Hydrogen-induced superabundant vacancies in electrodeposited Fe-C alloy films

Fe-C alloy films containing supersaturated C and H were prepared by electrodeposition, and investigated for the hydrogen behavior in annealing processes utilizing X-ray diffraction and thermal desorption spectroscopy. The H content xH (xH = H/Fe) in the films increased from about 0.031 in pure Fe to about 0.36 in Fe-C alloy (xC = C/Fe = 0.073) in proportion to the C content. The lattice contraction of about 0.2% was observed in pure Fe films, whereas the lattice expansion increasing with C content was observed in Fe-C alloy films. Both the lattice contraction of the Fe films and the lattice expansion of the Fe-C alloy films were decreased as H was desorbed during heat treatments. The atomistic structure of vacancy-hydrogen and vacancy-carbon-hydrogen clusters in Fe-C alloy films is discussed, based on these experimental results.