A Study of Dislocation: Hydrogen Interaction in Titanium-Aluminum Alloys via Internal Friction Measurements

This study investigates the interactions between hydrogen and dislocations in alpha titanium-aluminum alloys using internal friction measurements conducted within a temperature range of 200 K to 500 K. The primary goal is to observe and analyze the damping peaks associated with these interactions across different titanium-aluminum binary alloys which contain varying concentrations of aluminum (0 to 3 at. % Al). The experiment revealed a damping peak centered around 390 K at 10 MHz, with the activation energy and attempt frequency determined for pure titanium at 0.28 eV and 4x10^10 sec^-1, respectively. It was found that both room temperature plastic deformation and the presence of hydrogen are necessary for the generation of the peak. Additionally, the relaxation strength showed a quadratic increase at low hydrogen levels, plateauing when reaching critical hydrogen concentrations of 8 ppm, 40 ppm, and 90 ppm for increasing aluminum content. These findings indicate that the enhancement of critical hydrogen concentration with aluminum addition aligns with the rise in hydrogen solubility, although the measured critical concentrations remained below equilibrium solubility levels. The proposed mechanism involves the interaction of hydrogen di-interstitials with dislocation loops, paralleling previous theoretical models of point defect-dislocation interactions.