Composite strategy for improving the thermal barrier application of high-entropy alloy coating

High-entropy alloys (HEAs) attracted great interest in a wide range of structural and functional application, such as the newly developed metal-based thermal barrier coatings. However, the high temperature-sensitivity of thermal conductivity made a challenge for their practice. Herein, we proposed a composite strategy to address this problem and synthesized AlCoCrFeNiTi HEA coatings composited with yttria-stabilized zirconia (YSZ) additions. The metallic matrix of composite coatings inherits a simple body-centered cubic (BCC) structure and a microstructure feature of ultrafine grains in size of 200–500 nm, whereas the dispersed YSZ additions depict a typical tetragonal structure and a high deformation/deposition-sensitivity to their initial content. The heterogeneous splats form a weak contact interface due to the rapid-quenching of droplets and the nanoscale oxide film formed on the surface of HEA splats. The moderate YSZ additions with lamellar deposition structure effectively hinder the radial heat flux, granting the HY10 (HEA-10%YSZ) composite coating an extremely low thermal conductivity of 3.63 W/(m·K) at 800 °C, whose underlining mechanism is disclosed as the suppression of electron thermal conductivity. Meanwhile, the HY10 composite coating maintains a high fracture toughness of 2.90 MPa·m^1/2 that is comparable to the monolithic HEA coating, demonstrating a limited damage of brittle ceramic particles on mechanical properties. The proposed composite strategy paves the way for improving the thermal barrier application of HEA coatings and the regulating mechanisms provide an inspiration for future works aiming to formulate the design of extensive metal-matrix composite coatings.