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

An experimental study of the influence of substitutional atomic order on hy drogen Snoek peaks in the Fe-35.5 at.% Ni FCC invar alloy was carried out. This alloy experiences spinodal decomposition to Ni-enriched and Ni-deplete d 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 irradiati on, or after ageing at 600 degrees C. An analysis of the structure of the S noek peaks was performed on the basis of modern concepts of hydrogen-probe mechanical spectroscopy. It was shown that the main contribution to relaxat ion is due to transitions of hydrogen atoms between octahedral interstitial sites containing three atoms of Fe and three atoms of Ni in the vertices o f octahedra. The influence of the substitutional atomic order in invar on t he hydrogen Snoek peak was discussed. (C) 2000 Elsevier Science S.A. All ri ghts reserved.