Metallurgical and Materials Transactions A

, Volume 40, Issue 7, pp 1588–1603 | Cite as

Strengthening Mechanisms in Polycrystalline Multimodal Nickel-Base Superalloys

  • R.W. Kozar
  • A. Suzuki
  • W.W. Milligan
  • J.J. Schirra
  • M.F. Savage
  • T.M. Pollock


Polycrystalline γ-γ′ superalloys with varying grain sizes and unimodal, bimodal, or trimodal distributions of precipitates have been studied. To assess the contributions of specific features of the microstructure to the overall strength of the material, a model that considers solid-solution strengthening, Hall–Petch effects, precipitate shearing in the strong and weak pair-coupled modes, and dislocation bowing between precipitates has been developed and assessed. Cross-slip-induced hardening of the Ni3Al phase and precipitate size distributions in multimodal microstructures are also considered. New experimental observations on the contribution of precipitate shearing to the peak in flow stress at elevated temperatures are presented. Various alloys having comparable yield strengths were investigated and were found to derive their strength from different combinations of microconstituents (mechanisms). In all variants of the microstructure, there is a strong effect of antiphase boundary (APB) energy on strength. Materials subjected to heat treatments below the γ′ solvus temperature benefit from a strong Hall–Petch contribution, while supersolvus heat-treated materials gain the majority of their strength from their resistance to precipitate shearing.


Yield Strength Ni3Al Strengthening Mechanism Precipitate Size Pair Coupling 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The authors express their gratitude to Mike Long, Engineous Software (SIMULIA, Province, RI), for his assistance with iSight software, and to Dennis Dimiduk and Triplicane Parthasarathy for their valuable discussions. The financial support of the DARPA/AIM project under Grant No. F005484, sponsored by Pratt & Whitney, is gratefully acknowledged.


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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2009

Authors and Affiliations

  • R.W. Kozar
    • 1
    • 2
  • A. Suzuki
    • 1
    • 3
  • W.W. Milligan
    • 4
  • J.J. Schirra
    • 5
  • M.F. Savage
    • 6
    • 7
  • T.M. Pollock
    • 1
  1. 1.Department of Materials Science and EngineeringUniversity of MichiganAnn ArborUSA
  2. 2.Materials TechnologyBettis Atomic Power LaboratoryWest MifflinUSA
  3. 3.Ceramic and Metallurgy TechnologiesGE Global ResearchNiskayunaUSA
  4. 4.Department of Materials Science and EngineeringMichigan Technological UniversityHoughtonUSA
  5. 5.Aircraft GroupPratt & WhitneyEast HartfordUSA
  6. 6.Materials and Processes EngineeringPratt & WhitneyEast HartfordUSA
  7. 7.Group Strategy and DevelopmentPratt & WhitneyEast HartfordUSA

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