遠心鋳造法により作成したTi-Ni合金素子の形状記憶特性に及ぼす時効処理条件の影響

抄録

A heat-engine using Ti-Ni shape memory alloy (SMA) driven by low-temperature waste heat energy has been investigated for waste heat recovery potential system. In order to improve the cooling efficiency of the SMA element, we proposed the use of a tape-shaped SMA element instead of a wire-shaped SMA element. However the manufacturing cost of the tape-shaped SMA fabricated by arc melting method is higher than that of a wire or coil shaped SMA. To reduce the manufacturing cost, we fabricated a tape-shaped SMA element by the centrifugal casting method using an alloy fabricated by the powder metallurgy method, and investigated the effect of aging-treatment temperature at 573 to 673 K for 72 ksec on shape memory characteristics of this tape-shaped Ti-Ni SMA specimen fabricated by the centrifugal casting method.

Transformation temperatures decrease with increase of aging treatment temperature rises up to 623K, above which they increase. This tendency is thought to be due to variations of Ni-rich precipitations and dislocation density by the variation of aging treatment temperature.

In addition, mechanical properties deteriorate as aging treatment temperature increase, because the precipitations and dislocation density decrease with increase of aging treatment temperature. From these results, it is thought that optimum aging treatment temperature of tape-shaped Ti-Ni SMA specimen fabricated by the centrifugal casting method is below 573K.