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The electrodeposition of tungsten at moderate temperatures (4 and WCl5 in 1-ethyl-3-methylimidazolium chloride (EMIC) and EMIC–AlCl3 ionic liquids at 80 °C–120 °C. W-rich films with a thickness of approximately 1 μm were obtained from the Lewis acidic EMIC–AlCl3–WCl5 bath, whereas the other baths did not yield any deposits. The films obtained from the EMIC–AlCl3–WCl5 bath at 80 °C had higher W contents of 54 at.% than those obtained at 120 °C. X-ray absorption near-edge structure spectra of the W-rich films indicated that W existed in an oxidized state. The findings of this study can be used as a guide to explore optimal electrolytes and electrolytic conditions for the electrodeposition of metallic W at moderate temperatures.

We have investigated the effects of solute oxygen on the kinetics of diffusionless isothermal omega (DI-ω) transformation in β-titanium vanadium alloys. This transformation constitutes a third category of ω transformation beside the athermal and isothermal modes. Thermal analysis, hardness and internal friction measurements were conducted after quenching oxygen-containing and near-oxygen-free alloys with ~ 21 at%V from the β-stable temperature. At this level of vanadium concentration, the athermal ω transformation is not expected. It is found that the DI-ω transformation more rapidly progresses in the low oxygen alloy and the relaxation strength of the elementary process of {111}β collapse is significantly reduced.

Nanocomposite microstructures dominating the anisotropic elastic properties in carbon fibers were studied, to construct a micromechanics model that can explain the anisotropic elastic properties of carbon fibers. Aluminum-based composites containing five types of carbon fibers were prepared, and their anisotropic elastic properties were measured using resonant ultrasound spectroscopy combined with electromagnetic acoustic resonance. Then, all the independent elastic stiffness components of the carbon fibers were extracted from those of the composites using a composite model based on Eshelby's inclusion theory, Mori–Tanaka mean-field theory, and effective-medium approximation. Moreover, we newly developed a nanocomposite microstructure model that can fully reproduce all the anisotropic constants of carbon fibers exhibiting a wide variety of Young's moduli. In the developed model, the microstructures of carbon fibers were approximated as nanocomposites comprised of an amorphous carbon matrix and graphite-crystal inclusions that are aggregations of graphite nanocrystallites. Based on this nanocomposite microstructure model, the shape of the graphite-crystal inclusions and the elastic properties of the amorphous carbon matrix were analyzed, considering the volume fraction and orientation of the graphite nanocrystallites, as determined using X-ray diffraction. The analysis revealed that the shapes of the graphite-crystal inclusions are flat ellipsoids elongated along the fiber axis, and the aspect ratio of the graphite-crystal inclusions dominantly affects the anisotropy in the Young's modulus. This indicates that the graphite nanocrystallites are connected along the in-plane directions of the graphitic layers, and not the shape of nanocrystallites but their two-dimensional connectivity dominates the anisotropic elastic modulus in carbon fibers.

Diffusionless isothermal omega ($\mathrm{DI}\text{\ensuremath{-}}\ensuremath{\omega}$) transformation, which was recently defined in Phys. Rev. Materials 3, 043604 (2019), is classified into a third category of the $\ensuremath{\omega}$ transformation modes, other than the well-known isothermal and athermal modes. This work reveals the characteristic features of the $\mathrm{DI}\text{\ensuremath{-}}\ensuremath{\omega}$ transformation in the $\ensuremath{\beta}$-titanium vanadium alloy system, specifically, focusing on variations in the microstructure and mechanical properties with the proceeding of the $\mathrm{DI}\text{\ensuremath{-}}\ensuremath{\omega}$ transformation. After quenching alloys of Ti-15at%V, Ti-21at%V, and Ti-27at%V down to below room temperature from the $\ensuremath{\beta}$-stable temperature, in addition to the occurrence of the athermal $\ensuremath{\omega}$ transformation for Ti-15at%V, all of the alloys gradually undergo the $\mathrm{DI}\text{\ensuremath{-}}\ensuremath{\omega}$ transformation upon aging at a temperature as low as 373 K, leading to a moderate increase in the hardness. The degree of the hardness increase in these alloys can be successfully explained by a local instability concept based on quenched-in thermal concentration fluctuations. It is also shown that internal friction (Ti-21at%V) diminishes after the low-temperature aging, which indicates the annihilation of such unstable regions showing a dynamic collapse of ${{111}}_{\ensuremath{\beta}}$ pairs to form a transient $\mathrm{DI}\text{\ensuremath{-}}\ensuremath{\omega}$ phase. Comparison of inelastic x-ray scattering and ultrasound measurements can see a trail of the $\mathrm{DI}\text{\ensuremath{-}}\ensuremath{\omega}$ transformation remaining even in the Ti-27at%V alloy, which has no obvious athermal omega transformation temperature. Based on the results, the difference between athermal $\ensuremath{\omega}$ and $\mathrm{DI}\text{\ensuremath{-}}\ensuremath{\omega}$ transformations is finally discussed.

Tane M., Nishiyama H., Umeda A., et al. Diffusionless isothermal omega transformation in titanium alloys driven by quenched-in compositional fluctuations. Physical Review Materials 3, 043604 (2019); https://doi.org/10.1103/PhysRevMaterials.3.043604., In titanium alloys, the ω(hexagonal)-phase transformation has been categorized as either a diffusion-mediated isothermal transformation or an athermal transformation that occurs spontaneously via a diffusionless mechanism. Here we report a diffusionless isothermal ω transformation that can occur even above the ω transformation temperature. In body-centered cubic β-titanium alloyed with β-stabilizing elements, there are locally unstable regions having fewer β-stabilizing elements owing to quenched-in compositional fluctuations that are inevitably present in thermal equilibrium. In these locally unstable regions, diffusionless isothermal ω transformation occurs even when the entire β region is stable on average so that athermal ω transformation cannot occur. This anomalous, localized transformation originates from the fluctuation-driven localized softening of 2/3[111]β longitudinal phonon, which cannot be suppressed by the stabilization of β phase on average. In the diffusionless isothermal and athermal ω transformations, the transformation rate is dominated by two activation processes: a dynamical collapse of {111}β pairs, caused by the phonon softening, and a nucleation process. In the diffusionless isothermal transformation, the ω-phase nucleation, resulting from the localized phonon softening, requires relatively high activation energy owing to the coherent β/ω interface. Thus, the transformation occurs at slower rates than the athermal transformation, which occurs by the widely spread phonon softening. Consequently, the nucleation probability reflecting the β/ω interface energy is the rate-determining process in the diffusionless ω transformations.

Changes in the elastic properties during room-temperature aging (RT aging) of metastable Ti–Nb-based alloy single crystals with low body-centered cubic (bcc)-phase stability were investigated. The elastic stiffness components of Ti–Nb–Ta–Zr alloys with different Nb concentrations were measured by resonant ultrasound spectroscopy during RT aging; the results revealed that shear moduli c ′ and c 44 were increased by RT aging. In the alloy with the lowest Nb concentration, i.e., with the lowest bcc phase stability, shear moduli c ′ and c 44 were enhanced by the largest amount. The increase rates were ∼5% for 1.1 × 10 7 s (127 days), whereas the bulk modulus was hardly changed by aging. In Ti–Nb–Ta–Zr–O alloys with different oxygen concentrations, shear moduli c ′ and c 44 of the alloy with the lowest oxygen concentration increased most significantly. Moreover, the electrical resistivity of Ti–Nb–Ta–Zr and Ti–Nb–Ta–Zr–O alloys was increased by RT aging. Importantly, the enhancements of shear moduli and electrical resistivity were suppressed by increases in the bcc-phase stability (i.e., increase in the Nb concentration) and oxygen concentration; these factors are known to suppress ω (hexagonal) phase formation. However, transmission electron microscopy (TEM) observations revealed that only a diffuse ω structure—an ω -like lattice distortion—was formed after RT aging. On the basis of alloying element effects, TEM observations, and analysis of the changes in elastic properties by using a micromechanics model, it was deduced that the enhancements of shear moduli and electrical resistivity were possibly caused by the formation of a diffuse ω structure.

Nanoporous gold (NPG) with sponge-like structures has been studied by atomic-scale and microsecond-resolution environmental transmission electron microscopy (ETEM) combined with ab initio energy calculations. Peculiar surface dynamics were found in the reaction environment for the oxidation of CO at room temperature, involving residual silver in the NPG leaves as well as gold and oxygen atoms, especially on {110} facets. The NPG is thus classified as a novel self-activating catalyst. The essential structure unit for catalytic activity was identified as Au–AgO surface clusters, implying that the NPG is regarded as a nano-structured silver oxide catalyst supported on the matrix of NPG, or an inverse catalyst of a supported gold nanoparticulate (AuNP) catalyst. Hence, the catalytically active structure in the gold catalysts (supported AuNP and NPG catalysts) can now be experimentally unified in low-temperature CO oxidation, a step forward towards elucidating the fascinating catalysis mechanism of gold., Nanoporous gold (NPG) has gained significant attention, but its catalytically active structure has not yet been clarified. Here, the authors identify the catalytically active and dynamic structure in NPG by combining atomic-scale and microsecond-resolution environmental transmission electron microscopy with ab initio calculations.

The effects of stacking sequence and short-range ordering of solute atoms on the elastic properties of Mg–Zn–Y alloy single crystals with an 18R- or 10H-type long-period stacking ordered (LPSO) structure were studied. Instead of single crystals, the growth of which can be quite difficult, two directionally solidified (DS) Mg–Zn–Y alloy polycrystals, mainly consisting of 18R- or 10H-type LPSO structure, were prepared. X-ray pole figure analyses revealed that fiber textures, which differed in the two prepared alloys, were formed in the DS polycrystals. For the DS polycrystals, a complete set of elastic constants was measured during cooling from 300 to 7.5 or 5.5 K. By analyzing the elastic stiffness of DS polycrystals on the basis of a newly developed inverse Voigt–Reuss–Hill approximation, in which the detailed crystallographic texture could be taken into account, the elastic stiffness components of the single-crystalline LPSO phases from 300 to 7.5 or 5.5 K were determined. The elastic properties of the 18R- and 10H-LPSO phases were also evaluated by first-principles calculations based on density functional theory. Comparison of the measured elastic properties at 5.5 or 7.5 K with the first-principles calculations revealed that the elastic properties of the LPSO phase were virtually dominated by the stacking sequence of the LPSO structures and the formation energy of short-range ordered solute atom clusters, formed at the four consecutive atomic stacking layers. Importantly, the effects of the formation energy and stacking sequence were significant in the elastic moduli related to the atomic bonding between the stacking layers.

The tensile and compressive deformation in porous Mg with unidirectionally oriented cylindrical pores and a unique fiber texture in which the normal direction of the {1 0 1 ¯ 3} plane was preferentially oriented was studied. Porous Mg specimens with unidirectional pores and texture were prepared by unidirectional solidification in a hydrogen atmosphere using a continuous-casting technique and their quasi-static tensile deformation and quasi-static and dynamic compressions were investigated. In tensile loading parallel to the orientation direction of the pores (the “pore direction”), the porous Mg exhibited a large tensile elongation of ∼60% strain despite the presence of ∼42% porosity, whereas it showed high energy absorption of ∼30 kJ kg−1 along the same direction. To clarify these superior mechanical properties, the underlying operative deformation modes and rotation of crystallographic orientation during loadings were analyzed by X-ray pole figures, optical microscopy and crystal plasticity finite-element modeling. The analyses revealed that in the initial stage of both the compression and tensile loadings along the pore direction, basal slip mainly operated. Importantly, the activity of basal slip was enhanced during the tensile loading by rotation of the crystallographic orientation, which resulted in high tensile elongation. On the other hand, the activation of basal slip was initially suppressed by the crystal rotation during compression. However, the localization of basal slip originating from the elongated grains with the unique texture subsequently enhanced the activity of basal slip, which suppressed the steep increase in the flow stress. This unique localized deformation gave rise to the superior impact energy absorption.

The elastic properties of single-crystalline ω (hexagonal) phase of titanium are studied. Understanding the elastic properties is important for the development of biomedical titanium alloys with a low Young’s modulus. However, the elastic properties of the ω phase have remained unclear because of the difficulty in preparing a large single crystal consisting of a single phase of the ω phase, even though the ω phase has been believed to exhibit a higher elastic modulus than the β (body-centered cubic) phase. In this work, pure titanium was severely deformed by high-pressure torsion processing, to obtain polycrystalline specimens consisting exclusively of the ω phase, which is metastable at room temperature. For the ω-phase polycrystal, the complete set of elastic stiffness components was measured by RUS combined with laser Doppler interferometery. By analyzing the elastic stiffness of the ω-phase polycrystal on the basis of an inverse Voigt–Reuss–Hill approximation, the elastic stiffness components of the single-crystalline ω phase were determined. The Young’s modulus of the ω phase along 〈0001〉 was found to be clearly higher than that along 〈 1 1 2 ¯ 0 〉 , and the shear modulus also exhibited anisotropy. Importantly, the Young’s modulus and shear modulus of the metastable ω phase were higher than those of the β phase and also higher than those of the α (hexagonal close-packed) phase, which is stable at room temperature. Furthermore, analysis by a micromechanics model using the determined elastic stiffness deduced the effect of ω phase formation on the elastic properties of β-phase titanium alloys.

The elastic properties of an Mg85Zn6Y9 (at.%) alloy single crystal with a long-period stacking-ordered (LPSO) structure, synchronized with periodic enrichment of Zn and Y atoms, were investigated, the properties having remained unclear because of the difficulty in growing large single crystals. Directionally solidified (DS) Mg85Zn6Y9 alloy polycrystals consisting of a single phase of the 18R-type LPSO structure were prepared using the Bridgman technique. For the DS polycrystals, a complete set of elastic constants was measured with resonant ultrasound spectroscopy combined with electromagnetic acoustic resonance, in which the texture formed by the directional solidification was taken into account. By analyzing the elastic stiffness of DS polycrystals on the basis of a newly developed inverse Voigt–Reuss–Hill approximation, the elastic stiffness components of the single-crystalline LPSO phase were determined. It was revealed that the Young’s modulus of the LPSO phase along 〈0 0 0 1〉 in the hexagonal expression was clearly higher than that along 〈 1 1 2 ¯ 0 〉 , and the Young’s modulus and shear modulus were clearly higher than those of pure magnesium. These findings were validated by first-principles calculations based on density functional theory. Analyses by first-principles calculations and micromechanics modeling indicated that the long periodicity of the 18R-type stacking structure hardly enhanced the elastic modulus, whereas the Zn/Y-enriched atomic layers, containing stable short-range ordered clusters, exhibited a high elastic modulus, which contributed to the enhancement of the elastic modulus of the LPSO phase in the Mg–Zn–Y alloy.

The ω transformation and its correlation with elastic properties were investigated in cold-worked Ti–36Nb–2Ta–3Zr–xO mass% alloys with low body-centered cubic (β) phase stability, known as gum metal. Analysis of the temperature dependence of the ω (hexagonal) phase formation using transmission electron microscopy and of the elastic properties of solution-treated and cold-worked alloys using resonant ultrasound spectroscopy revealed that in the solution-treated 0.36% and 0.51% O alloys, the high concentration of oxygen suppressed ω-phase formation from room temperature to a fairly low temperature of ∼13 K. However, the ω phase was formed by cold working at room temperature in the 0.30% and 0.47% O alloys. Importantly, the fraction of the ω phase clearly increased upon cooling, which indicates that the formation of the ω phase is thermodynamically favorable near and below room temperature in the cold-worked 0.30% and 0.47% O alloys. This formation of the ω phase and the low stability of the β phase related to the low electron/atom (e/a) ratio were the dominant factors determining the elastic properties near and below room temperature in the cold-worked Ti–Nb–Ta–Zr–O alloys.

Lotus-type porous materials exhibit some unique anisotropic mechanical and thermal properties which are very useful for a number of industrial applications. This paper evaluates several computational models for determining the compressive engineering elastic modulus and engineering yield stress of lotus-type iron in transversal and longitudinal direction in regard to pore orientation with parametric nonlinear finite element computational simulations for porosities ranging from 0 to 0.65. The considered pore topologies of evaluated computational models are either regular (indirectly reconstructed) or irregular (directly reconstructed). Comparison of computational results, experimental tests and analytical estimations shows good correlation of some evaluated computational models. The simplified porous model with π/4 rotated aligned regular pores can be recommended for fast computational estimation of lotus-type material behaviour under mechanical loading, when some material parameters for homogenised lotus-type material modelling have to be determined.

Dynamic and quasi-static compressive deformation of as-cast and normalized porous S15CK carbon steels with cylindrical pores oriented in one direction was investigated at 298 and 77 K, using the split Hopkinson pressure bar method and a universal testing machine, combined with an acoustic emission measurement system, to clarify the formation mechanism of a plateau stress region where deformation proceeds with almost no stress increase. Dynamic and quasi-static compressions perpendicular to the orientation of the pores at 298 and 77 K do not produce a plateau stress region in the as-cast and normalized porous S15CK, because the localized crack formation and slip deformation that originate from the large concentration of stress around pores promotes densification in the early stage of the stress–strain curves. When the samples undergo dynamic compression parallel to the pore direction at 77 K, the matrix becomes brittle, and cracks are easily formed. However, the pores do not easily collapse, because they are oriented along the compressive direction. Therefore, densification occurs at a higher strain level. In addition, the formation of small cracks in the matrix decreases the work hardening rate. As a result, a plateau stress region with high stress amplitude and wide strain range appears, which is independent of the microstructure. This mechanism for the formation of the plateau stress region is completely different from that of metal foams with isotropic pores, which is based on sequential inhomogeneous deformation. As a result, energy absorption 10 times that of commercial aluminum foams is achieved.

The origin of the low Young’s modulus of cold worked Ti–36Nb–2Ta–3Zr–xO mass% polycrystals with a body-centered cubic (β-phase) structure, referred to as gum metal, was investigated with a focus on the roles of oxygen concentration, the electron–atom (e/a) ratio, and the cold working process. Analysis of the temperature dependence of the microstructures and elastic properties of single crystals at x = 0.09, 0.36, 0.51% O using transmission electron microscopy and an electromagnetic acoustic resonance method, respectively, revealed that the shear moduli c′ and c44 of the 0.36 and 0.51% O alloys softened upon cooling near room temperature (RT) and exhibited low values at RT. This was because suppression of the α″ martensitic transformation by oxygen addition led to retention of the low stability single β-phase state at RT. The Hill approximation indicated that the low c′ and c44 values caused by softening gave rise to the low Young’s modulus, which is common to some Ti–Nb-based alloys with an e/a ratio of ∼4.24. Analysis of the microstructures and elastic properties of solution-treated and cold worked x = 0.06, 0.30, 0.47% O alloy polycrystals at RT revealed that the Young’s modulus increased upon 90% cold working due to formation of the α″ martensite phase (0.09% O) and ω phase (0.09, 0.30, and 0.47% O) with a high elastic modulus in the β-phase matrix. However, increasing the oxygen concentration suppresses the increase in Young’s modulus because oxygen addition decreases the amount of α″ and ω phases formed while retaining the low stability β phase. Therefore, cold working combined with oxygen addition produces a low Young’s modulus compatible with high strength.

The formation mechanism of a high density of nanovoids by annealing amorphous Al 2 O 3 thin films prepared by an electron beam deposition method was investigated. Transmission electron microscopy observations revealed that nanovoids ∼1–2 nm in size were formed by annealing amorphous Al 2 O 3 thin films at 973 K for 1–12 h, where the amorphous state was retained. The elastic stiffness, measured by a picosecond laser ultrasound method, and the density, measured by X-ray reflectivity, increased drastically after the annealing process, despite nanovoid formation. These increases indicate a change in the amorphous structure during the annealing process. Molecular dynamics simulations indicated that an increase in stable AlO 6 basic units and the change in the ring distribution lead to a drastic increase in both the elastic stiffness and the density. It is probable that a pre-annealed Al 2 O 3 amorphous film consists of unstable low-density regions containing a low fraction of stable AlO 6 units and stable high-density regions containing a high fraction of stable AlO 6 units. Thus, local density growth in the unstable low-density regions during annealing leads to nanovoid formation (i.e., local volume shrinkage).

The composition and temperature dependence of the elastic properties and phase stability of quaternary Ti–Nb–Ta–Zr β-phase alloys with a body-centered cubic structure, developed for biomedical applications, were investigated using their single crystals, in order to clarify the origin of the low Young’s modulus in polycrystals. Transmission electron microscopy observations clarified that α ″ martensitic transformation occurred in a temperature range that depended on the β-phase stability below room temperature. Electromagnetic acoustic resonance measurements clarified that the shear moduli c ′ and c 44 of single crystals softened upon cooling from room temperature and became rather low near the martensitic transformation start temperature, i.e. the lower limit of β-phase stability. An analysis by the Hill approximation indicates that low c ′ and c 44 caused the low Young’s modulus, and thus it is probable that the softening in c ′ and c 44 is the origin of the low Young’s modulus.

Numerical calculations for porous magnesium with cylindrical oriented pores showed significant influences of active deformation modes in magnesium (Mg) on distinctive "two-stage deformation behavior" during compression. Calculated results also imply that larger grain aspect ratio results in better energy absorption efficiency.

Porous Al-5 mass%Ti alloy was fabricated by unidirectional solidification in hydrogen atmosphere, using a continuous casting technique. The porous Al-Ti alloy was prepared at different transfer (solidification) velocities, and the effect of transfer velocity on the pore morphology was investigated. It was found that the pore shape changes with increasing transfer velocity, while the porosity does not change with increasing transfer velocity. In the case of a low transfer velocity (0.5 mm·min -1 ), elongated pores surrounded by the columnar microstructure are formed, which indicates that the pores grow along the solidification direction together with the solid phase. In the case of a middle transfer velocity (5.0 mm·min -1 ), elongated pores surrounded by the columnar microstructure and needle or plate-like Al 3 Ti alloys are formed. In the case of a high transfer velocity (10.0mm·min -1 ), spherical pores surrounded by the equiaxed microstructure are formed, because the primary crystals formed in the solidification front prevent the growth of elongated pores. It is suggested that the pore morphology is closely related with the solidification rate.

Lotus-type porous aluminum with cylindrical pores oriented in one direction was fabricated by a casting method utilizing the decomposition of moisture in a vacuum. Hydrogen decomposed from moisture is utilized for cylindrical pores to grow during unidirectional solidification. However, pores are not formed in the case of a casting in hydrogen or argon atmosphere, because hydrogen or argon gas pressure suppresses the pore growth. The porosity of lotus aluminum does not depend on the moisture amount, which indicates that the moisture amount is almost saturated within the amount used in this study. The average pore diameter does not depend on the moisture amount, because the pore diameter depends mainly on ambient pressure and solidification rate. The distribution of pores becomes homogeneous by decreasing melting temperature, because the rate of the reaction of moisture possibly becomes low (more suitable for pore growth) by decreasing the melting temperature.

The cause of a low Young’s modulus was investigated in quaternary β-type Ti–Nb–Ta–Zr alloys, as the modulus is decreased to prevent bone absorption and degradation of bone quality when these alloys are implanted into human bones. This investigation was carried out using the alloys′ single crystals. Acoustic measurements and analysis by the Hill approximation revealed that a low Young’s modulus in a polycrystalline form is caused by the low shear modulus c′, related to the low β-phase stability, low c44, and relatively low bulk modulus B compared with those of binary Ti-based alloys. Furthermore, it was found that the single crystals had strong orientation dependence on Young’s modulus, where that in the 〈1 0 0〉-direction E100 is the lowest of all crystallographic orientations. For quaternary Ti–29Nb–13Ta–4.6Zr alloy (mass%), E100 is only ∼35 GPa, which is similar to Young’s modulus of human cortical bones as a result of the low B and c′. These results indicate that decreases in c′, c44 and B are essential for decreasing Young’s modulus of novel β-type Ti alloys which are expected to be developed in the near future.

Lotus-type porous copper with long cylindrical pores aligned in one direction parallel to the solidification direction was fabricated by unidirectional solidification of the melt in a mixed gas of hydrogen and argon. Compression tests were performed in the direction parallel to the cylindrical pores in order to investigate the relationship between the specimen size and compressive yield strength. The compressive yield strengths and the standard deviation decrease with an increase in specimen size. Increments of the standard deviation are caused by the standard deviation of porosity occurred by inhomogeneous pore diameter and irregular pore arrangement.

The stress shielding effect often degrades the quality and quantity of bones near implants. Thus, the shape and structure of metallic biomaterials should be optimally designed. A dominant inorganic substance in bones is a 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 bones 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 or 100 mm� , to evaluate the BAp orientation of bones. Two animal models were prepared: (1) a nail model (� : 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 (� : 3.4 mm, mean pore diameter: 170 mm, SUS304L), which was used to understand the effect of the unidirectional-elongated pore direction in an 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 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 tissues such as the orientations of collagen fiber, BAp, and blood vessels. The orientation degree of 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, optimal design of metallic biomaterials such as implant shape, pore size, elongated pore direction, etc., should be based on the anisotropy of the bone microstructure. [doi:10.2320/matertrans.47.2233]

Ni3Al with and without boron was melted and unidirectionally solidified in pressurized hydrogen atmosphere by using a continuous zone melting method. For Ni3Al without boron, cylindrical pores elongated in the direction parallel to the solidification direction, are formed in Ni3Al matrix. On the other hand, no pore is formed in Ni3Al with 0.23 mol% B solidified under the same condition. This result suggests that the solubility gap of hydrogen between liquid and solid Ni3Al with boron is extremaly small.

Effects of specimen thickness on the tensile strength of lotus-type porous copper were investigated. The ultimate tensile strength in the direction perpendicular to the longitudinal axis of pores hardly depends on the thickness of a specimen when the width of the specimen is large enough compared with the pore diameter, while the ultimate tensile strength increases with an increase in the thickness when the width is not large enough compared with the pore diameter. The 0.2% offset strength in the direction and strain at the peak stress depend on the thickness of specimens; the 0.2% offset strength decreases with an increase in the thickness, and the strain at peak stress increases with the increase in the thickness.

We studied the elastic properties of lotus-type porous iron experimentally and theoretically. First we determined the elastic constants of lotus iron fabricated by the continuous zone-melting method by using the acoustic resonance techniques. All the elastic moduli are found to follow the well-known power-law formula. Next, we extended the effective-mean-field (EMF) theory so as to consider effects of the pore orientation on the effective elastic constants. The model calculations proved that the extended EMF theory is capable of calculating satisfactorily the elastic properties of lotus metals.

We studied the elastic constants of a lotus-type porous copper, regarding it as a composite material showing hexagonal elastic symmetry with the c-axis along the longitudinal direction of the pores. We used the combination of resonance ultrasound spectroscopy and electromagnetic acoustic resonance methods to determine the elastic constants of the composite. The resulting Young’s modulus E∥ decreases linearly and c33 does slowly with porosity, while E⊥ and c11 drop rapidly and then slowly. Micromechanics calculations considering the elastic anisotropy of the copper matrix can reproduce the measured anisotropic elastic constants. This indicates that the elastic properties of various types of porous metals can be predicted and designed with the present approach using micromechanics modeling.

application/pdf, Article, Journal of Applied Physics . 2014, 116 (3)

application/pdf, Article, Journal of Applied Physics. 2011, 110 (64324)

Lotus-type porous magnesium was fabricated through thermal decomposition of MgH2 powders as a source of hydrogen. Liquid magnesium was cast into a mold in which MgH2 powders were placed and solidified unidirectionally in the mold, which achieved the growth of unidirectional elongated pores in magnesium matrix. The fabrication method is safer than a conventional method using pressurized hydrogen atmosphere, because the risk of explosion can be avoidable. The effect of the amount of MgH2 powders and the distance from the bottom of the ingot on the porous structure was investigated, which clarified that the two factors have the large influence on the pore growth.