Preparation and properties of CMAS resistant bixbyite structured high-entropy oxides RE2O3 (RE = Sm, Eu, Er, Lu, Y, and Yb): Promising environmental barrier coating materials for Al2O3f/Al2O3 composites

Abstract

Abstract Y 2 O 3 is regarded as one of the potential environmental barrier coating (EBC) materials for Al 2 O 3f /Al 2 O 3 ceramic matrix composites owing to its high melting point and close thermal expansion coefficient to Al 2 O 3 . However, the relatively high thermal conductivity and unsatisfactory calcium-magnesium-aluminosilicate (CMAS) resistance are the main obstacles for the practical application of Y 2 O 3 . In order to reduce the thermal conductivity and increase the CMAS resistance, four cubic bixbyite structured high-entropy oxides RE 2 O 3 , including (Eu 0.2 Er 0.2 Lu 0.2 Y 0.2 Yb 0.2 ) 2 O 3 , (Sm 0.2 Er 0.2 Lu 0.2 Y 0.2 Yb 0.2 ) 2 O 3 , (Sm 0.2 Eu 0.2 Er 0.2 Y 0.2 Yb 0.2 ) 2 O 3 , and (Sm 0.2 Eu 0.2 Lu 0.2 Y 0.2 Yb 0.2 ) 2 O 3 were designed and synthesized, among which (Eu 0.2 Er 0.2 Lu 0.2 Y 0.2 Yb 0.2 ) 2 O 3 and (Sm 0.2 Er 0.2 Lu 0.2 Y 0.2 Yb 0.2 ) 2 O 3 bulks were prepared by spark plasma sintering (SPS) to investigate their mechanical and thermal properties as well as CMAS resistance. The mechanical properties of (Eu 0.2 Er 0.2 Lu 0.2 Y 0.2 Yb 0.2 ) 2 O 3 and (Sm 0.2 Er 0.2 Lu 0.2 Y 0.2 Yb 0.2 ) 2 O 3 are close to those of Y 2 O 3 but become more brittle than Y 2 O 3 . The thermal conductivities of (Eu 0.2 Er 0.2 Lu 0.2 Y 0.2 Yb 0.2 ) 2 O 3 and (Sm 0.2 Er 0.2 Lu 0.2 Y 0.2 Yb 0.2 ) 2 O 3 (5.1 and 4.6 W·m −1 ·K −1 ) are only 23.8% and 21.5% respectively of that of Y 2 O 3 (21.4 W·m −1 ·K −1 ), while their thermal expansion coefficients are close to those of Y 2 O 3 and Al 2 O 3 . Most importantly, HE RE 2 O 3 ceramics exhibit good CMAS resistance. After being attacked by CMAS at 1350 °C for 4 h, the HE RE 2 O 3 ceramics maintain their original morphologies without forming pores or cracks, making them promising as EBC materials for Al 2 O 3f /Al 2 O 3 composites.