The advancement of Generation IV Lead-cooled Fast Reactors (LFRs) is critically dependent on the development of fuel cladding materials capable of withstanding severe liquid metal corrosion (LMC) while maintaining high-temperature creep strength and radiation tolerance. Standard nuclear-grade austenitic steels, such as 15-15Ti, offer proven radiation tolerance but suffer from rapid dissolution in liquid lead environments. Conversely, alumina-forming alloys such as Fe-10Cr-4Al + RE (FeCrAl) exhibit superior corrosion resistance but lack adequate high-temperature mechanical properties and are susceptible to irradiation swelling. A promising solution is the fabrication of composite fuel rods, in which a thin, protective FeCrAl layer is deposited onto a 15-15Ti base tube with a wall thickness of 0.5 mm. However, conventional cladding processes utilising powders or macro-wires (>1 mm) are unsuitable for this application due to excessive heat input, which causes high dilution, coarse-grained microstructures, and adverse effects on the base tube.

This dissertation develops and investigates Laser Micro-Wire Cladding (LMWC), using a 200 μm diameter wire, as a manufacturing process for composite nuclear fuel tubes. The central research challenges addressed include understanding the process characteristics, the determination and optimisation of stable processing parameters and techniques, resolving the relationship between process variables and material characteristics, and the assessment of LMWC as a manufacturing process for LFR fuel rods. By employing custom high-speed imaging (HSI) and comprehensive microstructural characterisation, this research advances the understanding of the complex size effects associated with downscaling laser wire cladding. A shift in melt transfer is identified, replacing the conventional spreading melt pool with a surface-tension-dominated 'melt bridge'.

To counteract inherent melt transfer instability and the flexibility of the thin wire feedstock, a novel wire-bending technique was developed, enforcing consistent wire-to-substrate contact and expanding the stable process window. This technique was subsequently coupled with an investigation into process parameters, revealing that laser spot size and track overlap are essential parameters to control in order to balance wetting behaviour and heat input, thereby minimising porosity and dilution.

The LMWC process was used to manufacture FeCrAl/15-15Ti composite tubes that were analysed by SEM, EDS, EBSD, synchrotron XRD, and APT, demonstrating defect-free claddings with a suitable microstructure and adequate mechanical properties. Furthermore, the uniquely calm melt dynamics of LMWC restrict mixing, confining diluted substrate elements close to the interfacial region. At this interface, elemental counter-diffusion drives a localised phase transformation in the substrate from austenite to fine-grained ferrite. Crucially, the low thermal input confines the heat-affected zone to less than 150 μm, successfully preserving the precipitates and the bulk mechanical properties of the underlying pressure boundary.

Finally, this work demonstrates that the fully ferritic cladding’s grain morphology can be independently tuned through process parameter selection. Refining the microstructure suppresses the inherent susceptibility of FeCrAl to brittle cleavage fracture, yielding a highly ductile coating. This work validates that LMWC is a robust manufacturing technology capable of producing metallurgically bonded, defect-free, and accident-tolerant fuel claddings for next-generation nuclear reactors.