「スマートマテリアル」 Ｔｉ‐Ｎｉ‐Ｎｂ合金の形状記憶効果における二方向ひずみの発現について〜二方向ひずみに及ぼす付加ひずみの影響〜

Abstract

A promising field for application of shape memory alloys (SMAs) in the near future is in micro-actuator technology. Two-way shape memory effect (TWSME) is particularly suitable for application in actuators, since pre-determined responses can be obtained very easily by thermal changes to shape memory elements. In this paper, the TWSME, Ti-Ni-Nb alloy, was investigated quantitatively by applying various levels of pre-deformation. Deformation in a complete martensite phase was applied as a thermomechanical treatment in order to obtain the two-way memory strain. The experimental results indicated that the deformation mechanism in martensite phase was martensite orientation accompanied by dislocation slip. The dislocation due to the slip deformation is the origin of the internal stress field that is necessary to generate the two-way memory strain. However, excessive introduction of dislocation tends to decreases the two-way memory strain. The maximum two-way memory strain observed in this experiment was 2.1% at an applied strain of 18%. In addition, pre-deformation increases the temperature of reverse transformation, but decreases the temperature of martensitic transformation. These experimental results can be explained by using the series-parallel combined model suggested in our previous study.