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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Frictional Ignition of Metals in High Pressure Oxygen: A Critical Reassessment of NASA Test Data
In this paper we develop a material index for selecting alloys resistant to frictional ignition in high pressure oxygen environments. A previous ignition-resistance metric proposed by NASA WSTF varies strongly and unpredictably with test conditions, thus limiting its usefulness. The material index developed here incorporates key material properties that strongly influence ignition behaviors, including friction coefficient, ignition temperature, and thermal effusivity. Finite element simulations were used to compute ignition temperatures for 15 alloys based on published frictional ignition data from NASA White Sands Testing Facility (WSTF). These values were used with the material index to construct property diagrams for ranking the materials based on their intrinsic frictional ignition resistance. The results demonstrate that nickel-based superalloys with low iron content are less likely to ignite under frictional heating than ferrous alloys and nickel-based superalloys with high content iron. The material index is then used to predict material performance outside of the test conditions, highlighting the effect of ambient temperature on nominal ignition resistance. We conclude by developing an empirical relation between ignition temperature and enthalpy of oxidation which can guide design of new ignition-resistant alloys.
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- Award ID(s):
- 2004913
- NSF-PAR ID:
- 10454089
- Date Published:
- Journal Name:
- AIAA Scitech 2023
- 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/10.2514/6.2023-1489
