Defect formation analysis and microstructure-guided process design for large-scale complex thin-walled superalloy double-ring casting boss in investment casting

Large-scale complex thin-walled superalloy components manufactured via investment casting present significant challenges in defect-free formation, particularly at geometric discontinuities such as bosses where abrupt thickness variations occur. This study employs an integrated methodology combining numerical simulation with advanced microstructural characterization techniques including scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to systematically investigate the forming quality of double-ring thin-walled castings. The results indicate that defects in bosses arise from insufficient feeding and elemental segregation, while oversized risers further reduce the cooling rate in thin-walled sections. Based on numerical simulation findings, the gating system was optimized by adding supplemental runners at bosses and end lugs while reducing riser height from 153 mm to 113 mm. Post-optimization, shrinkage porosity defects at bosses were eliminated with homogeneous elemental distribution. The presence of high-angle grain boundaries between grains and dislocation pile-ups at γ"/γ phase interfaces with low lattice distortion confirms the enhanced casting quality after optimization.