Two-way shape memory effect of TiNi alloys induced by hydrogenation

An investigation on the two-way shape memory effect (TWSME) induced by an electrochemical hydrogenation has been conducted on two TiNi shape memory alloys (SMAs) (Ti49.2Ni50.8 and Ti51.1Ni48.9 denoted as materials A and B, respectively). While a bending constraint has been applied during hydrogenation, the effects of current density, solution temperature, and charging period are studied. A two-way shape memory behavior was observed on the bent, hydrogenated specimens. The measured ratio of TWSME of specimen A is greater than that of specimen B. The variation of the TWSME of the specimens is relatively small during the first 50 thermal cycles. The TWSME increases first and then decreases with increasing either current density or charging period of the electrochemical hydrogenation. The X-ray diffraction peak corresponding to hydrides in the hydrogenated specimen still exists but becomes weaker after three months of "resting," and the TWSME obviously decreases with decreasing amount of hydrides.