高温腐食環境下における構造用セラミックスの破壊挙動

概要

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Fracture behavior of Si_3N_4 and SiC ceramics was investigated in corrosive environments at high temperature. Corrosion tests were made under various stress conditions using specimens coated with molten salts at l000℃ in air. Flexural strengths of corroded specimens were investigated at room temperature. Stress-time-dependent and stress-cycle-dependent fracture tests were also performed in air at l000℃ using specimens coated with a moltan salt. The following results were obtained by analyzing the chemical reaction and fracture process. ( 1 ) Molten salts of sodium corroded Si3N4 at l000℃ in air. The major mode of corrosion attack was the dissolution of the grain boundary phase. The formation of large pits resulted in strength degradation. Strength degradation of SiC was only 5%. ( 2 ) Applied stress affected the morphology of bubbles in layers corroded by molten salts. A model is proposed for the defect formation under tensile and compressive stress. ( 3 ) Stress-cycle-dependent strength of Si_3N_4 was lower than stress-time-dependent strength under a sodium salt condition at 1000℃.
社団法人日本機械学会の論文
1992-08-25