Multi-Constraint Screening-Guided IN718 Addition for Crack Suppression and Improved Mechanical Properties of Laser-Directed Energy-Deposited IN738LC

IN738LC is a γ′-strengthened superalloy for hot-section components up to 900 °C, but its high Al + Ti content makes it susceptible to cracking during laser-directed energy deposition (LDED). Adding IN718 suppresses cracking but degrades the intrinsic γ′ fraction and the calculated high-temperature strength. A multi-constraint screening framework bounded the admissible composition, and experiments identified the lowest effective addition among the tested compositions: the γ′-solvus criterion allowed up to about 12 wt%, whereas the Fe ≤ 0.5 wt% criterion limited standard-compliant additions to about 2 wt%. Because the IN738LC + 2% deposit still cracked, IN738LC + 3% was selected (nominal Fe 0.65 wt%) together with 5 wt%. Cracks in the as-built IN738LC are associated with γ/γ′ eutectic liquid films; none were detected in the inspected regions of the IN738LC + 3% and IN738LC + 5% deposits. IN738LC + 3% showed the highest room-temperature ultimate tensile strength (UTS; 1467 MPa) with 13.8% elongation, versus 1240 MPa and 3.9% for the cracked IN738LC, and the best 900 °C properties (632 MPa, 8.0%); the room-temperature gain contains an inseparable crack-elimination contribution, isolated by comparing the two deposits in which no macroscopic cracks were detected. The framework provides quantitative bounds and trend indicators for crack-susceptible alloy design in the IN738LC–IN718–LDED system.