Reconsideration of Numerical Model for Hydrogen Thermal Desorption Spectra of Iron with Hydrogen-Enhanced Strain-Induced Vacancies

Abstract We successfully reproduced the experimental thermal desorption spectra of hydrogen from a small iron sample containing hydrogen-enhanced strain-induced vacancies by revising a previously proposed numerical model (Ebihara et al. in Metall Mater Trans A 52A:257, 2021). In the revised model, we adopted concentration variables for mono- and cluster-vacancies, which are separately defined based on the number of trapped hydrogen atoms. This eliminates the continuous-number representation of the number of trapped hydrogen evaluated from the product of the hydrogen occupancy and the trap site concentration in the original model. According to the revision, the migration of mono- and cluster-vacancies trapping hydrogen, which must be assumed to simulate the thermal desorption spectra in the original model, became unnecessary. Simulation results obtained using the revised model revealed that the spike-like desorption on the peak attributed to mono- and cluster-vacancies in the spectra simulated by the original model was an artifact caused by the migration of mono- and cluster-vacancies trapping hydrogen. Furthermore, it was also suggested that not only mono-vacancies but also cluster-vacancies can exist in the specimens after deformation during hydrogen charging. Additionally, it was confirmed that dissociation of a mono-vacancy from cluster-vacancies trapping of hydrogen atoms needs to be considered to examine the effect of the thermal aging process, in which both hydrogen atoms and vacancies are decreased.