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Part A: Materials Science

Evolution of long-period stacking order (LPSO) in Mg97Zn1Gd2 cast alloys viewed by HAADF-STEM multi-scale electron tomography

ORCID Icon, , , , &
Pages 1945-1960 | Received 09 Jul 2017, Accepted 14 Apr 2018, Published online: 02 May 2018
 

Abstract

We have studied three-dimensional (3D) structures and growth processes of 14H-type long-period stacking order (LPSO) formed in Mg97Zn1Gd2 cast alloys by single tilt-axis electron tomography (ET) using high-angle annular dark-field scanning transmission electron microscopy. Evolution of the solute-enriched stacking faults (SFs) and the 14H LPSO by ageing were visualised in 3D with a high spatial resolution in multi-scale fields of views from a few nanometres to ~10 μm. Lateral growth of the solute-enriched SFs and the LPSO in the (0 0 0 1)Mg plane is notable compared to the out-of-plane growth in the [0 0 0 1]Mg direction. The 14H LPSO grows at the cost of decomposition of the (Mg, Zn)3Gd-type precipitates, and accompany a change of in-plane edge angles from 30 to 60°. We have updated the Time–Temperature–Transformation diagram for precipitation in Mg97Zn1Gd2 alloys: starting temperatures of both solute-enriched SFs and LPSO formation shifted to a shorter time side than those in the previous diagram.

Acknowledgements

The authors wish to thank Prof. Y. Kawamura and Dr. M. Yamasaki in Kumamoto University for providing us Mg–Zn–Gd alloys, and Ms. K. Ito for 3D reconstruction.

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