Abstract
Single-phase high- and medium-entropy alloys with face-centred cubic (fcc) structure can exhibit high tensile ductility1,2 and excellent toughness2,3, but their room-temperature strengths are low1–3. Dislocation obstacles such as grain boundaries4, twin boundaries5, solute atoms6 and precipitates7–9 can increase strength. However, with few exceptions8–11, such obstacles tend to decrease ductility. Interestingly, precipitates can also hinder phase transformations12,13. Here, using a model, precipitate-strengthened, Fe–Ni–Al–Ti medium-entropy alloy, we demonstrate a strategy that combines these dual functions in a single alloy. The nanoprecipitates in our alloy, in addition to providing conventional strengthening of the matrix, also modulate its transformation from fcc-austenite to body-centred cubic (bcc) martensite, constraining it to remain as metastable fcc after quenching through the transformation temperature. During subsequent tensile testing, the matrix progressively transforms to bcc-martensite, enabling substantial increases in strength, work hardening and ductility. This use of nanoprecipitates exploits synergies between precipitation strengthening and transformation-induced plasticity, resulting in simultaneous enhancement of tensile strength and uniform elongation. Our findings demonstrate how synergistic deformation mechanisms can be deliberately activated, exactly when needed, by altering precipitate characteristics (such as size, spacing, and so on), along with the chemical driving force for phase transformation, to optimize strength and ductility.
Original language | English |
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Pages (from-to) | 245-249 |
Number of pages | 5 |
Journal | Nature |
Volume | 595 |
Issue number | 7866 |
DOIs | |
State | Published - Jul 8 2021 |
Funding
Acknowledgements This research was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division (testing and analysis of mechanical properties and responsible deformation mechanisms, TEM characterization of the FNAT-4h alloy, and writing of the manuscript) and by the Laboratory Directed Research and Development programme of Oak Ridge National Laboratory (ORNL) (microstructural characterization and first-principles calculations), managed by UT-Battelle, LLC, for the US Department of Energy. Y.Y. acknowledges CompuTherm for providing the phase diagram calculation software Pandat. Resources at ORNL’s High Flux Isotope Reactor for small-angle neutron scattering, Spallation Neutron Source for neutron diffraction, and Center for Nanophase Materials Sciences for atom probe tomography were used in this study, which are US DOE Office of Science User Facilities.