Etude radiocristallographique des transformations d'ordre de type α_désordre<->I_ordre dans les alliages ternaires or cuivre nickel et l'alliage binaire de composition remarquable AuCu₃

The study of the scattering outside the Bragg reflexions shows no local order in the ordered phase I of alloys such as Au (50 at. %) Cu (46 at. %) Ni (4 at. %) even for the smallest degree of long range order. The modulation of the scattering appears only with the presence of short range order in the disordered α phase. There is evidence of a two-phase region on the equilibrium diagram at the AuCu₃ stoichiometric composition.