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Insights into formation and stability of τ-MnAlZx (Z = C and B)

Fang, Hailiang; Cedervall, Johan; Martinez, Francisco LU ; Matej, Zdenek LU ; Bednarcik, Jozef; Ångström, Jonas; Berastegui, Pedro and Sahlberg, Martin (2017) In Journal of Alloys and Compounds 692. p.198-203
Abstract

The τ-phase MnAl alloys are promising candidate for rare earth free permanent magnets. In this study, In order to better understand the MnAl ε→τ phase transition mechanism in a continuous cooling process and metastable MnAl τ-phase high temperature stability, Mn0.54Al0.46, Mn0.55Al0.45C0.02 and Mn0.55Al0.45B0.02 alloys were systematically studied by in situ synchrotron X-ray powder diffraction (SR-XRD). The relationship between τ-phase formation tendency and different cooling rates of Mn0.55Al0.45C0.02 was investigated. Besides, the high temperature stabilities of undoped τ-MnAl and carbon/boron doped τ-MnAl were... (More)

The τ-phase MnAl alloys are promising candidate for rare earth free permanent magnets. In this study, In order to better understand the MnAl ε→τ phase transition mechanism in a continuous cooling process and metastable MnAl τ-phase high temperature stability, Mn0.54Al0.46, Mn0.55Al0.45C0.02 and Mn0.55Al0.45B0.02 alloys were systematically studied by in situ synchrotron X-ray powder diffraction (SR-XRD). The relationship between τ-phase formation tendency and different cooling rates of Mn0.55Al0.45C0.02 was investigated. Besides, the high temperature stabilities of undoped τ-MnAl and carbon/boron doped τ-MnAl were studied. Differential thermal analysis (DTA) was also employed to study the phase transformation as well. The research results show that a high cooling rate of 600 °C/min leads to a 50/50 wt% mixture of ε- and τ-phase; almost pure τ-phase was obtained when cooled at a moderate cooling rate of 10 °C/min; while for a slow cooling rate of 2 °C/min, the τ-phase partially decomposed into β and γ2 phases. No intermediate ε’-phase was observed during the ε→τ phase transition during the experiments. For the boron and carbon doped τ-MnAl, the 800 °C high temperature stability experiments reveal that C stabilizes the τ-MnAl while doped B destabilises the tetragonal structure and it decomposes into β- and γ2-phases.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
In situ, Permanent magnet, Phase stability, Phase transition, Powder diffraction, Thermal analysis
in
Journal of Alloys and Compounds
volume
692
pages
6 pages
publisher
Elsevier
external identifiers
  • Scopus:84988037285
ISSN
0925-8388
DOI
10.1016/j.jallcom.2016.09.047
language
English
LU publication?
yes
id
18a062ff-d411-4dd0-bd71-6192e923ed7f
date added to LUP
2016-10-18 13:42:39
date last changed
2016-10-18 13:45:34
@misc{18a062ff-d411-4dd0-bd71-6192e923ed7f,
  abstract     = {<p>The τ-phase MnAl alloys are promising candidate for rare earth free permanent magnets. In this study, In order to better understand the MnAl ε→τ phase transition mechanism in a continuous cooling process and metastable MnAl τ-phase high temperature stability, Mn<sub>0.54</sub>Al<sub>0.46</sub>, Mn<sub>0.55</sub>Al<sub>0.45</sub>C<sub>0.02</sub> and Mn<sub>0.55</sub>Al<sub>0.45</sub>B<sub>0.02</sub> alloys were systematically studied by in situ synchrotron X-ray powder diffraction (SR-XRD). The relationship between τ-phase formation tendency and different cooling rates of Mn<sub>0.55</sub>Al<sub>0.45</sub>C<sub>0.02</sub> was investigated. Besides, the high temperature stabilities of undoped τ-MnAl and carbon/boron doped τ-MnAl were studied. Differential thermal analysis (DTA) was also employed to study the phase transformation as well. The research results show that a high cooling rate of 600 °C/min leads to a 50/50 wt% mixture of ε- and τ-phase; almost pure τ-phase was obtained when cooled at a moderate cooling rate of 10 °C/min; while for a slow cooling rate of 2 °C/min, the τ-phase partially decomposed into β and γ<sub>2</sub> phases. No intermediate ε’-phase was observed during the ε→τ phase transition during the experiments. For the boron and carbon doped τ-MnAl, the 800 °C high temperature stability experiments reveal that C stabilizes the τ-MnAl while doped B destabilises the tetragonal structure and it decomposes into β- and γ<sub>2</sub>-phases.</p>},
  author       = {Fang, Hailiang and Cedervall, Johan and Martinez, Francisco and Matej, Zdenek and Bednarcik, Jozef and Ångström, Jonas and Berastegui, Pedro and Sahlberg, Martin},
  issn         = {0925-8388},
  keyword      = {In situ,Permanent magnet,Phase stability,Phase transition,Powder diffraction,Thermal analysis},
  language     = {eng},
  month        = {01},
  pages        = {198--203},
  publisher    = {ARRAY(0x9d83a00)},
  series       = {Journal of Alloys and Compounds},
  title        = {Insights into formation and stability of τ-MnAlZ<sub>x</sub> (Z = C and B)},
  url          = {http://dx.doi.org/10.1016/j.jallcom.2016.09.047},
  volume       = {692},
  year         = {2017},
}