title: Microstructural evolution and mechanical properties of biomedical Co-Cr-Mo alloy subjected to high-pressure torsion.
abstract: The effects of severe plastic deformation through high-pressure torsion (HPT) on the microstructure and tensile properties of a biomedical Co-Cr-Mo (CCM) alloy were investigated. The microstructure was examined as a function of torsional rotation number, N and equivalent strain, εeq in the HPT processing. Electron backscatter diffraction analysis (EBSD) shows that a strain-induced martensitic transformation occurs by the HPT processing. Grain diameter decreases with increasing εeq, and the HPT-processed alloy (CCMHPT) for εeq=45 exhibits an average grain diameter of 47nm, compared to 70μm for the CCM alloy before HPT processing. Blurred and wavy grain boundaries with low-angle of misorientation in the CCMHPT sample for εeq<45 become better-defined grain boundaries with high-angle of misorientation after HPT processing for εeq=45. Kernel average misorientation (KAM) maps from EBSD indicate that KAM inside grains increases with εeq for εeq<45, and then decreases for εeq=45. The volume fraction of the ε (hcp) phase in the CCMHPT samples slightly increases at εeq=9, and decreases at εeq=45. In addition, the strength of the CCMHPT samples increases at εeq=9, and then decrease at εeq=45. The decrease in the strength is attributed to the decrease in the volume fraction of ε phase, annihilation of dislocations, and decrease in strain in the CCMHPT sample processed at εeq=45 by HPT.
authors.affiliation: Graduate Student, Department of Materials Science, Tohoku University, Sendai 980-8579, Japan. Electronic address: murat@imr.tohoku.ac.jp.
authors.forename: Murat
authors.initials: M
authors.lastname: Isik
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Electronic address: niinomi@imr.tohoku.ac.jp.
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Niinomi
authors.affiliation: Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan. Electronic address: k_cho@imt.eng.osaka-u.ac.jp.
authors.forename: Ken
authors.initials: K
authors.lastname: Cho
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Electronic address: nakai@imr.tohoku.ac.jp.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Nakai
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Electronic address: liuhuihong@imr.tohoku.ac.jp.
authors.forename: Huihong
authors.initials: H
authors.lastname: Liu
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Electronic address: hakan@imr.tohoku.ac.jp.
authors.forename: Hakan
authors.initials: H
authors.lastname: Yilmazer
authors.affiliation: Department of Materials Science and Engineering, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan; WPI, International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka 819-0395, Japan. Electronic address: horita@zaiko.kyushu-u.ac.jp.
authors.forename: Zenji
authors.initials: Z
authors.lastname: Horita
authors.affiliation: Graduate School of Science and Engineering, Ibaraki University, Hitachi 316-8511, Japan. Electronic address: s.sato@mx.ibaraki.ac.jp.
authors.forename: Shigeo
authors.initials: S
authors.lastname: Sato
authors.affiliation: Department of Materials Processing, Tohoku University, Sendai 980-8579, Japan. Electronic address: narut@material.tohoku.ac.jp.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Narushima
mesh_terms: D000497:Alloys / Q000737:chemistry*; D002857:Chromium; D003035:Cobalt; D008422:Materials Testing; D055595:Mechanical Phenomena; D008982:Molybdenum; D011312:Pressure; D019415:Torque
chemical_list: D000497:Alloys; D002857:Chromium; D003035:Cobalt; D008982:Molybdenum
keywords: Biomaterials; Co–Cr–Mo alloys; Grain refinement; High-pressure torsion; Martensitic phase transformation