Phase stability and thermal conductivity of nanostructured tetragonal yttria–stabilized zirconia thermal barrier coatings deposited by air–plasma spraying

High performance thermal barrier coatings (TBCs) produced from nanocrystalline 4 mol.% Y2O3–stabilized ZrO2 (4YSZ) powder show significant thermal and mechanical property advantages compared with current benchmark products. The objective of the present study was to investigate the phase stability and thermal conductivity of the nanostructured 4YSZ coatings plasma–sprayed from the sol–spray pyrolysis powder. Characterization results indicated that the as–sprayed 4YSZ coatings were chemically very homogeneous and had a completely tetragonal–prime (t′) structure. Such a uniform composition was almost entirely consistent with that of the feedstock powder. The grain size of as–sprayed 4YSZ coatings was in the range of 35 ~ 75 nm, which resulted in an extremely low thermal conductivity of 0.8–1.2 W m–1 K–1 in the coatings. The high–temperature aging test showed that no monoclinic ZrO2 (m–ZrO2) phase present at all of the 4YSZ coatings after a heat treatment at 1473 K for 1–650 h. Furthermore, the phase composition of the 4YSZ coating kept t′–ZrO2 structure after 1500 thermal cycles at a peak surface temperature of 1373 K. The relative phase stability was attributed to the highly pure t′ phase composition and uniform constituents in the 4YSZ coatings. These results suggested that the development of high performance 4YSZ ceramic powders was benefit to improve the coating properties for TBC application.