FeCrAl / 15-15Ti composite tubes as LFR fuel cladding

The deployment of Lead-cooled Fast Reactors (LFRs) requires fuel cladding materials capable of withstanding the highly corrosive liquid lead environment while maintaining high-temperature mechanical integrity. This study investigates the fabrication of composite fuel cladding tubes consisting of a nuclear-grade 15-15Ti austenitic steel substrate coated with a corrosion-resistant Fe-10Cr-4Al+RE alloy using Laser Micro-Wire Cladding (LMWC). By utilising a fine, 200 µm Fe-10Cr-4Al+RE wire, dense and defect-free coatings were deposited with minimal thermal impact on the thin-walled substrate. Microstructural characterisation using SEM, EBSD, and synchrotron XRD revealed a fine-grained ferritic clad with a low dilution of 7.4%. Elemental analysis of the laser-clad layer showed an inhomogeneous distribution of substrate elements, which remained stratified near the interface, preserving a composition close to the feedstock at the coating’s surface. A detailed analysis of the clad-substrate interface identified a chemically driven phase transformation, where the interdiffusion of Al and Ni destabilised the austenitic substrate, leading to localised transformation to ferrite, and the formation of small-angle grain boundaries. Mechanical testing, including ISO 8492 tube flattening tests, demonstrated exceptional ductility and interfacial adhesion, with the clad layer outperforming the 15-15Ti substrate. These findings validate LMWC as a promising manufacturing route for LFR fuel cladding, capable of producing protective coatings while preserving the certified properties of the underlying pressure boundary material.