MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
Structural and Compositional Modulation in Transformation of LPSO Structure in Mg97Zn1Y2 Cast Alloys
Takanori KiguchiYu NinomiyaKensuke ShimmiKazuhisa SatoToyohiko J. Konno
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2013 Volume 54 Issue 5 Pages 668-674

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Abstract

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 14H-type 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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© 2013 The Japan Institute of Metals and Materials
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