Papers by Author: Mitsuo Niinomi

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Authors: Hisao Fukui, W. Yang, Shozo Tsuruta, K. Kaikawa, A. Sugimura, Shoji Takeda, Mitsuo Niinomi
Abstract: An intensive amplitude arrangement for reciprocal tribocontact of biomedical alloys, Ag-20.0Pd-14.5Cu-12.0Au, Au-5.0Pt-2.0Pd-9.2Ag-15.0Cu and Ti-29Nb-13Ta-4.6Zr was conducted in order to check the details of friction and wear alterations around the transition from fretting to sliding. It is shown that the friction force exhibits stagnation for the Ag alloy and decrease for the Au alloy and the Ti alloy in certain domain of oscillating amplitude. Beyond the domain the friction force increases with the amplitude, and below the lower threshold and above the upper threshold triboevent is complete fretting and sliding respectively. Observation of friction-force waveform and SEM topography found, a hybrid mechanism of fretting and sliding is dominant in the amplitude domain, and the strong adhesion between the self-mated alloys is responsible to this exhibition.
Authors: Mitsuo Niinomi, Masaaki Nakai, Toshikazu Akahori, Harumi Tsutsumi
Abstract: Negative thermal expansion, i.e. a type of shrinkage that occurs during heating, was observed in cold-rolled Ti-29Nb-13Ta-4.6Zr alloy (mass%) (TNTZ). The reduction ratio of cold rolling was systematically changed, and then the thermal expansion rate was measured using a dilatometer. The cyclicity of thermal expansion was also examined for the cold-rolled TNTZ. Further, the effect of oxygen content on the thermal expansion behavior of the cold rolled TNTZ was examined. With an increase in the reduction ratio of cold rolling, the thermal expansion rate of TNTZ cold-rolled parallel to the rolling direction (RD) decreases, but it increases in TNTZ cold-rolled parallel to the transverse direction (TD). The cyclicity of above-mentioned anomalous thermal expansion is observed in a temperature range below 473 K, but it is not observed when the specimen is heated to above 573 K in the first cycle. The oxygen suppresses the negative thermal expansion behavior of TNTZ.
Authors: Kengo Narita, Mitsuo Niinomi, Masaaki Nakai, Toshikazu Akahori, Harumi Tsutsumi, Kazuya Oribe
Abstract: Implanting a spinal fixture using metallic rods is one of the effective treatments for spinal diseases. Because cyclic bending stress is loaded on the implant rods when patients move their upper bodies in daily life, bending fatigue properties are important for the implant rod. Further, the implant rods are bended plastically into a curved shape of spine by hand in a surgical operation. In that case, keeping shape is important, namely bending spring back properties are important factors. On the other hand, a biomedical β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (mass %) alloy (TNTZ), has been developed by the authors. Currently, this alloy are investigated to be applied to the above mentioned implant rod practically. Therefore, four-point bending fatigue and three point-bending spring back properties of TNTZ subjected various heat treatments were examined in this study. TNTZ rods were subjected to solution treatment, and then some of them were subjected to aging treatment at 673 K or 723 K for 259.2 ks, followed by water quenching. Then, four-point bending fatigue and three-point bending spring back tests were carried out on TNTZ rods subjected to the various heat treatments mentioned above. The bending fatigue strength at 2.5 million cycles in the high cycle fatigue region are not much different among any TNTZ rod. However, the bending fatigue strength of the Ti-6Al-4V ELI (Ti64) rod exceeds the fatigue strengths of every TNTZ rods in both low and high cycle fatigue regions. On the other hand, the lower spring back, which is a favorable property, was obtained for some TNTZ rod than Ti64 rod.
Authors: Toshikazu Akahori, Mitsuo Niinomi, Masaaki Nakai, Michiharu Ogawa
Abstract: The tensile and plain fatigue properties of the β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr alloy (TNTZ), which was subjected to various thermomechanical treatments, and cast TNTZ were investigated in order to judge its potential for biomedical and dental applications. The tensile strengths of TNTZ aged after solution treatment and that aged after cold rolling decrease with an increase in the aging temperature; however, their elongation exhibits an opposite trend. TNTZ composed of the ω phase or the ω and α phases in the β phase exhibits a tensile strength of about 1000 MPa or more. The tensile properties of the cast TNTZ with and without a surface reaction layer is are not significantly different, and are almost identcal to those of as-solutionized TNTZ. The plain fatigue strengths of TNTZ aged after solution treatment and those of TNTZ aged after cold rolling increase with the aging temperature. In particular, TNTZ aged at 723 K after cold rolling exhibits the highest fatigue strength in both the low- and high-cycle fatigue life regions. Further, the plain fatigue limit, which is about 770 MPa, is nearly equal to that of hot-rolled Ti-6Al-4V ELI alloy subjected to aging after solution treatment; Ti-6Al-4V ELI alloy is a representative α+β-type titanium alloy for biomedical applications. The plain fatigue strength of cast TNTZ with a surface reaction layer is considerably less than that of the as-cold-rolled and as-solutionized TNTZ. Consequently, in the low-fatigue life region, the fatigue crack easily occurs at the surface reaction layer, which is brittle, and in the high-fatigue life region, the fatigue crack occurs at the sites of casting defects (shrinkage). The fatigue limits range from 180 MPa to 200 MPa.
Authors: Mitsuo Niinomi, Toshikazu Akahori, Tsutomu Takeuchi, Shigeki Katsura
Abstract: Duplex calcia coating method where firstly fine calcia was coated on wax pattern and then fine calcia reinforced silica fiber was coated on the fine calcia coated wax pattern, that is, duplex calcia coating method, was applied for making mold. The surface of Ti-29Nb-13Ta-4.6Zr cast using the duplex calcia coating method show very fine metallic lust. The thickness of alpha case formed on the surface of Ti-29Nb-13Ta-4.6Zr is much thinner comparing with the case where the commercial magnesia mold for casting conventional titanium and its alloys for dental applications is used. The duplex calcia coating method is highly expected to be put into practical use for dental precision casting of Ti-29Nb-13Ta-4.6Zr. The dental crown of Ti-29Nb-13Ta-4.6Zr is successfully fabricated using duplex calcia coating method.
Authors: Ying Long Zhou, Mitsuo Niinomi, Toshikazu Akahori, Hisao Fukui
Abstract: In the present study, the effects of Ta content on the dynamic Young’s modulus and tensile properties of Ti−Ta alloys were investigated in order to find a Ti−Ta alloy that gives low modulus and high strength for biomedical applications. For this purpose, the ingots of Ti−Ta alloys with Ta contents from 10 to 50 mass % were melted, and then rolled into the plate of 3 mm thick. All the specimens were solution treated at 1223 K in the b field for 3.6 ks and then quenched in ice water. Subsequently, some of them were aged at 773 K for 259.2 ks followed by a rapid quenching in ice water. The corrosion capacity and biocompatibility of typical Ti−Ta alloy were also evaluated. The experimental results indicate that the Ti−30% Ta alloy has better mechanical biocompatibility, corrosion capacity and cyto-toxicity than Ti−6Al−4V alloy used as a standard biomaterial, and thus it will be of considerable development for biomedical applications.
Authors: Yoon Seok Lee, Mitsuo Niinomi, Masaaki Nakai, Junko Hieda, Takashi Maeda, Yoshihisa Shirai, Ikuhiro Inagaki
Abstract: In the Present Study, the Effects of the Microstructural Morphologies of a Ti-6Al-4V (Ti-64) Alloy on its Fatigue Behavior Were Investigated. Ti-64 Bars Were Subjected to Two Different Thermo-Mechanical Processing Methods. The First Sample, Referred to as Material-A, Had a Forged Microstructure with the Average Primary α Volume Fraction of 44%. The Second One, Referred to as Material-B, Had a Hot-Rolled Microstructure with the Average Primary α Volume Fraction of 43%. Fatigue Tests Were Performed on each Sample to Obtain S-N Curves. The Microstructure of each Sample Was Observed Using an Optical Microscopy in Order to Measure the Grain Sizes of the Primary α and Secondary α Phases. The Results of the Fatigue Tests Indicated that Material-B Demonstrates Better Fatigue Strength than Material-A. The Microstructure of the Longitudinal Section of each Material Was Also Observed to Analyze the Results of the Fatigue Tests. The Measured Diameters and Volume Fractions of the Primary α Phases of the Two Types of Materials Are Similar. On the other Hand, the Secondary α Width of each Material Is Different. It Is Found that Fatigue Strength Is Related to the Width of the Secondary α Phase.
Authors: Yong Hwan Kim, Mitsuo Niinomi, Toshikazu Akahori, Masaaki Nakai, Harumi Tsutsumi, Hisao Fukui
Abstract: Hardness of Ag-20Pd-12Au-14.5Cu (mass%) subjected to a solution treatment (ST) at a temperature over 1073 K followed by water quenching increases drastically. This unique hardening behavior is not clarified becasue of their complex microsturucures. In this study, the relationship between the unique hardening behaviour and the microstructure of dental Ag-20Pd-12Au-xCu subjected to ST with different Cu/Ag ratios was investigated. The Vickers hardness of Ag-20Pd-12Au-14.5Cu increases remarkably from 192 to 286 Hv after ST whereas that of Ag-20Pd-12Au-6.5Cu decreases and that of Ag-20Pd-12Au-20Cu increases slightly after ST, respectively. The spotty regions are observed in only certain areas of Ag-20Pd-12Au-14.5Cu subject to ST. It is considered that the appearance of the spotty regions affects mainly to the unique hardening behaviour in Ag-20Pd-12Au-xCu.
Authors: Mitsuo Niinomi, Alisha L. Hutson, Eric B. Shell, Daniel Eylon, Theodore Nicholas
Authors: Mitsuo Niinomi, Masaaki Nakai, Toshikazu Akahori, Harumi Tsutsumi
Abstract: Oxygen plays very important roles in titanium and its alloys. Solute oxygen in titanium alloys leads to solid solution strengthening, suppressing the precipitation of the athermal omegaor orthorhombic martensite phase, enhancing the formation of the -case, etc. The proper using oxygen is effective to improve the mechanical functionalities of titanium alloys. However, the role of oxygen in titanium alloys is still not well understood. Therefore, the effect of oxygen on the mechanical functionalities such as strength-ductility balance, hardness, and Young’s modulus in Ti-29nb-13Ta-4.6Zr was investigated.
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