Study of hydrogen in metals: investigation by the internal friction technique of the interaction between hydrogen atoms and dislocations in face centered cubic metals

In the range 77 K - 300 K, internal friction of hydrogenated nickel and copper is investigated by the means of an inverted torsion pendulum which allows thermomechanical treatments to be performed ''in situ'' (such as annealing, hydrogen loading from the vapour phase, cold-working). Hydrogen loaded specimens cold worked at low temperatures (T < 77 K) exhibit when warmed up a dislocation pinning stage (in the range 110 K - 170 K for Ni, in the range 150 K - 200 K for Cu). The kinetics of pinning, studied in the case of nickel, have shown the interaction between /lydrogen and dislocations to be a long range effect. If the hydrogen content is high enough, (some 10. 10^-6 atomic) the pinning stage is followed by an internal friction peak called M at 235 K. A comparaison between bath systems Fe-N and Ni-H leads to identify M with the KOSTER peak that can be observed in body centered metals. With copper containing 5.10^-6 hydrogen a relaxation peak called P_H is observed at 150 K. An experimental study of this peak has been carried out. It suggests P_H to be due to the thermomechanical breakway of dislocations pinned by hydrogen atoms. Assumptions made in the present study call further experimental and theoretical work. (author)