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<p>TMS-238MoIr previously achieved a record creep rupture life of 4044&#xa0;hours at 1100&#xa0;°C/137&#xa0;MPa—more than twice that of the sixth-generation Ni-base single crystal superalloy TMS-238—corresponding to a temperature capability of 1136&#xa0;°C (Larson–Millar conversion by 1000&#xa0;hours rupture life under 137&#xa0;MPa). This alloy was designed to enhance the high-temperature low-stress creep performance of TMS-238 by adding 1.5 at.&#xa0;pct Mo and 2 at.&#xa0;pct Ir. This study investigates the mechanisms behind this exceptional high-temperature creep performance and its limitations at other conditions by comparing it to a counterpart alloy, TMS-238MoRu (TMS-238 + 1.5 at.&#xa0;pct Mo and 2 at.&#xa0;pct Ru). At 1100&#xa0;°C/137&#xa0;MPa, TMS-238MoIr's superior life was attributed to the combined effects of a refined <i>γ</i>/<i>γ</i>′ interfacial dislocation network achieved through increased magnitude of lattice misfit by Mo addition, and the suppression of topologically close-packed (TCP) phases by Ir. In contrast, TMS-238MoRu failed in only 870&#xa0;hours due to extensive TCP precipitation. The high <i>γ</i>/<i>γ</i>′ coherency stress and decreased stacking fault energy in both modified alloys induced stacking faults in the <i>γ</i> matrix during the initial heat treatment, before the creep test. These pre-existing faults served as potent nucleation sites for TCP phases at temperatures below 900&#xa0;°C. Consequently, TCP precipitate-assisted deformation significantly reduced the creep lives of both concept alloys at 900&#xa0;°C/392&#xa0;MPa. These findings demonstrate that lattice misfit tuning must be carefully balanced with stacking fault energy and <i>γ</i>/<i>γ</i>′ phase stability to optimize creep performance across a wide range of temperatures in advanced Ni-base superalloys.</p>

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Challenging the Limit of Strengthening by γ/γ′ Lattice Misfit on the High Temperature Creep Properties of Ni-Base Single Crystal Superalloy

  • 期刊论文

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  • 发表日期：

    2026年1月7日

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  • Satoshi Utada,
  • Tadaharu Yokokawa,
  • Toshiharu Kobayashi,
  • Michinari Yuyama,
  • Hiroshi Harada,
  • Toshio Osada,
  • Kyoko Kawagishi

摘要

TMS-238MoIr previously achieved a record creep rupture life of 4044 hours at 1100 °C/137 MPa—more than twice that of the sixth-generation Ni-base single crystal superalloy TMS-238—corresponding to a temperature capability of 1136 °C (Larson–Millar conversion by 1000 hours rupture life under 137 MPa). This alloy was designed to enhance the high-temperature low-stress creep performance of TMS-238 by adding 1.5 at. pct Mo and 2 at. pct Ir. This study investigates the mechanisms behind this exceptional high-temperature creep performance and its limitations at other conditions by comparing it to a counterpart alloy, TMS-238MoRu (TMS-238 + 1.5 at. pct Mo and 2 at. pct Ru). At 1100 °C/137 MPa, TMS-238MoIr's superior life was attributed to the combined effects of a refined γ/γ′ interfacial dislocation network achieved through increased magnitude of lattice misfit by Mo addition, and the suppression of topologically close-packed (TCP) phases by Ir. In contrast, TMS-238MoRu failed in only 870 hours due to extensive TCP precipitation. The high γ/γ′ coherency stress and decreased stacking fault energy in both modified alloys induced stacking faults in the γ matrix during the initial heat treatment, before the creep test. These pre-existing faults served as potent nucleation sites for TCP phases at temperatures below 900 °C. Consequently, TCP precipitate-assisted deformation significantly reduced the creep lives of both concept alloys at 900 °C/392 MPa. These findings demonstrate that lattice misfit tuning must be carefully balanced with stacking fault energy and γ/γ′ phase stability to optimize creep performance across a wide range of temperatures in advanced Ni-base superalloys.