Abstract
Cu-Ni alloys contain clusters of one type of atom. These clusters have a mean size of 44 atoms in an almost equiatomic alloy, annealed for 50 h at 300°C. At least 18% of the alloy undergoes this segregation. These results are in accordance with many physical properties of these alloys but throw some doubt on the conclusions of recent works about the inapplicability of the rigid-band model to this system.