Curvature-induced asymmetric solidification in laser deposition of single-crystal superalloys: Multiphysics modeling and microstructural analysis

This study investigates the single-crystal epitaxial growth behavior of nickel-based single-crystal superalloys during curved-path laser-directed energy deposition using a thermo-fluid-solid coupled numerical model. The results reveal that the core mechanism underlying the curvature-induced asymmetric epitaxial growth is the outward deflection of heat flow toward the outer side of the curved track.This deflection arises from the continuously changing scanning direction along the curved path, which creates a non-uniform radial distribution of laser energy input and cooling conditions. Consequently, the thermal gradient (G) and solidification rate (R) differ substantially between the inner and outer sides, leading to asymmetric epitaxial growth height, radial PDAS gradients, and altered columnar-to-equiaxed transition (CET) behavior. Under optimized low laser power (700 W) and high scanning speed (11 mm/s), a peak epitaxial growth fraction of 72.7% was achieved. Microstructural analysis confirms γ/γ′ phase consistency but reveals radial PDAS gradients and Al segregation in inter-dendritic zones due to cooling rate variations (10 ³ –10 ⁴ K/s). The model, validated against experimental melt-pool geometry, provides mechanistic insight into the asymmetric solidification behavior under curved scanning, laying a foundation for the precision repair of complex single-crystal components.