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Home  >  Journal list  >  MATERIALS TRANSACTIONS  >  Vol.55  No.7 (2014)  >  pp.1051-1057

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Precipitation Sequence in the Mg–Gd–Y System Investigated by HRTEM and HAADF-STEM

Yuuki Matsuoka1), Kenji Matsuda2), Katsumi Watanabe1), Junya Nakamura3), Williams Lefebvre4), Daisuke Nakagawa1), Seiji Saikawa2), Susumu Ikeno5)
1) Graduate School of Science and Engineering for Education, University of Toyama 2) Graduate School of Science and Engineering for Research, University of Toyama 3) Department of Metallurgy, Materials Science, and Materials Processing, Tohoku University 4) Universite de Rouen, GPM, UMR, CNRS 5) Hokuriku Polytechnic Collage

In this work, the early stage of precipitation have been investigated in a Mg–2.9 at% Gd–0.8 at% Y by high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and high resolution transmission electron microscopy (HRTEM).
At the underaged condition, precipitates observed by HRTEM were classified as follows; mono-layer, a part of β″, β′. By HAADF-STEM, zig-zag structure, small hexagonal network, and β′ could be recognized. The small “super hexagons” are the first precipitates in this alloy. This structure, referred to as the pre β″-phase, displays a short range similar to the one present in the D019 structure. This phase is formed during quenching and prevails over the zig-zag structure at the beginning of aging. The zig-zag contrast is one of the variations of this small hexagonal network or heterogeneous nucleation during aging. Finally, we concluded that the proposed precipitation sequence is as follows: SSSS → pre β″-phase having D019-SRO → β″-phase → β′-phase. The comparison of HRTEM, HAADF-STEM and simulated images have helped to clarify the meaning of HRTEM features.

magnesium–gadolinium–yttrium alloys, age-hardening, precipitation, high resolution transmission electron microscopy (HRTEM), high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM)

Received: January 21, 2014
Accepted: February 25, 2014 , Published online: June 25, 2014
Copyright © 2014 The Japan Institute of Light Metals



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