Computer Simulation of the Structure Associated with Local Order in Alloys

Abstract

Atomic configurations of binary alloys have been generated by a computer using experimentally measured short-range and long-range order parameters and 4000-16 000 atoms. This program did not use energetic considerations; atoms were selected at random and interchanged, if the change in the parameters was toward the experimental values, until computed and experimental values coincided. In systems based on the fcc lattice it is shown that the three first short-range order parameters are sufficient to give a reliable picture of the structure of the real alloy. For ${\mathrm{Cu}}_3$Au above the critical temperature, small ordered volumes suspended in a random matrix were observed. Below the critical temperature, two-dimensional antiphase domains were found. For ${\mathrm{Cu}}_{72}$ ${\mathrm{Au}}_{28}$ the regions were two-dimensional at low temperatures, but three-dimensional closer to the critical temperature. Some of the excess Au atoms were found in domain boundaries. The rest of them were distributed at random over the matrix. With Cu-14 at.% Al, there were chains of Al second neighbors. The results are discussed in terms of a number of experimental observations and theroetical suggestions.