Shape Memory Alloys: A Summary of Recent Achievements |
| Journal |
Materials Science Forum (Volume 583) |
| Volume |
Advances in Shape Memory Materials |
| Edited by |
V.A. Chernenko |
| Pages |
21-41 |
| DOI |
10.4028/www.scientific.net/MSF.583.21 |
| Online since |
May, 2008 |
| Authors |
Peter Entel,
Vasiliy D. Buchelnikov,
Markus E. Gruner,
Alfred Hucht,
Vladimir V. Khovailo,
Sanjeev K. Nayak,
Alexey T. Zayak
|
| Keywords |
First Principles Calculation, Magnetic Field-Induced Effect, Magneto-Caloric Effect, Shape Memory Alloy (SMA) |
| Abstract |
The Ni-Mn-Ga shape memory alloy displays the largest shape change of all known
magnetic Heusler alloys with a strain of the order of 10% in an external magnetic field of
less than one Tesla. In addition, the alloys exhibit a sequence of intermediate martensites
with the modulated structures usually appearing at c/a < 1 while the low-temperature non-
modulated tetragonal structures have c/a > 1. Typically, in the Ni-based alloys, the martensitic
transformation is accompanied by a systematic change of the electronic structure in the vicinity
of the Fermi energy, where a peak in the electronic density of states from the non-bonding Ni
states is shifted from the occupied region to the unoccupied energy range, which is associated
with a reconstruction of the Fermi surface, and, in most cases, by pronounced phonon anomalies.
The latter appear in high-temperature cubic austenite, premartensite but also in the modulated
phases. In addition, the modulated phases have highly mobile twin boundaries which can be
rearranged by an external magnetic field due to the high magnetic anisotropy, which builds up
in the martensitic phases and which is the origin of the magnetic shape memory effect. This
overall scenario is confirmed by first-principles calculations. |
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