Revealing the Microstates of Body-Centered-Cubic (BCC) Equiatomic High Entropy Alloys
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Attributing to the attractive mechanical properties, e.g., high yield strength and fracture toughness, the atomic and electronic basis for high entropy alloys (HEAs) are under extensive studies. In the present work, the local atomic arrangement of body-centered-cubic (BCC) equiatomic HEAs are revealed by the CN14 cluster-plus-glue-atom model and the 32 atoms special quasirandom structures. Moreover, the cluster-plus-glue-atom model is utilized to generate ordered and disordered configurations. The bonding lengths among the same and different alloying elements are comprehensively compared in term of their partial pair correlation function (PCF). According to the specific (well-defined) position of each partial PCF of the BCC structure, the order–disorder/random configurational transitions are revealed by the absence of partial PCF peaks. Here, the WMoTM1TM2 (TM = Ta, Nb, and V) BCC equiatomic refractory HEAs are selected as a case study. Through mixing various groups of alloying elements, the atomic-size differences not only result in the lattice mismatch/distortion but also yield the formation of weak spots. Their bonding-charge density captures the electron redistributions caused by the coupling effect of the lattice distortion and valance electron differences among various elements, which also presents the physical nature of the loosely-bonded weak spots and the tightly-bonded clusters. It is worth mentioning that both the PCF and the negative enthalpy of mixing can be utilized to characterize the clusters or the short range ordering in the HEAs. The microstates revealed by the cluster-plus-glue-atom model are in line with the novel small set of the ordered structures method reported in the literature.
Keywordsbonding charge density cluster-plus-glue-atom model high entropy alloys small set of ordered structures (SSOS) special quasirandom structures (SQS)
The present work was financially supported by the National Natural Science Foundation of China (Grants 51690163, 50871013, 51271018, 51271151, and 51571161), the United States National Science Foundation (Grant DMR-1006557), and the US Army Research Laboratory (Project No. W911NF-08-2-0084). WYW acknowledges the support from the project of SKL-AMM-USTB (Grant Number 2016-Z07) and the Fundamental Research Funds for the Central Universities in China (Grant Number G2016KY0302). PKL would like to acknowledge the Department of Energy, Office of Fossil Energy, National Energy Technology Laboratory (DE-FE-0008855 and DE-FE-0024054, and DE-FE-0011194), the US Army Research Office project (W911NF-13-1-0438), the National Science Foundation (DMR-1611180), and the Department of Materials Science and Engineering, National Tsing Hua University, Taiwan, for their support. First-principles calculations were carried out on the LION clusters at the Pennsylvania State University supported by the Materials Simulation Center and the Institute for CyberScience and the clusters at the Northwestern Polytechnical University. Calculations were also carried out on the CyberStar cluster funded by NSF through Grant OCI-0821527and the XSEDE clusters supported by NSF through Grant ACI-1053575.
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