title: Effects of chromium and nitrogen content on the microstructures and mechanical properties of as-cast Co-Cr-Mo alloys for dental applications.
abstract: The microstructure and mechanical properties of as-cast Co-(20-33)Cr-5Mo-N alloys were investigated to develop ductile Co-Cr-Mo alloys without Ni addition for dental applications that satisfy the requirements of the type 5 criteria in ISO 22674. The effects of the Cr and N contents on the microstructure and mechanical properties are discussed. The microstructures were evaluated using scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDS), X-ray diffractometry (XRD), and electron back-scattered diffraction pattern analysis. The mechanical properties were evaluated using tensile testing. The proof strength and elongation of N-containing 33Cr satisfied the type 5 criteria in ISO 22674. ε-phase with striations was formed in the N-free (20-29)Cr alloys, while there was slight formation of ε-phase in the N-containing (20-29)Cr alloys, which disappeared in N-containing 33Cr. The lattice parameter of the γ-phase increased with increasing Cr content (i.e. N content) in the N-containing alloys, although the lattice parameter remained almost the same in the N-free alloys because of the small atomic radius difference between Co and Cr. Compositional analyses by EDS and XRD revealed that in the N-containing alloys Cr and Mo were concentrated in the cell boundary, which became enriched in N, stabilizing the γ-phase. The mechanical properties of the N-free alloys were independent of the Cr content and showed low strength and limited elongation. Strain-induced martensite was formed in all the N-free alloys after tensile testing. On the other hand, the proof strength, ultimate tensile strength, and elongation of the N-containing alloys increased with increasing Cr content (i.e. N content). Since formation of ε-phase after tensile testing was confirmed in the N-containing alloys the deformation mechanism may change from strain-induced martensite transformation to another form, such as twinning or dislocation slip, as the N content increases. Thus the N-containing 33Cr alloy with large elongation is promising for use in dentures with adjustable clasps through one piece casting.
authors.affiliation: Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Yushima, Bunkyo-ku, Japan.
authors.forename: Keita
authors.initials: K
authors.lastname: Yoda
authors.lastname: Suyalatu
authors.forename: Atsushi
authors.initials: A
authors.lastname: Takaichi
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Nomura
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Tsutsumi
authors.forename: Hisashi
authors.initials: H
authors.lastname: Doi
authors.forename: Shingo
authors.initials: S
authors.lastname: Kurosu
authors.forename: Akihiko
authors.initials: A
authors.lastname: Chiba
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Igarashi
authors.forename: Takao
authors.initials: T
authors.lastname: Hanawa
mesh_terms: D002857:Chromium / Q000032:analysis*; D008422:Materials Testing / Q000379:methods*; D055595:Mechanical Phenomena; D008982:Molybdenum / Q000032:analysis; D009584:Nitrogen / Q000032:analysis*; D013052:Spectrometry, X-Ray Emission; D013314:Stress, Mechanical; D013674:Technology, Dental / Q000379:methods*; D013718:Tensile Strength; D014800:Vitallium / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D002857:Chromium; D014800:Vitallium; D008982:Molybdenum; D009584:Nitrogen