Crack healing and strength-ductility enhancement of CM247LC alloy via laser powder bed re-melting followed by hot isostatic pressing and heat treatment

High crack susceptibility remains a critical challenge in laser powder bed fusion of nickel-based superalloys with high γ'-volume fractions. This study systematically analyzes the crack formation mechanisms, melt pool morphology, and microstructural evolution of CM247LC alloy by optimizing selective laser re-melting (SLRM) parameters (laser power: 176 W, scan speed: 1143 mm/s, hatch spacing: 0.11 mm) combined with hot isostatic pressing (HIP: 1240 °C/150 MPa/4 h) and heat treatment (HT: 1260 °C solution treatment +870 °C aging). Results indicate that cracks primarily propagate along high-angle grain boundaries, with initiation closely linked to elemental segregation (O, Al, C, Ti) and residual stress concentration. Increasing the re-melting volumetric energy density (E_v) to 56.8 J/mm³ significantly enhances the melt pool depth-to-width ratio (D/W = 0.62), exacerbating temperature gradients and stress concentrations, thereby elevating crack susceptibility. After SLRM + HIP + HT treatment, the grain aspect ratio decreases from 7.32 to 3.66, while serrated grain boundaries and uniformly distributed γ'-phases effectively inhibit crack propagation and reduce residual stress. The final specimens exhibit exceptional strength-ductility synergy: ultimate tensile strength of 1352 ± 16 MPa, yield strength of 988 ± 25 MPa, and elongation of 11.5 ± 0.8 %, representing improvements of 23.0 %, 18.9 %, and 79.7 %, respectively, compared to the as-built selective laser melting samples.