Interdiffusion behavior between Cr and Zr and its effect on the microcracking behavior in the Cr-coated Zr-4 alloy

Abstract

High-temperature chromium (Cr)-zirconium (Zr) interdiffusion commonly occurs in Cr-coated zircaloys applied for enhanced accident-tolerant fuel (ATF) claddings. Such interdiffusion changes the interfacial microstructure and thus the fracture mechanism of the coating under external loading. In this study, the interdiffusion behavior in a magnetron sputtered Cr coating deposited on a Zr-4 alloy was studied in a vacuum environment at 1160 °C. In addition, the effect of interdiffusion on the microcracking behavior of the Cr coating was determined by in situ three-point bending tests. The experimental results show that the interdiffusion behavior resulted in the formation of a ZrCr 2 layer, accompanied by the consumption of Cr coating and interfacial roughening. The growth of the diffusion layer followed a nearly parabolic law with respect to annealing time, and the residual stress of the annealed coating decreased with increasing annealing time. Under external loading, a large number of cracks were generated in the brittle interlayer, and some interfacial cracks were formed and grew at the ZrCr 2 /Zr-4 interface. Despite the remarkable microcracks in the ZrCr 2 layer, the vacuum-annealed Cr coating has significantly fewer cracks than the original coating, mainly because of the recrystallization of the coating during annealing.

In-situ study on the tensile property and fracture behavior of Cr coating for nuclear fuel cladding

“…Because of the intermediate diffusion layer's formation, the Zr-4 substrate has excellent adhesion to Cr coating, which will form various intermediate phases but will not affect the substrate and coating's bonding state. [3]. Furthermore, the Cr coating can provide a dense Cr 2 O 3 protective film in a water vapor environment.…”

Microstructural Evolution of Irradiated Cr-Coated Zr-4 under In Situ Transmission Electron Microscopy Heating

“…Regarding the influence of temperature, many studies demonstrated that the phenomenon of structural and composition change in Cr-coated Zr-4 was found at high temperatures, such as phase transition in the substrate, element interdiffusion [20,21], grain coarsening, and void and intermetallic layer generations [22]. Huang et al [23] indicated that the microstructure of the Zr-4 alloy substrate changed via recrystallization at high temperatures, and an intermetallic layer of Cr 2 Zr was formed.…”

“…Huang et al [23] indicated that the microstructure of the Zr-4 alloy substrate changed via recrystallization at high temperatures, and an intermetallic layer of Cr 2 Zr was formed. Jiang et al [20,24] indicated that high temperatures caused the crystallizing morphology of the Cr coating to change from columnar grains to equiaxial grains. Simultaneously, grain coarsening and a brittle intermetallic ZrCr 2 layer formed at the interface, which easily cracked under stress.…”