# Sustainable High Corrosion Resistance in High-Concentration NaCl Solutions for Refractory High-Entropy Alloys with High Strength and Good Plasticity

## TL;DR

A new alloy shows high corrosion resistance and strength in salty environments, outperforming stainless steel.

## Contribution

A refractory high-entropy alloy with exceptional corrosion resistance and mechanical properties in high-salt conditions is introduced.

## Key findings

- The alloy shows better corrosion resistance in 23.5 wt.% NaCl than 304 L stainless steel.
- The alloy's corrosion current density is two orders of magnitude lower than stainless steel.
- The alloy maintains high strength and plasticity with carbon addition.

## Abstract

Among corrosive environments, Cl− is one of the most aggressive anions which can cause electrochemical corrosion and the resultant failures of alloys, and the increase in Cl− concentration will further deteriorate the passive film in many conventional alloys. Here, we report single-phase Nb25Mo25Ta25Ti20W5Cx (x = 0.1, 0.3, 0.8 at.%) refractory high-entropy alloys (RHEAs) with excellent corrosion resistance in high-concentration NaCl solutions. According to potentiodynamic polarization, electrochemical impedance spectroscopy, corroded morphology and the current–time results, the RHEAs demonstrate even better corrosion resistance with the increase in NaCl concentration to 23.5 wt.%, significantly superior to 304 L stainless steel. Typically, the corrosion current density (icorr) and over-passivation potential (Et) reached the lowest and highest value, respectively, in the 23.5 wt.% NaCl solution, and the icorr (2.36 × 10−7 A/cm2) of Nb25Mo25Ta25Ti20W5C0.1 alloy is nearly two orders lower than that of 304 L stainless steel (1.75 × 10−5 A/cm2). The excellent corrosion resistance results from the formation of passive films with fewer defects and more stable oxides. Moreover, with the addition of the appropriate C element, the RHEAs also demonstrated improved strength and plasticity simultaneously, for example, the Nb25Mo25Ta25Ti20W5C0.3 alloy exhibited an average yield strength of 1368 MPa and a plastic strain of 19.7%. The present findings provide useful guidance to address the conflict between the excellent corrosion resistance and high strength of advanced alloys.