Dynamic Polarization Behaviors of Equimolar CoCrFeNi High-Entropy Alloy Compared with 304 Stainless Steel in 0.5 M H2SO4 Aerated Aqueous Solution

• Published in: Materials 2022-10, Vol.15 (19), p.6976
• Main Authors: Yen, Chao-Chun, Tsai, Ting-Lun, Wu, Bo-Wei, Lo, Yu-Chieh, Tsai, Ming-Hung, Yen, Shiow-Kang
• Format: Article
• Language: English
• Subjects: Aeration; Alloys; Anodic polarization; Aqueous solutions; Austenitic stainless steels; Bond energy; Cathodic polarization; Corrosion currents; Corrosion potential; Corrosion resistance; Current density; Density functional theory; Electrodes; Energy; First principles; High entropy alloys; Intermetallic compounds; Manganese; Mass spectrometry; Metals; Oxide coatings; Scientific imaging; Stainless steel; Sulfuric acid
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma15196976

Three corrosion potentials and three corrosion current densities are clearly identified before the passivation for both dynamic polarization curves of equimolar CoCrFeNi high-entropy alloy (HEA) and 304 stainless steel (304SS) in 0.5 M H2SO4 aerated aqueous solution, by decomposing anodic and cathodic polarization curves. The passivated current density of the former is greater than the latter, compliant with not only the constant of solubility product (ksp) and redox equilibrium potential (Eeq) of each metal hydroxide but also the sequence of bond energy (Eb) for monolayer hydroxide on their facets derived from the first principle founded on density function theory. However, the total amount of ion releasing from HEA is less than 304SS, since the hydroxide/oxide film formed in the air of the latter containing greater amounts of Fe(Ⅱ) and Mn(Ⅱ) is less stable around corrosion potentials while they are further oxidized into more stable Fe(Ⅲ) and Mn(ⅢorⅣ) with much lower ksp, leading to the much less increasing ratios of ion releases from 0.25 to 0.6 V.