Nanostructured thermal barrier coatings

Thermal spray zirconia-8. wt% yttria (YSZ) deposits have been employed as thermal barrier coatings (TBCs) in the hot sections of gas turbines. The use of nanostructured YSZ represents an alternative for improving the performance of these coatings. Before spraying, finely dispersed particles must be agglomerated. Air plasma-sprayed nanostructured zirconia coatings consist of only the non-transformable tetragonal phase and the microstructure is composed of nanozones (unmelted or partially melted particles), splats, microcracks and highvolume spheroidal pores. The results indicate that the microhardness, elastic modulus and roughness of the nanostructured zirconia coatings exhibit the following trends: the smoother the roughness, the higher the microhardness and elastic modulus. The decrease of thermal diffusivity of the nanostructured coating was attributed to the increase of grain boundaries, micropores and defective crystal structure. The smaller the micropores are, the more interfaces are produced, and the effect on the phonon scattering is higher, resulting in the reduction of thermal diffusivity. Meanwhile, the nanostructured TBC also exhibits the promising thermal cyclic oxidation resistance.