The Novel Hybrid Model for the Design of Al-Co-Cr-Ni-Fe High Entropy Alloys (HEAs)

Yang, Songge

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The Novel Hybrid Model for the Design of Al-Co-Cr-Ni-Fe High Entropy Alloys (HEAs)

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The Al-Co-Cr-Fe-Ni system has been one of the most thoroughly studied systems in high entropy alloys (HEAs) due to their promising mechanical properties. However, the prediction of phase stabilities and mechanical properties in this system with a full composition range could be challenging purely based on experiments. To accelerate the development of novel HEAs, the current work developed a hybrid high-throughput (HT) CALPHAD and ab initio modeling approach, which can quickly investigate the phase stabilities and mechanical properties of single FCC and BCC phases. Additionally, the thermodynamic database of Fe-Cr and Ni-Cr binary systems is remodeled based on the ab initio results. The main accomplishment of the present work includes four parts: 1) HT-CALPHAD modeling of Al-Co-Cr-Ni-Fe system with FCC and BCC phase. In this section, 3561 non-equiatomic compositions were randomly generated in order to investigate the phase stability of single FCC and BCC phases. Meanwhile, we proposed a data screening procedure to screen out the good candidates within these compositions, considering the temperature range, average density, and melting temperature, etc. 2) High-throughput ab initio modeling of the formation enthalpy of the Al-Co-Cr-Fe-Ni alloys. In this chapter, we predicted the difference of the formation enthalpy between the FCC and BCC phase with the special quasi-random structure (SQS) method. Particularly, the relative stabilities between these two phases of 180 compositions are studied. Finally, the stabilities between the FCC and BCC phase of this quinary system were contoured. 3) High-throughput ab initio modeling of the physical and elastic properties of the FCC Fe-Co-Cr-Ni alloys: In this part, the physical properties of non-equiatomic FCC quaternary Fe-Co-Cr-Ni systems at 0K were investigated. The predictions will start with pure elements of the Fe-Co-Cr-Ni system and will be continued with binaries, ternaries, and finally, quaternary compositions. Finally, the comparison between ab initio modeling and available experimental data from the literature is discussed. 4) An integrated CALPHAD/ab initio remodeling of the thermodynamic of Fe-Cr and Ni-Cr binary system. Significant discrepancies have been observed and discussed on the lattice stability of Cr between the ab initio and the CALPHAD approach. In this part, we systematically examined the lattice stability of Cr derived by both approaches. Meanwhile, the present work successfully integrated the ab initio results into the CALPHAD platform for the modeling of Fe-Cr and Ni-Cr binary systems.

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