Microstructural damage assessment in alloy 617M near high cycle fatigue threshold at elevated temperature

• Published in: Fatigue & fracture of engineering materials & structures Vol. 47; no. 4; pp. 1445 - 1465
• Main Authors: Kale, Sandeep, Thawre, M. M., Peshwe, D. R., Nagesha, A., Sarkar, Aritra, Dandekar, Tushar R.
• Format: Journal Article
• Language: English
• Published: Oxford Wiley Subscription Services, Inc 01.04.2024
• Subjects: Carbides; Cyclic loads; Damage assessment; Dynamic strain aging; Fatigue failure; Fatigue life; Fatigue limit; Fatigue strength; Fatigue tests; High cycle fatigue; High temperature; Metal fatigue; microstructural characteristics; Nickel base alloys; Precipitates; Precipitation hardening; superalloy 617M; Superalloys; Twin boundaries; γ′‐phase precipitation
• ISSN: 8756-758X; 1460-2695
• DOI: 10.1111/ffe.14253

High cycle fatigue (HCF) behavior of Ni superalloy 617M is investigated at 973 K and R‐ratio −1 on a resonance‐based fatigue testing system at 85 Hz frequency. The alloy experiences an abrupt drop in fatigue life within a narrow domain of 2.5–5 MPa near its fatigue strength at 320 MPa. Electron microscopy and diffraction techniques were employed to thoroughly analyze the nominal fatigue damage. The characterization revealed the significance of precipitation of secondary phases M23C6, Ti (C, N), and γ′ phase in dictating the HCF strength of the alloy. Cyclic loading at high temperature causes γ‐matrix hardening and secondary phase precipitation synergistically strengthening the material beyond its yield strength. Conjunctively, dynamic strain aging was also seen to play a major role in the evolution of fatigue damage. The work highlights the collective contribution of γ′‐phase precipitation, carbides, and dynamic strain aging and their influence on the HCF behavior of alloy 617M. Highlights Response of alloy 617M under high cycle fatigue load is studied at high temperature. Near fatigue limit, sharp drop in fatigue life causes nominal microstructural damage. Precipitation of phases γ′ and carbides in matrix, DSA, and cyclic hardening strengthens alloy. Precipitates at the grain and twin boundaries weakened the fatigue resistance of alloy.