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The role of entropy and enthalpy in high entropy carbides
[Display omitted] •The group IVB and VB carbides prefer to mix with similar sized carbides.•The minimum solution temperature is nearly independent on the number of elements.•The mixing enthalpy is as important as the mixing entropy in forming single phase HECs.•The thermodynamic stability of HECs is...
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Published in: | Computational materials science 2022-07, Vol.210, p.111474, Article 111474 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | [Display omitted]
•The group IVB and VB carbides prefer to mix with similar sized carbides.•The minimum solution temperature is nearly independent on the number of elements.•The mixing enthalpy is as important as the mixing entropy in forming single phase HECs.•The thermodynamic stability of HECs is largely controlled by the mixing enthalpy.•Synthesized HECs should be referred as the multi-principal component carbide.
The thermodynamic stability of equiatomic mixed carbides, commonly referred to as high entropy carbides (HECs), is investigated via the CALculation of PHAse Diagrams (CALPHAD) approach for mixed carbides consisting of the group IVB and VB transition metal carbides as well as tungsten carbide. The Gibbs free energy of the B1-structured mixed carbides is computed using the compound energy formalism while that of the Bh-structured mixed carbides is evaluated using a point-defect model. The required thermodynamic data for the CALPHAD approach are obtained from density functional theory calculations and the Debye-Grüneisen model. The lower temperature limit at which the HECs mix in thermodynamic equilibrium is determined via numerical and analytical approaches. We find that enthalpy of mixing is at least as important as configurational mixing entropy in these mixed transition metal carbide compounds. The lower limit temperature where an equiatomic solid solution is present is largely independent of the number of components with the only exception being solutions containing tungsten carbide, where a weak temperature dependence is noted. Furthermore, the only equiatomic solid solutions that are thermodynamically stable below approximately 1000 K are those stabilized by enthalpy alone, indicating that many currently fabricated HECs are not at equilibrium at room temperature. Collectively, our results demonstrate that the formation of these carbides is controlled by the competition between entropy and enthalpy, or enthalpy alone, and thus these materials should be referred to as multi-principal component carbides since the former terminology can be misleading. |
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ISSN: | 0927-0256 1879-0801 |
DOI: | 10.1016/j.commatsci.2022.111474 |