B2 long-range order in mechanically alloyed Fe53.3−0.6xCo46.7−0.4xSnx (2 ≤ x ≤ 26) annealed at moderate temperatures

• Published in: Journal of materials science Vol. 51; no. 12; pp. 5775 - 5790
• Main Authors: Malaman, B., Le Caër, G., Costa, B. F. O.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-06-2016
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crystallography and Scattering Methods; Materials Science; Original Paper; Polymer Sciences; Solid Mechanics; CoFe2O4; Heusler Alloy; Mechanical Alloy; Neutron Diffraction Pattern; Annealed Alloy
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-016-9879-6

Recent interest in Fe–Co–Sn alloys stems from Heusler alloys. A Co
2
FeSn Heusler alloy is found to be unstable relative to other phases from ab initio calculations. However, it may be synthesized by non-equilibrium techniques. The present work focuses similarly on metastable ordered phases in ternary Fe–Co–Sn alloys. First, disordered phases of Sn in near-equiatomic Fe–Co are prepared by high-energy ball-milling. As-milled powders are then annealed to possibly produce long-range ordered phases. As-milled powders, of overall composition Fe
53.3−0.6
x
Co
46.7−0.4
x
Sn
x
(2 ≤ 
x
 ≤ 34), consist of a single supersaturated bcc phase for
x
 < ~15 at.%. For larger values of
x
, they are primarily composed of a bcc phase, whose tin content still increases up to ~26 at.%, and of extra phases, which include hexagonal (Fe,Co)
3
Sn
2
. Neutron diffraction patterns and
119
Sn Mössbauer spectra prove that bcc phases of as-milled alloys order to CsCl (B2)-type structures for
x
 ≤ 26 when annealed at 673 K. In addition,
119
Sn Mössbauer spectra reveal that a Sn content of ~15 at.% marks the separation between domains with different short-range orders. From previous and present results, metastable B2 ordering of Sn-rich Co–Fe–Sn alloys is concluded to occur over a significant concentration range.