Corrosion Behavior of (Copper/Nickel) step-wise Functionally Graded Materials

The present paper involves studying of the corrosion behaviour of five layers Cu/Ni Functionally Graded Materials (FGMs) in a 3.5 % NaCl solution to examine corrosion potentials (Ecorr.), corrosion current densities (icorr.) and Tafel slope. Three series of FGMs samples, labeled A1-A6, B1-B6, and C1-C6 were prepared using different experimental conditions of compaction pressure (0.7, 1 and 1.3 MPa), sintering temperature (650, 750 and 850oC) and sintering time (1 and 2 hours). The polarisation method was conducted at 3 mV/s of a scan rate, and room temperature. According into the potentiodynamic polarization test, it was found that the sintering time of 2 hrs at constant temperature, and pressure enhances the corrosion potential towards stabilization the protective surface layer. A3, A4 are samples designation corresponding to different experimental settings determined by design of experiments. Corrosion current density measurements showed that A4 sample had the highest (673.20 μA/cm²), while A3 sample had the lowest icorr (0.8508 μA/cm²). Tafel slope analysis revealed that A3 sample had the highest anodic, and cathodic slopes, and was associated with the lowest corrosion rate. The corrosion resistance (Rp) data supported these results, with A3 showing the highest resistance, confirming its superior corrosion resistance (Rp). This behaviour may be related into the noble properties of copper, and the protection of cupric oxide (CuO) compared to (NiO).