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.
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ABSTRACT: The purpose of this study was to evaluate mechanical properties, surface characteristics and castability of Zr-14Nb dental castings. The mean 0.2% proof and ultimate tensile strengths of Zr-14Nb were approximately 68% and 76% those of Ti-6Al-7Nb, respectively, while they were comparable to Co-29Cr-6Mo. Elongation of Zr-14Nb was the highest of all alloys tested. The hardened reaction layer was formed on the surfaces of the Zr-14Nb castings. The layer consisted of oxygen and aluminum originating form investment. The castability of Zr-14Nb was comparable to that of Ti-6Al-7Nb. Dental castings of Zr-14Nb reveal mechanical properties that were within the range of the other dental alloys. Further improvements in castability and minimization of the surface reaction layer are needed for applications in dental prostheses.Dental Materials Journal 10/2014; 33(5):631-7. DOI:10.4012/dmj.2014-117 · 0.94 Impact Factor
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ABSTRACT: In this study, the microstructures, mechanical properties, corrosion behaviors, in vitro cytocompatibility and magnetic susceptibility of Zr-1X alloys with various alloying elements, including Ti, Nb, Mo, Cu, Au, Pd, Ag, Ru, Hf and Bi were systematically investigated to explore their potential use in biomedical application. The experimental results indicated that annealed Zr-1X alloys consisted entirely or primarily of α phase. The alloying elements significantly increased the strength and hardness of pure Zr and had relatively slight influence on elastic modulus. Ru was the most effective enhancing element and Zr-1Ru alloy had the largest elongation. The results of electrochemical corrosion indicated that adding various elements into Zr improved its corrosion resistance as indicated by the reduced corrosion current density. The extracts of the studied Zr-1X alloys produced no significant deleterious effect to osteoblast-like cells (MG 63), indicating good in vitro cytocompatibility. All except for Zr-1Ag alloy showed decreased magnetic susceptibility compared to pure Zr and Zr-1Ru alloy had the lowest magnetic susceptibility value, being comparable to that of α'-phase Zr-Mo alloy and Zr-Nb alloy and far lower than that of Co-Cr alloy and Ti-6Al-4V alloy. Among the experimental Zr-1X alloys, Zr-1Ru alloy possessing high strength coupled with good ductility, good in vitro cytocompatibility and low magnetic susceptibility, may be a good candidate alloy for medical devices within a magnetic resonance imaging (MRI) environment.Acta biomaterialia 08/2013; DOI:10.1016/j.actbio.2013.07.035 · 5.68 Impact Factor
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ABSTRACT: Cooling rate and composition dependences of the magnetic susceptibility for Zr54-xCu30+xAl8Ag8 glassy alloys which are candidate materials for magnetic resonance imaging (MRI) were investigated. Lower magnetic susceptibility was achieved by reducing Zr content in the present series of the alloys, and also by higher cooling rate during the preparing glassy alloys. The magnetic susceptibility values were hard to be explained by the simple free-electron model. It is suggesting that the effects of the enhancement of the density of states by 4d-conduction band should be taken into the consideration. The results obtained by utilizing the pair correlation functions suggested that the different magnetic susceptibilities between the ribbon and bulk glassy alloys were originated from the structural difference in the middle range order caused by the different cooling rates.MATERIALS TRANSACTIONS 08/2013; 54(8):1356-1360. DOI:10.2320/matertrans.MF201306 · 0.61 Impact Factor