Chemical, morphological and corrosion characterisations of electrodeposited Ni-Fe-P coatings

Fe-P, Ni-P and Ni-Fe-P alloys were prepared by galvanostatic electrodeposition over copper electrodes in aqueous media in order to obtain a corrosion resistant layer. All electrodeposits were prepared in optimized conditions at acidic medium (pH < 2.0), using 80 mA cm−2 for Fe-P and Ni-P alloys and 60 mA cm−2 for Ni-Fe-P alloy at 55 °C. The morphology of the electrodeposits was evaluated by scanning electron microscopy, which revealed a nodular, hemispheric grains in Ni-P and Ni-Fe-P alloys and the same grains with cracks in Fe-P alloy. X-ray diffraction (XRD) measurements showed characteristic peaks for Fe and Ni, and P incorporation was observed due to characteristic peak at 2θ ≈ 50°, which means that P atoms amorphized the structure of the electrodeposits. Energy Dispersive X-Ray Spectroscopy (EDS) measurements showed the following composition for all alloys (mass percentage): Fe91.1%-P4.3%, Ni88.5%-P9.7%, Ni46.5%-Fe39.4%-P12.6%. Linear potentiodynamic polarization showed the following order for crescent nobility corrosion potential: Ecorr (Fe-P) < Ecorr (Ni-P) < Ecorr (Ni-Fe-P). Although Ni-P presented lower anodic current values than Ni-Fe-P in polarization curves, the analysis of E-Ecorr polarization curves in these studies showed that Ni-Fe-P and Fe-P coatings had the lowest and highest anodic current values, respectively, among the three electrodeposits. The same trend was observed in electrochemical impedance spectroscopy when a nested circuit for two capacitance events was applied, having Ni-Fe-P layer the highest polarization resistance value among the three and Fe-P the lowest polarization resistance, showing the viability of anticorrosion properties of Ni-Fe-P layers.