Ｎｉ基単結晶超合金の引張・圧縮‐繰返しねじり負荷での多軸低サイクル疲労寿命評価

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This paper studies on the tension-torsion multiaxial low cycle fatigue of YH61 nickel base single crystal superalloy at high temperature. Strain controlled tension-torsion low cycle fatigue tests were carried out at 1173K using YH61 hollow cylinder specimens of which specimen axis was <001> crystallographic direction. Mises equivalent total strain range gave a large scatter in the correlation of multiaxial low cycle fatigue lives. On the other hand Mises equivalent plastic strain and Mises equivalent stress ranges correlated the multiaxial low cycle fatigue lives with a small scatter. The deformation behavior of the single crystal superalloy showed strong anisotropy under multiaxial loading due to the crystallographic texture, and the unsatisfactory life correlation with Mises total strain range resulted from the anisotropic deformation behavior of the specimen. A new strain parameter, taking account of the anisotropy of elastic constants into account was proposed, and the parameter estimated the multiaxial low cycle fatigue lives within a factor of 2 scatter band.