J. Phys. IV France
Volume 112, October 2003
Page(s) 1017 - 1020

J. Phys. IV France
112 (2003) 1017
DOI: 10.1051/jp4:20031054

Development of the Co-Ni-AI ferromagnetic shape memory alloys

K. Oikawa1, T. Omori2, Y. Sutou2, R. Kainumal1 and K. Ishidal1

1  National Institute of Advanced Industrial Science and Technology, 4-2-1 Nigatake, Miyagino-ku, Sendai 983-8551, Japan
2  Department of Materials Science, Graduate School of Engineering, Tohoku University, Aoba-yama 02, Sendai 980-8579, Japan

Ferromagnetic shape memory alloys have been developed in the Co-Ni-AI temary system with $\beta +\gamma$ two-phase structure. The $\beta$(B2) phase of the Co-33Ni-27Al and Co-34Ni-28Al alloys exhibits both paramagneticlferromagnetic transition and a thermoelastic martensitic transformation from $\beta$ to $\beta'$ (L1 0). The microstructure of both alloys shows the primary $\beta$ phase surrounded by the $\gamma$(A1) phase which brings about the drastic effect in the improvement of the hot workability. By annealng in the two-phase region after solution treatment, the $\gamma$ phase precipitates along grain boundaries in the $\beta$ phase, besides in the $\beta$ grain. The alloys annealed at 1273 K showed a good cold workability and a thermal activated shape memory effect. These ferromagnetic and ductile shape memory alloys are very promising for one of the new smart matenals.

© EDP Sciences 2003