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In the previous study, TMS-238MoIr achieved a creep rupture life of 4044 h at 1100 °C / 137 MPa, more than twice that of the sixth-generation Ni-based single crystal superalloy TMS-238, corresponding to a temperature capability of 1136 °C (Larson-Millar conversion by 1000 h 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. % Mo and 2 at. % Ir. In this study, creep testing and microstructural analysis were conducted to evaluate creep properties and γ/γ′ phase stability of TMS-238MoIr and its counterpart TMS-238MoRu (TMS-238 + 1.5 at.% Mo and 2 at.% Ru) to understand the possibility and limit of these conceptual alloys. In contrast to TMS-238MoIr, TMS-238MoRu exhibited a significantly shorter rupture life of 870 h due to extensive TCP phase precipitation. Both modified alloys showed refined γ/γ′ interfacial dislocation networks, attributed to increased magnitude of negative lattice misfit from Mo partitioning into the γ phase. However, severe internal stress also induced planar faults in the γ matrix during heat treatment, which likely acted as nucleation sites for Topologically Closed Packed (TCP) phases at intermediate temperature around 900°C. TCP phase promoted void-assisted recrystallization and crack propagation, significantly reducing creep life of the concept alloys at 900 ºC and 392 MPa. These findings demonstrate that lattice misfit tuning must be balanced with phase stability to optimize creep performance in advanced Ni-base superalloys.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: Ni-base single crystal superalloy, Creep, Dislocation, Time Temperature Transformation diagram, Topologically closed packed phase

Date published: 2026-01-07

Publisher: Springer Science and Business Media LLC

Journal:

• Metallurgical and Materials Transactions A (ISSN: 10735623) vol. 57 issue. 5 p. 1794-1812

Funding:

• 科学技術振興機構 JPNJAL1302 (ALCA「超合金タービン翼の直接完全リサイクル法の開発」)

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1007/s11661-025-08089-5

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Updated at: 2026-04-20 13:48:18 +0900

Published on MDR: 2026-04-20 16:27:31 +0900