In-situ synthesis of gadolinium niobate quasi-binary composites with balanced mechanical and thermal properties for thermal barrier coatings

Abstract

Yttria-stabilized zirconia (YSZ) has been used as a thermal barrier coating (TBC) material in gas turbines for several decades. Although continuous efforts have been made to develop novel TBC materials that can work at a higher temperature, no single material other than YSZ has all the desired attributes for the TBCs. In this paper, we report the in-situ synthesis of quasi-binary GdNbO4/Gd3NbO7 composites based on the simple Gd2O3-Nb2O5 binary phase diagram. The fracture toughness of these quasi-binary composites is remarkably enhanced compared with the value predicted by the rule of mixtures because the ferroelastic domain switching is more activated due to the residual stress in the quasi-binary composites, which triggers more crack defections due to the enlarged process zone. Additionally, the Gd3NbO7 phase provides a low thermal conductivity due to the substantial chemical inhomogeneity, which diffuses phonons. Gd3NbO7/GdNbO4 exhibits a balanced thermal conductivity of 1.6 W/(m·K) at 1073 K and a toughness value of 2.76 MPa·m0.5, and these values are among the best comprehensive properties that have been obtained for new TBC materials. The work demonstrates a feasible approach of designing a new TBC material with balanced properties and can be easily fabricated.