Ni基超合金Alloy617の高温クリープ疲労負荷による粒界強度劣化機構の検討

  • 鈴木 亘
    東北大学 大学院工学研究科 ファインメカニクス専攻
  • 鈴木 研
    東北大学 工学研究科付属先端材料強度科学研究センター
  • 三浦 英生
    東北大学 工学研究科付属先端材料強度科学研究センター

書誌事項

タイトル別名
  • Degradation of the Strength of Grain Boundaries in Ni-base Superalloy Alloy617 Under Creep-Fatigue Loading at Elevated Temperatures

抄録

<p>Ni-base superalloys such as Alloy 617 has been used for boiler pipes or tubes in the A-USC because of its high strength and oxidation and corrosion resistances at elevated temperatures. It is concerned, however, that thermal stress during the operation increases because this alloy has higher coefficient of thermal expansion compared to conventional ferritic steels. Moreover, frequent output change is required for thermal power plants because of co-existence with renewable energies. Therefore, it is necessary to consider the effect of creep-fatigue damage. Even though the conventional linear damage rule has been used for the evaluation of creep-fatigue damage, it was found that the critical damage to final fracture decreases drastically depending on loading conditions. The main reason of this drastic decrease is attributed to the change of crack path from transgranular to intergranular under creep-fatigue loadings. The main reason for the intergranular crack was considered to be the degradation of the crystallinity and strength around grain boundaries due to creep-fatigue damage. In this study, in order to quantitatively evaluate the change of the effective strength of a grain and a grain boundary, EBSD analysis and a micro tensile test system with FIB equipment were applied to single-crystal specimens and bicrystal specimens cut from initial and damaged materials. The IQ value which indicated the total density of defects such as vacancies, dislocations, and local strain was used for evaluating the crystallinity of these micro specimens. As a result, it was quantitatively confirmed that the strength of a grain decreased with the damage. Moreover, the result of bicrystal specimens suggested that the degradation of the IQ value in the vicinity of a grain boundary under creep-fatigue loading caused intergranular cracking.</p>

収録刊行物

  • 年次大会

    年次大会 2019 (0), J04234P-, 2019

    一般社団法人 日本機械学会

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