Enhanced Grain Refinement and Porosity Control of the Polycrystalline Superalloy by a Modified Thermally Controlled Solidification

An integrated technique, combining the modified thermally controlled solidification (MTCS) process with the mixed refiner of Co₃FeNb₂ and CrFeNb ternary intermetallic compounds, has been designed to enhance grain refinement and restrain porosity in polycrystalline IN718 C superalloy. The refinement efficiency of integrated technique is quite superior to that by convention casting (CC) process with refiner, as experiment results show that the grain size is refined from 3 340 to 126 µm and, during the refinement process, the microstructure of IN718 C superalloy evolves from dendrite to granular structure. Meanwhile, comparing with the CC process, this integrated technique has significantly eliminated porosities and dramatically improved the mechanical properties.