Abstract:Nickel-based superalloys are widely used in critical hot-section components of high-end equipment such as aero-engines and gas turbines due to their excellent mechanical properties and oxidation resistance at elevated temperatures. As an advanced manufacturing method, laser directed energy deposition (L-DED) has demonstrated great potential in the repair of complex components, owing to its advantages such as mold-free near-net shaping, controllable energy input, small heat-affected zone, and dense microstructure in the deposited layer. However, during L-DED repair process, nickel-based superalloys undergo complex rapid melting and solidification, as well as repeated thermal cycling, resulting in unique microstructural features and a high tendency to develop typical metallurgical defects, such as pores, cracks, stray grains, and microstructure degradation, which can significantly degrade their mechanical performance. The typical defects and their control methods, as well as microstructural evolution characteristics were reviewed, and the key mechanical properties, including room-temperature tensile strength, high-temperature creep resistance, and fatigue performance, between directly deposited and repaired nickel-based superalloys were compared. Furthermore, based on existing theoretical models, the mechanisms of defect formation and microstructural evolution were analyzed, highlighting the current technical challenges and limitations in this field. This review provides a theoretical foundation and direction for the process optimization, microstructural control, and performance enhancement of L-DED-repaired or L-DED-formed nickel-based superalloys.