Thermal analysis of metastable Fe-Cu-Ag prepared by mechanical alloying

The thermal properties of metastable Fe-Cu-Ag alloys have been investigated using differential scanning calorimetry, complementing an earlier x-ray diffraction and Mossbauer 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 400 degrees C is found to correspond to a gradual decomposition of the alloy, while exotherms above 400 degrees C 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.