Nanomechanical behavior and structural stability of a nanocrystalline CoCrFeNiMn high-entropy alloy processed by high-pressure torsion

Authors
Lee, Dong-HyunChoi, In-ChulSeok, Moo-YoungHe, JunyangLu, ZhaopingSuh, Jin-YooKawasaki, MegumiLangdon, Terence G.Jang, Jae-il
Issue Date
2015-09-28
Publisher
CAMBRIDGE UNIV PRESS
Citation
JOURNAL OF MATERIALS RESEARCH, v.30, no.18, pp.2804 - 2815
Abstract
A CoCrFeNiMn high-entropy alloy (HEA), in the form of a face-centered cubic (fcc) solid solution, was processed by high-pressure torsion (HPT) to produce a nanocrystalline(nc) HEA. Significant grain refinement was achieved from the very early stage of HPT through 1/4 turn and an nc structure with an average grain size of similar to 40 nm was successfully attained after 2 turns. The feasibility of significant microstructural changes was attributed to the occurrence of accelerated atomic diffusivity under the torsional stress during HPT. Nanoindentation experiments showed that the hardness increased significantly in the nc HEA during HPT processing and this was associated with additional grain refinement. The estimated values of the strain-rate sensitivity were maintained reasonably constant from the as-cast condition to the nc alloy after HPT through 2 turns, thereby demonstrating a preservation of plasticity in the HEA. In addition, a calculation of the activation volume suggested that the grain boundaries play an important role in the plastic deformation of the nc HEA where the flow mechanism is consistent with other nc metals. Transmission electron microscopy showed that, unlike conventional fcc nc metals, the nc HEA exhibits excellent microstructural stability under severe stress conditions.
Keywords
STRAIN-RATE SENSITIVITY; MECHANICAL-PROPERTIES; ACTIVATION VOLUME; DEFORMATION-BEHAVIOR; PLASTIC-DEFORMATION; GRAIN-GROWTH; TEMPERATURE; EVOLUTION; NANOINDENTATION; HARDNESS; STRAIN-RATE SENSITIVITY; MECHANICAL-PROPERTIES; ACTIVATION VOLUME; DEFORMATION-BEHAVIOR; PLASTIC-DEFORMATION; GRAIN-GROWTH; TEMPERATURE; EVOLUTION; NANOINDENTATION; HARDNESS; high-entropy alloy; high-pressure torsion; nanocrystalline metal; nanoindentation
ISSN
0884-2914
URI
https://pubs.kist.re.kr/handle/201004/124996
DOI
10.1557/jmr.2015.239
Appears in Collections:
KIST Article > 2015
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