Title: Electron concept for hydrogen brittleness of metals

Abstract

The reversible or ”true” hydrogen embrittlement, HE, is related with movement of dislocations accompanied by hydrogen migration and, for this reason, manifests itself in a certain range of temperatures and strain rates, where hydrogen atoms can follow dislocations. The proposed concept attributes HE to hydrogen effect on the weakening of interatomic bonds within hydrogen atmospheres around the dislocations, which locally affects the shear modulus µ and, consequently, decreases the start stress of dislocation sources, τ ≈ 2µb/L, where L is a distance between pinning points, diminishes the line tension of dislocations, ϒ ≈ (µb2/4π)/log(ℜ/5b), where ℜ is the radius of the dislocation curvature, which enhances mobility of dislocations, and reduces a distance between dislocations in their plane assembles, d ≈ (πµb)/16(1-ν)nτ, where τ is the shear stress in the slip plane, which increase the number of dislocations, n, in the pileups and, correspondingly, the stress at a leading dislocation τL = nτ. This concept is substantiated by the ab initio calculated hydrogen-decreased density of electron states at the Fermi level in Fe-, Ni and Ti-based alloys, corresponding increase in the concentration of free electrons measured using the electron spin resonance and studies of hydrogen effect on dislocation properties by means of mechanical spectroscopy.