Investigation of mechanosynthesized Fe50Ni40Al10 powders

The synthesis of Fe50Ni40Al10 powder mixture has been performed in a high-energy planetary ball mill. The phase transformations and structural changes occurring during mechanical alloying were investigated by X-ray diffraction (XRD) and Mössbauer spectroscopy. XRD analysis and Rietveld method revealed the formation of a single nanocrystalline fcc γ-Ni(Fe,Al) solid solution with a lattice parameter close to aγ-Ni(Fe,Al)=0.3612 nm, after 4 h of milling. The final powder is characterized by an average crystallite size of 14 nm accompanied by the introduction of a lattice strain of order of 1.37%. These values are markedly higher than those reported for mechanically alloyed Fe50Ni50 powders. It was found that the formation of the bcc phase, which coexisted with the fcc structure in the Fe-Ni phase diagram, was inhibited. However, mechanical alloying process gives rise to the Ni3Al intermetallic phase, at the early stages of milling. Mössbauer spectroscopy showed that all powders exhibited a ferromagnetic behavior and no paramagnetic phase was detected. The addition of low aluminium content caused more broadening of hyperfine field distributions and lower magnetic field due to the diffusion of Al atoms into γ-FeNi lattice.