La2Hf2O7 ceramics as potential top-coat materials for thermal/environmental barrier coatings

Abstract

Abstract La 2 Hf 2 O 7 (LH) ceramics with pyrochlore structure have excellent phase stability up to 1600\u202f°C, and far superior sintering resistance as well as comparable mechanical properties to typical 8\u202fwt% yttria-stabilized zirconia (8YSZ). More importantly, they have the coefficients of thermal expansion (CTEs) of 8.76\u202f×\u202f10 −6 \u202fK −1 , lower than that of 8YSZ (10.38\u202f×\u202f10 −6 \u202fK −1 ), and thermal conductivities of 1.34\u202fW/m·K at 1000\u202f°C, approximately 40% lower than that of 8YSZ (2.1–2.22\u202fW/m·K). These comprehensive properties promote them as thermal insulation top-coats in thermal/environmental barrier coatings (T/EBCs) on ceramic-matrix composites (CMCs) or top-coats of double-ceramic-layered thermal barrier coatings (DCL-TBCs) on superalloys.