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Entropy 2018, 20(9), 654;

Entropy Determination of Single-Phase High Entropy Alloys with Different Crystal Structures over a Wide Temperature Range

Metals and Alloys, University Bayreuth, 95447 Bayreuth, Germany
UES, Inc., 4401 Dayton-Xenia Rd., Dayton, OH 45432, USA
Institut für Mikrostrukturforschung, Forschungszentrum Jülich, 52425 Jülich, Germany
Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden), 01069 Dresden, Germany
TU Bergakademie Freiberg, Institut für Werkstoffwissenschaft, 09599 Freiberg, Germany
NETZSCH Group, Analyzing & Testing, 95100 Selb, Germany
Author to whom correspondence should be addressed.
Received: 31 July 2018 / Revised: 17 August 2018 / Accepted: 20 August 2018 / Published: 30 August 2018
(This article belongs to the Special Issue New Advances in High-Entropy Alloys)
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We determined the entropy of high entropy alloys by investigating single-crystalline nickel and five high entropy alloys: two fcc-alloys, two bcc-alloys and one hcp-alloy. Since the configurational entropy of these single-phase alloys differs from alloys using a base element, it is important to quantify the entropy. Using differential scanning calorimetry, cp-measurements are carried out from −170 °C to the materials’ solidus temperatures TS. From these experiments, we determined the thermal entropy and compared it to the configurational entropy for each of the studied alloys. We applied the rule of mixture to predict molar heat capacities of the alloys at room temperature, which were in good agreement with the Dulong-Petit law. The molar heat capacity of the studied alloys was about three times the universal gas constant, hence the thermal entropy was the major contribution to total entropy. The configurational entropy, due to the chemical composition and number of components, contributes less on the absolute scale. Thermal entropy has approximately equal values for all alloys tested by DSC, while the crystal structure shows a small effect in their order. Finally, the contributions of entropy and enthalpy to the Gibbs free energy was calculated and examined and it was found that the stabilization of the solid solution phase in high entropy alloys was mostly caused by increased configurational entropy. View Full-Text
Keywords: HEA; entropy; multicomponent; differential scanning calorimetry (DSC); specific heat HEA; entropy; multicomponent; differential scanning calorimetry (DSC); specific heat

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Haas, S.; Mosbacher, M.; Senkov, O.N.; Feuerbacher, M.; Freudenberger, J.; Gezgin, S.; Völkl, R.; Glatzel, U. Entropy Determination of Single-Phase High Entropy Alloys with Different Crystal Structures over a Wide Temperature Range. Entropy 2018, 20, 654.

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