Current developments and challenges in thermal barrier coatings

Some of the recent developments and challenges in thermal barrier coatings (TBC) are discussed. A wide flexibility of coating morphologies can be obtained by atmospheric plasma spraying (APS), and the size of microstructural features within the coatings is typically governed by that of the feedstock. By means of suspension plasma spraying (SPS), high segmentation crack densities can be obtained in TBCs while the porosity is maintained at a considerably higher level than by APS. Partially yttria stabilised zirconia (YSZ) with 6 to 8 wt-% yttria content is frequently used as TBC material due to its high thermal expansion coefficient and its relatively good fracture toughness. A strategy to improve the efficiency of gas turbines is abradable TBCs which are widely used in compressors and high-pressure stages. The infiltration of TBC microstructures by thin oxide layers applied by atomic layer chemical vapour deposition can yield improved sintering stability.