties leading to increased lifetime of superalloy turbine blades and engine efficiency. The new generation turbines generate higher gas temperatures, which seriously affects the thermal stability of the state-of-the-art TBC materials, mainly because of considerable phase transformation- and/or sintering-induced volume changes. These processes cause degradation of columnar microstructure of electron-beam physical vapor deposited (EB-PVD) coatings and raise modulus of elasticity and as a result, the internal stresses. One of the suggested strategies for the improvement of sintering resistance is to infiltrate TBCs with another oxide. This aims to reduce the diffusion rate at the nano-structured feather-arm features and to avoid inter-columnar pore closure. This paper deals with infiltration of EB-PVD PYSZ-structures with a liquid-phase precursor based on alumina and titania to inhibit sintering. After heat-treatment of infiltrated coatings at 1000 and 1100 °C, microstructure is characterized by SEM/EDX and compared with as-coated state-of-the-art material aged under same conditions. The mechanism, which may stop or inhibit the sintering at TBCs is discussed. Attributions to the thermal stability and the potential use of the infiltration technique in EB-PVD-coatings are addressed.