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

摘要

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 1160C.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 ZrCr2 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 ZrCr2/Zr-4 interface.Despite the remarkable microcracks in the ZrCr2 layer,the vacuum-annealed Cr coating has significantly fewer cracks than the original coating,mainly because of the recrystallization of the coating during annealing.