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CoNi-based superalloys offer excellent high-temperature properties; yet, Co is also a strategic alloying element, and its content should only be as high as necessary. This study investigates Fe as a partial substitute for Co to reduce costs while evaluating its impact on mechanical properties. To evaluate this, we systematically investigate the effect of Fe substitutions on thermophysical properties, microstructure, partitioning behavior, lattice misfit, yield strength, and creep performance of three polycrystalline CoNi-based superalloys derived from CoWAlloy1 (Co–32Ni–12Cr–6Al–3W–2.5Ti–1.5Ta–0.4Si–0.1Hf–0.08B all in at. %). In these alloys, 4, 8, and 12 at. % Co is replaced with Fe. Increasing Fe content results in a gradual reduction in the solvus, solidus, and liquidus temperatures by 3.0, 1.9, and 1.4 °C per at. % Fe, respectively. The γ′ volume fraction and the lattice misfit decrease by about 0.7% and 0.01%, respectively, per at. % Fe substitution for Co. Fe predominantly partitions to the γ matrix, enhancing the partitioning of Co and Ni while reducing that of Al, Cr, and Ta, with no significant effect on Ti and W. Substituting Co with Fe moderately reduces yield and creep strength, primarily due to the decreasing γ′ volume fraction and a transition in the dominant deformation mechanisms from stacking fault shearing and microtwinning to matrix-based deformation as Fe content increases. Beneficial elemental segregation behaviors and localized phase transformations along creep-induced stacking faults remain active in alloys with high Fe content. These findings highlight the potential of Fe alloying to reduce costs while maintaining high-temperature strength in CoNi-based superalloys.
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Supersolvus Hot Workability and Dynamic Recrystallization in Wrought Co–Al–W-Base Alloys.
Gamma-prime strengthened Co–Al–W-based superalloys offer a unique combination of weldability, mechanical strength, creep resistance, and environmental resistance at temperature—leading many to consider the system as an alternative to nickel-base superalloys for future generation turbine engine hardware. However, little information exists regarding the deformation processing required to turn these novel alloys into useable product forms with appropriate microstructure refinement. Supersolvus thermomechanical processing sequences were successfully demonstrated using right-cylindrical upset specimens for two wrought γ′-strengthened cobalt-base superalloys at industrially relevant temperatures and deformation rates. Hot flow behavior and microstructure evolution were quantitatively characterized and compared to available information on a legacy nickel-base system, Waspaloy. Further, density functional theory was used to explore the compositional dependency of the intrinsic material properties influencing single-phase hot working behavior of model Ni–Al binary and Co–Al–W ternary systems. The apparent similarity in the supersolvus thermomechanical processing behavior of Co–Al–W-base systems and their two-phase γ–γ′ Ni-base counterparts suggests conventional pathways, models, and equipment may be leveraged to speed transition and implementation of wrought Co–Al–W-base alloys for components where their properties may be advantageous.
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- PAR ID:
- 10197010
- Date Published:
- Journal Name:
- Superalloys 2020
- Page Range / eLocation ID:
- 857-869
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1007/978-3-030-51834-9_84
