Hydrogen-enhanced microplasticity of austenitic steels studied by means ofinternal friction

Hydrogen-induced damping at low temperatures is studied in austenitic steel s Cr18-Ni16-Mn10, Cr25-Ni20 and Cr25-Ni40. The orientation dependence of th e hydrogen-caused Snoek-like relaxation measured in single crystals gives e vidence for the orthorhombic symmetry of the s-H complexes created by hydro gen and substitutional atoms in the gamma solid solution. The observed spli tting of the Snoek-like relaxation peak is analysed on the basis of the rel axation theory caused by non-cubic defects in the cubic matrix. It is shown that the increase in the chromium and nickel content changes the symmetry of the s-H complexes. Based on the analysis of the experimental data in Arr henius coordinates and on the temperature of the Snoek-like peak caused by the local jumps of hydrogen atoms, one can suppose that chromium increases the enthalpy of the local migration of hydrogen atoms in s-H complexes wher eas nickel decreases it. Hydrogen charging diminishes the critical strain a bove which internal friction depends on the strain and increases the dampin g in its strain-dependent range. The results are interpreted in terms of hy drogen-caused decrease in the start stress of the localised plastic deforma tion and an increased mobility of emitted dislocations, which is consistent with the hypothesis of the hydrogen-enhanced localised plasticity. (C) 200 1 Elsevier Science B.V. Ail rights reserved.