Browsing by Author "Shieh, Sean R."

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Deviatoric deformation kinetics in high entropy alloy under hydrostatic compression
(2019-07-05)
Huang, E-Wen
;
Lin, Chih-Ming
;
Juang, Jenh-Yih
;
Chang, Yao-Jen
;
Chang, Yuan-Wei
An equiatomic CoCrFeMnNi high-entropy alloy under hydrostatic compression is investigated using insitu angular-dispersive X-ray diffraction to explore the polymorphism in high entropy alloy systems. The metallic system is of face-centered-cubic structure at ambient condition and applied hydrostatic pressures up to 20 GPa via diamond anvil cell. The angle-resolved diffraction-intensity evolutions of multiple diffraction peaks were collected simultaneously to elucidate the phase stability examinations. The phase transformation from face-centered-cubic to hexagonal-close-packed structure was evidently observed in CoCrFeMnNi alloy accompanied by a deviatoric strain subjected to the hydrostatic compression. We found lattice-asymmetric crossover before and after the phase transformation subjected to hydrostatic compression surroundings. Deviatoric strain triggers fcc-hcp phase transformation as local heterogeneity-driven lattice distortion is significant for CoCrFeMnNi alloy. (c) 2019 The Authors. Published by Elsevier B.V.
Irreversible phase transformation in a CoCrFeMnNi high entropy alloy under hydrostatic compression
(2018-03-01)
Huang, E-Wen
;
Lin, Chih-Ming
;
Jain, Jayant
;
Shieh, Sean R.
;
Wang, Ching-Pao
An equal-molar CoCrFeMnNi, face-centered-cubic high-entropy alloy system is investigated using in-situ angular-dispersive X-ray diffraction under hydrostatic compression up to 20 GPa via diamond anvil cell. The evolutions of multiple diffraction peaks are collected simultaneously to elucidate the phase stability field. The results indicated that an irreversible phase transformation had occurred in the high entropy alloy upon decompression to ambient pressure. A reference material (n-type silicon-doped gallium arsenide) was investigated following the same protocol to demonstrate the different deformation mechanisms. It is suggested that the atomic bonding characteristics on the phase stability may play an important role in the high entropy alloys.