Development of Novel Functionally Graded Al2O3-Lanthanum Hexaaluminate Ceramics for Thermal Barrier Coatings

Lanthanum hexaaluminate (LHA) has superior thermo-chemical stability at temperatures higher than 1000 degrees C and is a promising competitor to Y-ZrO2-based thermal barrier coatings (TBCs). The yet unresolved problem is control of microstructure of high LHA content ceramics and adjustment of porosity upon, to arrive at a material exhibiting low thermal conductivity at high temperature combined with structural reliability. Therefore, a functionally graded alumina/lanthanum hexaaluminate (FGLHA) with a gradient in composition was developed. The thermal diffusivity and thermal conductivity of FGLHA were compared with the one of the monolithic composite ceramics. The alumina-rich composites showed excellent mechanical properties whereas the LHA-rich composites presented lower thermal conductivity.