We investigated the effects of carbon concentration on the microstructures and tensile properties of Ni-free Co-29Cr-9W-1Si-C (mass%) alloys used as disk materials in dental technology based on computer-aided design and computer-aided manufacturing (CAD/CAM). The alloy specimens, which contained carbon in different concentrations, were prepared by conventional casting. The precipitates changed from intermetallic compounds in the low-carbon alloys, e.g., the s and Laves phases, to M23C6-type carbide (M: metal) with increasing bulk carbon concentration. M23C6 dramatically enhanced the 0.2% proof stress, which then gradually increased with increasing carbon content in the alloys. The elongation-to-failure also increased with increasing carbon content. The coarse M23C6 particles formed by higher concentrations of carbon were detrimental to ductility, however, and a maximum elongation-to-failure was obtained at a carbon concentration of ~0.1 mass%. In addition, we applied hot-deformation processing to the cast-alloy specimens and revealed that compared to as-cast alloys, the hot-rolled alloys with added carbon showed an excellent combination of high strength and high ductility. The current study can thus aid in the design of biomedical, carbon-containing, Co-28Cr-9W-1Si-based alloys.
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