Dynamic self-organization in Cu alloys under ion irradiation

Phase separation in dilute Cu_(1-x)Mx films under irradiation with 1.8 MeV Kr⁺ ions at elevated temperatures has been studied for 0.10 < x < 0.15 and M = Ag, Co, Fe, Mo and Nb. In all systems compositional patterning was observed on a mesoscopic length scale within a fixed temperature interval. At lower temperatures most of the alloys formed nearly homogeneous solid solutions, while at higher temperatures these same alloys underwent macroscopic phase separation. The upper temperature limit for patterning increased with decreasing solute diffusivity in the Cu matrix, reported in the absence of irradiation. The heat of mixing of the alloy, however, also played a role in the patterning behavior. For Cu90Mo10, which has a high positive heat of mixing, no upper or lower temperature limits for patterning were observed. Molecular dynamics computer simulations reported here explain why Cu₉₀Mo₁₀ behaves differently from the other alloys.