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

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.

Neutron Irradiation of Alloy N and 316L Stainless Steel in Contact with a Molten Chloride Salt

“…This mechanism is not likely relevant to molten salt because a protective oxide scale does not form. The previously mentioned study by Zhou et al [13] attributed irradiation decelerated corrosion of a Ni-Cl alloy in FLiNaK salt to a solid-state mechanisms in which irradiation-produced interstitials aided the migration of Ni to grain boundaries, resulting in a "self-healing" effect. Again, if this mechanism was active in the present experiment, there is no explanation for why it is not active in alloy N, other than concluding that the total attack in the alloy N samples were too low to show any significant effects.…”

“…Zhou et al conducted experiments in which Ni-Cr alloys were exposed to FLiNaK salt while simultaneously irradiated with a proton beam, and found that irradiation decelerated corrosion of the alloy [13]. They attributed this deceleration to grain boundary self-healing due to the abundance of irradiation-produced interstitials in the irradiated alloy This paper reports the method and results of an experiment in which molten salt capsules were exposed to neutron irradiation to study the effect of radiation on material corrosion.…”

Application of NEAMS Codes to Capture MSR Phenomena

“…Another phenomenon that needs further experimental investigation is the effect of irradiation on corrosion. Recent studies have shown that proton irradiation decelerated intergranular corrosion of Ni-Cr alloys in molten salts [29]. It is unclear if neutron irradiation will have the same effect, but additional experiments are warranted.…”

The effect of Cr alloying on defect migration at Ni grain boundaries

“…As one example of the importance of understanding the fundamental mechanisms of transport within GBs of alloys, consider recent experiments by Zhou et al that examined the corrosive behavior of Ni-Cr alloys in contact with FLiNaK molten salt [15]. They found that the salt preferentially attacks the GBs and, further, preferentially leaches out the Cr from the GBs.…”