Bifunctional nanoprecipitates strengthen and ductilize a medium-entropy alloy

Ying Yang (), Tianyi Chen, Lizhen Tan, Jonathan D. Poplawsky, Ke An, Yanli Wang, German D. Samolyuk, Ken Littrell, Andrew R. Lupini, Albina Borisevich and Easo P. George ()
Additional contact information
Ying Yang: Oak Ridge National Laboratory
Tianyi Chen: Oak Ridge National Laboratory
Lizhen Tan: Oak Ridge National Laboratory
Jonathan D. Poplawsky: Oak Ridge National Laboratory
Ke An: Oak Ridge National Laboratory
Yanli Wang: Oak Ridge National Laboratory
German D. Samolyuk: Oak Ridge National Laboratory
Ken Littrell: Oak Ridge National Laboratory
Andrew R. Lupini: Oak Ridge National Laboratory
Albina Borisevich: Oak Ridge National Laboratory
Easo P. George: Oak Ridge National Laboratory

Nature, 2021, vol. 595, issue 7866, 245-249

Abstract: 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.

Date: 2021
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DOI: 10.1038/s41586-021-03607-y

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