Effect of Minor P and C Regulation on Microstructure Evolution and High-Temperature Properties of Selective Laser...

Selective laser melting (SLM) produces elemental segregation and nonequilibrium secondary phases in GH4169 superalloys, but the effects of P and C variations on grain-boundary phase evolution and high-temperature tensile behavior remain unclear. Alloys with primarily varied P (0.034-0.058 wt.%) and C (0.009-0.066 wt.%) contents were fabricated and heat treated identically. Microstructures were characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM), and tensile properties were evaluated at 650 °C. The as-built alloys exhibited columnar grains, cellular substructures, cell-wall segregation, and Nb-rich Laves-phase particles. After heat treatment, cellular substructures largely disappeared, γ″ precipitates formed in the γ matrix, and fine Ti/Al-rich particles were tentatively attributed to γ'; δ phase, residual Laves phase, and MC-type carbides were present at grain boundaries. Increasing P reduced the δ-phase area fraction from 2.20% to 1.38% and changed its distribution from continuous chains to semi-continuous and discrete arrangements. Increasing C raised the MC-type carbide area fraction from 0.34% to 1.48% while decreasing the δ-phase area fraction from 1.68% to 0.98%, accompanied by carbide coarsening. The 0.050P alloy exhibited the highest yield and ultimate tensile strengths, whereas the 0.009C alloy showed the best strength-ductility balance. These results reveal distinct P- and C-related changes in grain-boundary phase evolution and tensile behavior at 650 °C.