Effects of Frequency and Hydrogen Environment on Fatigue Life of Thin Wires of TiNi Super-Elastic Alloy

Abstract

In this study, the fatigue behavior of TiNi Super Elastic Alloy under hydrogen environments were investigated by using thin wires with the diameter of 0.7 mm. Fatigue tests with stress ratio of R = 0.1 were conducted in two environments: in air and NaOH solution with hydrogen charging (current density J = 127 mA/mm²).Frequency were 2Hz and 10Hz. Fatigue life decreased in hydrogen environments than that in air. Frequency does not effect of the fatigue life in air, while fatigue life in hydrogen environment are time deperdent in the region of low stress amplitude. In microscopic observation, brittle surface layer was formed and surface spalling occurred only for J = 127 mA/mm².