The role of metastable LPSO building block clusters in phase transformations of an Mg-Y-Zn alloy
- Authors
- Kim, Jin Kyung; Ko, Won Seok; Sandlöbes, Stefanie; Heidelmann, Markus; Grabowski, Blazej; Raabe, Dierk
- Issue Date
- Jun-2016
- Publisher
- Elsevier BV
- Keywords
- Density functional theory (DFT); Long period stacking ordered structure; Magnesium alloy; Phase transformation; Transmission electron microscopy (TEM)
- Citation
- Acta Materialia, v.112, pp 171 - 183
- Pages
- 13
- Indexed
- SCI
SCIE
SCOPUS
- Journal Title
- Acta Materialia
- Volume
- 112
- Start Page
- 171
- End Page
- 183
- URI
- https://scholarworks.bwise.kr/hanyang/handle/2021.sw.hanyang/52489
- DOI
- 10.1016/j.actamat.2016.04.016
- ISSN
- 1359-6454
1873-2453
- Abstract
- We present a systematic atomic scale analysis of the structural evolution of long-period-stacking-ordered (LPSO) structures in the (i) α-Mg matrix and in the (ii) interdendritic LPSO phase of an Mg97Y2Zn1 (at. %) alloy annealed at 500°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 α-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 α-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 α-Mg matrix and the interdendritic LPSO phase are a mixture of 14H and α-Mg. © 2016 Acta Materialia Inc.
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