Forced mixing and nanoscale decomposition in ball-milled Cu-Ag characterized by APFIM

Ag50Cu50 alloys are prepared by high energy ball milling at different controlled temperatures, 85 K, 315 K and 453 K, with milling times long enough to reach steady-state. Atom probe field ion microscopy (APFIM) is used to characterize the atomic mixing forced by low temperature milling and to study the nanocomposite materials stabilized by elevated temperature milling. A new method is devised that makes it possible to prepare sharp tips from ball-milled powders. Statistical analysis of the APFIM composition profiles is used to determine the degree of mixing as a function of the length scale. These results are compared with the ones obtained from kinetic Monte Carlo simulations. Cryo-milling results in nearly random mixing of copper and silver, whereas the mixing achieved by milling at 315 K is calculated to be around 70%. 453 K milling results in the decomposition into copper-rich and silver-rich regions at a scale of approximate to 25 nm. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.