Mechanical properties of titanium-zirconium binary alloys were investigated in order to reveal their possible use for new biomedical materials and to collect useful data for alloy design through a hardness test, a tensile test, and optical microscopy. The hardness of the alloy containing 50% zirconium was approximately 2.5 times as large as the hardness of pure titanium and pure zirconium. Tensile tests showed a similar tendency. No changes between hardness of as cast specimens and as homogenized specimens were observed, nor were changes in microstructures noted. Comparisons between the Ti-6Al-4V alloy and the Ti-Zr-6Al-4V alloy indicated that a titanium-zirconium alloy could provide a base material for a new biomedical alloy. From these results, it was concluded that new alloys for biomedical materials should be designed as titanium-zirconium base alloys.

Real-time, in situ electrochemical quartz crystal microbalance (EQCM) measurements are conducted to better understand the electrocrystallization of calcium phosphates (CaP) on CP-Ti. X-ray photoelectron spectroscopy is used to identify the exact phase deposited, so that reliable estimation of the electrochemical processes involved is made. Analysis of the integrated intensity of the oxygen shake-up peaks, in combination with the determination of Ca/P and O/Ca atomic ratios, enables to determine unambiguously that the octacalcium phosphate (OCP) is formed. Its role as a precursor to hydroxyapatite (HAp) is discussed. After an incubation period, the process by which OCP is formed follows a Faradaic behavior. The incubation time may be related to the need for local increase of pH before precipitation from solution can occur. The standard enthalpy of activation is approximately 40 kJ/mol, which excludes diffusion-controlled processes from being rate determining. The OCP deposit has thickness approximately 0.61 microm, apparent density approximately 0.95 g/cm3, 63.6% porosity, and deposition rate of 23.5 ng/(cm2 s) or 15 nm/min. The low-equivalent weight value of 20.5 g/equiv, and the associated remarkably high number of electrons transferred in the reaction n approximately 24, indicates that most of the current is consumed either by electrolysis of water or by a complex set of parasitic reactions. The low-solubility product allows precipitation of CaP even at relatively low concentrations of calcium and phosphate/hydrogen phosphate ions. It is shown that HAp most likely forms via transformation of precursor phases, such as OCP, rather than directly.

With the aim of applying a novel titanium alloy, Ti-6Al-7Nb, to a dental casting material, a comprehensive research work was carried out on its characteristics, such as castability, mechanical properties and corrosion resistance in the present study. As a result, Ti-6Al-7Nb alloy exhibited sufficient castability by a dental casting method for titanium alloys and enough mechanical properties for dental application. It is also showed excellent corrosion resistance through an immersion test in 1.0% lactic acid and an anodic polarization test in 0.9% NaCl solution. From these results, it is concluded that this Ti-6Al-7Nb alloy is applicable as a dental material in place of Ti-6Al-4V alloy, which includes cytotoxic vanadium.

Two types of nanoclusters, i.e. Cluster (1) and Cluster (2), play a strongly important role in the bake-hardening (BH) response in Al-Mg-Si alloys. Different formation behaviors of two types of nanoclusters were studied by means of hardness, differential scanning calorimetry (DSC), electrical resistivity measurement, transmission electron microscopy (TEM) and high resolution TEM observation in the both Cu-free and Cuadded Al-Mg-Si alloys. As the results, Cluster (1) formed during natural aging at room temperature causes a deleterious effect, whereas Cluster (2) formed by the pre-aging at 100 C is effective for the suppression of the negative effect on the two-step aging behavior of the both Cu-free and Cu-added alloys. On the other hand, the microalloying of Cu strongly affects the nanocluster formation due to the strong interaction with Mg, Si atoms and vacancies. The first-principle calculation for the two-body interaction energies provides quite useful information to understand the early stage of the phase decomposition. The effects of nanoclusters and the Cu addition on the age-hardening behaviors of Al-Mg-Si alloys are discussed based on the multi-step age-hardening phenomena.

Poly(ethylene glycol), PEG, is a biofunctional molecule that inhibits the adsorption of proteins. Therefore, the immobilization of PEG on a metal surface is an important step in making metal surfaces biofunctional. The bonding manner of PEG to a titanium surface is significant for the design of PEG-immobilized materials; however, there are few characterization techniques for the determination of the immobilization manner of PEG. In this study, PEG terminated at one or both terminals with amine bases was immobilized on a titanium surface with electrodeposition and immersion. The electrodeposition was carried out with À5 V for 300 s. The immobilization manner of PEG was characterized using X-ray photoelectron spectroscopy (XPS) with an angle-resolved technique and glow discharge optical emission spectroscopy (GD-OES). As a result, not only electrodeposition but also immersion led to the immobilization of PEG onto a titanium surface. However, more terminated amines combined with titanium oxide as an ionic NH-O with electrodeposition, while more amines randomly existed as NH 3 þ in the PEG molecule with immersion. Moreover, the difference in the amine termination resulted in a different manner of bonding. The PEG terminated at both terminals immobilized in a U shape, and the PEG terminated at one terminal immobilized a brush. Characterization with XPS and GD-OES is useful to determine the immobilization mode of PEG to a solid surface.

Electrochemical treatments are expected to be effective for the coating of calcium phosphate ceramics to a titanium substrate. In the present study, two types of chronoamperometry with a step potential and a cyclic wave potential at low voltage (up to 2.0 V) and low current density were performed in Hanks' solution to modify the surface characteristics of titanium. Titanium oxide film formed by self-passivation, that formed as reconstructed film during electrochemical treatments, and a calcium phosphate layer precipitated through treatments were characterised by X-ray photoelectron spectroscopy. The thickness and compositions of the surface films and layers were quantified from the XPS results. Calcium phosphate formation during immersion in Hanks' solution for 1.0 Ms was evaluated by scanning electron microscopy with energy-dispersive X-ray spectrometry. The results confirmed that the electrolytic treatments in this study were effective to accelerate calcium phosphate formation on titanium in Hanks' solution in spite of their lower voltage than conventional methods. The results also suggested that the hydroxyl group in the surface oxide film might contribute to the formation of calcium phosphate. This technique is a promising process for the treatment of thin titanium materials.

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The objective of this study was to investigate the structure and strength at the bonding interface of a titanium (Ti)-segmented polyurethane (SPU) composite through (3-trimethoxysilyl) propyl methacrylate (gamma-MPS) for artificial organs. The effects of the thickness of the gamma-MPS layer on the shear bonding strength between Ti and SPU were investigated. Ti disks were immersed in various concentrations of gamma-MPS solutions for several immersion times. The depth profiles of elements and the thickness of the gamma-MPS layer were determined by glow discharge optical emission spectroscopy and ellipsometry, respectively. The bonding stress at the Ti/gamma-MPS/SPU interface was evaluated with a shear bonding test. Furthermore, the fractured surface of a Ti-SPU composite was observed by optical microscopy and characterized using X-ray photoelectron spectroscopy. Consequently, the thickness of the gamma-MPS layer was controlled by the concentration of the gamma-MPS solution and immersion time. The shear bonding stress at the interface increased with the increase of the thickness of the gamma-MPS layer. Therefore, the control of the thickness of the gamma-MPS layer is significant to increase the shear bonding stress at the Ti/gamma-MPS/SPU interface. These results are significant to create composites for artificial organs consisting of other metals and polymers.