Microstructure Characteristics of Ferrous P/M Compacts Plated Using Electroless Nickel-Phosphorus Process

To improve fatigue property and corrosion resistance of powder metallurgy (P/W) ferrous parts, a new technique was conducted, in which after compacting a dense surface layer first formed on the green compacts through chemical treatment and then sintering. Green compacts of iron powders were chemically treated by means of electroless nickel-phosphorus (EN) plating before sintering. Samples with the density ranged from 6.2~7.0 g·cm^-3) were used in the experiments. After plating and sintering at temperature of 1 170℃, the morphology of the dense EN coating on various densified samples was examined with a scanning electronic microscope, and energy dispersive spectroscopy was used to analyze the nickel and phosphorus contents of the coating. The result shows that nickel content decreased in a gradient pattern. The diffusion distance of Ni can attain 220 llm, while some phosphorus existed in the form of Fe₂P particles and segregated within ferrous substrate and spherated the porosity of the coating.