Browsing by Author "Hu, Alice"

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An optimized random structures generator governed by chemical short-range order for multi-component solid solutions
(2019-12-01)
Yu, Peijun
;
Chou, Jyh-Pin
;
Lo, Yu-Chieh
;
Hu, Alice
;
材料科學與工程學系
Multi-component random solid solutions have caused much interest for research because they often exhibit excellent mechanical properties. Many computational efforts have been made through various length scales, by first principles, molecular dynamics or finite elements. Here, a quasi-simulated-annealing (Markov Chain Monte Carlo algorithm) with prior burn-in procedure using chemical short-range order parameters as input values is developed for searching the global optimal distribution of species with regard to the phase stability of face-centered cubic CoCrNi alloys. The results show that this new approach could effectively generate the stable structures with a desired concentration and moreover, the stacking fault energies of these configurations have less uncertainties statistically.
Phase transformation assisted twinning in a face-centered-cubic FeCrNiCoAl0.36 high entropy alloy
(2019-12-01)
Yu, Peijun
;
Feng, Rui
;
Du, Junping
;
Shinzato, Shuhei
;
Chou, Jyh-Pin
The FeNiCoCr-based high entropy alloys (HEAs) exhibit excellent mechanical properties, such as twin-induced plasticity (TWIP) and phase transformation plasticity (TRIP) that can reach a remarkable combination of strength and ductility. In the present work, the face-centered-cubic (FCC) single-crystal FeNiCoCrAl0.36 HEAs were studied, using the density functional theory (DFT) combined with the phonon calculation to estimate the stacking fault energies, temperature-dependent phase stabilities of different structures. And the kinetic Monte Carlo (kMC) was used to predict the substructures evolution based on the transition state energies obtained from DFT calculations. We proposed two different formation paths of nano-twins in this Al-composited HEA and found that short-range hexagonal-close-packed (HCP)-stacking could occur in this HEA. The DFT calculations suggest that this HEA has negative stacking fault energy (SFE), HCP formation energy, and twin-formation energy at OK. Phonon calculations indicate that at the finite temperature, the competing FCC/HCP phase stability and propensity for twinning make it possible to form HCP-like twin boundaries. The kMC simulations suggest that under deformation, TWINs could form within the HCP laths which differs from the study of others. With the great agreement of results from kMC simulations and experiments, this twin-hcp laminated substructure formation path offers a new concept of designing TWIP HEAs containing tunable twin structures with HCP and TWIN lamellae structures, which could result in better mechanical properties of HEAs. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
The influence of dilute aluminum and molybdenum on stacking fault and twin formation in FeNiCoCr-based high entropy alloys based on density functional theory
(2019-07-29)
Yu, Peijun
;
Zhuang, Yu
;
Chou, Jyh-Pin
;
Wei, Jie
;
Lo, Yu-Chieh
Stacking faults, as defects of disordered crystallographic planes, are one of the most important slipping mechanisms in the commonly seen lattice, face-centered cubic (FCC). Such defects can initiate twinning which strengthens mechanical properties, e.g. twinning-induced plasticity (TWIP), of high entropy alloys (HEAs) at cryogenic temperatures. In this work, by using density functional theory (DFT), the twinning initiated from stacking faults is discussed with regard to two different solute elements, Al and Mo, in the FeNiCoCr HEAs. Our results show that adding aluminum (Al) has noticeable enhancement of twinnability while molybdenum (Mo) only induces more stacking faults in the FeNiCoCr-based HEAs.