Effect of Sr2Nb2O7 addition on fracture toughness and thermal conductivity of Y2O3-stabilized HfO2 ceramics

Abstract

Low fracture toughness limits the application of cubic-phase HfO2 based ceramics as a novel thermal barrier coating material. In this study, Sr2Nb2O7 was introduced into the 24 mol% Y2O3-stabilized HfO2 (YSH24) to improve the fracture toughness. A series of dual-phase composite ceramics with a formula of xSr2Nb2O7/(1-x)YSH24 (x = 0, 0.01, 0.02) were prepared by solid-state sintering. The effect of Sr2Nb2O7 addition on microstructure, fracture toughness, and thermal conductivity of the dual-phase composite ceramics was investigated. The results showed that the perovskite (P) phase with a simple cubic structure of Nb2O5-doped SrHfO3 was generated after Sr2Nb2O7 was introduced. The compositions of x = 0.01 and 0.02 consisted of a mixture of the matrix fluorite (F) phase and a small amount of layer-like P phase. The maximum fracture toughness of 2.47 MPa m1/2 was achieved for xSr2Nb2O7/(1-x)YSH24 dual-phase composite ceramics when x = 0.01, which is approximately 98% higher than that of YSH24. It was surprising that the thermal conductivity of the x = 0.01 composition was as low as 1.63 W m−1 K−1 at 1200 °C, and the radiative thermal conductivity was reduced by 86% compared to YSH24. The findings should provide insight into the simultaneous improvement of fracture toughness and thermal conductivity of ceramic materials and contribute additional assistance in selecting the materials for advanced thermal barrier coatings.