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Influence of Annealing on Microstructure and Mechanical Properties of a Nanocrystalline CrCoNi Medium-Entropy Alloy

1
Department of Materials Physics, University of Leoben, Jahnstraße 12, 8700 Leoben, Austria
2
Materials Chemistry, RWTH Aachen University, Kopernikusstrasse 10, 52074 Aachen, Germany
3
Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, 40237 Düsseldorf, Germany
4
Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstraße 12, 8700 Leoben, Austria
5
Institute of Materials Research, Helmholtz-Zentrum Geesthacht, 21502 Geesthacht, Germany
*
Author to whom correspondence should be addressed.
Materials 2018, 11(5), 662; https://doi.org/10.3390/ma11050662
Received: 5 April 2018 / Revised: 17 April 2018 / Accepted: 19 April 2018 / Published: 24 April 2018
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Abstract

An equiatomic CrCoNi medium-entropy alloy was subjected to high-pressure torsion. This process led to a refinement of the microstructure to a grain size of about 50 nm, combined with a strong increase in the materials hardness. Subsequently, the thermodynamic stability of the medium entropy alloy was evaluated by isothermal and isochronal heat treatments. Annealed samples were investigated by scanning and transmission electron microscopy as well as X-ray diffraction, and were subjected to tensile tests to establish microstructure-property relationships. Furthermore, a comparison of mechanical properties with a grade 316L stainless steel was performed in order to evaluate if the CrCoNi alloy is competitive with commercially available structural materials in the nanocrystalline state. A minority phase embedded in the face-centered cubic matrix of the CrCoNi alloy could be observed in multiple annealed states, as well as the as-received and high-pressure torsion processed material. For 200 h of annealing at 500 °C, it was determined that the minority phase has a hexagonal-closed-packed crystal structure. A possible explanation for the formation of the phase is a preferential segregation of Co to stacking faults. View Full-Text
Keywords: high-entropy alloy; high pressure torsion; severe plastic deformation; nanocrystalline; heat treatment; phase decomposition; mechanical properties high-entropy alloy; high pressure torsion; severe plastic deformation; nanocrystalline; heat treatment; phase decomposition; mechanical properties
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Schuh, B.; Völker, B.; Todt, J.; Kormout, K.S.; Schell, N.; Hohenwarter, A. Influence of Annealing on Microstructure and Mechanical Properties of a Nanocrystalline CrCoNi Medium-Entropy Alloy. Materials 2018, 11, 662.

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