Influences of Al2O3 addition on the thermophysical properties of AlMO4 (M = Ta, Nb) ceramics

The application of ceramic coatings on SiC-CMCs (ceramic matrix composites) and superalloy surfaces is indispensable in protecting them from adverse environmental impacts. AlMO4 (M = Ta, Nb) oxides are studied as candidate thermal and environmental barrier coatings (T/EBCs) to provide thermal and environmental protection for CMCs and superalloy substrates. In this work, the influences of Al2O3 addition on the properties of AlMO4 are investigated, with the characteristics of Al2O3 and AlMO4 grain distributions being one of the key points. The addition of Al2O3 leads to slight changes in the thermal conductivity and thermal expansion coefficients (TECs) of AlMO4, which ensure that the TECs of AlMO4 match those of CMC substrates, and they can provide good thermal insulation. The addition of Al2O3 inhibits the growth of AlTaO4 and AlNbO4 grains, which has a positive consequence on their thermal conductivity and hardness. This work further indicates that AlMO4 has excellent chemical compatibility with the thermally grown oxides (SiO2 and Al2O3) of CMCs and superalloy substrates. It is believed that the generation of thermal grown oxides will not significantly depress the properties of AlMO4 oxides, which allows them to be applied as high-temperature T/EBCs.