Hydrogen effects on the plasticity of nickel and binary nickel-chromium alloy

Abstract

This chapter examines the effect of solute drag on the flow stress of hydrogen-containing nickel and Ni-Cr. The static strain ageing (SSA) experiments provide the quantitative data to evaluate this phenomenon. The maximum pinning stress increases with hydrogen concentration in pure Ni and Ni-16Cr. At room temperature, the corresponding solute drag yields a hardening contribution to the flow stress, up to 20 MPa for a concentration of 1900 at.ppm. Incorporating the shielding of pair interactions into classical results of the dislocation theory, an analytical expressions is proposed for the effect of solute hydrogen on the mechanisms and dislocation properties: the line energy and line tension of curved dislocations, the critical shear stress for the expansion of a dislocation loop, and the cross-slip of screw dislocation. Based on these analytical results, numerical simulations are developed to evaluate the role of hydrogen on the activity of a Frank-Read source and on the stability of dislocation junctions. The detailed modeling provides quantitative tools for interpreting the mechanical testing of hydrogen-containing samples in terms of dislocation mechanisms.