ON THE RELATIONSHIPS BETWEEN THE SELF-DIFFUSION PARAMETERS AND THE THERMODYNAMIC PROPERTIES IN B2 INTERMETALLIC COMPOUNDS

The activation energies and pre-exponential factors for the self-diffu sion coefficients in B2 intermetallic compounds are shown to be relate d to the partial molar enthalpies and entropies of the component eleme nts. The frequently observed decreases of the activation energy and pr e-exponential factor with deviations from stoichiometry are in accord with the corresponding decreases in the partial molar enthalpy and ent ropy. The extensive amounts of experimental data for NiAl are used to verify these relationships. It was found that the decrease of the expe rimentally determined activation energies for Ni in NiAl are in reason able agreement with the decrease in partial enthalpy. The agreements b etween the decrease of the pre-exponential factor and partial entropy are excellent in view of the fact that the experimental values cover f ive orders of magnitude.