Liwei Zhu, You Saito, Koji Koike, Kensuke Kuroda, Masazumi Okido
It has been reported that hydrophilicity and hydrophobicity of implants influenced the bioactivity. However, it is hard to maintain the hydrophilicity in case of being stored in air. So it is critical to find a way to maintain implants’ hydrophilicity. In general, silicate has been known to contribute the hydrophilicity. In this study, the silicate containing CaTiO3 films have been prepared on Ti substrates by two-step treatment for biomaterial applications. The hydrophilicity, osteoconductivity and protein adsorption of treated specimens have been investigated. The 1st step treatment for Ti is to form TiO2 as precursors, either by anodizing in sulfuric acid solution at 298 K, liquid phase oxidation in nitric acid solution with hydrogen peroxide at 353 K, or thermal oxidation at 673 K in air. Hydrothermal treatment in silicate containing alkaline solution is the 2nd step to convert TiO2 to silicate containing CaTiO3 films. The SEM, XRD, XPS, WCA (water contact angle) investigations and protein adsorption measurements have been carried out to characterize the surface properties. This surface maintained 10 deg. in WCA after 7 d exposure in air, while the specimen without silicate has WCA of more than 40 deg. The osteoconductivity is evaluated based on the contact ratio of formed hard tissue on the implanted specimens after 14 d implantation in rats’ tibia at in vivo test. The as-prepared film not only has exhibited smooth and superhydrophilic surface, but also has achieved high osteoconductivity and great protein adsorption capacity.
This review confirms that the Love equation which connects the load on a rigid cone loaded normally on an elastic half-space, and its penetration into the half space, has been verified by several theoreticians. Furthermore, the predictions of the Love equation have been experimentally validated. It is argued here that a modification of the Love equation made about 20 years ago is incompatible with several theoretical treatments as well as with the expression for radial surface particle displacement outside the contact. Moreover, it is also shown that normal loading behaviour of a rigid cone on an elastic half-space cannot be likened to that of the normal loading behaviour of a rigid three-sided or a four-sided pyramid. Lastly, corrections are made to some important expressions given in a well cited paper by Sneddon (1965).
In this study, the effect of Cl removal in bottom ash via a carbonation treatment with CO2 was investigated by comparing it with a water washing treatment. First, this was also focused on examining the existence of Cl contained in the bottom ash. The overall (soluble and insoluble) Cl content was close to that of bottom ash with fine particle. Next, the washing with water was confirmed and it was not effective in decreasing the Cl content because of the existence of insoluble Cl. Whereas, the removal effect of Cl via carbonation with CO2 was very high compared to the washing treatment because of the decomposition of Friedel’s salt (main insoluble Cl).
In addition, the kinetics data pertaining to the decomposed Friedel’s salt as the carbonation process proceeds was confirmed. The theoretical was well fitted to the kinetics data. The variation of the rate is constant upon decomposition with the reaction temperature followed the Arrhenius equation (19.676 kJ/mol of activation energy) and the orders with respect to water-to-solution and particle size were also obtained. The decomposition rate of Friedel’s salt based on diffusion through the product layer of shrinking core model could be expressed by the equation.
Saya Ajito, Eiji Tada, Azusa Ooi, Atsushi Nishikata
In this study, pH measurement was performed in a thin electrolyte droplet with a thickness <1000 µm by the measurement of the equilibrium electrode potential of an Sb/SbxOy electrode used as a pH sensor. The equilibrium potential of the Sb/SbxOy electrode was evaluated by using the Kelvin probe (KP) technique. To investigate the potential response of the Sb electrode in a thin electrolyte droplet, the dependency of the Volta potential difference between the Sb and a gold wire as a KP on electrolyte droplet thickness was measured. The Volta potential difference had a linear response with respect to the buffer solution pH, independent of the droplet thickness. This result indicates that the KP technique, combined with an Sb electrode, is sensitive to the pH of a thin electrolyte droplet of thickness ≥50 µm. This pH measurement technique was also applied to measure pH in a corrosion model of steel. The corrosion model consisted of two steel plates in the same plane as the anode and cathode, with a constant current between them. During the corrosion process, the pH value decreased from 6 to 5 near the anode and increased from 6 to 12 at the cathode. The changes in pH measured in the thin electrolyte droplet were in good agreement with the color changes of the solution containing pH indicators.
The compressive deformation behavior and magnetic volume susceptibility were investigated for Au2CuAl biomedical shape memory alloys in a compositional range from 25 to 45 mol%Cu. Compression tests revealed that the stress for martensite variant reorientation was 282 MPa in Au2CuAl, and the value increased with the Cu content. On the other hand, the slip stress was higher at intermediate compositions. Moreover, intergranular fracture was suppressed during compressive deformation. Calculated antiphase boundary (APB) energies suggest the dissociation of superlattice dislocation, which leads to the active slip of 〈111〉-type. The measured magnetic volume susceptibility was −2.7 × 10−6 in Au2CuAl, hence, this alloy is judged to be metal-artifact-free in magnetic resonance imaging (MRI). The magnetic susceptibility increased up to +7.0 × 10−6 with increasing Cu content.
We study plastic flow in the vicinity of an indenter-material interface in wedge indentation of aluminum using high speed in situ imaging and particle image velocimetry (PIV) analysis. Displacement and strain fields in the indentation zone are obtained at high-resolution for different indenter angles and two lubrication conditions. These fields can be used to demarcate essential features of the material flow phenomena. The deformed layers close to the indenter wall fit a classical boundary layer profile in the framework of a Bingham-solid. Equivalent Bingham viscosities and boundary layer scaling relations are obtained. The viscosity values appear to reflect the nature of the friction interaction at the indenter-material interface and can potentially be used as a discriminating parameter for evaluating contributions to deformation and dissipation arising from interface friction.
In the present study, a newly established in situ indentation technique by the use of an optically transparent indenter and an immersion liquid, so-called “modified optical indentation microscopy”, was applied for an investigation on the plastic deformation behavior of various samples during indentation. In this technique, the gap between the indenter and the specimen surface is filled with the immersion liquid such as silicone oil and kerosene to widely observe the specimen surface during indentation. In the in situ observations by this technique using polycrystalline pure Mg, the occurrence of various plastic deformation mechanisms and the increase of the anisotropic contact area during indentation can be recognized. Moreover, the increase and the decrease of the contact area which is corresponding to superelasticity during indentation were observed by this technique using the TiNi superelastic alloy. The results of the in situ observations were consistent with the analysis results based on the Hertz theory.
The selective laser melting could be employed in fabrication of near-net shape products for airplane and biomedical applications from Ti–6Al–4V alloy, which is difficult-to-process material. In this method, the localized laser irradiation forms the unique Ti–6Al–4V microstructures which correspond to the laser scanning patterns and local thermal history as it could be observed from sample cross-sections with OM or SEM. In this study, the effects of heat treatments on mechanical properties of Ti–6Al–4V samples produced by selective laser melting are discussed based on quantitative analysis of microstructures with image processing and machine learning tools. It was found that microstructures of heat-treated samples retained their original morphologies and secondary α phase precipitated regularly at β grain boundaries with increased treatment time. These microstructures were appropriately segmented and classified. Each α particle geometrical characteristics were successfully extracted and evaluated by image analysis. Importantly, the hardness of the heat-treated samples was lower compared to that of as-built ones and it tended to increase with the area fraction of α phase, the α particle width, and the nearest neighbor distance between α particles.
Keisuke Asai, Satoshi Yoshida, Akihiro Yamada, Jun Matsuoka, Andrei Errapart, Charles R. Kurkjian
In this study, micro-photoelastic measurements were performed to obtain three-dimensional stress maps of silica and soda-lime glasses during ball indentation. The stress components were calculated from retardations and azimuths, which were determined from photoelastic measurements with a spatial resolution of about 1 µm. During loading, it was observed that the tensile stress in the radial direction is generated near the surfaces of both glasses. During unloading, however, it was found that stress distributions of silica and soda-lime glasses are different from each other. It is concluded that the different stress distributions during indentation result in different crack geometries, ring and radial cracks.
A. Toshimitsu Yokobori, Jr., Go Ozeki, Toshihito Ohmi, Tadashi Kasuya, Nobuyuki Ishikawa, Satoshi Minamoto, Manabu Enoki
Hydrogen embrittlement cracking caused at a weld joint is considered to be dominated by hydrogen diffusion and concentration driven by thermal stress induced by heat transfer during cooling process. The gradient of hydrostatic stress component is considered to be a driven force of hydrogen transportation. However, this problem concerns the occurrence phenomenon during cooling process. Therefore, diffusion coefficient, yield stress and Young’s modulus are changed corresponding with temperature change. Especially, diffusion coefficient shows the space gradient corresponding with space gradient of temperature caused by heat transfer. This affects the diffusion equation of hydrogen as a driven force of hydrogen diffusion. Under these backgrounds, to clarify not only the effect of local thermal stress but also that of space gradient of diffusion coefficient on hydrogen release and trap, the hydrogen diffusion analysis based on our proposed α multiplication and FEM-FDM methods was conducted by introducing the terms of gradients of diffusion coefficient and temperature into the diffusion equation. The following results were obtained. The space gradient of diffusion coefficient was found to contribute the release of hydrogen from the site of stress concentration when the gradient of local hydrogen concentration takes the same sign as that of diffusion coefficient. Concerning the prevention of hydrogen embrittlement cracking at weld joint, these results show that not only Pre-Heat Treatment (PHT) which is a mechanical factor, but also the space gradient of diffusion coefficient which is a factor of material science was found to be one of effective factor of release of hydrogen from a site of stress concentration.
Solubility of CaS in molten CaCl2–65 mol%LiCl eutectic salt was examined by sampling of CaS saturated salt and ICP analysis. The handling in dried environment and an adequate mass of melt were applied for reliable measurements, in addition to suppression of inclusion of CaS particles. The solubility limit was found to be 0.22 ± 0.05, and 0.31 ± 0.05 mol%CaS at 873 K and 973 K, respectively. This saturation value was less than 1.77 ± 0.1 mol%CaS in pure CaCl2 at 1173 K.
The range of application of molecular dynamics (MD) simulations is rapidly expanding owing to the recent advance in high-performance computing. Since only the coordinate and velocity of atoms in the system are directly obtained from MD simulations, it is important to correctly understand how the coordinate and velocity of atoms are converted into thermodynamic and interfacial properties. Here, MD-based techniques for estimating the thermodynamic and interfacial properties of metallic materials are assessed by considering practical examples of the melting point of a pure metal, the solidus and liquidus compositions of a binary alloy, the grain boundary energy, the solid-liquid energy, and the kinetic coefficient.
Igor I. Maslenikov, Vladimir N. Reshetov, Alexey S. Useinov
The transparent indenter which can used as an optical objective were tested to obtained a spectra during the indentation. A special device which comprises the transparent indenter and actuator was developed and embedded into the Raman spectrometer. An indentation into the silicon sample was performed and phases that exist under the load and without it were identified.
A spinal cage is one of the primary spinal devices used for the treatment of spinal diseases such as lumbar spondylolisthesis. Since it is set in the intervertebral space that causes instability to promote the fusion of the adjacent vertebral bodies, it requires the early induction of healthy bones. For this reason, in most cases, an autogenous bone extracted from the patient’s ilium is implanted in the interior of the cage to stimulate bone formation. However, collecting autogenous bone involves secondary surgery and several clinical problems such as pain in the part from which it is collected. Additionally, the effect of the autogenous bone graft itself has not been sufficiently studied yet. Moreover, the mechanical functions of trabecular bones in a vertebral body are governed by the anisotropic structure of the trabeculae and the preferential orientation of the apatite/collagen in a trabecula with respect to the principal stress. Despite this fact, after the implantation of the cage, the mass of the bones is evaluated with soft X-ray photography, which does not guarantee an accurate measurement of bone functions. In this study, the effect of the autogenous bone graft on the spinal cage was verified based on structural anisotropy of trabecular bones and the preferential orientation of apatite/collagen in a trabecula using sheep. The autogenous bone graft demonstrated a significant effect on the increase of bone mass and anisotropy of the trabecular structure. However, compared to the trabecular anisotropy of normal parts, the anisotropy of the trabecular structure and apatite c-axis orientation of the parts with autogenous bone graft were considerably lower, indicating a minimal effect of the autogenous bone graft. Therefore, it was suggested that early stabilization of the spinal cage requires another strategy that rapidly forms the unique hierarchical anisotropic structure of trabecular bones.
A magnesium matrix composite comprising Mg–0.5 mass%Ca and 10 vol.% β-tricalcium phosphate (TCP) particles was processed with the aim of developing biodegradable material. The composite was produced by extruding a mixture of two component powders at 538 K. The matrix of the extruded composite comprised fine equiaxed grains (grain size: 1.3 µm). Moreover, isolated β-TCP particles and agglomerated particles (size: 10–15 µm) were observed. Owing to grain refinement, the composite exhibited a high yield strength (>300 MPa) at room temperature and behaved in a superplastic manner at ∼548 K.
Satoshi Yoshida, Thu Huyen Nguyen, Akihiro Yamada, Jun Matsuoka
In-situ structural changes of glass under a sharp diamond indenter are evaluated by using a micro-Raman spectrophotometer coupled with a self-made indentation equipment. This set-up enables us to obtain in-situ Raman spectra of glass under a Vickers indenter and to observe transient and permanent structural changes in glass. It is found that in-situ Raman spectra of silica glass under the Vickers indenter show distinct peak-broadening, which is not observed in the in-situ Raman spectra of hydrostatically compressed silica glass, nor in those of soda-lime silicate glass. This suggests that the indentation-induced shear stress causes the glass structure to be deformed into a different one with a wider bond angle distribution. Such a shear-induced structural change could play a key role on the contact damage of glass, especially for glass with a high degree of polymerization, like silica glass.
The temperature dependence of 0.2% proof stress was investigated in Ti–0.49 mass%O with an α single phase. The 0.2% proof stress decreased as the temperature increased from 77 to 573 K. The athermal stress, which was defined as the average of the stress values for which the temperature dependence was absent above 573 K, was found to be 70 MPa. The temperature dependence of the effective stress indicates that the temperature dependence of the effective stress changed at around 400 K. To study the thermally activated process that controls the yielding in Ti, the temperature dependence of the activation volume was also measured. An inverse temperature dependence of the activation volume was found at between 325 and 400 K, suggesting that the thermally activated process of dislocation glide changed at this temperature. Prismatic slip with 〈a〉 dislocations was dominant at low temperatures, whereas other slips were activated at high temperatures. The activation enthalpy for the dislocation glide was also measured between 77 and 573 K.
To characterize the relationship between the cyclic yield and monotonic tensile properties of HAZ microstructures, incremental step tests were carried out on a total of eight microstructures of low-carbon steel that had been subjected to several simulated HAZ heat treatments. The results showed that most of the cyclic stress-strain relationships evaluated using incremental step tests roughly agreed with those from constant-stress amplitude tests. Furthermore, the cyclic yield stresses of simulated HAZ microstructures were proportional to these tensile strengths, similar to ordinary carbon and low-alloy steels. Although cyclic yield coefficients were also proportional to these tensile strengths, the slope of the proportional line is steeper than that of ordinary steels. Approximation formulas using monotonic tensile stress to calculate cyclic hardening coefficients for simulated HAZ were therefore determined as the least-squares line compiled from the experimental data.
The formation of site-percolated states of exact equiatomic high-entropy alloys (HEAs) with body-centered-cubic (bcc) and face-centered-cubic (fcc) structures was investigated where their critical concentrations (pcsite) are given as 0.245 and 0.198, respectively, from conventional percolation theory. Molecular dynamics simulations were performed for WNbMoTa and WNbMoTaV HEAs with a bcc structure and AuCuNiPt and AuCuNiPdPt HEAs with an fcc structure. The simulation conditions included a generalized embedded atom method potential under NTp ensemble where the number of elements (N), absolute temperature (T), and pressure (p) were maintained constant. N-element alloys (N = 4 and 5) with a fraction of constituent elements (x = 1/N) were initially prepared in 10 × 10 × 10 supercells randomly in terms of chemical species and were simulated under atmospheric pressure at T = 1000 K. The total pair-distribution functions of the alloys revealed that the nearest neighbor distance (dn) for fcc ranged from 0.20 to 0.33 nm, whereas dn and the second neighbor distance (dnn) for bcc ranged from 0.235 to 0.305 nm and 0.305 to 0.370 nm, respectively. A 3-dimensional topological analysis for atomic correlations revealed that the alloys were in percolated and isolated states, respectively, when x ≥ pcsite and x < pcsite and that the values of 1/pcsite correspond to the ideal values of N for exact equi-atomic HEAs. Furthermore, it was observed that exact equi-atomic quaternary alloys (N = 4) with a bcc structure and quinary alloys (N = 5) with an fcc structure are in the critically percolated states.
Cast Mg85Y9Zn6 has an 18R-type LPSO structure. However, Mg85Y9Zn6 recovered after being subjected to a loading pressure of 7 GPa at 973 K shows a fine dual-phase structure composed of a face-centered cubic (fcc) structure showing a superlattice (D03), as well as a hexagonal close-packed structure (hcp:2H). The D03/hcp structure transformed to 18R-type LPSO during heating at ambient pressure. In this research, the transformation process from the D03/hcp structure to 18R-type LPSO structure was discussed by means of in situ XRD and first-principles calculation. At first, lattice volume of 2H increased with an increase in the temperature, because of the Zn and Y emitted from the D03 phase into the 2H lattice. After the volume expansion of 2H lattice, the structure collapsed due to insert of random stacking faults (SFs). Then, a formation of 18R-type LPSO structure occurred. Based on a first-principles calculation for pure Mg, volume expansion of the 2H lattice causes the transformation to an 18R structure. Furthermore, the results of free energy calculations for the hcp and fcc structures in the Mg–Y–Zn ternary system show that the segregation of Y and Zn atoms on SFs occurs by the Suzuki effect. These segregated Y and Zn atoms in SF layers, which have a local fcc structure, create a synergy between the stacking and chemical modulations. Present result insists that the volume increase of 2H lattice takes place first, and then the transformation from the hcp structure to 18R stacking occurs.