Hydrogen-vacancy interactions in Fe-C alloys.

Energetics and concentrations of hydrogen-containing point defect clusters (PDCs) in Fe-C alloys are calculated and cast into a PDC dominance diagram. Because of the strong binding effects of iron vacancies on the stability of the clusters, hydrogen accumulation requires the total hydrogen and vacancy concentrations to be comparable. As a result of the interplay between repulsive and attractive binding processes, PDC populations in Fe-C-H effectively decouple into the binary systems Fe-C and Fe-H. This results in significant vacancy-hydrogen PDC populations even for low total hydrogen concentrations.