FATIGUE CRACK GROWTH CHARACTERISTICS OF CR-COATED ZIRCONIUM ALLOY CLADDING TUBES

Chromium (Cr)-coated zirconium (Zr) alloy cladding has attracted considerable attention in the field of accident-tolerant fuels owing to its excellent high-temperature oxidation resistance and accident tolerance. However, the effect of Cr coatings on the fatigue crack growth behavior of Zr alloy cladding remains insufficiently understood, particularly regarding the quantitative influence of coating thickness on fatigue crack growth characteristics. In this study, fatigue crack growth tests were performed on uncoated, 10 μm Cr-coated, and 15 μm Cr-coated Zr alloy cladding tubes. Crack length-cycle number curves and average crack growth rates under different coating conditions were determined, enabling quantitative comparison of crack growth responses among the three coating conditions. Finite element analysis was further conducted to examine the effect of coating thickness on the local stress distribution near the root of the initial notch. This analysis was used to clarify the mechanical origin of the experimentally observed thickness effect. The results show that the effect of the Cr coating on crack growth behavior is strongly thickness-dependent. Under the same loading conditions, the average crack growth rate of the 15 μm Cr-coated specimens was reduced by approximately 19.4%-43.6% compared with that of the uncoated specimens, indicating a retardation of crack growth. In contrast, the average crack growth rate of the 10 μm Cr-coated specimens increased by approximately 20.3%-27.5%, showing no crack growth suppression effect. Finite element analysis indicates that the mismatch in elastic modulus between the Cr coating and the Zr substrate alters the local stress distribution near the notch root. A thicker coating helps reduce the local tensile stress and thereby retards crack growth, whereas a thinner coating increases the local tensile stress and accelerates crack growth. These results reveal the role of coating thickness in regulating crack growth behavior and provide experimental evidence and mechanical insight for thickness optimization and damage-tolerance design of Cr-coated Zr alloy claddings.