Effect of microstructure on the performance of Zr6Ta2O17 ceramics as thermal barrier coatings

In this study, Zr6Ta2O17 ceramics with porous, fine-grained, and coarse-grained structures were obtained via in situ solid-state reactions, and their mechanical characteristics were examined. The significantly low thermal conductivity of dense Zr6Ta2O17 ceramics (1.0 W m-1 K-1) was due to the grain boundary gap caused by superstructured grains. A calcium-magnesium-alumina-silicate (CMAS) corrosion experiment demonstrated that the formation of an interlocking structure composed of ZrO2, CaTa2O6, and ZrSiO4 prevented the penetration of CMAS impurities, thereby revealing the application potential of porous ceramics. In dense Zr6Ta2O17 ceramics, the low-volume diffusion induced by an entropy-stable structure is conducive for corrosion resistance; however, the grain boundary is vulnerable to attacks by CMAS, which can be mitigated by the formation of a coarse crystal structure, thereby effectively improving the corrosion performance. This work provides a critical perspective on the thermal barrier coating design of A6B2O17 (A = Zr, Hf; B--Nb, Ta) ceramics.