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Anomalous Evolution of Strength and Microstructure of High‐Entropy Alloy CoCrFeNiMn after High‐Pressure Torsion at 300 and 77 K
Author(s) -
Podolskiy Aleksey V.,
Shapovalov Yuriy O.,
Tabachnikova Elena D.,
Tortika Aleksandr S.,
Tikhonovsky Mikhail A.,
Joni Bertalan,
Ódor Eva,
Ungar Tamas,
Maier Stefan,
Rentenberger Christian,
Zehetbauer Michael J.,
Schafler Erhard
Publication year - 2020
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201900752
Subject(s) - materials science , nanocrystalline material , alloy , high entropy alloys , microstructure , hydrostatic pressure , grain size , torsion (gastropod) , hydrostatic equilibrium , dislocation , severe plastic deformation , crystallography , condensed matter physics , thermodynamics , metallurgy , composite material , nanotechnology , medicine , chemistry , physics , surgery , quantum mechanics
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.