In the present study, a Mn–Cu-based damping alloy with a nominal composition of Mn–25Cu–2Al was produced by ball milling and spark plasma sintering. The phase composition, microstructure, compactness, micro-hardness, damping capacity of these materials were systematically investigated. Experimental results show that the ball milling mixed particles are mainly composed of α-Mn and γ-Cu. The microstructure of the alloy sintered at 730°C is mainly composed of γ-MnCu, γ-CuMn and α-Mn. With the increase of sintering temperature, γ-CuMn and α-Mn gradually disappear by the mutual diffusion of Mn and Cu elements. During 850°C sintering, the alloy is mainly single γ-MnCu solid solution. At the same time, as the sintering temperature increases, the compactness and damping capacity of the alloys increases and the micro-hardness decreases.

Metallic silicon powder has been widely used for the production of various industrial materials and parts such as refractory ceramics, solar cells, military parts and so on. Herein, we attempted to prepare pure silicon powder from SiO₂ by a magnesium thermal reduction process. A mixed-phase, Mg₂Si + MgO, was obtained by the reduction of SiO₂ powder by magnesium gas at 1223 K for 20 h. To extract pure silicon powder, Mg was separated by evaporation under vacuum through Mg₂Si decomposition above 1073 K, leading to the formation of Si + MgO, and the MgO by-product was eliminated by dissolution in an aqueous hydrochloric acid solution. X-ray diffraction analysis confirmed the formation of pure Si powder and particle size shown in microstructure and oxygen content were analyzed to be 1∼5 µm and 1.5∼6 wt.%, respectively.

Spinnable carbon nanotubes enable us to produce carbon nanotube assemblies such as yarn and sheet without binder. Untwisted carbon nanotube yarn is one of the assemblies. Untwisted carbon nanotube yarns are composed of unidirectionally aligned carbon nanotubes along with the yarn axis, and thus untwisted carbon nanotube yarns are an ideal preform for composite fabrication with high mechanical performance. In this study, untwisted carbon nanotube yarns with varied densities were prepared by using spinnable carbon nanotube forests, and the tensile properties were examined. Furthermore, an analytical model of tensile properties for untwisted carbon nanotube yarns was proposed based on the shear-lag model. The proposed model can predict the tensile behavior of an untwisted yarn from the tensile modulus and strength of a carbon nanotube, the volume packing fraction of carbon nanotubes for the untwisted yarn, and shear stress exerted on the slipped region of a carbon nanotube. Then, the proposed model was applied to estimate the elastic modulus and tensile strength of a carbon nanotube from the tensile properties of untwisted carbon nanotube yarns. In our case, the estimated tensile elastic modulus of a carbon nanotube was about 200 GPa, and the estimated tensile strength of a carbon nanotube was about 1.9 GPa.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 69 (2020) 847–854.

In this study, we attempted to nullify the harmful influences of processing marks on the fatigue strength of Ti–6Al–4V alloy by particle collision treatments. As the surface treatments, fine particle bombarding (FPB) and shot peening (SP) were applied to form hardened layers and introduce compressive residual stress. The surface of the objective material was polished to a mirror surface to eliminate the influences of machining on specimens and was then grinded with emery papers (#80) to make uniform processing marks. After the particle collision treatments, the surface conditions, hardness distributions and residual stress were systematically examined, and their relationships with the fatigue strength were considered in detail. On observation of the surfaces, the processing marks were eliminated by the particle collision treatments. At the same time, the surface hardness was increased and high compressive residual stress was introduced. As a result, the fatigue strength was markedly improved by the treatments beyond the level of the material with the processing marks without deterioration of the mechanical properties. The improvement rates of the fatigue strength were high, at 75% by FPB treatment and 58% by SP treatment.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Jpn. 69 (2020) 915–920.

Mg₉₆Zn₂Y₂ alloys were subjected to equal channel angular pressing (ECAP) to systematically investigate changes in microstructure and tensile properties over eight passes. Mg₉₆Zn₂Y₂ as-cast specimens consisted of three phases: α-Mg; LPSO (long period stacking ordered), and Mg₃Zn₃Y₂. The phases proved stable against induced strain, enduring eight passes of ECAP, resulting in high-strain deformation. Deformation microstructure by ECAP can be divided into two regions: dynamically recrystallized (DRXed) α-Mg grain regions; and deformed regions including LPSO phase with kink deformation. The mean grain size of α-Mg grains decreased up to four passes of ECAP. However, the mean grain sizes in 4-pass and 8-pass specimens were 1.44 µm and 1.85 µm, indicating that mean grain size saturates due to dynamic recrystallization (DRX) after four ECAP passes. Basal texture of α-Mg grains inclined from tensile direction after one pass of ECAP; the intensity increased with increasing number of ECAP pass. LPSO texture also formed but with low intensity even after eight passes of ECAP. ECAP suppressed greatly DRX compared to extrusion under comparable strain. 0.2% proof stress increased up to four passes of ECAP and subsequently saturated due to DRX. On the other hand, elongation increased with increasing volume fraction of DRXed α–Mg region.

The 6061-T6 sheet and the DP 780 steel sheet were joined under the condition with the gap length d of 1.17 to 1.42 mm and discharge energy W of 3.0 kJ. The impact speed ranged from 430 to 460 m/s. The weld width showed a tendency to increase due to the increase of the collision speed. However, when the gap length exceeds 1.59 mm (impact speed of >460 m/s), the weld width became narrow. Considering that the electromagnetic force continues to apply on the flyer sheet after collides with the fixed sheet, it is desirable to perform the welding in a time shorter than the time t_m when the collision time reaches the maximum current value. Therefore, the collision time is considered to be one of factors that affect the welding condition. As a result of experiments in consideration of above conditions, it was possible to achieve a strong lap joint of the 6061-T6 sheet and the DP 980 steel sheet, although the welding condition was limited as compared with the case of the DP 780 steel sheet. Thus, sound lap joint between 6061-T6 sheet and high-tensile steel sheet with 1 GPa class was achieved by magnetic pulse welding.

This Paper was Originally Published in Japanese in J. JILM 69 (2019) 541–547.

The effects of grain size and grain boundary stability on the mechanical and fatigue properties of nanocrystalline nickel thin films were examined. We found that the grain size of nanocrystalline nickel thin films tended to decrease with the amount of sodium allylsulfonate, and the grain size on the solution side was larger than that on the substrate side. The dependence of the grain size on the 0.2% proof strength, the tensile strength, and the fatigue limit could be expressed by the Hall–Petch equation. The 0.2% proof strength and tensile strength of the annealed film are lower than those of the as-deposited film, while the fatigue limit of the annealed film was higher than that of the as-deposited film. The grain boundary stability and dislocation density are responsible for the effect of annealing. The fracture strain of the annealed film is lower than that of the as-deposited film, indicating that annealing makes the film brittle.

To characterize the thermal activation process of dislocation motion in the creep region, thermal activation parameters must be determined. However, the activation volume has never been used to directly understand dislocation motion in this region. In this study, the effective stress and activation volume during creep in Al–Mg solid-solution alloys were determined using indentation techniques. The obtained effective stress and activation volume corresponded to the results obtained from the uniaxial test. At the tested creep rate of , the obtained activation volume decreased with increasing solute concentration, a trend opposite to that of the effective stress. Using this activation volume and previously reported computer simulation results of the interactions between dislocations and solute atoms, the thermal activation process of dislocation motion during creep in several Al–Mg solid-solution alloys was investigated. The thermally activated dislocation length decreased with increasing stress and was smaller than that between the forest dislocations. The results indicated that dislocations during creep could overcome thermal obstacles when the corresponding effective stress was interpolated against the increase/decrease in thermally activated dislocation length, and each dislocation fragment on the length between forest dislocations moved individually through each thermal activation process.

A wear test set-up is designed and employed to investigate the damage behavior and failure mechanisms of cemented carbide against Si₃N₄ ceramic under impact-sliding wear conditions to understand the damage trend of cutting tools under complex relative motions. The wear profile, damage morphology, and chemical components of the cemented carbide are analyzed for different number of test cycles. The results demonstrate that the damage type of the cemented carbide under impact-sliding wear conditions is primarily delamination of the impact area, whereas the damage of the sliding zone is negligible. The damage characteristics of impact-sliding wear of cemented carbide do not change significantly with an increase in the number of cycles, but the wear rate decreases. Oxidative wear is observed in the impact area, producing black wear debris consisting of WO₃. The failure of the cemented carbide under impact-sliding wear conditions is primarily mainly caused by delamination induced by fatigue wear, as well as oxidative wear.

Electromagnetic pulse welding is a new promising method for solid-state joining of dissimilar materials. However, little understanding of the dynamic phenomena that leads interface morphology and intermetallic compounds to change. Initially, using Ansys Maxwell proved that the eddy current heat had a softening effect on aluminum alloy, and could press into the stainless steel in the semi-melted state. IMCs layer transferred from the unwelded zone (FeAl) to the flat welded zone (Fe₂Al₅+FeAl₂+FeAl) to the wave interface (α-Al+FeAl₃), the state of jet determined interface performance. Then, these insights were verified by SPH simulation, dispersed jet made soft aluminum alloy to produce the wave interface, a beam jet that aluminum particles were wrapped by steel particles produced the flat interface. Combination shear tests, the welded interface with high strength was characterized by large waveform, molten metal and a small amount of steel particles, formed Al-rich FeAl₃. The welded seam with low strength shown brittle fracture characteristic of spherical intermetallic compounds iron-rich FeAl formed by retention jets. Therefore, the dominant mechanism of interface formation is that the compression and impact effect of jet accompanied by a softening effect of eddy current heat on aluminum alloy.

Copper tubes are used in refrigerator and air conditioning unit heat exchangers. However, in some cases, the areas in copper tubes subjected to mechanical processing experience pitting corrosion. Therefore, a test scheme to rapidly evaluate the corrosion resistance of copper tubes in these sections and the effectiveness of the initial treatment on corrosion resistance were investigated. The initial treatment is a chemical treatment that improves the corrosion resistance of copper tubes. The corrosion of copper tubes was investigated by observing the surface after immersing the copper tube in various solutions containing hydrogen peroxide, chloride ions, sulfate ions, benzotriazole and hydrogen carbonate ions for one day. The test solution that contained a combination of 10 mg/L hydrogen peroxide (H₂O₂), 300 mg/L chloride ions (Cl⁻), 300 mg/L sulfate ions (SO₄²⁻) and 10 mg/L benzotriazole was found to replicate actual corrosion processes on the copper tubes over 1 day. The results indicated a high tendency for corrosion to occur in the mechanically processed sections. The improved corrosion resistance in these sections from the initial treatment was also confirmed in the test solution. Additionally, the corrosion resistance in the mechanically processed sections of copper tubes was weaker as the residual carbon amount increased.

This Paper was Originally Published in J. Soc. Mater. Sci., Japan 69 (2020) 804–809. All figures and tables (except Figs. 4, 5 and Table 3) and all captions of figures and tables (except Tables 4, 6) were slightly modified.

The effect of Ta addition on the pitting corrosion resistance of duplex stainless steels was investigated in both cases without and with deoxidization/desulfurization by the addition of Al and Ca. The pitting corrosion resistance was improved by the addition of Ta with two proposed mechanisms. For steels without Al and Ca, the MnS inclusions which act as initiation sites of the pitting corrosion are modified to the electrochemically-stable (Ta,Mn) oxysulfides. For steels with Al and Ca, the pitting initiation sites (CaS and (Al,Ca)oxides) are coated with the stable Ta-containing nitrides resulting in the suppression of pitting corrosion propagation.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 69 (2020) 237–245.

Amorphous alloys are advantageous to obtain excellent catalytic activity from a disordered atomic arrangement and more dangling bonds. The compositional range of the Ni–B amorphous alloy was thermodynamically predicted. The function of the Gibbs energy of mixing, , and the activities of the Ni and B components, , and, , of the liquid phase was extrapolated to room temperature. The negative was found from X_Ni = 0.45 to 0.92, indicating the existence of the liquid phase as metastable state, i.e. formation of amorphous alloy. The small and , that is, the strong attractive interaction between the Ni and B components suggested the liquid phase structure was stable. The Ni–B amorphous alloys were prepared from aqueous solution using reducing agent consistent well with the thermodynamic prediction. The preparation method from aqueous solution was useful to prevent from thermal migration of the atoms toward the equilibrium state. The quasi equilibrium oxygen pressures, (Ni_{in amor.}), and, (B_{in amor.}), of Ni and B components in the amorphous alloys were evaluated from and . (B_{in amor.}) was found to be smaller than (Ni_{in amor.}), revealing that B components in amorphous alloy were preferentially oxidized and inhibited Ni oxidation. Not only a characteristic disordered atomic arrangement but also chemical alloying effect of B results in the excellent catalytic activity of the Ni–B alloy.

Two types of intermediate layer (IML) were formed at the magnetic pulse welded Al/Fe joint interface. To clarify the formation mechanism of IML, the cooling process at the joint interface and formation process of IML were analyzed by the simulation and experiment. The simulation results showed that the crest zone of wavy interface underwent an extremely high temperature rise during the collision process, the high temperature leads to a local melting behavior at the joint interface. After the collision, a large temperature difference of 1000∼1500 K between joint interface and base metals caused a rapid cooling occurred at the interface with a cooling rate reached around 10⁷∼10⁹ K/s. Meanwhile, local melting zone (LMZ) changed into IML during a rapid solidification that proceeded from the outside and finished at the center area of LMZ. The morphology and composition percent of IML calculated by the numerical analysis was quantitatively in good agreement with experimental analysis results. A reasonable explanation has been made on the formation mechanism of IML at magnetic pulse welded Al/Fe joint interface.

In this study, punchless punching by the compression ignition of octane and the effect of varying the amount of fuel on punchability were investigated. In the experiment, the compression in compression ignition was applied using a drop hammer. As the amount of fuel increased, the variation in the initial height of the hammer required for completing the piercing could be divided into the following four parts of the basis on the amount of fuel. In the first part, corresponding to the smallest amount of fuel, the height exhibited a large decrease. In the second part, the height decreased by a small amount. In the third part, the height increased. Finally, in the fourth part, corresponding to the largest amount of fuel, the height remained constant. The four parts were believed to be caused by differences in the chemical reactions. Moreover, the optimum amount of fuel for punching was the largest amount of fuel under the conditions of the first part.

This Paper was Originally Published in Japanese in J. JSTP 61 (2020) 93–98.

In order to elucidate the mechanism of nodule count increase by Bi, we analyzed spheroidal graphite cast iron with increased nodule count by Bi addition. In the Scanning Electron Microscope - Energy Dispersive X-ray Spectrometry (SEM-EDS) analysis, Bi was identified to be present near the center of the spheroidal graphite. The center of this spherical graphite was pretreated by Focused Ion Beam (FIB) micro sampling method to prepare analytical sample and analyzed by Transmission Electron Microscope - Energy Dispersive X-ray Spectrometry (TEM-EDS). As a result, it was found that Bi exists as Bi–La–Ce–Sb oxide on the outer periphery of the graphite core centered on (MgCa) S.

To verify the effect of the Bi–La–Ce–Sb oxide on the increase in nodule count, we first used mechanical alloying to prototype a Bi–La–Ce–Sb oxide having the same composition as that observed via TEM-EDS. This oxide was then added to the molten spheroidal graphite cast iron. As a result, nodule count did not increase with the addition of the prototype Bi–La–Ce–Sb oxide alone, but when the prototype Bi–La–Ce–Sb oxide and Fe–Si inoculants were mixed and added, the nodule count increased more than when only the Fe–Si inoculants was added.

From these results, it is considered that the effect of increasing nodule count by Bi addition is that Bi acts on graphite nucleus as an oxide.

This Paper was Originally Published in Japanese in J. JFS 91 (2019) 221–227. Some spelling errors were modified.

Magnesium specimens were impacted by a spherical alumina projectile at a velocity around 7 km/s under two environment temperatures of room temperature (∼300 K) and low temperature (∼173 K). To clarify deformation and fracture mechanisms, macro- and micro-structure were inspected by using micro-X ray computed tomography and scanning electron microscope (SEM) with electron back scattering diffraction (EBSD). In addition, simulation of the hyper-velocity impact was conducted using Smoothed Particle Hydrodynamics method to investigate the cumulative strain and temperature rise during the deformation. After a projectile impacted a target, a crater was formed on the target together with several cracks. In a closed portion below the crater formed at room temperature, fine grains and subgrains were observed by SEM/EBSD. From the calculation results, a temperature rise around 0.5 Tm (Tm; melting temperature of magnesium) and cumulated strain over 0.6 was suggested at 0.5 mm away from the edge of the crater. Therefore, the microstructure evolution was expected to be induced by the recrystallization and recovery due to the strain cumulated during the impact and the resultant temperature rise. On one hand, inspection of microstructure near the cracks revealed that microcracks were tended to propagate along grain boundary.

This Paper was Originally Published in Japanese in J. JILM 69 (2019) 287–292.

The present study demonstrates that the bioactivation of bioinert yttria-stabilized tetragonal zirconia (YSZ) substrates is achieved through a chemical treatment process using a calcium phosphate slurry. The slurry processing is simple: a YSZ substrate was buried in a slurry agent prepared by mixing calcium phosphate powder and distilled water, and thereafter, the slurry including the substrate was heated in air. Treating by the processing, tiny hydroxyapatite (HAp) particles were deposited on the YSZ surface. The amount of the particles increased with an increase in the heating temperature up to 1223 K, while setting the temperature beyond 1373 K induced thermal decomposition into tricalcium phosphate (TCP) and calcium oxide (CaO). When immersing in Hanks’ balanced saline solution to evaluate bioactivation, HAp precipitation was only observed on the slurry-treated surface, and the mass thickness of the precipitation was enhanced with increasing heating temperatures up to 1223 K. Slurry-treated YSZ at 1223 K did not adversely affect the adhesion and proliferation of osteoblast-like cells. On the other hand, calcification of the cells was significantly promoted, indicating the activation of bone formation. In conclusion, slurry processing is a valuable technique that enhances the bioactivity of YSZ substrates with a simple one-step process.

In tensile tests, α-Mg/C14–Mg₂Ca eutectic alloy with a lamellar structure is plastically deformed above 473 K but ruptures before yielding at temperatures below 423 K. This study investigates the effect of the α/C14 interface on the creep strength of α-Mg/C14–Mg₂Ca eutectic alloy at 473 K under 40 MPa stress. The creep curves of the alloy exhibited three stages: a normal transient creep stage, minimum creep-rate stage, and accelerating stage. The minimum creep rate was proportional to the lamellar spacing, indicating that the α/C14 lamellar interface plays a creep-strengthening role. In high-resolution transmission electron microscope observations of the specimens after the creep test, a-dislocations appeared within the α-Mg lamellae and were randomly distributed on the α/C14 interface. It was deduced that the α/C14 interface presents a barrier to dislocation glide and does not annihilate and/or rearrange the dislocations caused by the creep test.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 85 (2021) 223–228.

“The 12th Japanese-Polish Joint Seminar on Micro and Nano Analysis” was held in Fukuoka, Japan from August 29 to September 1, 2018, and the proceedings were published in May, 2019, as a special issue of Materials Transactions (Vol. 60, No. 5). The main purpose of this seminar is to discuss the structural analysis of materials by electron microscopy techniques. Among the papers presented at the seminar, this article briefly reviews the following topics: observations of dislocations in a thick specimen by ultra-high voltage electron microscopy, suppression of geometric phase shift due to antiphase boundaries in dark-field electron holography, and structural characterization of amorphous materials by electron diffraction techniques.

Microscopic-scale strain distributions in a martensitic steel were visualized during tensile deformation over a wide range, including a necking deformation, using the digital image correlation method on replica films. An inhomogeneous strain distribution was developed from the initial stage of deformation. The strain distribution was successfully visualized even in the late stage of deformation after necking occurred. It was found that the high- and low-strain regions formed at the initial stage of deformation were maintained even during necking deformation. The von Mises equivalent strain in the high-strain region was ten times larger than that in low-strain region. Therefore, it can be concluded that martensitic structure has significant inhomogeneous deformability attributed to its microstructure, and its characteristic hardly changes even in the late stage of necking deformation.