Synthesis of Invar alloy powders by electroless plating

The preparation of Invar powders was attempted by electroless nickel (EN) coating on iron powders followed by heat treatment. The experimental results showed that a pretreatment in slight alkaline solution before EN coating was required to obtain a uniform deposit of Ni on Fe powder. The amount of Ni, which meets the Invar composition could be coated by adjusting the EN solution volume-to-Fe weight ratio. X-ray diffraction, energy dispersive spectroscopy and X-ray mapping were employed to examine the homogeneity of the various heat-treated EN-coated powders. A homogeneous Fe–Ni powders with Invar composition could be successfully synthesized with proper control of the EN bath and subsequent heat treatment. In this study, no deflocculant was added in the plating bath. The van der Waals forces between the as-coated particles caused them to attract each other. As revealed in Figs. 4 and 8(c), a clear Ni layer appeared in the interface of the agglomerated particles. These results indicated that agglomeration occurred right after EN coating, regardless of post heat treatment.