Proton irradiation-decelerated intergranular corrosion of Ni-Cr alloys in molten salt

Weiyue Zhou,Yang Yang,Michael P Short,Kevin B Woller,Peter W Stahle,Guiqiu Zheng,Andrew M Minor

doi:10.1038/s41467-020-17244-y

Abstract

The effects of ionizing radiation on materials often reduce to “bad news”. Radiation damage usually leads to detrimental effects such as embrittlement, accelerated creep, phase instability, and radiation-altered corrosion. Here we report that proton irradiation decelerates intergranular corrosion of Ni-Cr alloys in molten fluoride salt at 650 °C. We demonstrate this by showing that the depth of intergranular voids resulting from Cr leaching into the salt is reduced by proton irradiation alone. Interstitial defects generated from irradiation enhance diffusion, more rapidly replenishing corrosion-injected vacancies with alloy constituents, thus playing the crucial role in decelerating corrosion. Our results show that irradiation can have a positive impact on materials performance, challenging our view that radiation damage usually results in negative effects.

Highlights

The effects of ionizing radiation on materials often reduce to “bad news”
We show that proton irradiation can decelerate corrosion of Ni–Cr alloys in molten salt, contradicting radiation accelerated corrosion observed in liquid lead[14], molten salt[15], and waterbased environments[1] while corroborating others[16]
In our Ni–Cr binary alloy, Cr is preferentially depleted by molten salt because the redox potential of Cr is considerably lower than that of Ni in our LiF–NaF–KF+EuF3 (FLiNaK+EuF3) fluoride salt[19]

Summary

Introduction

The effects of ionizing radiation on materials often reduce to “bad news”. Radiation damage usually leads to detrimental effects such as embrittlement, accelerated creep, phase instability, and radiation-altered corrosion. Observations of structural materials from the Molten Salt Reactor Experiment showed low corrosion rates[5]. This suggests that the influence of irradiation on corrosion in molten salts might be different from that in water-based systems. We show that proton irradiation can decelerate corrosion of Ni–Cr alloys in molten salt, contradicting radiation accelerated corrosion observed in liquid lead[14], molten salt[15], and waterbased environments[1] while corroborating others[16]. To explore the contribution of possible interactions, we first show that proton irradiation renders the salt more corrosive by a comparative experiment showing radiation accelerated corrosion in pure Fe. a deceleration mechanism has to exist for the case of Ni–Cr alloys, which we propose to be the coupling between radiation-enhanced diffusion and corrosion-driven fluxes

Methods

Results

Conclusion