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

Published online by Cambridge University Press:  01 March 2012

D. Y. Cong
Affiliation:
Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, Shenyang, 110004, China
Y. D. Wang
Affiliation:
Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, Shenyang, 110004, China
J. Z. Xu
Affiliation:
Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, Shenyang, 110004, China
L. Zuo
Affiliation:
Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, Shenyang, 110004, China
P. Zetterström
Affiliation:
Department of Structural Chemistry, Stockholm University, S-10691 Stockholm, Sweden
R. Delaplane
Affiliation:
The Studsvik Neutron Research Laboratory (NFL), Uppsala University, S-61182 Nyköping, Sweden

Abstract

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.

Type
Representative Papers from the Chinese XRD 2006 Conference
Copyright
Copyright © Cambridge University Press 2007

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