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Materials (Basel). 2017 Aug 31;10(9). pii: E1016. doi: 10.3390/ma10091016.

In situ Observation of Phase Transformation in MnAl(C) Magnetic Materials.

Author information

1
Powder & Ceramic Division, Korea Institute of Materials Science, Changwon, Gyeongnam 51508, Korea. pzsi@cjlu.edu.cn.
2
College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, China. pzsi@cjlu.edu.cn.
3
Powder & Ceramic Division, Korea Institute of Materials Science, Changwon, Gyeongnam 51508, Korea. qianhuidong@kims.re.kr.
4
Powder & Ceramic Division, Korea Institute of Materials Science, Changwon, Gyeongnam 51508, Korea. cjchoi@kims.re.kr.
5
Powder & Ceramic Division, Korea Institute of Materials Science, Changwon, Gyeongnam 51508, Korea. jpark@kims.re.kr.
6
Powder & Ceramic Division, Korea Institute of Materials Science, Changwon, Gyeongnam 51508, Korea. hsh6188@kims.re.kr.
7
College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, China. hongliang_ge@cjlu.edu.cn.
8
Powder & Ceramic Division, Korea Institute of Materials Science, Changwon, Gyeongnam 51508, Korea. kiranshinde@kims.re.kr.

Abstract

The phase transformation in two modes, including both displacive and massive growth of τ-phase from ε-MnAl(C), was observed by in situ transmission electron microscopy. The exact temperature range for different phase transformation modes was determined by magnetic measurements. The displacive growth of ε→τ in Mn54Al46 (or Mn54Al46C2.44) occurs at temperatures below 650 K (or 766 K), above which both modes coexist. One-third or less of the ε-phase can be transformed into τ-phase via displacive mode while the remaining two-thirds or more via massive mode. In bulk τ-phase, most τ-nanocrystals formed via displacive mode are distributed in the matrix of large τ-grains that formed via massive mode. The typical massive growth rate of the τ-phase is 8-60 nm/s, while the displacive growth rate is low. A more complete understanding of the ε→τ phase transformations in the MnAl-based magnets was provided in this work, based on which the annealing process for ε→τ was optimized and thus high purity τ-phase with high saturation magnetization was obtained.

KEYWORDS:

Mn54Al46; MnAl; MnAlC; diffusion; magnetic properties; phase transformation

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