Long-period ordered structure in a high-strength nanocrystalline Mg-1 at% Zn-2 at% Y alloy studied by atomic-resolution Z-contrast STEM
✍ Scribed by E. Abe; Y. Kawamura; K. Hayashi; A. Inoue
- Book ID
- 104402818
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 522 KB
- Volume
- 50
- Category
- Article
- ISSN
- 1359-6454
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✦ Synopsis
The microstructure of a nanocrystalline Mg 97 Zn 1 Y 2 (at%) bulk alloy prepared by warm extrusion of rapidly solidified powders has been investigated by a combination of techniques, such as conventional high-resolution transmission electron microscopy (HRTEM), atomic-resolution high-angle annular dark field scanning-TEM (HAADF-STEM) with Zcontrast and energy-dispersive X-ray spectroscopy (EDS) with a sub-nanometer electron probe. We show that a novel long-period ordered structure is formed in the alloy, whose unit cell is composed of six close-packed planes of the magnesium crystal with a stacking sequence of ABCBCBЈ where A and BЈ layers are significantly enriched by Zn and Y. The lattice is distorted from an ideal hexagonal lattice of 6H-type (ABCBCB), which is probably due to an asymmetry of the chemical order with respect to the 6H-type stacking order. The present results demonstrate that the additional elements of a few atomic percent to Mg lead to formation of a long-period chemical-ordered as well as stackingordered structure, as directly revealed by a unique Z-contrast method.