Metastable nanocrystalline FCC and BCC Fe-Cu solid solutions were synthesized from elemental powders using a high-energy ball mill in air atmosphere. The structural and morphological changes during mechanical milling were investigated by X-ray diffraction and scanning electron microscopy. The patterns so obtained were analyzed using the X'Pert High Score Plus program. The final product of the mechanical alloying process was nanocrystalline double-phase FCC Cu(Fe) and BCC Fe(Cu) solid solutions with a mean crystallite size in the range of a few nanometers. Moreover, the mechanical alloying of Fe-Cu, in air atmosphere, resulted in partial oxidation to Cu2O and CuO. Prolonged milling supported the formation of CuO oxide and the interdiffusion between FCC-Cu(Fe), BCC-Fe(Cu) and cupric oxide (CuO). Scanning electron microscopy results showed that flattened Fe-Cu powders were laid and welded on each other and tended to form a matrix of randomly welded thin layers of highly deformed particles. (C) 2012 Elsevier B.V. All rights reserved.