Ni基単結晶超合金CMSX-10の高温疲労における破壊プロセスの解明と表面酸化層除去のき裂発生に及ぼす効果(<特集>高温強度)

概要

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Fatigue tests were conducted at 1273K using smooth bar specimens of a nickel-based single crystal superalloy CMSX-10, and small cracks were observed on the surface of the specimens by means of microscope. It was clarified by the observation that fatigue fracture of CMSX-10 takes place as follows;(1)Oxide-layer was formed on the surface of the specimen. (2)A lot of small cracks of the size of about 100μm were initiated perpendicular to the stress axis on the surface of the oxide-layer. (3)Some of them grew and penetrated the oxide-layer to reach the base metal. Processes(1)to(3)were completed at the very early stage of fatigue life. (4)Growth of the cracks that reached the base metal brought about the final fracture. As the formation of oxide-layer on the surface of the specimen was considered to be a trigger of crack initiation, a fatigue test was also conducted with repeated removal of the oxide-layer by emery paper and diamond paste. In this test, no crack appeared on the surface of the specimen even at 20000 cycles when a lot of cracks were observed in the normal fatigue tests. This proves that removal of the oxide-layer retards the initiation of small cracks and extends the fatigue life.
社団法人日本材料学会の論文
2001-02-15