Enhancing the radiation- and oxidation-resistance of Cr-based coatings via structure regulation and composition optimization

Abstract

Cr coatings, as protective coatings of Zr-alloy fuel claddings, inevitably suffer from irradiation damage before they would possibly run into the accident condition. This study evaluates the radiation and oxidation tolerance of three Cr-based coatings with different microstructures (Cr, CrAlSi, and CrAlSiN) through He2+ ion irradiation and 1200 °C steam oxidation. The Cr and CrAlSi coatings experienced significant structural degradation, characterized by He bubble aggregation and amplified Kirkendall effects at elevated temperatures. In contrast, the irradiated CrAlSiN coating maintained structural integrity without measurable irradiation hardening. Following annealing at 800 °C for 30 min, approximately 40 % of injected He atoms were released, indicating a “self-healing” mechanism. The mechanism is attributed to uniformly distributed, low-density channels that act as sinks and release paths for irradiation-induced defects. Density functional theory simulations suggest that N atoms promote significant rearrangement of ions surrounding the free volume, inhibiting the formation of sites capable of trapping He atoms. Moreover, the CrAlSiN coating exhibited superior oxidation resistance compared to the Cr and CrAlSi coatings, even under high-temperature steam conditions. Notably, the irradiated CrAlSiN sample displayed a significantly thinner oxide scale compared to the pristine one (almost half), owing to a more protective oxide scale and rapid outward diffusion of Cr, Al, and Si through nanochannel veins. These findings illuminate the effects of structure and composition on irradiation and oxidation behavior in Cr-based coatings, offering insights for developing new-generation accident-tolerance fuel coatings for Zr-alloy claddings.