Development of New B2 Type Shape Memory Alloys end theirs Application for Multi-functional Devices.

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Shape memory (SM) material which possesses double functions of thermo-sensor and actuator is one of the typical smart materials. Although the SM devices yield larger power and displacement than the ferroelectric one, they have a very serious problem in which the response for input signal is too slow, because the thermal conductivity in the SM devices is a rate determining process. Recently, ferromagnetic Shape memory (FSM) alloys that can be operated by magnetic field have been developed in the Ni-Mn-Ga system. In the present study, new type of FSMAs, Co-Ni-Al alloys with B2 bcc ordered structure were investigated.. The details of results obtained by the present work are as follows:(1) Transformation temperatures: Martensitic transformation temperature (Ms) and Curie temperature (Tc) were determined by DSC and VSM measurement. Some alloys have Ms and To in relatively high temperatures region over room temperature. This result means that the Co-Ni-Al alloys can be a candidate of the promising FSMA.(2) Crystal structure: The parent and martensits phases have B2 and Ll_0 structures, respectively. The c/a ration of the Ll_0, phase is 0.81.(3) Shape memory and mechanical properties: Coexistence with γ phase improves the ductility of alloys and a perfect SM can be obtained by a training treatment.(4) Magnetic properties: Magnetic anisotropies of austenite and martensite phases were determined using single crystals, and magnetostriction of about 0.3% was detected.(5) FSM wire, FSM wire with 0.5 to 1.0mmf could be produced by conventional techniques of rolling and drawing. The obtained wire showed a pseudoelastic behavior.