The AlNbTiZr medium-entropy alloy (MEA) coatings with different Al contents were prepared on N36 zirconium alloy substrates by RF magnetron co-sputtering. The morphology, microstructure, mechanical properties, surface wettability and corrosion resistance of the AlNbTiZr MEA coatings were studied to evaluate the surface protection behavior of zirconium alloy cladding under operation conditions of a pressurized water reactor. The results showed that all the coatings were composite structures with amorphous and bcc-structured nanocrystals. With the increase of Al content, both the elastic modulus and hardness decreased first and then increased. The hydrophobicity of the coatings was enhanced compared with that of the substrate. The 10.2 at.% Al AlNbTiZr coating had the best corrosion resistance and the minimum oxygen penetration depth, which originated from the formation of a denser oxide layer consisting of Nb₂Zr₆O₁₇ and ZrO₂. This study provides an improved idea for the design and development of Al-containing MEA coating materials for accident tolerant fuel.

The structural evolution of Cr-coated Zr-4 after irradiation was studied via in situ TEM in the temperature range from room temperature to 1000 °C. The results show that the krypton bubbles appeared at ~700 °C, and their size increased with increasing temperatures. The grain size and shape of the irradiated Zr-4 substrate changed with increasing temperature, and finally, columnar crystals appeared, which was related to the compressive stress induced via irradiation. The Cr₂Zr C14 phases formed at both the interface and the substrate at 700 °C and 1000 °C. Moreover, the accelerated failure process of irradiated Cr coating at high temperatures was observed via in situ TEM analysis.

We investigated the impact of Au ion irradiation on the corrosion behavior of medium-entropy alloy coatings (MEAs), with and without Al addition, in simulated primary water of pressurized water reactors (PWRs). The results indicated the formation of double-layer oxide films on the surfaces of both types of coatings, consisting of outer oxide particles and a protective inner oxide layer. The high-fluence irradiation modified the microstructures of both coatings and accelerated their corrosion kinetics. However, the coating with a slight addition of Al demonstrated superior post-irradiation corrosion resistance owing to its enhanced lattice distortion effect within the system, inhibited atomic diffusion, and reduced impact of irradiation on its phase structure. A comprehensive discussion was carried out on the corrosion processes of the coatings, both irradiated and non-irradiated.