Cr₄₀Co₄₀Ni₂₀ Multi-Principal Element Alloy Outperforms Inconel 625: A Passivation and Corrosion Resistance Study in Chloride Media

The corrosion resistance of the Cr₄₀Co₄₀Ni₂₀ multi-principal element alloy was evaluated in chloride-rich electrolyte. The alloy was synthesized via vacuum induction melting and subjected to thermomechanical processing, including homogenization at 1100 °C, rolling to a final thickness of ∼1 mm, and recrystallization heat treatment at 1050 °C for 30 min. Structural characterization using X-ray diffraction, scanning electron microscopy, and electron backscatter diffraction confirmed a refined and homogeneous single-phase microstructure with an average grain size of ∼20 μm. The corrosion behavior was analyzed through cyclic potentiodynamic polarization and electrochemical impedance spectroscopy in 0.6 M and 0.1 M NaCl solutions. The results revealed that Cr₄₀Co₄₀Ni₂₀ alloy is corrosion-resistant, forming a highly protective and stable passive film. The polarization resistance was measured at 200 kΩ·cm² in 0.6 M NaCl, significantly higher than the ∼120 kΩ·cm² observed for Inconel 625, indicating superior passivation. Electrochemical impedance spectroscopy analyses demonstrated a capacitive-like response with phase angles close to −85° and a resistivity at metal/oxide interface profile suggesting an insulator-like passive layer with a resistivity of 10⁹ Ω·cm, outperforming Inconel 625.