The structural and magnetic properties of mechanically alloyed Fe - Cu - Ag at room temperature have been investigated using Mössbauer spectroscopy, x-ray diffraction and differential scanning calorimetry. The elements are naturally immiscible, but through prolonged and energetic ball milling (70 hours at 600 rpm) one can make metastable alloys, the structure of which depends on the elemental composition. In the binary Cu - Ag and Fe - Cu systems, crystalline single-phase solid solutions result, whereas in Fe - Ag the alloying is limited, with the product a mixture of elemental particles. In the ternary system it is possible to produce copper- and silver-rich single-phase fcc alloys, but not the equivalent bcc iron-based structure. As the proportions of the three elements become more equal, the resulting structure becomes highly disordered or amorphous. The composition range of this amorphous phase is different to that observed in sputtered Fe - Cu - Ag systems.
The thermal properties of metastable Fe-Cu-Ag alloys have been investigated using differential scanning calorimetry, complementing an earlier x-ray diffraction and Mössbauer spectroscopy study. Samples were mechanically alloyed under nitrogen in a high-energy ball mill for 70 hours. DSC and x-ray data on milled and unmilled elemental powders show that Fe sustains more lattice distortion than Cu or Ag, with an rms strain of order 0.6%. In the equimolar binary alloys Fe-Cu, Fe-Ag and Cu-Ag the presence of DSC exotherms below is found to correspond to a gradual decomposition of the alloy, while exotherms above denote recrystallization and grain growth. The absence of low-temperature DSC exotherms in Fe-Ag confirms phase segregation in this granular alloy. In equimolar Fe-Cu-Ag, DSC curves after successive heat treatments indicate a highly disordered state, with fine-scale residual crystallinity. Heating promotes the decomposition of this metastable state into polycrystalline and segregated Fe, Cu and Ag.
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