THE MICROSTRUCTURE OF CU-AL

The short-range ordered state of thermal equilibrium for a single crys tal of Cu-14.4 at.%Al aged at 483 K has been investigated at room temp erature by diffuse X-ray scattering. From the short-range order scatte ring separated by the Georgopoulos-Cohen method, effective pair intera ctions V-lmn were determined. At least the first 11 V-lmn were require d to reproduce the topology of the short-range order scattering. A str uctural analysis of modeled short-range ordered crystals as well as th e values for the ground state energy of various Ll(2)-based superstruc tures suggest that at low temperatures the D0(23) structure is more st able for stoichiometric Cu3Al than any of the long-period Ll(2)-based superstructures observed at higher temperatures.