On the mechanism of a hydrogen peak of internal friction in high-alloyed FCC iron

• Published in: Scripta materialia 1998-05, Vol.38 (12), p.1769-1774
• Main Authors: Asano, Shigeru, Usui, Makoto, Shimada, Yoshiharu
• Format: Article
• Language: English
• Subjects: Anelasticity, internal friction, stress relaxation, and mechanical resonances; Applied sciences; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Mechanical and acoustical properties of condensed matter; Metals. Metallurgy; Physics
• ISSN: 1359-6462; 1872-8456
• DOI: 10.1016/S1359-6462(98)00107-9

In 1975, an internal friction peak was found for the type-310 austenitic stainless steel subjected to electrolytic hydrogen charging and attributed to some hydrogen-related relaxation. Since that time, this kind of a hydrogen internal friction peak has been confirmed for all types of austenitic stainless steels and also for many iron-base fcc alloys such as Fe-Ni, Fe-Cr-Ni, Fe-Cr-Mn, Fe-Ni-Mn, Fe-Cr-Ni-Mn. Most investigators have assumed that this hydrogen peak originates in a Snoek-type relaxation of hydrogen complexes dissolved in the fcc iron lattice, like that of interstitial solute atoms in the bcc iron lattice. However, there is a controversy on the structure of hydrogen complexes. Recent discussion is focused on two possibilities: the hydrogen-hydrogen pairs (H-H pairs) and the hydrogen-substitutional solute pairs (H-S pairs). In order to discriminate the above two possibilities, it is necessary to clarify the relationship between relaxation strength and hydrogen concentration. The purpose of this paper is to examine such a relationship in detail for the hydrogen peak of internal friction in Fe-45Ni and Fe-35Ni alloys together with austenitic stainless steel 310S, by employing the gas-phase method for hydrogen charging in place of the usual electrolytic method. The observations on relaxation strength led to the conclusion that the most probable mechanism for a hydrogen peak of internal friction in high-alloyed fcc iron is a stress-induced reorientation of the H-H pairs, rather than the H-S pairs. However, there remain further questions in the kinetics of formation of the H-H pairs and the effect of alloying elements on relaxation strength. These might come to a settlement through consideration on the electronic state of high-alloyed fcc iron.