Excellent strength-plasticity synergy of laser directed energy deposited IN738LC superalloy with ultrafine bimodal γ′ phases

Nickel-based superalloys are critical for hot-end components under extreme conditions owing to their excellent high-temperature properties, but their high inherent cracking susceptibility poses a major challenge to laser additive manufacturing. In this paper, an innovative deposition strategy combining interlayer cooling and interlayer power reduction is proposed to fabricate a crack-free IN738LC superalloy via laser directed energy deposition. The tailored layer-by-layer thermal history accompanying this deposition strategy results in an ultrafine bimodal distribution of γ′ phases, with the primary γ′ phases measuring approximately 20–30 nm and the secondary γ′ phases less than 10 nm. During tensile deformation, the as-deposited IN738LC superalloy exhibits sustained strain hardening capability via multiple deformation mechanisms involving dislocation slip, stacking faults, L-C locks, and nanotwins induced by the ultrafine bimodal distribution of γ′ phases. The as-deposited IN738LC superalloy exhibits remarkable mechanical properties: a yield strength of 1044 MPa, an ultimate tensile strength of 1382 MPa, and an elongation of 16.43%, indicating an excellent strength–plasticity balance. This study provides a simplified manufacturing approach and valuable insights for advancing laser additive manufacturing technology for difficult-to-weld nickel-based superalloys.