Ab initio explanation of disorder and off-stoichiometry in Fe-Mn-Al-C kappa carbides

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Authors

DEY P. NAZAROV R. DUTTA B. YAO M. HERBIG M. FRIÁK Martin HICKEL T. RAABE D. NEUGEBAUER J.

Year of publication 2017
Type Article in Periodical
Magazine / Source Physical Review B
MU Faculty or unit

Central European Institute of Technology

Citation
Web https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.104108
Doi http://dx.doi.org/10.1103/PhysRevB.95.104108
Keywords TOTAL-ENERGY CALCULATIONS; ATOM-PROBE TOMOGRAPHY; AUGMENTED-WAVE METHOD; LOW-DENSITY; MECHANICAL-PROPERTIES; HIGH-STRENGTH; TRIPLEX STEELS; BASIS-SET; ALLOYS; MICROSTRUCTURE
Description Carbides play a central role for the strength and ductility in many materials. Simulating the impact of these precipitates on the mechanical performance requires knowledge about their atomic configuration. In particular, the C content is often observed to substantially deviate from the ideal stoichiometric composition. In this work, we focus on Fe-Mn-Al-C steels, for which we determined the composition of the nanosized carbides (Fe,Mn)_3AlC by atom probe tomography in comparison to larger precipitates located in grain boundaries. Combining density functional theory with thermodynamic concepts, we first determine the critical temperatures for the presence of chemical and magnetic disorder in these carbides. Second, the experimentally observed reduction of the C content is explained as a compromise between the gain in chemical energy during partitioning and the elastic strains emerging in coherent microstructures.
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