title: Effects of carbon concentration on microstructure and mechanical properties of as-cast nickel-free Co-28Cr-9W-based dental alloys.
abstract: We determined the effects of carbon concentration on the microstructures and tensile properties of the Ni-free Co-29Cr-9W-1Si-C (mass%) cast alloys used in dental applications. Alloy specimens prepared with carbon concentrations in the range 0.01-0.27 mass% were conventionally cast. Scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) revealed that precipitates had formed in all the alloy specimens. The σ phase, a chromium-rich intermetallic compound, had formed in the region between the dendrite arms of the low-carbon-content (e.g., 0.01 C) alloys. Adding carbon to the alloys increased the amount of interdendritic precipitates that formed and changed the precipitation behavior; the precipitated phase changed from the σ phase to the M23C6 carbide with increasing carbon concentration. Adding a small amount of carbon (i.e., 0.04 mass%) to the alloys dramatically enhanced the 0.2% proof stress, which subsequently gradually increased with increasing content of carbon in the alloys. Elongation-to-failure, on the other hand, increased with increasing carbon content and showed a maximum at carbon concentrations of ~0.1 mass%. The M23C6 carbide formed at the interdendritic region may govern the tensile properties of the as-cast Co-Cr-W alloys similar to how it governed those of the hot-rolled alloys prepared in our previous study.
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Electronic address: k_yamanaka@imr.tohoku.ac.jp.
authors.forename: Kenta
authors.initials: K
authors.lastname: Yamanaka
authors.affiliation: Department of Materials and Environmental Engineering, Sendai National College of Technology, 48 Nodayama, Medeshima-Shiote, Natori 981-1239, Japan.
authors.forename: Manami
authors.initials: M
authors.lastname: Mori
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Chiba
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D003722:Dental Alloys / Q000737:chemistry*; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry; D013718:Tensile Strength; D013816:Thermodynamics; D014414:Tungsten / Q000737:chemistry*
chemical_list: D003722:Dental Alloys; D002857:Chromium; D003035:Cobalt; D002244:Carbon; D009532:Nickel; D014414:Tungsten
keywords: Biomedical Co–Cr–W alloy; Carbon addition; Mechanical properties; Precipitation; γ→ε martensitic transformation