Evaluation of hydrogen diffusion and trapping in nickel Alloy 625 by thermal desorption spectroscopy
Xu Lu, Tom Depover, Roy Johnsen
Abstract
This study presents hydrogen diffusion and trapping in the nickel Alloy 625 by employing the hot extraction test and the thermal desorption spectroscopy (TDS) analysis. Combined with electrochemical permeation test, the impact of grain size and grain boundary carbide on hydrogen diffusion are investigated. The results manifeste that the effective hydrogen diffusivity can be expressed as D=1.03×10−7exp(−46.44kJmolRT)m2/s for the sample with a grain size of ∼8 μm. The diffusion activation energy ED for hydrogen is determined as 42.05–48.10 kJ/mol. The activation energy E associated with interstitial sites/elastic field of dislocations and reversible traps is 17.92–20.73 kJ/mol and 24.87–27.13 kJ/mol, respectively. Moreover, the reduction in grain size and the presence of grain boundary carbide can lower hydrogen diffusivity by locally changing the diffusion and trapping behavior of hydrogen.