Al2O3-derived entropy-stabilized AB2O4spinels as thermomechanically compatible interlayers for thermal barrier coating systems

Abstract

Thermal barrier coating (TBC) systems require materials with low thermal conductivity and sufficient thermomechanical compatibility to withstand severe thermal cycling in gas turbine environments. From an Al2O3-based materials design perspective, the incorporation of MgO promotes the formation of thermodynamically stable MgAl2O4 spinel phases that are chemically compatible with Al2O3-based thermally grown oxide (TGO). In this study, entropy-stabilized AB2O4 spinel ceramics were synthesized via solid-state reactions by incorporating multiple cations with similar ionic radii at the A2+and B3+sites. Their intrinsic thermal and mechanical properties were systematically evaluated using dense bulk ceramic specimens as a screening approach. Owing to enhanced lattice distortion arising from compositional complexity, the entropy-stabilized spinel ceramics exhibited reduced thermal conductivity over the temperature range from room temperature to 1000 °C. The combined effects of lattice distortion and modified metal–oxygen bonding are discussed in terms of suppressed phonon transport. In addition, the synthesized AB2O4 spinels exhibited coefficients of thermal expansion comparable to those of Al2O3-based TGO, suggesting improved thermomechanical compatibility at the top coat/TGO interface. Compared with yttria-stabilized zirconia, the entropy-stabilized spinels demonstrated improved chemical compatibility with Al2O3-derived oxide environments. These results suggest that Al2O3-derived entropy-stabilized AB2O4 spinels merit consideration as interlayer materials for TBC systems, providing thermomechanical compatibility with Al2O3-based TGO and a moderate increase in thermal resistance at the interface. The present study serves as a bulk-material screening step, and further coating-scale validation is identified as an important direction for future work.