Hydrogen Permeation Behavior of Uncoated and Copper-Coated DC01 Sheets Under Static Biaxial Stress

In pressurized hydrogen vessels, barrier coatings on steel are exposed to hydrogen and biaxial tensile stress simultaneously. This study investigates the hydrogen permeation behavior of uncoated and electroplated copper-coated DC01 sheets under static elastic biaxial tension with the hoop-to-axial stress ratio of a 700 bar Type I pressure vessel. Electrochemical permeation measurements according to ISO 17081 were performed on 0.2 mm thick DC01 specimens using a Devanathan–Stachurski cell. A cross-tension specimen and a dedicated loading device superimposed the biaxial stress during permeation testing. For uncoated specimens, biaxial stress tended to decrease the mean effective diffusion coefficient by 34% and to increase the steady-state permeation flux by about 5%, although not statistically significant for three specimens per condition. A repeated measurement after unloading indicated reversibility. In the unstressed state, no permeation transient was detected through a 5 µm electroplated copper layer. Under biaxial tensile stress, however, the copper-coated specimens showed a measurable permeation signal, with a permeation reduction factor of 230 and an apparent coating diffusion coefficient of 4.94 × 10−14 m2 s−1. The results show that elastic biaxial stress markedly reduces the barrier effectiveness of the electroplated copper coating, whereas its effect on substrate permeation is small.