High-temperature oxidation of thick Cr coating prepared by arc deposition for accident tolerant fuel claddings

A thick Cr coating of about 20 mm is prepared by using a large arc-source deposition system on Zr-4 alloy substrate, for the purpose of testing high-temperature accident tolerance of fuel claddings. The coating system, made by Dalian Nano-Crystal Tech, Co., Ltd, is equipped with large arc sources of phi 155mm in diameter that fabricates thick coatings rapidly (> 3 mu m/h). The coating is heated at 1000 degrees C, 1100 degrees C, and 1200 degrees C for 1 h and is cooled in air down to room temperature. After the oxidation, the thick Cr coating presents three different layers, top oxide Cr2O3, residual Cr, and Cr-Zr inter-diffusion layer. It is noted especially that even after the toughest test (1200 degrees C/1 h), the outer oxide layer remains continuous and well adheres to the Zr-4 substrate, with a residual Cr layer thickness of 6.8 mm. This result clearly suggests that the 20 mu m Cr coating has sufficient accident tolerance. Sub-surface voids are frequently observed, the formation of which is clearly related to Sn/Cr segregations and transformation from beta-Zr(O) to brittle alpha-Zr in the substrate alloys near the surface. (C) 2019 Elsevier B.V. All rights reserved.