Strength prediction of Ni-base disc superalloys: Modified γ′ hardening models applicable to commercial alloys

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 799; p. 140103
• Main Authors: Wu, L., Osada, T., Watanabe, I., Yokokawa, T., Kobayashi, T., Kawagishi, K.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 02-01-2021; Elsevier BV
• Subjects: Compression tests; Compressive strength; Deformation; Hardening; Heat-treatments; Mathematical models; Negligence; Ni-base superalloys; Nickel base alloys; Precipitation; Single crystals; Strength; Strengthening; Superalloys; γ/γ; Precipitation; γ/γ; Deformation; Heat-treatments; Ni-base superalloys; Strength
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2020.140103

The reported strength predictions of γ′ hardening so far for polycrystalline Ni-base superalloys tend to be underestimated. This is mostly due to the difficulty in isolating the γ′ hardening amidst the complicated multi-level strengthening mechanisms of the alloy and negligence of the contribution from γ/γ′ mixture strength. For these reasons, a series of single-crystal tie-line model alloys with specially designed γ′ size and volume fractions was adopted in this work, allowing a direct validation of classical γ′ particle hardening equations for the first time. Using the iso-work assumption, γ′ particle strengthening and γ/γ′ mixture strength at 650 °C were individually extracted from the compression test results. It was found that the classical strengthening models were unable to predict the expected strength increment with increasing γ′ volume fractions. Modified versions of the classical equations were proposed, which gave improved predictability across wider γ’ volume fractions and served as important basis for strength design application.
•Unique model alloys were utilized for the direct validation of classical interfacial strengthening models.•Hardening by γ/γ′ rule of mixture is significant to the overall strength.•Classical strengthening models are unable to capture the expected strength increment with increasing γ′ volume fraction.•New strengthening models proposed for improved strength predictability.