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The role of metastable LPSO building block clusters in phase transformations of an Mg-Y-Zn alloy

Title
The role of metastable LPSO building block clusters in phase transformations of an Mg-Y-Zn alloy
Author
김진경
Keywords
Magnesium alloy; Long period stacking ordered structure; Phase transformation; Transmission electron microscopy (TEM); Density functional theory (DFT)
Issue Date
2016-06
Publisher
PERGAMON-ELSEVIER SCIENCE LTD
Citation
ACTA MATERIALIA, v. 112, Page. 171-183
Abstract
We present a systematic atomic scale analysis of the structural evolution of long-period-stacking ordered (LPSO) structures in the (i) alpha-Mg matrix and in the (ii) interdendritic LPSO phase of an Mg97Y2Zn1 (at. %) alloy annealed at 500 degrees C, using high resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Various types of metastable LPSO building block clusters have been observed in both regions. The thermodynamic phase stabilities computed by density functional -theory calculations explain the diversity of the LPSO structures which are distinguished by their different arrangements of the Y/Zn enriched LPSO building blocks that have a local fcc stacking sequence on the close packed planes. A direct evidence of the transformation from 18R to 14H is presented. This finding suggests that LPSO structures can change their separation distance quantified by the number of alpha-Mg layers between them at a low energy penalty by generating the necessary Shockley partial dislocation on a specific glide plane. Based on our results the most probable transformation sequence of LPSO precipitate plates in the alpha-Mg matrix is: single building block -> various metastable LPSO building block clusters 14H, and the most probable transformation sequence in the interdendritic LPSO phase is: 18R -> various metastable LPSO building block clusters -> 14H. The thermodynamically most stable structures in both the a-Mg matrix and the interdendritic LPSO phase are a mixture of 14H and alpha-Mg. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
URI
https://www.sciencedirect.com/science/article/pii/S1359645416302725https://repository.hanyang.ac.kr/handle/20.500.11754/100538
ISSN
1359-6454; 1873-2453
DOI
10.1016/j.actamat.2016.04.016
Appears in Collections:
COLLEGE OF ENGINEERING SCIENCES[E](공학대학) > MATERIALS SCIENCE AND CHEMICAL ENGINEERING(재료화학공학과) > Articles
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