In-situ study on the tensile behavior of Cr-coated zircaloy for accident tolerant fuel claddings

In this study, the tensile behavior of Cr-coated zircaloy (Zr-4) for accident tolerant fuel claddings was investigated by in-situ observation and finite element (FE) analysis. The evolution of surface cracks in the Cr coating was experimentally observed, and the surface crack density was precisely predicted by the shear-lag model considering the effect of the residual stress. Moreover, the interfacial cracking behavior was numerically analyzed using the cohesive zone model. Finally, the interfacial fracture parameters of the coating system were evaluated based on the experimental results and FE calculations. The results exhibited that after the initiation, the surface crack density increased rapidly with the tensile strain, followed by a plateau stage under continuous tension. The fracture strength and interfacial shear strength of the Cr coating were evaluated as 382 MPa and 108 MPa, respectively. In addition, no interfacial spallation occurred under tension, indicating excellent interfacial adhesion properties of the Cr coating. However, a few short interfacial cracks were found to be initiated from the vertical crack tips, owing to the large local interfacial peeling and shear stresses. The FE analyses suggested that the lower limits of the interfacial fracture strength, sigma(0) , and the fracture toughness, G(c), of the Cr coating were in the range of 100 MPa-150 MPa and 100 J/m(2) -125 J/m(2) , respectively. Concurrently, sigma(0) and G(c), for the entire Cr coating-Zr-4 substrate system were estimated to be generally large, i.e., above 250 MPa and 200 J/m(2), respectively.