Influence of carbon content on the thermally controlled solidified microstructure and creep properties of IN718 superalloy

Carbon (C) regulation is an effective strategy for optimizing grain boundary precipitates and enhancing mechanical properties in superalloys. In this work, IN718 alloys with different C contents were fabricated using modified thermally controlled solidification to systematically investigate the influence of C on microstructural evolution and creep properties. The results demonstrate that increasing C content refines the grain size to approximately 78 μm, with porosity remaining under 0.62% and no dendritic structures observed. Microstructural analysis reveals that as C content increases, the volume fraction of MC carbides increases from 0.7% to 1.3%, and their morphology evolves from blocky to skeletal or coarse blocky forms, while Laves phases are significantly reduced. Concurrently, δ phases transform from acicular to granular morphology with volume fraction decreasing from 12.2% to 1.7%, and γ" phase volume fraction also decreases substantially from 31.9% to 24.7%. Additionally, with increasing C content, the creep life of the alloys exhibits a trend of initially decreasing from 404.9 h to 86.8 h and then increasing to 328.9 h, while the steady-state creep rate shows the opposite trend. The creep lives at 0.036 and 0.12 wt.% C are 4.7 and 3.8 times that at 0.096 wt.% C, respectively.