Journal
MATERIALS TRANSACTIONS
Volume 54, Issue 5, Pages 668-674Publisher
JAPAN INST METALS
DOI: 10.2320/matertrans.MI201221
Keywords
magnesium alloy; long-period stacking order (LPSO); diffusional-displacive transformation; ledge; aging
Funding
- Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan [23109006]
- Kawamura laboratory
- Kumamoto University
- Mr. Manabu Itoh, Institute for Materials Research, Tohoku University
- Grants-in-Aid for Scientific Research [23360283] Funding Source: KAKEN
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This study investigated modulation of the long period stacking order (LPSO) structure in aged Mg97Zn1Y2 alloys using conventional transmission electron microscopy (TEM) and aberration-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The irregular stacking sequence of a fragment of 24R-type LPSO acts as a catalyst for the transformation from 18R- to 14-Htype LPSO. The elementary step of the transformation from 18R- to 24R-type takes place by the ledge-pair movement on different (0001)(Mg) planes with Shockley partial dislocations. Each ledge has a transition region in front of it. The transition regions are HCP-type stacking sequence with lower Zn and Y concentrations than those of the FCC-type enrichment layer. The solute elements migrate easily in the region, where solute elements produce a kind of diffusion field. Therefore, structural modulation occurs by a mechanism resembling diffusional-displacive transformation. Local strain analysis using HAADF-STEM images has elucidated that lattice spacing of (0001)(Mg) in the FCC-type enrichment layer is shorter than that in the HCP-type transition region. These structural and compositional irregularities are an elementary step in the transformation of LPSO in Mg97Zn1Y2 alloys. A diffusional-displacive type transformation mechanism in LPSO has been proposed.
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