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Yeqing Wang (1,2), Jianrong Gao (1), Yang Ren (3), Vincent De Andrade (3), Ashwin J. Shahani (2)
The Journal of The Minerals, Metals & Materials Society, 72, June 2020: 2965–2973. DOI: 10.1007/s11837-020-04237-x
Metastable spiral MgZn2/Zn eutectics grow in binary Zn-3 wt.% Mg alloys at small liquid undercooling. In this article, we report growth of a new class of three-phase spiral structures in metastable solidification of Ni-doped Zn-3Mg alloys. Thermodynamic calculations demonstrated that a minor Ni substitution for Zn allows for peritectic growth of the Mg2Zn11 phase following secondary MgZn2 growth. In situ synchrotron x-ray diffraction confirmed such metastable solidification reactions and suggested concomitant growth of MgZn2, Mg2Zn11 and Zn close to the end of solidification. Synchrotron x-ray nano-tomography revealed a localized three-phase spiral structure, wherein Mg2Zn11 grows at the phase-interface of the metastable eutectic. Such a novel spiral structure can be attributed to competitive growth of a metastable binary eutectic and a peritectic phase in metastable solidification. Ni doping increases the nucleation rate of MgZn2 and the driving force for peritectic growth of Mg2Zn11, thus leading to the formation of the three-phase spiral structure.
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(1) Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang, 110819, China.
(2) Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.
(3) Advanced Photon Source, Argonne National Laboratory, Argonne, IL, 60439, USA.
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