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Sci Rep. 2019 Feb 27;9(1):2948. doi: 10.1038/s41598-019-39570-y.

FCC to BCC transformation-induced plasticity based on thermodynamic phase stability in novel V10Cr10Fe45CoxNi35-x medium-entropy alloys.

Author information

1
Center for High Entropy Alloys, Pohang University of Science and Technology, Pohang, 790-784, Korea.
2
Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang, 790-784, Korea.
3
Center for High Entropy Alloys, Pohang University of Science and Technology, Pohang, 790-784, Korea. bbosil7@postech.ac.kr.

Abstract

We introduce a novel transformation-induced plasticity mechanism, i.e., a martensitic transformation from fcc phase to bcc phase, in medium-entropy alloys (MEAs). A VCrFeCoNi MEA system is designed by thermodynamic calculations in consideration of phase stability between bcc and fcc phases. The resultantly formed bcc martensite favorably contributes to the transformation-induced plasticity, thereby leading to a significant enhancement in both strength and ductility as well as strain hardening. We reveal the microstructural evolutions according to the Co-Ni balance and their contributions to a mechanical response. The Co-Ni balance plays a leading role in phase stability and consequently tunes the cryogenic-temperature strength-ductility balance. The main difference from recently-reported metastable high-entropy dual-phase alloys is the formation of bcc martensite as a daughter phase, which shows significant effects on strain hardening. The hcp phase in the present MEA mostly acts as a nucleation site for the bcc martensite. Our findings demonstrate that the fcc to bcc transformation can be an attractive route to a new MEA design strategy for improving cryogenic strength-ductility.

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