2117 Co-Ni-Al基強磁性形状記憶合金における超弾性特性(S06-3 形状記憶合金の特性と応用技術(3),S06 形状記憶合金の特性と応用技術)

Abstract

Ferromagnetic shape memory alloys (FSMAs) have received considerable attention as sensor/actuator materials due to their multi-functional characteristics. Recently, the present authors have developed Co-Ni-Al alloys as a new type of FMSAs. A Co-Ni-Al single crystal shows a reversible magnetic-induced strain of about 0.06% when slight pre-deformation is applied to the austenite phase. Furthermore, polycrystalline Co-Ni-Al alloys with the β(B2)+γ(Al) two-phase structure exhibit good ductility and shape memory properties. In the present study, the superelastic (SE) properties of the β+γ two-phase Co-Ni-Al polycrystalline alloys were investigated by tensile-testing. It was found that the SE properties in the β+γ two-phase condition strongly depend on the volume fraction of γ phase, and that the specimen with having about 8% γ phase shows the highest degree of SE. Furthermore, the SE properties were enhanced by controlling the βgrain size. Consequently, a SE strain of about 6% was achieved in a sheet specimen with the large βgrains.