Microstructural understanding of CrN layer as a barrier against Cr-Zr interdiffusion in Cr-coated zirconium alloy for accident tolerant fuel claddings

In this study, a Cr-CrN-Cr coating was fabricated on Zr alloy to explore the barrier effect of the CrN layer on Cr-Zr interdiffusion. Steam oxidation tests were conducted using both a thermogravimetric analyzer and a tube furnace to examine the oxidation resistance and coating evolution of the sample under high-temperature conditions. Atomic scale characterizations were performed on the sample after exposure. After HT annealing, a ZrN layer composed of nano equiaxed grains was successfully formed between the residual coating and Zr substrate, serving as a diffusion barrier for both the Cr-Zr interdiffusion and nitrogen/oxygen inward diffusion. Nano twin crystals were observed within the ZrN grains, and the growth of twin boundaries was along multi-directions. The coating evolution during HT annealing was analyzed, and the impact of ZrN layer on the inhibition of Cr-Zr interdiffusion was discussed.