OS0910 Effect of Environments on Fatigue Life of Shape Memory Alloy Thin Wires
Details
In this study, the fatigue behavior of TiNi alloy under various hydrogen environments was investigated by using thin wires with the diameter of 0.7 mm. Fatigue tests with stress ratio of R=0.1 were conducted in four environments: NaOH solution with hydrogen charging (current density J=127 mA/mm^2 and 0.0254 mA/mm^2), NaOH solution without charging, and water. Fatigue life decreased in these all hydrogen environments than in air. The effect of hydrogen charging current density on fatigue life was very small, but a brittle surface layer was formed and surface spalling occurred only for J=127 mA/mm^2. Comparing at the same value of the maximum stress, time to rupture for fatigue tests agreed with that for slow strain rate tests (SSRT) in a low stress region. On the other hand, in a high stress region, a large difference in time to rupture could be seen between fatigue tests and SSRT. Therefore, the fracture under high stress amplitude is controlled predominantly by damage due to cyclic stress, while fracture under low stress amplitude is controlled predominantly by hydrogen embrittlement.
