Shape Memory Effect Related to Thin Plate Martensite with Large Thermal Hysteresis in Ausaged Fe–Ni–Co–Ti Alloy

抄録

Behavior of martensitic transformation and shape memory effect in an Fe–31%Ni–10%Co–3% alloy were studied. The specimen which was ausaged at 873 K for 3.6 ks produces a thin plate martensite (Ms=193 K) with a large thermal hysteresis (i.e., As – Ms=150 K, Af – Ms=315 K). Despite the large thermal hysteresis, the forward and reverse transformations of thin plate martensite occur by a reversible movement of interface in the same manner as thermoelastic martensite. The ausaged specimen which is fully austenitic at room temperature shows a complete shape memory effect when the specimen is heated up above Af after the deformation at temperatures near or below Ms. The ausaged specimen hardly exhibits the shape memory effect when deformed at room temperature. However, when the ausaged specimen is once subzero cooled to liquid nitrogen to produce a large amount of martensite (about 70%), the almost complete shape memory effect occurs even by the deformation at room temperature. Furthermore, the subzero cooled specimen shows the partial shape memory effect when the specimen is cooled below Ms after the deformation at temperature around As. The deformation mode of specimen at various temperatures was investigated by microstructural observations and the origin of the shape memory effect in the present alloy was discussed.