Hydrogen diffusion coefficients through Inconel 718 in different metallurgical conditions

• Electrochemical hydrogen permeation studies in Inconel 718.
• Comparison of DH in cold rolled, solutionized and precipitation hardened specimens.
• TEM studies indicate hydrogen trapping at dislocations and precipitates.
• Repeated permeation transients revealed the presence of irreversible trap sites.

We report hydrogen permeation studies through cold rolled, solutionized, and precipitation hardened Inconel 718 foils. The effective hydrogen diffusion coefficient is considerably higher (5.3–6.8 × 10−11 cm2/s) for the solutionized Inconel 718 than for either the cold rolled (3.3–4.2 × 10−11 cm2/s) or precipitation hardened (2.1–2.9 × 10−11 cm2/s) specimens. Microstructural studies indicate that the reduced hydrogen diffusion coefficients in the latter specimens arise from hydrogen trapping at dislocations and precipitates that are present at much lower concentrations in the solutionized specimens. Also, repeated permeation transients provide evidence for irreversible hydrogen trapping in the cold rolled and precipitation hardened specimens, but such effects are insignificant in the solutionized specimens.