Hydrogen detrapping from grain boundaries and dislocations in high purity iron

Hydrogen detrapping in high purity iron was studied by measuring evolution rates of quenched-in hydrogen from 80 to 800 K using a quadrupole mass spectrometer in an ultra high vacuum system. The peak of the evolution rate was observed at 395 K in single crystal specimens and 415 K in polycrystalline specimens with a heating rate of 1 K min⁻¹. Effects of grain size and deformation on the evolution rate was also studied. It was shown that the results are consistent with the evolution rates calculated with the binding energy B = 0.51 ± 0.02 eV and the trap density term γC_{T = (4 ∼ 15) × 10⁻⁵} in polycrystalline iron, and B = 0.47 ± 0.02 eVand γC_T = (2 ∼ 13) × 10⁻⁵ in single crystal iron. The dominant traps are considered to be grain boundaries in polycrystalline specimens and dislocations in single crystal specimens.