MECHANICAL RELAXATION DUE TO HYDROGEN-SOLUTE COMPLEXES IN DILUTE NI-TI-H ALLOYS

Dilute nickel alloys charged with hydrogen are known to exhibit an int ernal friction peak, which is attributed to the reorientation of hydro gen-solute atom pairs. In order to determine the geometrical configura tion of the pair, we have studied anisotropy of the relaxation strengt h in dilute Ni-Ti-H alloy single crystals by low-frequency internal fr iction measurements. The orientation dependence of the peak height sug gests that the defect symmetry is [111] trigonal. One of the possible configurations is the Ti-H pair in which hydrogen occupies the second neighbour octahedral sites around the substitutional solute atom. The peak has been found to be suppressed by an external magnetic field, in dicating that magneto-elastic effects play an important role.