Mechanical behaviors of Cr coating on Zircaloy tubes prepared by pulsed laser deposition

Chromium-coated Zircaloy cladding is one promising candidate for accident-tolerant fuel (ATF), yet its mechanical reliability under loading remains insufficiently understood. This study aims to investigate the cracking behavior and fracture resistance of a thin nanocrystalline/amorphous chromium (Cr) coating fabricated by pulsed laser deposition (PLD) under hoop tensile strain. A 350-nm-thick Cr bilayer coating was deposited onto Zircaloy-4 substrates, and its hoop tensile response was evaluated using the advanced expansion due to compression (A-EDC) test. Key mechanical properties, including Young’s modulus (227 GPa), hardness (13.3 GPa), and residual stress (-1450 MPa), were measured by nanoindentation and X-ray diffraction (XRD). Detailed analyses by scanning electron microscopy (SEM) revealed the evolution of transverse and slanted cracks under increasing strain, with a superior first cracking strain of 3.2 %. A crack density-strain relationship was established and used to estimate the fracture strength (5.8 GPa) and interfacial shear strength (980 MPa) via a shear-lag model. The findings highlight the mechanical advantages of the nanocrystalline/amorphous structure, including grain refinement strengthening and the ductile-buffering effect of the amorphous layer. This study provides a new mechanical perspective for advancing the Cr-coated Zircaloy claddings for ATF applications.