Investigating the Influence of Cr and Mo Additions to Commercial Ni-Based Alloys Exposed to Neutral and Acidic Chloride Solutions

Abstract

The corrosion behaviour of four commercially available Ni-based alloys is presented for both natural and potential-controlled corrosion in chloride solutions. Electrochemical evidence suggests a balance of Cr and Mo is essential to maintaining passive film stability in chloride solutions, especially those in which acidic conditions may develop. In near-neutral solutions, increased Cr content results in lower corrosion rates and improved passive properties; however, an increase in Cr content above 15 wt.% provided only minor additional benefits. In acidic solutions, Mo content is essential to corrosion resistance and imparts two major benefits: increased film stability and rapid repassivation of breakdown events. Since localized corrosion and the critical chemistry which accompanies these processes are of concern in many chloride-containing applications, a delicate balance of Cr and Mo must be considered; although optimal concentrations have yet to be determined.

Investigating the Role of Mo and Cr during the Activation and Passivation of Ni-Based Alloys in Acidic Chloride Solution

“…According to previously reported polarization resistance (R P ) values, these current transients are commonly accompanied by potential transients ⩽ 3 mV. 30 During repeated activation processes, momentary increases in dissolution rates were consistently observed during the spontaneous passivation of alloy C-22 and, to a lesser extent for alloy BC-1. It is worth mentioning that with each dissolution transient, the separation between ν′ Mo (and ν′ Cr ) and ν Ni increased, suggesting an increased accumulation of Mo species following an "event" which then slowly approached congruent behaviour.…”

“…switched from net anodic to net cathodic between ∼-0.13 and -0.11 V, as previously observed for this alloy and shown to be due to the reduction of O 2 dissolved in the solution. 30 The electrochemical current densities (j e ) shown in Fig. 1, were compared to the elemental current densities obtained from AESEC measurements.…”

Potential Dependent Mn Oxidation and Its Role in Passivation of Ni38Fe20Cr22Mn10Co10Multi-Principal Element Alloy Using Multi-Element Resolved Atomic Emission Spectroelectrochemistry

“…Layered oxide circuit models were used to simulate the effect of a duplex oxide, as reported for a near equiatomic Ni-Fe-Cr-Mn-Co MPEA following high temperature oxidation 52,53,54 and aqueous passivation at room temperature. 26,27,39 For a Ni 38 Fe 20 Cr 22 Mn 10 Co 10 MPEA at E ap = 0.0 V vs SCE 27,39 and Ni 78 Cr 22 binary alloy, 41,55,56 57,58 was utilized (Fig. 8b).…”

Effect of Minor Mo Addition on Microstructure and Corrosion Resistance of High-Velocity Air Fuel-Sprayed Fe-Based Amorphous Coatings

“…Additionally, Ni can improve the forming ability of Fe-based amorphous alloys, because it belongs to the same period as Fe with the adjacent position in the periodic table, sharing similar atomic radii, outer electronic structures, and physicochemical properties with Fe. Similar atomic substitution can improve the chaos of amorphous alloy systems [4,19]. Therefore, Ni and Cr elements were added to the Fe-(B, Si)-Nb amorphous alloy system to form the FeNbBSiCrNi alloy.…”