The 65ZnO–30P₂O₅–5Nb₂O₅ (ZnPNbO) glass is one of the promising candidate antibacterial biomaterials; it is a safe material since the release of Zn²⁺ ions from the glass is well-controlled. To discuss the origin of this controlled release from the view point of its glass structure, the amount and state of bridging oxygen in the glass was examined using X-ray photoelectron spectroscopy, and compared with those in 65CaO–30P₂O₅–5Nb₂O₅ (CaPNbO) glass. The number of P–O–P bonds in ZnPNbO glass was larger and that of P–O–Nb bonds was smaller than those in CaPNbO glass. This was linked with the formation of a large number of P–O–Zn bonds. The outermost shell electron density of the cations in ZnPNbO glass decreased, and as a result, the binding energy of each element increased. These might be closely related to the controlled release of Zn²⁺ ions.

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Biomedical Ti–15Nb–25Zr–(0, 2, 4, 8)Fe (mol%) alloys are prepared by mixing pure element powders and spark plasma sintering (SPS). Specimens with diameters of 20 mm and thicknesses of 3 mm are obtained by sintering at 1000°C for 10 min followed by cooling in the furnace. Some of the specimens are then heat-treated at 900°C for 1 h followed by water quenching. Zr and Fe are dissolved in Ti; however, segregation of Nb is observed in all of the alloys. The β and α′′ phases are observed in the as-sintered and heat-treated specimens owing to the insufficient diffusion of the alloying elements. Fe stabilizes the β phase and provides a solution-strengthening effect. With the increase in the Fe content in the as-sintered specimen, the compressive strength and micro-Vickers hardness are improved in the Ti–15Nb–25Zr–(0, 2, 4)Fe alloys and slightly decreased in Ti–15Nb–25Zr–8Fe. The as-sintered Ti–15Nb–25Zr–4Fe alloy exhibits the maximum compressive strength of 1740 MPa. Although the plasticity is decreased by the Fe addition, a fracture strain of approximately 17% is obtained for Ti–15Nb–25Zr–4Fe, indicating a good plasticity. The heat treatment cannot eliminate the segregation of Nb, but can improve the plasticity and slightly increase the strengths of Ti–15Nb–25Zr–(0, 2, 4)Fe. Moreover, the heat-treated Ti–15Nb–25Zr–8Fe exhibits a high strength of approximately 1780 MPa and fracture strain of approximately 19%. Therefore, good comprehensive mechanical properties, including high strengths, high hardnesses, and good plasticities, can be obtained in Fe-added β-Ti alloys prepared by SPS and subsequent optional short heat treatment.

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The effect of the addition of oxygen on the formation of the microstructure quenched from the β phase of Ti–Nb alloy was investigated based on the solid solution treatment (SST) temperature in the β phase. The alloy ingots of Ti–(12, 14, and 18)-at% Nb–(0, 1, and 3)-at% O were arc-melted. They were homogenized at 1200°C for 3.6 ks and then hot-rolled at 850°C into 1.5-mm thick sheets. The specimens were solution-treated at 1050 to 1200°C for 0.6 ks and then quenched in iced brine. The microstructure of the Ti–(12, 14, and 18)-at% Nb alloys exhibited an α′′ phase regardless of the SST temperature. The addition of oxygen in the Ti–(14 and 18)-at% Nb alloys suppressed the β → α′′ martensitic transformation; therefore, the quenched structure became the β + ω_a phase. The further addition of oxygen suppressed the β → ω_a transformation during quenching. The effect of oxygen addition on the phase transformations of β → α′′ and β → ω_a during quenching from the β phase was weakened with an increasing SST temperature.

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The effect of Si addition on the microstructure and mechanical properties of a near-β titanium alloy Ti-17 with fully lamella microstructure was investigated. It was found that the microstructure of Ti-17 with silicon exhibited the absence of a continuously thick α layer along prior-β grain boundaries (grain boundary α), while the grain boundary α was distinctively formed in Ti-17 without Si. The formation of (Ti, Zr) silicide particles at the prior-β grain interior and its grain boundaries were observed, and the presence of these particles were related to the disappearance of grain boundary α similar to the oxygen scavenging effect of boride particles reported previously. With regard to mechanical properties, Ti-17 with silicon exhibits higher strength and lower ductility compared with Ti-17 without Si. Ductile transgranular fracture morphology was observed even on the fracture surface of Ti-17 with Si after tensile test.

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AB-type Zr–Ti–Nb–Ni alloys are good candidates as the negative electrode for Ni-metal hydride (MH) batteries because they have high discharge capacity around 330 mAh g⁻¹ at 303 K. The Zr_0.49Ti_0.5Nb_0.01Ni alloy consists of two phases, the primary-phase with B33-type orthorhombic structure and the secondary-phase with B2-type cubic structure. To compare electrochemical properties of each phase with the mother alloy, we synthesized the primary-phase and secondary phase alloys with compositions of Zr_0.54Ti_0.47Nb_0.01Ni_0.98 and Zr_0.47Ti_0.52Nb_0.01Ni, respectively. The discharge capacity was examined at 25 mA g⁻¹ and 303 K, showing that the primary-phase alloy has the highest value of 362 mAh g⁻¹ than the mother alloy (335 mAh g⁻¹) and the secondary-phase alloy (253 mAh g⁻¹). For cycle performance, all alloys were excellent (≧95%) at 100 mA g⁻¹ and 303 K. For high-rate dischargeability, the secondary-phase alloy was the best, probably because the stability of hydride for the secondary-phase alloy was lower than that for the mother and the primary-phase alloy.

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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.

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Anodizing Ti substrates in an ammonium nitrate/ethylene glycol electrolyte is an innovative process capable of fabricating nitrogen-doped photocatalytic titanium oxide (TiO₂) layer in one step. This fabricated layer comprises both rutile and anatase TiO₂ phases; however, a major phase contributing to its excellent visible-light responsive photocatalytic performance is still unknown. In the present work, the crystallographic phase of an anodic layer was controlled by exploiting a post-thermal treatment and relationship between the phase variation and photocatalytic performance was then investigated to determine the major phase contributing to this performance. Post-thermal treatment to the anodic TiO₂ layer had little influence on the surface morphology and nitrogen doping, but the crystallographic phase, more specifically the ratio of anatase to rutile phases, changed with the heating temperature. The photocatalytic activity, evaluated by methylene blue decolorization and ethylene decomposition, increased with an increase in the ratio of anatase phase, while the correlation with the rutile phase was not observed. X-ray diffraction (XRD) analysis using a grazing incidence geometry showed that the anatase phase was concentrated in the topmost surface region when compared with the rutile phase. In conclusion, the variation of the photocatalytic performance was related to the growth of the anatase TiO₂ phase in the layer, with the treatment temperature of 723 K showing the highest photocatalytic activity.

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The powder magnetic core having a spinel ferrite insulating layer has enabled high magnetic flux density and high electrical resistivity, because spinel ferrite exhibits magnetic insulating properties. However, its the electrical resistivity of the powder magnetic core was reduced after annealing at 873 K, since FeO was formed in the spinel ferrite insulating layer. The eutectoid transformation caused the decomposition of FeO, which decompose into Fe₃O₄ and α-Fe at the temperature range below 833 K. We verified the possibility of eutectoid transformation of FeO in the insulating layer by the two-step heat treatment at 873 K and 773 K. The presented results clearly showed that the two-step heat treatment increases the electrical resistivity of the insulating layer due to the disappearance of FeO by eutectoid transformation even in the insulating layer.

 

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 65 (2018) 171–175.

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The structure of the target vessel for the spallation neutron source will be modified. The Invar alloy which has a low coefficient of thermal expansion has to be reinforced by enclosing it completely in stainless steel using hot isostatic pressing bonding to reduce the thermal deformation of the additional flange. We examined the optimum temperature conditions for HIP bonding the Invar alloy and 316L stainless steel. The metallographic observation and mechanical tests on specimens bonded at 700°C, 900°C, 1100°C and 1200°C were conducted. The experimental results showed that the bonding region increased when the bonding temperature increased, but the tensile strength reduced when the bonding temperatures increased. The tensile strength of a specimen bonded at 1200°C was approximately 10% lower than that of the Invar bulk. From the residual stress analysis using the ABAQUS code, the tensile stress near the bonding region of the specimen bonded at 700°C was found to be 84 MPa; this stress increased with the bonding temperature up to 90 MPa. From these results, it is concluded that the optimum temperature for bonding temperature was 900°C.

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A study on the simultaneous separation of Zn and Mn from a feed solution containing various types of dissolved battery wastes was carried out by a solvent extraction process using D2EHPA. The selective recovery of Zn and Mn from feed solutions containing Cd ions is difficult due to their similar physicochemical behavior. Therefore, 99.9% of Zn, 99.8% of Mn, and 99.9% of Cd were extracted using the optimum conditions of 40 vol% D2EHPA, 40 vol% NaOH concentration, 2-stage countercurrent extraction, and an O/A ratio of 2. The Co-extracted Co could be scrubbed using pH 2 sulfuric acid at an O/A ratio of 1, and Cd was then scrubbed using 0.5 M Na₂S₂O₃. The results of the Cd scrubbing experiments indicated that the optimum conditions were 3-stage countercurrent scrubbing and an O/A ratio of 2, and the scrubbing efficiency of Cd was approximately 99.9%. The Zn and Mn that remained in the loaded organic could be enriched by increasing the O/A ratio of the stripping stage to 6. From this concentrated solution, high purity zinc manganese sulfate powder, which can be used as a raw material for fertilizer for crop cultivation, was manufactured.

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The log angles of a rotation matrix are three independent elements of the logarithm of the rotation matrix. Nye’s lattice curvature tensor κ_ij is discussed by using the log angles. For the change in a crystal orientation ΔR with the change in a position Δx_i, it is shown that the elements of κ_ij are written as κ_ij = Δω_i/Δx_j using the log angles Δω_i of ΔR. The log angles for the crystal rotation given by the axis/angle pair are also discussed.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 82 (2018) 415–418.

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AlCoCrFeNi high-entropy alloys (HEAs) were prepared by Bridgman solidification with different solidification rates, and the mechanical behavior of the HEAs was investigated over a wide strain rate range (∼10⁻³∼10³ s⁻¹). Microstructure observations suggest that, with increasing solidification rate, the microstructure evolves from coarse columnar grains to fine equiaxed ones. Through compression tests under both quasi-static and dynamic strain rates, the AlCoCrFeNi HEAs were found to possess positive strain-rate sensitivity (SRS), and the HEA with lower solidification rate exhibits higher SRS, which are attributed to the coarse grain size.

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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).

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Mechanical properties relating to the thermally activated process of yielding was investigated in Ti–6Al–4V with a bimodal microstructure, consisting of both primary alpha grains and lamellar colonies of secondary alpha/beta lamellae. The temperature dependence of yield stress, effective stress, activation volume, and activation enthalpy were investigated between 77 K and 650 K. The yield stress and effective stress decreased with increasing temperature. It was found that the temperature dependence of activation enthalpy for yielding shows values between those obtained from basal slips and prismatic slips investigated in single crystalline α-titanium. This suggests that the thermally activated processes which control the yielding of bimodal Ti–6Al–4V is the combination of basal and prismatic slips.

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The fatigue lives of forged Ti-17 using a 1500-ton forging simulator subjected to different solution treatments and a common aging treatment were evaluated under both load- and strain-controlled conditions: high and low cycle fatigue lives, respectively. Then, the tensile properties and microstructures were also examined. Finally, the relationships among fatigue lives and the microstructural factors and tensile properties were examined.

The microstructure after solution treatment at 1203 K, which is more than the β transus temperature, and aging treatment exhibits equiaxed prior β grains composed of fine acicular α. On the other hand, the microstructures after solution treatment at temperatures of 1063, 1123, and 1143 K, which are less than the β transus temperature, and aging treatment exhibit elongated prior β grains composed of two different microstructural feature regions, which are acicular α and fine spheroidal α phase regions. The 0.2% proof stress, σ_0.2, and tensile strength, σ_B, increase with increasing solution treatment temperature up to 1143 K within the (α + β) region, but decrease with further increasing solution treatment temperature to 1203 K within the β region. The elongation (EL) and reduction of area (RA) decrease with increasing solution treatment temperature, and it becomes nearly 0% corresponding to a solution treatment temperature of 1203 K. The high cycle fatigue limit increases with increasing solution treatment temperature up to 1143 K, corresponding to the (α + β) region. However, it decreases with further increase in the solution treatment temperature to 1203 K in the β region. The fatigue ratio in high cycle fatigue life region is increasing with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase, and it relates well qualitatively with the volume fraction of the primary α phase when the solution treatment temperature is less than the β transus temperature. The low cycle fatigue life increases with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase. The low cycle fatigue life relates well quantitatively with the tensile true strain at breaking of the specimen and the volume fraction of the primary α phase for each total strain range of low cycle fatigue testing.

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In this study, the microstructure, tensile strength, elongation, and reduction of area of near-β Ti alloys (Ti-17) were investigated after being subjected to solution and aging treatments. Ti-17 was forged at temperatures between 700 and 850°C followed by air cooling. Then, the forged Ti-17 was subjected to solution treatment at 800°C for 4 h followed by water quenching and aging treatment at 620°C for 8 h followed by air cooling. Tensile tests were performed at room temperature, 450°C, and 600°C. The change in microstructure at different forging temperatures was exhibited by only the volume fraction and morphology of the grain boundary (GB) α phase. That is, a granular GB α phase was formed in the samples forged at 700 and 750°C. Moreover, a film-like GB α phase was formed in the samples forged at 800 and 850°C. The tensile strength was the same for all the tested samples, indicating that the microstructure has little effect on the tensile strength. The elongation and reduction of area increased with decreasing volume fraction in the GB α phase. It is considered that the film-like morphology slightly improves ductility.

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The effects of {332}〈113〉 deformation twinning, one of the unique deformation modes for metastable β-type Ti alloys, on the fatigue behavior of Ti–Mn system alloys were investigated focusing on fatigue strength, fatigue crack initiation and propagation. Ti–7Mn and Ti–5Mn–3Mo (mass%) alloys which are primarily deformed by dislocation slips and {332}〈113〉 deformation twins, respectively, were subjected to fatigue tests conducted in tensile-tensile mode at room temperature, followed by fracture surface and deformation microstructure analyses. We found for the first time the Ti–5Mn–3Mo alloy has higher fatigue strength as compared to the Ti–7Mn alloy owing to the formation of the {332}〈113〉 deformation twins. The {332}〈113〉 deformation twins are to some extent responsible for the plastic strain accumulation in place of the dislocations during cyclic deformation. Thus, {332}〈113〉 deformation twinning prevents the accumulation of dislocations during cyclic deformation, thereby suppressing fatigue crack initiation. Moreover, formation of the {332}〈113〉 deformation twins around crack tip decreases stress concentration at the crack tip and changes the crack propagation direction, as a result, crack propagation speed is decreased. These results indicate that the {332}〈113〉 deformation twining is crucial for improving the fatigue properties of metastable β-type Ti alloys.

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The purpose of the present study is to investigate the melting properties, microstructures, tensile properties and fatigue properties of Sn–5Sb–(0.05–0.50)Ni (mass%) high-temperature lead-free solders. The solidus temperature and liquidus temperature of the Sn–5Sb–Ni solders are approximately equal to those of the Sn–5Sb alloy. From the result of EPMA mapping analysis and the Sn–Sb–Ni ternary phase diagram, the Sn–5Sb–Ni solders are found to consist of β-Sn, SbSn and NiSb phases. As the amount of Ni in the Sn–5Sb–Ni solder increases, the number of NiSb phases increases and the phases are coarsened so that the 0.1% proof stress and tensile strength increase, and the elongation decreases at 25°C. In contrast, the effects of the Ni content on the tensile properties are negligible at 150°C and 200°C. The fatigue ductility exponent α of the Sn–5Sb–Ni solders is smaller than that of the Sn–5Sb solder at 25°C. At 150°C and 200°C, the α values of Sn–5Sb–0.05Ni and Sn–5Sb–0.10Ni remain small, whereas those of Sn–5Sb–0.25Ni and Sn–5Sb–0.50Ni increase. This means that the Sn–5Sb–Ni solders with 0.05–0.10 mass% Ni have superior fatigue properties to the Sn–5Sb solder in the temperature range from 25°C to 200°C.

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Polycrystalline specimens of Pr_1−xSr_xFeO₃ (0.1 ≤ x ≤ 0.7) were synthesized using a solid state reaction method. All samples had a typical perovskite structure, where the orthorhombic (Pbnm) phase was dominant at x ≤ 0.5 and the rhombohedral (R-3c) phase was dominant at x ≥ 0.6. Since the B site is in the mixed valence state of Fe³⁺/Fe⁴⁺ and the spin quantum number is in the range of 0.86 ≤ s ≤ 1.15, it is expected that Fe³⁺ is in the spin state of low spin (LS) Fe³⁺ or intermediate spin (IS) Fe³⁺ and Fe⁴⁺ is in the spin state of LS Fe⁴⁺. As x increases, the ratio of IS Fe³⁺ decreases compared to that of LS Fe³⁺ at x ≥ 0.3, so that the P-type Seebeck coefficient is maintained up to x = 0.5. Although ZT = 0.002 (T = 850 K) of x = 0.7 which shows the maximum N-type thermoelectric characteristic is about 8% of ZT = 0.024 (T = 850 K) of x = 0.1 which shows the maximum P-type thermoelectric characteristic, both are the results of relatively high Seebeck coefficient, low electrical resistivity, and low thermal conductivity. Therefore, we strongly suggest that there is a possibility of application of PN elements which compose of the perovskite-type oxides.

 

This Paper was Originally Published in Japanese in J. Thermoelec. Soc. Jpn. 15 (2018) 3–13.

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This study presents application of an up-scaled high-pressure torsion (HPT) process to AZ31 and AZ61 Mg alloys for ultrafine grain refinement. Disks with 30 mm diameter were processed at room temperature under 6 to 7 GPa using the up-scaled HPT facility with a maximum capacity of 5 MN (500 ton). Microstructural evolution was evaluated by hardness measurement and microscopy observations including tensile testing. The grain size was well refined to ∼150 nm and ∼100 nm at the saturated state for the AZ31 and AZ61 alloys, respectively. Superplastic elongations of ∼520% and ∼550% were then attained in the corresponding alloys when tested in tension at elevated temperatures because of the grain boundary sliding controlled by grain boundary diffusion. Upsizing of the disk sample makes for a chance to extract the tensile specimens at different radial distance within the same disk and therefore the effect of the equivalent strain on the superplastic elongations was effectively evaluated.

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The continuous displacement cluster variation method (CDCVM) has introduced local atomic displacements into the theoretical framework of the cluster variation method (CVM) by viewing an atom displaced from a Bravais lattice point as a particular atomic species located at the lattice point. This idea of conversion from a freedom of local displacements into configurational freedom is extended in this paper to magnetic freedoms. Various magnitudes of local magnetic moments are considered as well as two spin directions, up and down. The approach is applied to pure Ni and its Curie temperature is explored with the entropy formula of the tetrahedron approximation in the CVM using the first-nearest-neighbor pair interaction energies extracted from the total energies of various spin configurations, which are estimated from electronic-structure calculations.

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L1₀-type FeNi alloys and α′′-Fe₁₆N₂ are candidates for permanent magnets without precious metals, but they are difficult to prepare because atomic diffusion is extremely slow below the order–disorder transition temperature of L1₀-FeNi (320°C) and because α′′-Fe₁₆N₂ is a metastable phase. Here, we report trials for preparing them using leaching, which is a method to obtain porous metals with a high surface area. We used such chemically active porous alloys as precursors for preparing L1₀-FeNi using the driving force of atomic diffusion and for preparing α′′-Fe₁₆N₂ using high reactivity with ammonia. No proofs for obtaining the L1₀-FeNi phase were observed, likely due to an Al impurity of 10 mol% and/or too small of a grain size. An Fe₁₆N₂ with α′′ phase was obtained. Although the saturation magnetization was smaller than that of Fe, a large coercivity (up to 121 kA m⁻¹) was obtained.

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In order to enhance the strength of 5083 Al alloy, fabrication of multi-walled carbon nanotubes (MWCNTs) reinforced 5083 Al alloy by the use of friction stir processing (FSP) was investigated. The MWCNT-reinforced Al alloy composites using sintered sheets of 5083 Al alloy-8%MWCNT were successfully fabricated. Grain refinement and many minute aluminum carbides (Al₄C₃) were observed in the composites fabricated. The proof stress of the composites fabricated with the 550°C sintered sheets considerably increased by 153 percent and the tensile strength increased by 55 percent compared with that of the base material.

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A two-step thermal oxidation process was applied to Ti–xNb binary alloys (x = 0, 1, 10, 15, and 30 at%) to prepare anatase-containing TiO₂ layers, and their photocatalytic activities were evaluated by measuring the water contact angle and decomposition of methylene blue (MB) under UV irradiation. The condition of the first-step treatment was fixed as heating in Ar–1%CO atmosphere at 1073 K for 3.6 ks, and the subsequent second-step treatment was conducted in air at 673–1073 K for 10.8 ks. The reaction layer formed after the two-step thermal oxidation consisted of TiO₂. The anatase fraction of the TiO₂ layers increased with decreasing second-step temperature and increasing Nb content of the Ti–Nb alloys. In addition, Nb and carbon were introduced into the TiO₂ layers. A water contact angle of around 5° was observed on the TiO₂ layers formed at the second-step temperatures of 673–973 K. The rate constant of MB decomposition showed a maximum for an anatase fraction of 0.6–0.8 at which the recombination of exited electrons and holes are suppressed. The TiO₂ layer formed on the Ti–10 at%Nb alloy exhibited a higher rate constant of MB decomposition compared with Ti–30 at%Nb, in which the TiNb₂O₇ phase formed. These results indicate that Nb is an effective alloying element for producing a photocatalytically active TiO₂ layer on Ti by the two-step thermal oxidation process. Nevertheless, the presence of an anatase-rich TiO₂ layer and an appropriate Nb content in TiO₂ are required for achieving high photocatalytic activities.

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A Ti–6Al–7Nb alloy was processed by severe plastic deformation through high-pressure sliding (HPS) at room temperature for grain refinement. The microstructure consists of grains with sizes of 200–300 nm in diameter having high and low angles boundaries. Superplasticity appeared with the total elongation of more than 400% and this was more likely when the tensile specimen is deformed in the direction parallel than perpendicular to the sliding direction. However, the superplastic elongation is almost the same irrespective of whether the sliding was made in the single direction or in the reversible directions as far as the total sliding distance is the same. The total elongation is invariably higher for the tensile testing at 1123 K than at the other temperatures, reaching the highest elongation of 790% at the initial strain rate of 1 × 10⁻³ s⁻¹. The strain rate sensitivity and the activation energy for the deformation were determined to be more than ∼0.3 and 199 kJ/mol, respectively. The microstructural observation reveals that the α phase region covers more than 85% of the tensile specimens after deformation and their grains are equiaxed in shape. It is concluded that the superplastic deformation is mainly controlled by grain boundary sliding through thermally activation by lattice diffusion.

 

This Paper was Originally Published in Japanese in J. JILM 68 (2018) 9–15.

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In this study, evaluation of fatigue crack properties in the Sn–5.0Sb/Cu joint was performed by using the inelastic strain energy density W_in around the crack tip which was calculated by FEM. W_in-c given by the multiplication of W_in obtained from an arbitrary-sized square region surrounding the crack tip by the side length of the square region – did not depend on the size of the square region and the element size. The fatigue crack propagated in the solder layer and the power law of Paris law type between its fatigue crack propagation rate and ΔW_in-c held. However, the power exponent in the fatigue crack propagation law differed depending on the regions of ΔW_in-c. The power exponent became about 1 in the low ΔW_in-c region and very large in the high ΔW_in-c region. In the low ΔW_in-c region, fatigue fracture propagated along the high angle grain boundaries formed ahead of the crack by the continuous dynamic recrystallization. On the other hand, the fracture transformed to static fracture mode in the high ΔW_in-c region and the cleavage fracture was observed. The large power exponent in the high ΔW_in-c region was attributed to the cleavage fracture.

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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.

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Fatigue crack propagation rate of pressure-sintered Ag nanoparticles was investigated and prediction method of fatigue crack propagation using strain energy density computed by FEM was proposed. The fatigue crack propagation rate was lower than that of pressureless-sintered Ag nanoparticles around ambient temperature. At high temperature, multiple small cracks occurred ahead of a main crack and they were connected with one another and the propagation rate of the main crack increased, so that properties of fatigue crack propagation in the high temperature region were close to those of pressureless-sintered Ag nanoparticles.

As the inelastic strain energy density and the length of its acquisition area were inversely proportional, the prediction of fatigue crack propagation that do not depend on the size of the area was possible by the use of the proportional constant of the relationship. The behavior of thermal fatigue crack propagation of sintered joint structure that was predicted by the derived fatigue crack propagation law was mostly in agreement with experimental behavior.

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Novel underfill resins combining a thermoset epoxy resin with thermoplastic polyester resins have been developed for self-organization soldering. Polyester-modified epoxy resins, which are hybrid resins, exhibited minimal viscosity at the melting point of the Sn–58 mass%Bi solder, with the viscosity dependent on the content and molecular mass of the blended polyester resin. Because the epoxy resin was sufficiently compatible with the polyester resin in the hybrid, the curing reaction of the hybrid resin was similar to that of the epoxy resin. The chemical structure of the polyester resin was retained in the cured hybrid resin, imparting thermoplasticity to the hybrid resins cured with repeated heating. Successful self-organization soldering was achieved using the developed hybrid-resin-based solder paste.

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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.

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Soldering is used to bond a semiconductor chip to a print circuit board (PCB). It is known that Sn, which is the base metal of Pb-free solder, shows remarkable crystal anisotropy. Clarifying the effect of Sn anisotropy on strain distribution is important for lifetime evaluation. The strain distribution in a micro specimen was measured under a tensile test by a digital image correlation method (DICM) with a microscope. Strain distributions were also analyzed by the finite element method with Hill’s anisotropic yield criterion and the crystal plasticity finite element analysis (CPFEA) with considering the critical resolves shear stress (CRSS) of each slip system. The deformation of the crystal structure of β-Sn depends on the size, number, and orientation of crystal grains. The CRSS was noticeably different for each slip system, and the yield stress varied with the orientation of crystal grains. Although the CPFEA without considering strain hardening was effective for predicting deformation within crystal grains, it is necessary to consider the strain hardening of crystals to predict the stress-strain curve of a micro specimen.

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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.

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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.

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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.

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Announcement Concerning Article Retraction
The following paper has been withdrawn from the database of Mater. Trans., because a description based on a misinterpretation of the experimental results was found by the authors in advance of publication after acceptance.
Mater.Trans. 52(2011) Advance view.
Improvement in Fatigue Strength of Biomedical β-Type Ti-Nb-Ta-Zr Alloy while Maintaining Low Young’s Modulus through Optimizing ω-Phase Precipitation

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