Y_2O_3被覆グラファイトの熱応力特性  [in Japanese] Thermal Stress Characteristics of Graphite Coated with Y_2O_3  [in Japanese]

The thermal stress of a graphite body coated with Y_2O_3 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 Y_2O_3 surface was studied by considering the stress relaxation. The analytical results indicated that the thermal stresses, σ_r,σ_t at the Y_2O_3 surface decreased with increasing thickness of Y_2O_3 and Nb layers. It was confirmed by experiments that the failure mode of the Y_2O_3/Nb/graphite composite was surface cracking by the thermal stresses, σ_r,σ_t induced during cooling. The critical heating temperature of the Y_2O_3/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 Y_2O_3 and Nb were improved by the recrystallization and sintering during the heating test.