Hydrogen-probe mechanical spectroscopy for studying local ordering in concentrated substitutional alloy

the Fe–35.5 at.% Ni FCC invar alloy was carried out. This alloy experiences spinodal decomposition to Ni-enriched and Nidepleted regions, and the Fe3Ni and FeNi type ordering in each of the regions. It was shown that hydrogen Snoek peaks in this alloy, observed in the vicinity of 185 K, substantially change in amplitude after 3 MeV electron irradiation, or after ageing at 600°C. An analysis of the structure of the Snoek peaks was performed on the basis of modern concepts of hydrogen-probe mechanical spectroscopy. It was shown that the main contribution to relaxation is due to transitions of hydrogen atoms between octahedral interstitial sites containing three atoms of Fe and three atoms of Ni in the vertices of octahedra. The influence of the substitutional atomic order in invar on the hydrogen Snoek peak was discussed.