Mechanosynthesis of Nanocrystalline Biphasic Ni-Fe Alloy Powders by Mechanical Alloying and Their Structural and Thermal Characterization

An equiatomic Ni-Fe alloy was synthesized through mechanosynthesis, under an argon atmosphere using a planetary ball mill, after 100 h. To assess the phase stability, the alloy was subsequently annealed at 923.15 K for 2 h. At the end of mechanosynthesis, X-ray diffraction analysis revealed the formation of two distinct solid phases, FCC γ-NiFe (wt% = 90.3%) and BCC α-FeNi (wt% = 9.7%). The lattice parameter of the FCC phase stabilized at 3.5748 Å, whereas the BCC phase exhibited a lattice parameter of 2.6608 Å. The average crystallite size was determined to be around 7 nm with the lattice strains quantified as 0.48% for both phases. This significant refinement of microstructure indicates extensive plastic deformation within the grains. Scanning electron microscopy revealed an angular particle morphology with an average particle size of 8.15 µm. Differential scanning calorimetry (DSC) analysis identified an exothermic transition at 623.15 K, corresponding to the Curie temperature of nickel, and another one at 873.15 K, attributed to the Curie temperature of Ni3Fe. These results demonstrate the efficiency of mechanosynthesis in producing biphasic Ni-Fe nanomaterials with tailored properties, characterized by a dominant FCC phase with a highly deformed nanocrystalline structure. These findings highlight the great influence of mechanical milling on the structural properties of the Ni-Fe alloy in terms of a high density of stored crystalline defects.