Author:

Keywords:

Cu-Au, ordering, X ray diffraction, 0204 Condensed Matter Physics, 0912 Materials Engineering, 0913 Mechanical Engineering, Materials

Abstract:

Rod-shaped copper-gold alloys with a gold content in the range 29.8-33.5 at.% were converted either into powder or into single crystals and heat treated so as to form the long period superlattice Cu/sub 3/Au/sub II/. Its structure was studied by means of X-ray diffraction techniques. Cu/sub 3/Au/sub II/ was found to grow directly from the disordered alpha -phase via short range order (SRO) and not via Cu/sub 3/Au/sub I/. Some evidence is given to the idea of alpha rarr Cu/sub 3/Au/sub II/ being a first order transition and to the existence of two two-phase regions: alpha -Cu/sub 3/Au/sub II/ and Cu/sub 3/Au/sub II/-Cu/sub 3/Au/sub I/ in the Cu-Au system. Based on the results of other investigators and of this work a modified phase-diagram is proposed. The period of the superlattice decreases with excess Au atoms and a model for non-stoichiometric Cu/sub 3/-Au/sub II/ is worked out, in which the pairwise interaction energy is reduced by an ordered arrangement of Au atoms near the antiphase boundaries, thereby stabilizing Cu/sub 3/Au/sub II/