The defects of the hot-dip galvanized coating found in the course of actual operation were sampled for clarifying the defect formation mechanism. The composition of galvanized coating was 43.4 mass%Zn-55 mass%Al-1.6 mass%Si. In the initial stage and middle stage of operation, five defects were selected from many defects. Observations of optical microscope and SEM, analyses by μ-XRF and SEM-EDS were carried out for the surface and the cross section of those defects. The results were summarized and classified into three kinds of formation mechanism as follows: (1) One is the defect occurred from the remained oxide film on the steel surface which was not reduced in the surface treatment process. (2) Second is the defect occurred from the dross (Fe-Al-(Si) intermetallic compound) formed in the bath. (3) Third is the defect occurred from the aggregation consisted of the dross (Fe-Al-(Si) intermetallic compound) and metal oxides (CaO, SiO2 and Fe2O3, and so on) existing as impurities.
The structure and formation of superabundant vacancies in electroplated Ni64Fe36 alloy films have been studied by XRD and thermal desorption spectroscopy. The films, as deposited, consist of fine grains of ca. 10 nm in size, which, upon heating, start to undergo a gradual grain growth at ~600 K, and a rapid growth above ~670 K. The desorption of hydrogen occurred in seven stages; P0(385 K), P1(440 K), P2(560 K), P3(670 K), P4(960 K), P5(1170 K), and P6(>1270 K). P0 is attributed to desorption of H atoms on regular interstitial sites, P1~P2 and P4~P5 to H atoms trapped by vacancies, and P6 to hydrogen bubbles precipitated in the matrix. P3 and a desorption peak of CO+ (1100 K) are attributed to the decomposition of occluded C, H compounds. Binding energies of H in these trapped states are estimated, and possible configurations of these vacancy-H clusters are discussed.
Titanium-zirconium (Ti-Zr) binary alloy has better corrosion resistance and mechanical properties than commercially pure Ti. The present study was designed to determine the biocompatibility of Ti-Zr alloy by an implantation test in animal bodies in comparison with pure Ti, Zr, and chromium (Cr) implants. Sample specimens were placed in a subcutaneous position in rats for 8 months. No significant decreases in body weight, the weight of any organ, or the weight of any organ relative to body weight were found in the implant groups compared to a no-implant control group. On hematological examination, small differences in several parameters were found in some groups, but these changes were not attributable to the materials implanted. Mitogen-induced blastogenesis was observed in similar degrees among all implant groups. These results suggest that the implantation of test samples did not cause systemic toxicity or a decrease in immune activity. The fibrous capsule membranes around the Ti and Ti-Zr alloy implants were thinner than those around Cr implants. The numbers of macrophages, inflammatory cells, and other cells involved in immune responses in and around the fibrous capsules of the Cr- and Ti-implant groups were higher than those of the Ti-Zr alloy- and Zr-implant groups. The Ti-Zr alloy had the lowest total score of tissue responses among the materials tested. None of the animals from the Ti-, Zr-, and Ti-Zr alloy-implant groups exhibited a skin reaction following exposure to Ti or Zr salt solutions. These results indicate the Ti-Zr alloy has better biocompatibility than Ti for use as an artificial surgical implant.
In the high pressure die casting products, it is difficult to prevent the formation of gas porosities, which adversely affect the mechanical properties or air-leakage resistances of such products. In this work, the products after casting were subjected to compression tests to reduce gas porosities having an inner pressure. From the experiments of compressing the products, the porosities were reduced efficiently by applying a 10% compressive strain. These porosities were quantitatively confirmed to be gas porosities by the analysis of the fractal dimensions of the shape of the porosities. From the finite element analysis of the model containing a circular defect with an inner pressure under compression, the porosities were reduced efficiently by applying a 10% compressive strain. From the results of both experiments and finite element analysis, it is concluded that compression processing is an effective method of reducing gas porosities and improving the mechanical properties and air-leakage resistances of die casting products.
The frictional wear characteristics of heat-treated Ti-29Nb-13Ta-4.6Zr (TNTZ) subjected to solution treatment (TNTZST) or aging treatments at 598, 673, and 723 K, respectively after solution treatment (TNTZ598 K, TNTZ673 K, and TNTZ723 K, respectively) and Ti-6Al-4V ELI (Ti64) subjected to aging treatment after solution treatment (T64STA) in air and simulated body environment (Ringer's solution) were investigated as a function of load in this study. Wear weight losses of TNTZST, TNTZ598 K, TNTZ673 K, TNTZ723 K, and Ti64STA are smaller in Ringer's solution than in air under both low and high loading conditions (1.96 and 29.4 N, respectively). This is considered to suggest that the frictional coefficient decreased because of the lubricant effect of Ringer's solution between the contact surfaces of specimen and zirconia ball as mating material. The wear losses of TNTZST, TNTZ598 K, TNTZ673 K, TNTZ723 K, and Ti64STA increase with increasing load in Ringer's solution. The wear losses of TNTZST, TNTZ598 K, TNTZ673 K, and TNTZ723 K at a low loading level are smaller than that of Ti64STA in Ringer's solution. On the other hand, the wear losses of TNTZ598 K and TNTZ673 K at a high loading level are larger than that of Ti64STA in Ringer's solution. This reason is that the transition point from sever wear to mild wear versus load is changed according to the materials.
Formation of the reaction product layer on the surface of biomedical titanium alloys, Ti-29Nb-13Ta-4.6Zr (TNTZ) and Ti-6Al-4V ELI (Ti64), during gas nitriding was investigated. These alloys were exposed to nitrogen atmosphere at 1023, 1073, 1123 and 1223 K. After the gas nitriding, a reaction product layer was observed on the surface of both alloys, and was analyzed using an X-ray diffraction (XRD), Auger electron spectroscopy (AES) and X-ray Photoelectron spectroscopy (XPS). The layer was comprised of two phases, which were outer oxide layer (mainly TiO2) and inner nitride layer (mainly TiN or Ti2N). In these layers, the thickness of the oxide layer particularly depended on the kinds of alloys. According to the thermodynamics and point defect theory, the growth rate of oxide layer is expected to be increased by the presence of Al in TiO2. Namely, the dissolution of Al into TiO2 may increase the number of oxygen vacancies, resulting in acceleration of oxygen diffusion inward. On the other hand, the elements that accelerate the growth of the oxide layer are not contained in TNTZ. Thus, the oxide layer formed on Ti64 was thicker than that of TNTZ. In a similar way, the elements that accelerate the growth of the nitride layer are not contained in both TNTZ and Ti64. Thus, the nitride layers with similar thicknesses may be formed on TNTZ and Ti64 during gas nitriding.
The phenomenon named Radiation Induced Surface Activation (RISA) was discovered recently. It is a phenomenon involving the activation of surfaces of metallic oxides attributable for strong affinity for water. In this work, we examined wettability increase under irradiations with γ-ray and UV, as well as its degradation under non-irradiation condition by measuring the changes of water contact angle on oxide layers formed onto Zircaloy-4 plates. The water contact angle for the sample surface decreased gradually under irradiation, and increased gradually by darkroom storage after irradiation. The theoretical formula, which describes the development of the hydrophilic surface under irradiation and its stability, was fitted to the experimental results. It caused us to propose the existence of two kinds of hydrophilic factors in terms of stability, whose formation probabilities depend on the type of irradiation.
Orientation of hydroxyapatite (HAp) crystals is one of the promising ways to utilize their anisotropic nature of chemical and biological properties. On the other hand, the development of superconducting magnet technology enables us to provide a high magnetic field which can control crystal orientation of non-magnetic materials with magnetic anisotropy. In this study, a horizontal 10 T static magnetic field was imposed on slurry containing HAp crystals under the horizontal mold rotation during slip casting process so as to introduce c-axis orientation for some amount of crystals in the sample, and then it was sintered in atmosphere without the magnetic field. From SEM observation and X-ray diffraction, it has been found that the c-axis of pillar shape HAp crystals of the sample treated with the magnetic field and the mold rotation were oriented to a particular direction and it was enhanced by the subsequent sintering process, while the c-axis crystal orientation of the sample treated without the magnetic field and with the mold rotation was not observed before and after the sintering.
The stress shielding effect often degrades the quality and quantity of bone near implants. Thus, the shape and structure of metallic biomaterials should be optimally designed. A dominant inorganic substance in bone is biological apatite (BAp) nanocrystal, which basically crystallizes in an anisotropic hexagonal lattice. The BAp c-axis is parallel to elongated collagen fibers. Because the BAp orientation of bone is a possible parameter of bone quality near implants, we used a microbeam X-ray diffractometer system with a beam spot, which had a diameter of 50 μmφ or 100 μmφ, to evaluate it. Two animal models were prepared: (1) a nail model (φ: 3.0 mm, SUS316L), which was used to understand the stress shielding effect in a rabbit tibial marrow cavity; and (2) a model of a lotus-type porous implant (φ: 3.4 mm, mean pore diameter: 170 μm, SUS304L), which was used to understand the effect of the unidirectional-elongated pore direction in anisotropic bone tissue of a beagle mandible. The porous implants were implanted so that the pore direction was parallel or perpendicular to the mesiodistal axis of the mandible. For the porous implant model, new bone formation strongly depended on the elongated pore direction and the time after implantation. For example, four weeks after implantation, new bone formed in pores of the implants, but the BAp orientation degree in the new bone was more similar to that in the original bone in the elongated pores parallel to the mesiodistal direction than that in the perpendicular pores. These differences in bone formation inside the parallel and perpendicular pores may be closely related to the anisotropy of original bone tissue such as the orientations of collagen fiber, BAp, and blood vessels. The orientation degree of the BAp also changed in the nail model. The stress shielding effect decreased the orientation degree of the BAp c-axis in the tibia along the longitudinal axis. Thus, the optimal design of metallic biomaterials, including such characteristics as implant shape, pore size, and elongated pore direction should be based on the anisotropy of the bone microstructure.
Quenching and annealing experiments with electric resistivity measurements were applied to magnesium to investigate the formation of thermal vacancies. Two specimens made from materials differing in impurity contents were examined. One of the specimens that was quenched into a methanol bath at -80°C from elevated temperatures ranging from 160 to 500°C revealed a significant decrease in electrical resistance during subsequent annealing for ten minutes in the bath. This decrease is attributed to the presence of hydrogen in solution, on the basis of annealing behaviors at low temperatures (-100~-60°C) after the quenching from 200°C. Another specimen, presumably containing smaller amounts of hydrogen, was quenched into iced water from elevated temperatures (200~560°C), which yielded results characterized by two thermal activation processes. These processes have the activation energies, 54.1 kJ/mol (0.56 eV) and 89.8 kJ/mol (0.93 eV) for lower and higher quenching temperature range, respectively. The former is ascribed to the formation energy of a vacancy interacting with hydrogen and the latter the intrinsic formation energy of a vacancy. The difference of these energies, namely 35.7 kJ/mol (0.37 eV), can be identified as the binding energy between a vacancy and a hydrogen atom.