Thermal Stress Characteristics of Graphite Coated with Y₂O₃

Abstract

The thermal stress of a graphite body coated with Y₂O₃ by plasma spraying was analyzed using a finite element method program. Especially, the effect of the intermediate layer Nb on the thermal stresses of the Y₂O₃ surface was studied by considering the stress relaxation. The analytical results indicated that the thermal stresses, σ_r, σ_t at the Y₂O₃ surface decreased with increasing thickness of Y₂O₃ and Nb layers. It was confirmed by experiments that the failure mode of the Y₂O₃/Nb/graphite composite was surface cracking by the thermal stresses, σ_r, σ_t induced during cooling. The critical heating temperature of the Y₂O₃/Nb/graphite composites was estimated by the finite element analysis. On the other hand, it was also confirmed that the strength and ductility of as-sprayed films of Y₂O₃ and Nb were improved by the recrystallization and sintering during the heating test.