A first-principles study on the early-stage corrosion of a NiWNb alloy in a chloride salt environment

TL;DR

This study uses first-principles calculations to analyze early-stage corrosion behavior of a NiWNb alloy in chloride salt, revealing that alloying elements enhance corrosion resistance and resist pitting, informing better material design for reactors.

Contribution

It provides a detailed atomic-level understanding of how NiWNb alloy components resist chloride-induced corrosion, which is novel for this alloy in salt environments.

Findings

Niobium and tungsten improve corrosion resistance.

Alloy constituents resist chlorine-induced dissolution up to 1/3 monolayer.

Chlorine prefers to adsorb on niobium sites.

Abstract

In this work a representative nickel superalloy, Ni70W20Nb10, was investigated in the presence of chlorine to quantify its early-stage dissolution behavior. Surface structures were generated from a bulk configuration sampled in equilibrium using a multi-cell Monte Carlo method for phase prediction. The predicted solid-phase at 800 C was Ni72W19Nb9 in a body-centered tetragonal crystal structure closely resembling the Ni4W structure. Chlorine adsorption onto the energetically favored (110) surface showed preference to niobium which acted as a trapping sink on the top surface of the slab model. Our findings suggested that niobium and tungsten enhanced the corrosion resistance of nickel as their presence created regions that were thermodynamically preferred by the incoming chlorine and less susceptible to chlorine-facilitated dissolution from the alloy. Nickel, niobium, and tungsten resisted chlorine-induced dissolution from the surface model up to a 1/3 monolayer coverage of chlorine indicating that all constituents of this alloy possessed superior resistance to localized surface degradation such as corrosive pitting. Further analysis and comparisons between the corrosion resistance of the three metallic species was performed. This work may provide insights that aid in the development of improved structural materials for molten salt reactors.