Fatigue Properties of Ti-Ni Shape Memory Alloy Springs

Yokohama R&D Laboratories, The Furukawa Electric Co., 2-4-3 Okano, Nishi-ku, Yokohama 220, Japan

Abstract

Fatigue properties of a Ti-Ni shape memory alloy coil spring are studied as a function of the amount of the B19’ martensite generating in thermal cycles The recovery force decays more with the number of cycles with an increasing amount of the martensite The temperature ranges of the R-phase and R→B19’ martensitic transformations also widen with the increasing martensite. The shape memory characteristic change of the coil spring results from the reduction in its free length. It is deduced from the change in the transformation temperatures that the free length reduction is caused by the introduction of dislocations during the thermal cycles.