Influence of carbon addition on mechanical properties and microstructures of Ni-free Co-Cr-W alloys subjected to thermomechanical processing

We report the effects of carbon concentration on the microstructures and tensile deformation behaviors of thermomechanically processed Ni-free Co-29Cr-9W-1Si-C (mass%) alloys designed for use as disk materials in CAD/CAM dental technology. The alloy specimens, which contained carbon in different concentrations, were prepared by casting and subsequent hot rolling. Overall, the developed Ni-free alloys with added carbon showed an excellent combination of high strength and high ductility. The precipitates were identified in all of the alloy specimens. Intermetallic compounds, i.e., the Laves and σ phases, were formed in the low-carbon alloys, whereas the precipitates changed to M₂₃C₆ carbide when the carbon concentration exceeded 0.1mass%. Carbon concentrations less than 0.1mass% exhibited minimal contribution to strengthening, but the formation of the M₂₃C₆ carbide particles increased the alloy strength. On the other hand, elongation-to-failure increased with increasing carbon content when the carbon concentration is relatively low. However, the coarse M₂₃C₆ carbide particles formed by higher concentrations of carbon were detrimental to ductility. Thus, a maximum elongation-to-failure was obtained at carbon concentrations of around 0.1mass%. The results of the current study can aid in the design of biomedical Co-28Cr-9W-1Si-based alloys containing carbon.