Stacking fault aggregation during cooling composing FCC-HCP martensitic transformation revealed by in-situ electron channeling contrast imaging in an Fe-high Mn alloy

Motomichi Koyama; Misaki Seo; Keiichiro Nakafuji; Kaneaki Tsuzaki

doi:10.1080/14686996.2021.1877570

Stacking fault aggregation during cooling composing FCC-HCP martensitic transformation revealed by in-situ electron channeling contrast imaging in an Fe-high Mn alloy

Sci Technol Adv Mater. 2021 Mar 15;22(1):135-140. doi: 10.1080/14686996.2021.1877570.

Authors

Motomichi Koyama^{1

2}, Misaki Seo³, Keiichiro Nakafuji³, Kaneaki Tsuzaki^{2

3

4}

Affiliations

¹ Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan.
² Elements Strategy Initiative for Structural Materials (ESISM), Kyoto University, Kyoto, Japan.
³ Faculty of Engineering, Kyushu University, Fukuoka, Japan.
⁴ Research Center for Structural Materials, National Institute for Materials Science, Tsukuba, Japan.

Abstract

To understand the mechanism of FCC-HCP martensitic transformation, we applied electron channeling contrast imaging under cooling to -51°C and subsequent heating to 150°C. The stacking faults were randomly extended and aggregated during cooling. The stacking fault aggregates were indexed as HCP. Furthermore, the shrink of stacking faults due to reverse motion of Shockley partials was observed during heating, but some SFs remained even after heating to the finishing temperature for reverse transformation (A_f: 104°C). This fact implies that the chemical driving force of the FCC/HCP phases does not contribute to the motion of a single SF but works for group motion of stacking faults.

Keywords: Metallic materials; SEM; STEM; Stacking fault; TEM; austenitic steel; electron channeling contrast imaging; in situ electron microscopy; martensitic transformation.

Grants and funding

This work was supported financially by JSPS KAKENHI (JP16H06365 and JP20H02457) and Elements Strategy Initiative for Structural Materials (ESISM) of Ministry of Education, Culture, Sports, Science and Technology (MEXT) Japan (JPMXP0112101000).