Alloying effects on thermodynamic characteristics of hydrogen in BCC iron

Substitutional impurities have significant effect on hydrogen behaviour in iron. It opens a possibility to control hydrogen degradation of steels through directional alloying. The paper contains a review of theoretical and experimental studies of the problem of trapping of hydrogen atoms by alloy impurities and using this effect for preventing hydrogen embrittlement. Influence of 3d, 4d and sp metals on the energy of solution of hydrogen in BCC iron matrix is then investigated by means of WIEN-2k software package realizing the linear augmented plane wave (LAPW), a full-electronic method of the density functional theory. Detailed consideration of the change of equilibrium lattice parameter due to hydrogen dissolution in the alloyed BCC iron lattice is performed. The issue of alloy effect on preferred filling by hydrogen of tetrahedral and octahedral sites of interstitial sublattice is studied. Electronic and elastic contributions to the energy of solution are isolated. Energies of hydrogen trapping by impurity atoms are calculated, and significant contributions of both electronic and elastic effects to the trapping energy are demonstrated. It is shown that the change of the energy of solution of hydrogen due to impurities may be linked with the disturbance that they create in the electronic density of the matrix.