Crystal structure and microstructure of Ni 50 Mn 38 Sb 12

Crystal structure and microstructure of Ni50Mn38Sb12 ferromagnetic shape
memory alloy
Chunyang Zhang1, 2, 3, Haile Yan1, 2, 3, Y. D. Zhang1, 2, C. Esling1, 2, X. Zhao3, L. Zuo3
Laboratoire d'Étude des Microstructures et de Mécanique des Matériaux (LEM3), CNRS UMR 7239,
Université de Lorraine, 57045 Metz, France
Laboratory of Excellence on Design of Alloy Metals for low-mAss Structures (DAMAS), Université de
Lorraine, 57045 Metz, France
Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University,
Shenyang 110819, China
Abstract. Ferromagnetic shape memory alloy is a kind of material which can realize shape
change under a magnetic field. Ni-Mn-Sb is one of the typical systems. Different from
Ni-Mn-Ga alloys, the shape memory effect of Ni-Mn-Sb alloys is realized through martensitic
transformation, where the austenite is ferromagnetic and the martensite is antiferromagnetic
or paramagnetic. When an external magnetic field is applied to Ni-Mn-Sb, the reverse
martensitic transformation (MT) temperature will be reduced. So alloys with MT temperature
just slightly higher than the room temperature (RT) is of practical significance. By applying
an external magnetic field, the reverse MT temperature will be reduced below RT, then the
alloy will transform to austenite, which gives rise to the shape change. It is clear that the
shape change during phase transformation is closely related to the crystal structures of the
parent and product phases and the organization of the martensite variants. So the investigation
of crystal structure and microstructure of Ni-Mn-Sb is very important and has not yet been
fully completed for these alloys.
In the present study, polycrystalline Ni50Mn38Sb12 alloy was first prepared by arc melting
using high-purity Ni, Mn and Sb. The prepared alloy was further spray cast into Cu mold in
order to obtain dense and bulk cylindrical samples. In order to homogenize the composition,
annealing was applied before and after the spray casting at 1173K for 24h followed by
quenching in water. The MT temperature, crystal structure and microstructure were
determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning
electron microscopy (SEM), respectively. The MT of Ni50Mn38Sb12 is 324.50K (51.35ºC),
which is just above the RT. XRD pattern reveals that the crystal structure of martensite at RT
is four-layered orthorhombic (4O). Backscattered electron (BSE) image shows that the
original austenite phase is composed of plates that consist of large amount of fine lamellae
with straight parallel lamellar boundaries. The width of the lamellae is in the sub-micrometric