Early-stage diffusion behavior of Cr-MEA coated Zr alloy accident tolerant fuel cladding materials at high temperature

Although Cr-coated Zr alloy accident tolerant fuel cladding materials have been under in-pile tests in light watercooled nuclear reactors, the Cr-Zr interdiffusion can lead to rapid failure of the coating. To address this issue, a Cr-Fe-Mo-Nb coating was fabricated as a diffusion barrier for Cr-coated Zr alloys. Diffusion tests in inert gas environment and oxidation tests in steam were performed at temperatures up to 1500 degrees C. The configurational entropy of the coating was calculated to be 1.39R, confirming it as a middle entropy alloy (MEA). The MEA layer effectively restricted both the outward diffusion of Zr and the inward diffusion of Cr. After high temperature annealing, Mo-rich segregations were observed, and some tiny pores formed near the Mo-rich particles. The rapid consumption of the barrier layer led to the formation of continuously distributed pores between the coating and Zr substrate, which was detrimental to the coating integrity and adhesion.