Effect of the Casting Methods on Microstructure and Room Temperature Mechanical Properties of K4800 Superalloy

The microstructure and room temperature mechanical properties of K4800 alloy test pieces cast by conventional gravity casting, centrifugal casting and adjusted pressure casting were comparatively studied. The results showed that both centrifugal casting and adjusted pressure casting could refine grain size, the typical grain size was 4.52 mm for normal gravity casting sample, but refined to about 0.28 mm for the sample of adjusted pressure casting, and about 2.22 mm for the sample of centrifugal casting. Meanwhile, the area fraction of shrinkage porosity was decreased from 1.75% of gravity casting sample to 0.27% and 0.25% of centrifugal and adjusted pressure casting samples, respectively. As-cast K4800 alloy by using different casting methods had similar microstructures, namely rod-shaped MC carbides and lamellar borides at grain boundaries, as well as the fine γ' phase within grains, but the sizes of the precipitates were refined for the centrifugal and adjusted pressure casting samples. Due to the reduction of casting defects, as well as the refinement of grain size and γ' phase, K4800 alloy samples prepared by adjusted pressure casting exhibited the much higher room temperature mechanical properties, with yield strength, ultimate tensile strength and plasticity of 798 MPa, 1152 MPa and 11.6%, respectively. Compared with gravity and centrifugal casting, its ultimate tensile strength has increased by 39.9% and 21.8%, and plasticity has increased by 70.4% and 52.5%.