A research team from Sichuan University systematically uncovered the microstructural degradation and failure mechanisms during laser additive repair of nickel-based single-crystal superalloys. By adjusting laser cladding parameters, they produced three types of crystalline integrity—single-crystal, pseudo-single-crystal, and polycrystalline. They found that while the pseudo-single-crystal state macroscopically retains near-single-crystal orientation, high-density geometrically necessary dislocations and low-angle grain boundaries act as short-range diffusion channels, triggering abnormal anisotropic γ' phase coarsening and carbide precipitation. Mechanical tests showed that the ductility of the pseudo-single-crystal state is lower than that of the polycrystalline state, and its fracture behavior differs from the uniform slip band deformation mode of single crystals. This study indicates that controlling dislocation density is as critical as controlling grain orientation in additive repair of single-crystal nickel-based superalloys.