Solidification Microstructure and Room-Temperature Mechanical Properties of K4750 Superalloy Prepared by Gravity Casting and Centrifugal Casting

The solidification microstructure and room-temperature mechanical properties of K4750 superalloys prepared by gravity casting and centrifugal casting were investigated. Their second phase distribution, grain size, element segregation, distribution of shrinkage defects, room-temperature mechanical properties and fracture morphology were analyzed comparatively. Results show that the as-cast K4750 superalloys prepared by both casting processes consist of γ matrix phase, intragranular MC-type carbide, fine and dispersed intragranular γ' phase, as well as MC-type and M23C6-type carbides at grain boundary. However, the precipitate size is found to be more refined in the centrifugal casting process. The average grain size of as-cast K4750 superalloy decreases from 4.52 mm (gravity casting) to 2.22 mm (centrifugal casting). Furthermore, the area fraction of shrinkage defects is reduced from 1.75% (gravity casting) to 0.27% (centrifugal casting). The K4750 superalloy prepared by gravity casting exhibits well-aligned dendritic structures, whereas centrifugal-cast superalloy shows fragmented dendrites and a reduced degree of elemental segregation. The K4750 superalloy samples prepared by centrifugal casting exhibit excellent room-temperature mechanical properties, with yield strength, ultimate tensile strength and elongation of 632 MPa, 938 MPa and 11.2%, respectively. Compared to the gravity-casting counterpart, its ultimate tensile strength is increased by 20.6%, which can be attributed to the combined effects of grain refinement, γ' phase refinement and a reduction in casting defects.