Processing the unprocessable: strategies for mitigating hot cracking in LPBF of high-performance nickel-based superalloys

Laser powder bed fusion (LPBF) offers design freedom for nickel-based superalloys used in aerospace and energy systems, yet its industrial adoption remains constrained mainly by hot cracking caused by steep thermal gradients, wide freezing ranges, and γ′-related ductility troughs. Many high-performance alloys, such as IN738LC, CM247LC, IN792, and IN939, that are readily cast or forged, remain difficult to process by LPBF or welding, with more weldable alloys, such as IN718 and IN625, are commonly used as benchmarks for cracking susceptibility. This review examines the fundamental mechanisms of solidification, liquation, and strain-age cracking in LPBF nickel-based superalloys. Evidence shows that solidification cracking risk increases sharply when the Scheil freezing range exceeds ∼280°C, a threshold surpassed by several γ′-strengthened alloys, while strain-age cracking is promoted by rapid γ′ precipitation in compositions with Al + Ti contents above ∼6 wt.%. The study further evaluates mitigation strategies categorised into intrinsic (inoculation, freezing-range engineering, and powder surface functionalisation) and extrinsic (beam shaping, preheating and post-processing, scan-strategy optimisation, and in-situ monitoring) strategies. Reported results show major reductions in crack density, including >96% for redesigned CM247LC and ∼85% for remelted IN939. However, metallurgical solutions that enable crack-free builds may reduce functional properties, resulting in tradeoffs.