Hydrogen-dislocation interaction in relation to hydrogen embrittlement and enhanced plasticity of metals

Abstract

Interaction between hydrogen atoms and dislocations is studied in the iron-, nickel-, and titanium-based alloys using ab initio calculations and experimental studies of the electron structure, as well as mechanical spectroscopy. It is obtained that hydrogen increases the density of electron states, DOS, at the Fermi level, which is responsible for the increased concentration of free electrons decreasing thereby the elasticity moduli, and results in the decreased line tension of dislocations causing their increased mobility. By means of mechanical spectroscopy, the hydrogen diffusion enthalpy, ΔHd, and that of binding between hydrogen atoms and dislocations, ΔHb, have been measured. It is shown that these values control temperature Tc for condensation of hydrogen atoms at dislocations. Consequently, in a definite range of temperatures and strain rates, dislocations move accompanied by hydrogen atmospheres, which is a reason for hydrogen embrittlement. Hydrogen embrittlement in the iron-, nickel- and titaniun-based alloys is analyzed in terms of this concept. Based on the obtained results, the use of hydrogen as a temporary alloying element increasing techological plasticity of β titanium alloys is interpreted.