title: Effects of phase constitution on magnetic susceptibility and mechanical properties of Zr-rich Zr-Mo alloys.
abstract: The effects of the microstructures and phases of Zr-rich Mo alloys on their magnetic susceptibilities and mechanical properties were investigated in order to develop a Zr alloy with low magnetic susceptibility for use in magnetic resonance imaging (MRI). The magnetic susceptibility was measured with a magnetic susceptibility balance, while mechanical properties were evaluated by a tensile test. The microstructure was evaluated with an X-ray diffractometer, an optical microscope, and a transmission electron microscope. Evaluation of the microstructures revealed that the α' phase was the dominant form at less than 2% Mo content in the as-cast alloy. The ω phase was formed in as-cast Zr-3Mo but disappeared with aging at 973 K. Magnetic susceptibility was reflected in the phase constitution: the susceptibility showed a local minimum at Zr-(0.5-1)Mo with mostly α' phase and a minimum at Zr-3Mo with mostly β and ω phases. The magnetic susceptibility of as-cast Zr-3Mo increased at 973 K due to disappearance of the ω phase. However, the susceptibility was still as low as that of as-cast Zr-1Mo. The ultimate tensile strength of α'-based Zr-Mo alloys was tailored from 674 to 970 MPa, and the corresponding elongation varied from 11.1% to 2.9%. Because Zr-Mo alloys containing ω phase were found, through tensile tests, to be brittle this phase should be avoided, irrespective of the low magnetic susceptibility, in order to maintain mechanical reliability. Elongation of the Zr-3Mo alloy was dramatically improved when the phase constitution was changed to α and β phases by aging at 973 K for 86.4 ks. The magnetic susceptibilities of the α'-based Zr-Mo alloys are one-third those of Ti-6Al-4V and Ti-6Al-7Nb, and thus these Zr alloys are useful for medical devices under MRI.
authors.affiliation: Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan.
authors.lastname: Suyalatu
authors.forename: Ryota
authors.initials: R
authors.lastname: Kondo
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Tsutsumi
authors.forename: Hisashi
authors.initials: H
authors.lastname: Doi
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Nomura
authors.forename: Takao
authors.initials: T
authors.lastname: Hanawa
mesh_terms: D000497:Alloys; D008280:Magnetics; D008855:Microscopy, Electron, Scanning; D008982:Molybdenum / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D000497:Alloys; D008982:Molybdenum; D015040:Zirconium