Anomalous Evolution of Strength and Microstructure of High-Entropy Alloy CoCrFeNiMn after High-Pressure Torsion at 300 and 77 K

Author(s)
Aleksey V. Podolskiy, Yuriy O. Shapovalov, Elena D. Tabachnikova, Aleksandr S. Tortika, Mikhail A. Tikhonovsky, Bertalan Joni, Eva Ódor, Tamas Ungar, Stefan Maier, Christian Rentenberger, Michael J. Zehetbauer, Erhard Schafler
Abstract

Ultrafine and nanocrystalline states of equiatomic face-centered cubic (fcc) high-entropy alloy (HEA) CoCrFeNiMn (“Cantor” alloy) are achieved by high-pressure torsion (HPT) at 300 K (room temperature, RT) and 77 K (cryo). Although the hardness after RT-HPT reaches exceptionally high values, those from cryo-HPT are distinctly lower, at least when the torsional strain lies beyond γ = 25. The values are stable even during long-time storage at ambient temperature. A similar paradoxal result is reflected by torque data measured in situ during HPT processing. The reasons for this paradox are attributed to the enhanced hydrostatic pressure, cryogenic temperature, and especially large shear strains achieved by the cryo-HPT. At these conditions, selected area electron diffraction (SAD) patterns indicate that a partial local phase change from fcc to hexagonal close-packed (hcp) structure occurs, which results in a highly heterogeneous structure. This heterogeneity is accompanied by both an increase in average grain size and especially a strong decrease in average dislocation density, which is estimated to mainly cause the paradox low strength.

Organisation(s)
Physics of Nanostructured Materials
External organisation(s)
B. Verkin Institute for Low Temperature Physics, National Science Center Kharkov Institute of Physics and Technology, Eötvös Loránd University Budapest, University of Manchester
Journal
Advanced Engineering Materials
Volume
22
No. of pages
8
ISSN
1438-1656
DOI
https://doi.org/10.1002/adem.201900752
Publication date
09-2019
Peer reviewed
Yes
Austrian Fields of Science 2012
Nanomaterials
Keywords
ASJC Scopus subject areas
,
Portal url
https://ucris.univie.ac.at/portal/en/publications/anomalous-evolution-of-strength-and-microstructure-of-highentropy-alloy-cocrfenimn-after-highpressure-torsion-at-300-and-77-k(556454d6-5842-47be-8ccd-6a70739abdb8).html