Microstructural understanding of CrN layer as a barrier against Cr-Zr interdiffusion in Cr-coated zirconium alloy for accident tolerant fuel claddings
Jianqiao Yang, Bochang Wang, Shurui Hu, Fen Zhao, Bo Han, Lunlin Shang, Yanguang Cui, Shuzhong Wang, Di Yun, Donghai Xu
Abstract
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.