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

Abstract

A thick Cr coating of about 20 μm 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 ϕ155mm in diameter that fabricates thick coatings rapidly (>3 μm/h). The coating is heated at 1000 °C, 1100 °C, and 1200 °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 °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 μm. This result clearly suggests that the 20 μm 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 β-Zr(O) to brittle α-Zr in the substrate alloys near the surface.