Refinement of solidification microstructures by carbon addition in biomedical Co–28Cr–9W–1Si alloys

• Effect of carbon content on microstructure of Co–Cr–W–Si alloy was observed.
• Grain boundary carbide precipitates increased with increasing carbon concentration.
• Interdendritic segregation of Cr, W, Si, and C causes interdendritic precipitation.
• Adding carbon decreased grain sizes of as-cast alloys.

The solidification microstructures of Co–28Cr–9W–1Si (wt%) alloys with different carbon contents (0.005–0.33 wt%) were characterized using scanning electron microscopy, electron backscatter diffraction, and electron probe microanalysis. The as-cast alloys exhibited cellular dendritic microstructures, and the amount of grain boundary carbide precipitates increased with increasing carbon concentration. It was revealed that the interdendritic segregation of Cr, W, Si, and C, resulted in interdendritic precipitation. Consequently, adding carbon was found to decrease the grain sizes of as-cast alloys. Our results will contribute to the development of disk materials made of biomedical Ni-free Co–Cr–W-based alloys with refined grain sizes.