Nanocomposites stabilized by elevated-temperature ball milling of Ag₅₀Cu₅₀ powders: An atom probe tomographic study

Ag₅₀Cu₅₀ alloys were prepared by high-energy ball milling at 393, 423, and 453 K. Atom probe tomography was used to characterize the microstructure and the local composition of the milled powders. The dynamical competition between the atomic mixing forced by milling and the phase separation promoted by thermodynamic driving forces results in the self-organization of the microstructure into compositional patterns. Three-dimensional atom reconstructions show that the length-scale of the compositional patterns increases with increasing milling temperature, from about 1 nm at 393 K to 3-5 nm at 423 K and 5-10 nm at 453 K. Interfaces of the nanocomposites produced by milling at 423 and 453 K, analyzed using the proxigram technique, are found to be quite diffuse, ∼2 nm. The results are discussed in the light of a new analysis of the chemical mixing forced by plastic deformation, and its role in the stabilization of compositional patterns.