Optimization and insights toward fully dense crack-free additive manufacturing of Hastelloy-X by selective laser melting technology

This study examines process susceptibility to porosity and cracking during selective laser melting (SLM) of Hastelloy-X and provides process insights for producing the crack-free fully dense components. It tries to develop an optimization framework by systematically investigating the effects of key process parameters on defect formation and microstructure. A single-track test was first employed to identify a preliminary defect-free process window by eliminating keyholing, balling, and lack-of-fusion phenomena. Cubic specimens were then fabricated using a strip scan strategy with a 67° rotation between layers, varying laser power (270–360 W) and scan speed (700–1100 mm/s). The relative density, crack density, and solidification microstructure of the as-built samples were characterized using optical microscopy and scanning electron microscopy (SEM). The results demonstrate a strong correlation between laser energy input and defect formation. The optimal parameters were found at a laser power of 270 W and a scan speed of 1100 mm/s, yielding a near-full density of 99.92 % and the lowest crack density (0.005 %). Higher laser powers promoted keyhole porosity (up to 90 μm) and increased liquation cracking due to greater thermal stresses. Microstructural analysis revealed a fine cellular-dendritic structure, with primary dendrite arm spacing refining from ∼1.5 μm to ∼0.7 μm as laser power decreased, indicating higher cooling rates. Cracks were predominantly identified as liquation cracks, associated with the presence of brittle phases at grain boundaries. The findings underscore that minimizing heat input is critical to controlling defect formation and refining microstructure, providing a viable pathway for manufacturing high-integrity Hastelloy X components for demanding applications.