Review of state-of-the-art and research frontiers in single-crystal turbine blade repair by laser directed energy deposition

Single-crystal (SX) turbine blades are widely used in aerospace turbine engines owing to their excellent high-temperature performance and creep resistance. However, they are exposed to harsh service environments, resulting in various forms of damage, such as wear, cracking, surface ablation, and corrosion, during service. In conventional engine maintenance, the damaged turbine blades are typically replaced by new ones. However, this approach is extremely cost-intensive and leads to significant wastage of resources and energy. Laser-directed energy deposition (L-DED) offers an advanced and efficient solution for repairing SX turbine blades, enabling the regeneration of SX microstructures or restoration of high-performance components, thereby significantly reducing repair costs and extending the blade service life. This paper systematically reviews the current research on L-DED repair technologies for SX turbine blades. Beginning with the theoretical basis of solidification, the competition between epitaxial growth and columnar-to-equiaxed transition (CET) in solidification dynamics is addressed, and the effects of process parameters on the repair of SX turbine blades are elucidated. Focusing on the multi-scale and multi-physics phenomena in the melt pool during repair, the relationship between the melt-pool characteristics and solidification microstructure is thoroughly discussed. In addition, the current methods for evaluating the repair performance and intelligent techniques for repair are summarized. Finally, the directions for future development are discussed, providing theoretical support for further advances in the repair of SX turbine blades by L-DED.