An investigation on fine-grain formation and structural character in cast IN718 superalloy

Fine-grain casting processes (FGCP) have been investigated since 1980. However, investigation in detail of the dendritic structure existing in fine-grain cast superalloy is scarce. An extra-fine-grain size (ASTM 3.5–5) in cast structures of IN718 has been achieved in this investigation by means of fine-grain casting technology with a wide range of cooling rates ranging from 0.13 to 9.48 °C/s. Typical dendritic and granular structure can be formed in fine-grain cast IN718. The character of the dendritic structure can be expressed by the dendritic morphology character parameter M. The granular structure can be formed by the coarsening of the dendritic structure during solidification. This mechanism is confirmed by an especially designed isothermal holding test at 1300 °C in the solid and liquid two-phase region of IN718 superalloy.