Enhanced grain refinement and tensile property improvement of CoCrMo alloy via variable-speed centrifugal casting

The influence of centrifugal casting kinetics on the grain refinement and tensile behavior of investment-cast CoCrMo alloys was investigated systematically. Variable-speed centrifugal casting, which introduces non-steady-state kinetics via periodic angular acceleration, can significantly reduce CoCrMo alloy's grain size and improve its tensile properties. Compared to gravity casting, variable-speed (300 - 350 rpm) casting with an oscillation period of 2 s can further reduce the grain size from 3.67 ± 0.12 mm to 0.36 ± 0.02 mm. Accordingly, the yield strength, ultimate tensile strength and engineering strain increased from 462 MPa, 667 MPa, and 11.72% to 532 MPa, 864 MPa, and 17.83%, respectively. These correspond to increases of 15.2%, 29.5%, and 52.1%, respectively. The superior mechanical performance is attributed to pronounced grain refinement driven by non-steady-state kinetics. Mechanistically, periodic angular acceleration induces shear disturbances that promote dendrite fragmentation and enhance equiaxed nucleation, resulting in a fine and uniform equiaxed microstructure.