Abstract
Ni-Fe-Cr-Al-Ti alloys, with Ni levels of about 45 at% have the potential to develop a microstructure consisting of a face-centered cubic (γ) matrix with homogeneously precipitated, nanoscale ordered γ′ precipitates similar to that found in traditional Ni-based superalloys with a significantly greater Ni content. Scanning electron microscopy, transmission electron microscopy, atom probe tomography, and CALPHAD-based thermodynamic modeling were employed to determine the phase stabilities and microstructural evolution in an age-hardenable 44.56Ni-26.6Fe-19.2Cr-1.0Co-3.4Al-4.4Ti-0.7Mo-0.14 C (at%) alloy. The primary heat treatment of solution annealing at 1121 °C for 4 h followed by age-hardening at 760 °C for 16 h resulted in a microstructure consisting of fine γ′ precipitates in an austenitic matrix along with grain boundary precipitates of carbides and other minor phases. Long-term aging at 900 °C for 250 h resulted in the coarsening of γ′ precipitates along with a change in the morphology from an initial spherical to a more cuboidal shape. In addition, the formation of plate-like η phase precipitates was observed, concomitant with the partial dissolution of the γ′ phase. The ability of computational thermodynamic models to predict microstructural characteristics is discussed.
Original language | English |
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Article number | 161207 |
Journal | Journal of Alloys and Compounds |
Volume | 886 |
DOIs | |
State | Published - Dec 15 2021 |
Funding
The authors would like to acknowledge Gregory A. Cox, Daniel Moore, Kevin Hanson, Cecil Carmichael, and Ian Stinson for alloy processing and heat-treatments, Tom Geer for sample preparation and metallography, and Dr.s Thomas Watkins and Allen Haynes for their review of the manuscript. GM would like to acknowledge Adam Hope, James Rule, and Paul Mason from Thermo-Calc® Software Inc. for helpful discussions. The authors would like to thank James Burns for assistance in performing APT sample preparation and running the APT experiments at the CNMS. This research was sponsored by the U.S. Department of Energy Office of Vehicle Technologies, Powertrain Materials Core Program. The Talos F200X S/TEM tool was provided by US DOE, Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science User Facilities. A portion of this research was performed in Environmental Molecular Sciences Laboratory (EMSL), a US DOE Office of Science User Facility sponsored by the Office of Biological and Environmental Research and located at PNNL. Some of the APT experiments were conducted at ORNL′s Center for Nanophase Materials Sciences (CNMS), which is a U.S. DOE Office of Science User Facility.
Keywords
- Atom probe tomography
- CALPHAD
- Fe-Ni-Cr–based superalloys
- γ′ precipitate