Neutron diffraction study on crystal structure and phase transformation in Ni-Mn-Ga ferromagnetic shape memory alloys

Crystal structure and phase transformation behaviors in two Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs) with compositions of Ni48Mn30Ga22 and Ni53Mn25Ga22 (at. %) as a function of temperature were investigated by in situ neutron diffraction experiments. Neutron diffraction technique proves to be highly efficient in characterizing structural transformation in Ni-Mn-Ga FSMAs, which consist of nearby elements in the periodic table. Our neutron results show that Ni48Mn30Ga22 has a cubic, L21 Heusler structure from 373 to 293 K. Its crystal structure changes into a seven-layered orthorhombic martensitic structure when cooled to 243 K, and no further transformation is observed upon cooling to 19 K. Neutron diffraction results also show that Ni53Mn25Ga22 has a tetragonal I4/mmm martensitic structure from 20 to 403 K. A pre-transformation around room temperature is observed from an abrupt jump in unit-cell volume of Ni53Mn25Ga22, which corresponds with an endothermic peak detected in a heated DSC curve.

Download Full-text

DETERMINATION OF CRYSTAL STRUCTURE AND CRYSTALLOGRAPHIC CHARACTERISTICS IN Ni-Mn-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS

International Journal of Modern Physics B ◽

10.1142/s0217979209061603 ◽

2009 ◽

Vol 23 (06n07) ◽

pp. 1771-1776

Author(s):

D. Y. CONG ◽

Y. D. ZHANG ◽

C. ESLING ◽

Y. D. WANG ◽

X. ZHAO ◽

...

Keyword(s):

Crystal Structure ◽

Shape Memory Alloys ◽

Shape Memory ◽

High Performance ◽

Room Temperature ◽

Martensitic Structure ◽

Magnetic Shape Memory ◽

Ferromagnetic Shape Memory Alloys ◽

Electron Backscattered Diffraction ◽

Ferromagnetic Shape Memory

Ni - Mn - Ga ferromagnetic shape memory alloys (FSMAs) have received great attention during the past decade due to their giant magnetic shape memory effect and fast dynamic response. The crystal structure and crystallographic features of two Ni - Mn - Ga alloys were precisely determined in this study. Neutron diffraction measurements show that Ni 48 Mn 30 Ga 22 has a Heusler austenitic structure at room temperature; its crystal structure changes into a seven-layered martensitic structure when cooled to 243K. Ni 53 Mn 25 Ga 22 has an I4/mmm martensitic structure at room temperature. Electron backscattered diffraction (EBSD) analyses reveal that there are only two martensitic variants with a misorientation of ~82° around <110> axis in each initial austenite grain in Ni 53 Mn 25 Ga 22. The investigation on crystal structure and crystallographic features will shed light on the development of high-performance FSMAs with optimal properties.

Download Full-text

Neutron Diffraction Studies of Magnetic Shape Memory Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.684.73 ◽

2011 ◽

Vol 684 ◽

pp. 73-84 ◽

Cited By ~ 4

Author(s):

José M. Barandiarán ◽

Jon Gutiérrez ◽

Patricia Lázpita ◽

J. Feuchtwanger

Keyword(s):

Crystal Structure ◽

Neutron Diffraction ◽

Shape Memory Alloys ◽

Shape Memory ◽

Site Occupancy ◽

Magnetic Shape Memory ◽

Ferromagnetic Shape Memory Alloys ◽

Magnetic Shape Memory Alloys ◽

Moment Distribution ◽

Ferromagnetic Shape Memory

The characteristics of neutron diffraction applied to the study of Ferromagnetic Shape Memory Alloys are revised. Main studies refer to crystal structure, preferential site occupancy, variant reorientation and magnetic moment distribution in the alloys

Download Full-text