Mitigating Solidification Cracking in LPBF-Processed K418 Superalloy via Substrate Preheating and Layer Thickness Optimization

This study systematically investigates the influence of key process parameters—layer thickness and substrate preheating—on solidification cracking in K418 nickel-based superalloy fabricated by laser powder bed fusion (LPBF). For a 30 μm layer, preheating to 350 °C combined with a volumetric energy density (VED) of 60–80 J/mm3 effectively suppressed hot cracking while achieving a relative density > 99%. Preheating to 200 °C showed limited effectiveness. Without preheating, increasing the layer thickness to 60 μm reduced cracking compared to 30 μm, yet preheating became counterproductive under this thicker condition due to excessive thermal accumulation and increased shrinkage stress. Microscopic analysis revealed that cracks propagated along high-angle grain boundaries accompanied by the segregation of low-melting-point elements (O, B, Si, C), with cracking attributed to thermal stress and grain boundary weakening during rapid solidification. This work establishes 350 °C preheating with moderate VED as an effective strategy for manufacturing high-density, crack-minimized K418 alloy components via LPBF.