Recent progress in the development of advanced materials based on the study of CALPHAD approach to the phase diagrams and microstructural control is presented. Thermodynamic databases on the Fe–S based system, Fe–Mn–Al based alloys, Cu-based alloys and Co-based superalloys have been constructed. By utilizing these databases and information on phase diagrams, the following advanced materials have been designed and developed; (i) Schaeffler-type Ti-based alloys, (ii) Pb-free machinable stainless steels using titanium carbosulphide, (iii) high strength Fe–Mn based alloys with low density, (iv) FSW (Friction Stir Welding) tool using Co-based superalloy strengthened by γ′ (Co₃ (Al, W)) phase, (v) Ni based metamagnetic shape memory alloys, (vi) Cu–Ni–Al based alloys with high strength and high electronic conductivity strengthened by γ′ (Ni₃Al) phase, and (vii) Ingrown nail correcting device and seismic application using Cu–Al–Mn based shape memory alloys. The alloy design and practical application of these materials focussing on the use of phase diagrams have been presented.

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The variation in the deformation behavior of a directionally solidified (DS) Mg-based long-period stacking ordered (LPSO)-phase crystal depending on the loading orientation was examined. The frequency of formation of the beak-like shape of the deformation band, which is known as one of the important deformation mechanisms in the LPSO phase, monotonically decreased as the inclination angle of the loading orientation with respect to the crystal growth direction in the DS crystal increased, and was accompanied by a decrease in the yield stress due to the activation of basal slip. Deformation bands formed along a direction approximately perpendicular to the grain boundary independent of the loading orientation. The crystal rotation axes selected in the deformation bands were perpendicular to [0001] in almost all grains, independent of the loading orientation. However, the rotation axes in the bands were not fixed but varied between ⟨1010⟩ and ⟨1120⟩; this variation was correlated with the loading axis. These observed features strongly suggest that the deformation bands formed in the LPSO phase are predominantly deformation kink bands and that the formation mechanism itself does not vary with the loading orientation but instead its details. The selectivity of the crystal rotation axis in the kink band is strongly affected by the loading orientation.

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In situ neutron diffraction measurements during compressive and tensile tests of an as-cast Mg₉₇Zn₁Y₂ alloy consisting of α phase (αMg) as the matrix and a long period stacking ordered phase (LPSO) with 25 vol%, were performed to understand deformation behavior of each phase and to monitor the occurrence of kinking during deformation. The deformation modes at the beginning stages of compressive and tensile tests below the applied true stresses of 130 MPa were quite similar. The LPSO grains yielded possibly via kinking during compressive deformation above the applied true stress of about 137 MPa. The stress partitioning among αMg grains was observed larger in the compressive deformation than in the tensile deformation, that might be due to the large load sharing of αMg grains as a result of the yielding of LPSO grains during compressive deformation.

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We have investigated a novel long-period stacking/order (LPSO) structure in a Mg₇₅Al₁₀Y₁₅ alloy, based on electron diffraction, scanning transmission electron microscopy (STEM) observations and first-principles calculations. Fundamental lattice of the present LPSO structure is identified as one of the stacking polytypes of 10H-type, and the in-plane 6×(1210)_hcp superlattice order is well developed as represented by the L1₂-type Al₆Y₈ cluster arrangement. We find that, across the stacking direction, the inter-cluster order tends to be further developed beyond its periodicity, showing an extra order which doubles the 10H-stacking periodicity. We have constructed the LPSO variant models including such extra inter-cluster order, and their formation energy comparison has confirmed that the extra order becomes indeed stable when the L1₂-Al₆Y₈ cluster contains interstitial atoms. The interstitial effects turn out to be prominent in favor of Y atom, as being consistent with the STEM observations.

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Thermodynamic behaviors of the Mg–Zn–Y, Mg–Co–Y and Mg–Zn–Ca ternary systems to form a unique solute-enriched stacking-fault (SESF), which is regarded as the structural-unit of the long-period stacking/order (LPSO) phase, have been investigated. The SESF in the hexagonal-close-packed (hcp) Mg matrix forms a local face-centered-cubic (fcc) environment, and hence our thermodynamic analysis is focused on the Gibbs energy comparison between hcp and fcc phases for arbitrary chemical compositions at finite temperatures in these ternary systems, using the calculation of phase diagrams (CALPHAD) method aided by the first principles calculations. It has been reported that the Zn/Y co-segregations at the SESF provide a remarkable condition that the fcc layers become more stable than the hcp-Mg matrix in the Mg–Zn–Y. Within the SESF, furthermore, the following spinodal-like decomposition into the Mg-rich fcc solid-solution and the Zn/Y-rich L1₂-type order phase causes a significant reduction of the total Gibbs energy of the system. It was suggested that the L1₂-type ordering of the Co-rich phase would not take place even though the spinodal-like decomposition is predicted to occur, which makes the LPSO phase metastable due to insufficient gain of the Gibbs energy in the Mg–Co–Y system. In the Mg–Zn–Ca system, the formation of SESF layers is also expected. However, neither the spinodal-like decomposition nor the chemical ordering would occur, which suggests that no Gibbs energy gain is provided for the formation of the LPSO phase. These spontaneous thermodynamic behaviors explain well why the SF layers can be remarkably stabilized in the LPSO-forming ternary Mg alloys, and also clarify phenomenological criteria of the LPSO formation in the Mg-based ternary systems.

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Mg alloys with a long-period stacking-order (LPSO) phase are categorized into two types. Those in which the LPSO phase forms in as-cast state are referred to as Type I, while those in which the LPSO phase does not appear until a heat treatment is performed are categorized as Type II. However, the reason that gives rise to these two types of alloy is still not well understood. In the present study, in an attempt to clarify this issue, three different Mg₈₅(Al,Zn)₆Gd₉ quaternary alloys were prepared. The α-Mg, Al₂Gd, Mg₃Gd and LPSO phases were identified in the as-cast quaternary alloys by microstructural observations, composition analysis and crystal structure analysis using electron probe microanalysis and X-ray diffraction. The results indicated that all the quaternary alloys could be categorized as Type I, even though ternary Mg₈₅Al₆Gd₉ and Mg₈₅Zn₆Gd₉ alloys were Type II. The crystal structure of the LPSO phase in the as-cast alloys is considered to be18R with dilute solute elements, and the fraction of this phase increases with increasing Zn content. The presence of this phase is thought to be the cause of destabilization of the primary Al₂Gd phase. It is thus concluded that the relative stability of phases in the vicinity of the LPSO phase is crucial in determining the type of Mg alloy formed.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 257–263.

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As a trial to realize kink band strengthening in titanium alloys, slight cold rolling followed by aging heat treatment were applied on Ti–12 mass% Mo alloys for obtaining mille-feuille-like layered hcp (α)/bcc (β) two phase structure. After slight cold rolling at rolling reduction of 5% and subsequent aging heat treatment at 973 K for 180 ks, plate-like α phases were precipitated in the β phase matrix and made an alternately stacked mille-feuille-like α/β layered structure. These α phases were precipitated on the boundary of {3 3 2}〈1 1 3〉 β type deformed twins introduced in the β phase matrix during the slight cold rolling. The thin film-like α phase precipitated at a very early stage of aging, and became thicker during aging to produce the mille-feuille-like α/β layered structure.

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This study conducts dislocation-based modeling and numerical analysis on the deformation fields of two-dimensional kink structures. Peierls-Nabarro model is used to express edge dislocations in the elastic medium which are implemented into the weak form stress equilibrium equation using the extended isogeometric analysis. Numerical analysis revealed that the macroscopic deformations of two types of ortho kinks and four types of ridge kinks, , agree well with the experimental results. Although most of the stress components are localized near the dislocation cores, only the component σ₂₂ in type ridge kinks showed broad distribution within the kink boundaries. On the other hand, deformation fields in type ridge kinks showed complementary rotation around the tip of kink structure. Such novel deformations would contribute to kink strengthening mechanism.

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The geometry of kink bands with the general shear direction on the unique slip plane was formulated and the connection between two kink bands formed by non-parallel shears on the slip plane was examined using rank-1 connection. For a kink deformation in a metal with a hexagonal lattice, we derived an equation that decomposes the general shear direction into two ⟨a⟩ basal slips. The rotation axis of the misorientation of kink band moves away rapidly from ⟨0110⟩ to ⟨1210⟩ as the second ⟨a⟩ basal shear component increased. We proved that any two kink bands formed by non-parallel basal shears can be rank-1 connected to each other. In addition to the wedge disclination, a mixed disclination at the junction of two kink bands formed by non-parallel basal shears was found.

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Disclination resulting from kink deformation of the long-period stacking-ordered phase of Mg–Zn–Y alloy affects the strength of the alloy. In this study, we examined theoretical aspects of the kinematic equation of defects, including dislocations and disclinations, based on the dual structure of strain and stress space. Two types of disclination, related to dislocation and bend-twist, were identified. Disclination types were distinguished based on incompatibility. In “dual strain space”, we show that incompatibility is due to a generalized stress function, i.e., the Beltrami stress function, which is a three-dimensional version of the Airy stress function that includes non-diagonal components.

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Nanocrystallization of amorphous ZrCu was induced by applying a pulse current (electropulsing), which exponentially decayed from a certain initial current density (i_d0) with the time constant of 3 ms. For electropulsing, the ribbon specimen was sandwiched between high-thermal-conductive AlN (thermal conductivity κ = 170 W/m/K at 273 K) plates to remove the Joule heat. Nanocrystallization was found when electropulsing was conducted in a vacuum below 10⁻² Pa at the pulse current of i_d0 ≥ 0.6 GA/m². In contrast, electropulsing conducted under 10⁵ Pa He (κ = 0.144 W/m/K at 273 K) required i_d0 above 1.1 GA/m². Thermal conductivity and heat capacity of 10⁵ Pa He were negligibly smaller than those of the AlN plates. The increase in i_d0 for nanocrystallization with increasing He pressure indicates that He penetrated the amorphous structure to inhibit the activation of cooperative motions of many atoms and larger i_d0 is required for nanocrystallization at higher He pressure.

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Oil quenching is an efficient heat treatment cooling method which can obtain a large cooling capacity by utilizing the boiling phenomenon. However, when the vapor film remains, the cooling speed is reduced only in the part, and the uneven cooling can cause heat treatment distortion, which is the biggest problem in the heat treatment process. In this paper, a quenching experiment was conducted by immersing a horizontal stainless steel disk specimen in quenching oil. Thermocouples which just located below the surface accurately measure the cooling curves of the top and bottom surfaces of the specimen.

In this study, the temperature-dependent heat transfer coefficients were identified from the cooling curves by the inverse method using the analytical solution derived from the Fourier heat conduction equation of the disk.

In addition, a visualization experiment was conducted, in which a laser beam sheet was put into the oil tank of the equipment, and the boiling phenomenon, the formation of a vapor film, and the film boiling phenomenon were observed using a high-speed video camera.

Furthermore, in order to verify the correctness of the heat transfer coefficient obtained by the inverse solution method, the heat transfer coefficient was substituted into the heat treatment simulation software “COSMAP” and the quenching distortion calculation was performed by executing the quenching simulation calculation of the disk. It was proved that the prediction accuracy was improved.

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This work investigated the influence of the number of rolling cycle on the microstructure evolution and mechanical characteristic of AZ31 magnesium alloy processed by accumulative roll bonding (ARB). Results show that the AZ31 alloy after ARB exhibit a typical mixed grain structure, which is mainly composed of refined grains and elongated original grains. Grain refinement is achieved by dynamic recrystallization (DRX), and fine DRXed grains formed the shear band in the direction of shear stress. Interface bonding is the result of DRX occurs on the contact surfaces, fine DRXed grains continually grew and replaced the coarse grains to achieve well bond of sheets. Microhardness was improved after ARB, and increased with the increasing of ARB cycle. The microhardness of inner plate was higher than that of outer plate due to the softening effect caused by the formation of shear bands. After ARB process, the increment of strength is caused by grain refinement, and the compromise of elongation can attribute to the nucleation and growth of internal microcrack.

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GTD-111 is a γ′ strengthened Ni-based superalloys, which is used in critical applications such as turbine blades. Liquation cracking during welding is recognized as being one of the most important problems of this type of components. The present paper outlines a new preweld heat treatment to control the liquation cracking occurred in HAZ regions of GTD-111 turbine blades. Different preweld heat treatments were carried out on the samples extracted from the root of turbine blades and then they welded by gas tungsten arc welding (GTAW) process The microstructural analysis of the joints was carried out using optical microscopy, scanning electron microscopy, and image analysis technique. The results showed that the preweld heat treatment regimes can obviously affect the intensity of liquation cracking. While the optimum solutionizing temperature and time were found to be 1180°C and 2 hours, the samples with no heat treatment showed the lowest resistance to liquation cracking. It was also concluded that the liquation cracking is mainly affected by the relative intensity of the base metal hardness, the average length and volume fraction of γ′ precipitates, presence of carbides, and the existence of low melting phases.

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To better understand the kinetics associated with the uphill diffusion of carbon (C) in the austenite (γ) phase of low-carbon steels, the effect of substitutional component M on the intrinsic diffusion coefficient, D_C^γ, of C in the γ phase of the ternary Fe–C–M system was quantitatively analyzed based on thermodynamics. Here, M corresponds to various metals, including Mn and Si. When the concentration, c_M^γ, of M in the γ phase is homogeneous, this effect was found to be negligible. In contrast, the effect was not negligible in the case of C diffusion trapped by M. If c_M^γ is inhomogeneous, D_C^γ varies depending on the concentration, c_i^γ (i = C and M), in the γ phase and the ratio of the gradient of c_C^γ to that of c_M^γ. In this case, D_C^γ takes positive or negative values, and the negative value results in the uphill diffusion of C. Using the (Fe–C)/(Fe–C–Si) diffusion couple as an example, the diffusional flux, J_C^γ, continuously varies with the distance, r, along the direction normal to the original interface, although the dependence of c_C^γ on r is irregular across the original interface. The extent of uphill diffusion can be estimated from the diagonal and off-diagonal diffusion coefficients for the intrinsic diffusion of C and from the value of c_i^γ.

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Additive metal manufacturing-has been attracting attention for various applications such as aircraft parts. However, the parts manufactured exhibit anisotropy characteristics due to the columnar crystal structure induced by rapid melting and solidification. In this work, an equiaxed solidification structure is obtained by adding Zr to promote nucleation. Samples were fabricated by additive manufacturing using Zr-added SUS304L powder. Their microstructures were observed by scanning electron microscopy and transmission electron microscopy. The mechanical and corrosion resistance properties were evaluated by comparison with samples fabricated by additive manufacturing using SUS316L. The microstructure observation revealed that the formation of columnar crystals in the SUS304L-Zr-3DP samples was suppressed compared with the SUS316L-3DP samples and that the average grain size was reduced to 1/3 or less. The transmission electron microscopy revealed a ZrN crystallized substance, which may have contributed to the suppression of columnar crystal formation. Tensile test results showed that the SUS304L-Zr-3DP exhibited isotropic mechanical properties. Corrosion resistance tests using electrochemical methods showed that they exhibited higher corrosion resistance than the SUS316L-3DP. These results demonstrate that the solidification structure formed during additive manufacturing can be controlled by adding Zr into the alloy matrix as nucleation sites.

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This work was motivated by the endeavour to experimentally determine the influence of crack position on the fatigue life of weldments. Plates were cut from a pipe of X52 pipeline steel – 830 mm in diameter and 10 mm in wall thickness – and their contact edges were then prepared for single-bevel butt welds. The plates were then welded by manual arc welding, and separate specimens – 10 mm in width and 5 mm in thickness – were cut from the weldment perpendicularly to the weld bead. The electro-spark method was then used to produce blunt crack discontinuities for the initiation of fatigue cracks. The cracked weldment specimens then underwent cyclic loading at reference force level F_max = 5.5 kN and stress asymmetry ratio R = F_min/F_max = 0.1. The test results made it possible to quantify the effects of the size and position of crack-like discontinuities on weld fatigue life.

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Tensile tests were applied to rolled Mg–Y alloy sheets with three at% of yttrium - Mg–0.54 at% Y, Mg–0.9 at% Y, and Mg–1.21 at% Y - to investigate effects of yttrium addition on activities of basal slip and non-basal slip systems so as to clarify the relationship between tensile properties and activities of slip systems. 0.2% proof stress of Mg–Y alloys increased with increasing yttrium content ranging from 0.5 to 1.2 at%. Ductility increased with increasing yttrium content until 0.9 at% but decreased when 1.2 at% was added. Frequencies of basal and non-basal slips increased by yttrium addition. The frequency of {1011} ⟨1123⟩ first order pyramidal slip (FPCS) increased with increasing yttrium content until 0.9 at% and decreased when 1.2 at% was added. With increasing yttrium content, the frequency of {1122} ⟨1123⟩ second order pyramidal slip (SPCS) decreased, while that of {1010} ⟨1120⟩ prismatic slip (PS) increased. The highest total frequency of non-basal slips was observed in Mg–0.9Y, showing the highest ductility. Enhancement of ductility on magnesium was caused by activation of both basal and non-basal slips through yttrium addition.

　

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 84 (2020) 44–49.

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In the present study, draw-bending tests were conducted to investigate the effects of holding time at the bottom dead center (holding-time dependency) and elapsed time after releasing from dies (elapsed-time dependency) on springback in steel, Al alloy, Mg alloy, and CP-Ti sheets experimentally. The amount of springback decreased with increasing the holding time, irrespective of the material. The decreasing amounts from the holding time of 5 min to 600 min were 29%, 11%, 8.1%, and 5.7% respectively for the Mg alloy, CP-Ti, Al alloy, and steel sheets. On the contrary to previous studies, it was presumed from simple analyses that the holding-time dependency would presumably be explained in terms of not only stress relaxation but also unloading behavior following stress relaxation. The amount of springback gradually increased with the elapsed time regardless of the material. The amounts of increase from just after releasing from dies were approximately 5.9% for one month in the CP-Ti sheet, 4.1% for 1.5 months in the Al alloy sheet, 1.6% for 1.5 months in the Mg alloy sheet, and 1.1% for 1.5 months in the steel sheet. This magnitude relationship was different from that of creep strains, indicating that the mechanism of the elapsed-time dependency could not be explained only from the creep behavior and there would be other factors that affect the elapsed-time dependency.

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Indentation tests using a spherical indenter were applied to six hexagonal close-packed structure single crystals - pure Mg, Mg–0.5 at%Al, Mg–0.5 at%Zn, Mg–0.5 at%Y, Mg–0.9 at%Y, and pure Zn single crystals – to investigate the roles both slips and twinning induce on the formation of indentation. When indented on (0001), all single crystals displayed circular morphology without slip lines or twins. Mg and Mg alloys’ indentation sizes were found dependent on critical resolved shear stress (CRSS) for basal slip in (0001) indentations, while Zn (0001) indentation size depends on CRSS for both basal and second order pyramidal slips. Conversely, when indented on (1010) and (1210), all single crystals displayed indentations elongated to [0001] surrounded by basal slip lines. Also, {1012} twins were observed in Mg–0.5 at%Al and Mg–0.5 at%Zn but were scarce in Mg–Y. Pure Zn displayed second order pyramidal slips. Sizes of both (1010) and (1210) indentations were found dependent on CRSS for basal slips and for {1012} twins.

　

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 458–464.

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Oxide Dispersion Strengthening copper (ODS-Cu) alloy has high strength, high thermal conductivity and superior irradiation resistance which are needed for fusion reactor divertor components. In this study, specimen size dependence of the yield stress in Cu and ODS-Cu which were made by mechanical alloying and hot pressing was investigated by micro-pillar compression test. The distributions of yield stress values were different between the sizes, 1, 3 and 5 µm cubic micro-pillars, which can be explained by the inhomogeneous spatial distributions of both the crystallographic grain in matrix and oxide-particles.

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Increased amounts of secondary copper resources with higher levels of impurities are being fed to copper smelters. To avoid passivation problems, low-grade copper that is derived from secondary resources is dissolved in sulfuric-acid solution, and the dissolved copper is recovered by electrowinning. Electrowinning is disadvantageous because of its higher power consumption compared with electrorefining. Based on an electroplating technique that uses basket electrolysis with a ball-shaped anode and another experimental approach of copper-scrap electrorefining in a basket, we investigated an electrorefining method that uses small low-grade copper shots (diameter of several millimeters) as an anode. It is expected that the copper-dissolution ratio will be higher, even with a small elution depth, because of the small primary-anode size and the effect of the three-dimensional shape. In addition, the current density for a shot-shaped anode can be lower than that for a plate-shaped anode at the same current and for the same occupied area, and would result in the inhibition of passivation. Rotating-disk-electrode equipment was used in the electrolysis experiments. Single-layered copper shots that contained 0.9 ± 0.2 mass% Pt (18 shots) in a platinum basket were used as an anode, and a copper rotating-disk electrode (7-mm diameter) was used as a cathode. The temporal changes in anode potential were measured at a constant current to investigate the electrolytic properties of a small shot-shaped anode during the electrorefining experiments. The current efficiency and final anode-dissolution ratio exceeded 90% up to an initial anode current density of ∼673 A/m². Stable electrolysis could be carried out with a copper shot-shaped anode that contained high levels of platinum.

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To elucidate the synergistic effects of gelatin, thiourea, and chloride ions on the deposition behavior, throwing power, and surface roughness of Cu obtained from electrorefining solutions, Cu electrodeposition was performed at a current density of 200 A·m⁻² and a charge of 5 × 10⁵ C·m⁻² in an unagitated sulfate solution containing 0.708 and 2.04 mol·dm⁻³ of CuSO₄ and H₂SO₄, respectively, at a temperature of 60°C. Gelatin and chloride ions have synergistic effects on the polarization for Cu deposition, and the polarization effect increased with each concentration. Thiourea was found to promote Cu deposition and decrease the polarization effects of gelatin and chloride ions as its concentration in the solution were increased. The throwing power and surface roughness of the deposited Cu changed depending on the concentration of the three additives. The throwing power of Cu significantly worsened with increasing concentrations of thiourea and its surface roughness decreased with decreasing concentrations of chloride ions. With increasing concentrations of gelatin, the throwing power of Cu improved and its surface roughness decreased. The correlation between the throwing power and polarization resistance of Cu deposition was observed, and the throwing power of Cu improved as its polarization resistance increased. Since the surface roughness of deposited Cu is a result of its micro deposition properties, it does not depend on polarization resistance alone. Thiourea appeared to promote Cu deposition at the concavity, and therefore, it decreased the surface roughness of the deposited copper.

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The removal of volatile organic compounds (VOCs) has been an urgent task all over the world because they are the main substances for environmental problems. Removal by adsorption technique is the most convenient method. Until now, adsorption by activated carbon has been studied in many cases. However, activated carbon has a fire risk and requires a large amount of energy to regenerate the adsorbent. Therefore, siliceous materials have been expected as novel adsorbents instead of activated carbon. We have been able to synthesize porous silica having super-micropores of about 0.8 nm by using collagen fibril as a template. In the present study, the author evaluates toluene dynamic adsorption/desorption properties of this super-microporous silica (SMPS) as well as the characterization studies. It was found that SMPS showed very high dynamic adsorption/desorption properties in comparison with other siliceous materials such as mesoporous silica MCM-41, commercial microporous silica gel, and HY zeolite. SMPS synthesized by using collagen fibril as a template can be expected as a novel VOCs adsorbent.

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The equilibrium constant of calcium oxidation is important to evaluate the ability of deoxidation of the dissolved oxygen in metals and the reduction of metal-oxide. Therefore, in this study, the equilibrium constant for calcium oxidation has been determined by a slag-metal equilibrium distribution method by using molten iron and/or titanium-based alloys. In general, this method can be used to determine the equilibrium constant for solved elements, e.g., as expressed by “CaO_(s) = Ca_{in metal} + O_{in metal}”. When the oxygen partial pressure and the activity of calcium in the surroundings are established, the equilibrium constant of “CaO_(s) = Ca_{(l, g)} + 1/2O_2(g)” is determined to be log[K] = −17.50 for titanium-based alloys at 1473 K and log[K] = −12.91 for molten iron at 1873 K. These values are essentially medians obtained using an experimental measurement of the oxygen partial pressure and are based on the definition of the activity of calcium in the slag as given in literature. The temperature dependence of these results has been determined as follows:

log[K] = 4.814 − 32960 (1/T) (1473–1873 K)

or

ΔG° = 631 − 0.0922T [kJ/mol] (1473–1873 K)

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In die casting, it has been shown that the hypereutectic Al–25%Si alloy has excellent fluidity. In this study we clarified that the semisolid Al–25%Si alloy showed better fluidity than did the molten-metal ADC12 alloy, which is a popular Al–Si–Cu alloy for die casting. The result obtained suggests that Al–25%Si alloy is suitable for manufacturing thin die cast products. By using the Al–25%Si alloy, a heat sink model having fins with 50 mm height, thin tops 0.5 mm thick and a draft angle of 0.5°, could be successfully cast at a plunger speed 1.6 m·s⁻¹. It was found that heat dispersion heat dissipation characteristics were not influenced by the reduction in fin thickness. It is concluded that thinner fins manufactured using the semisolid Al–25%Si alloy are useful in reducing the production weight of the heat sink.

 

This Paper was Originally Published in Japanese in J. JSTP 59(693) (2018) 183–188.

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Alternating and one-way tool paths were applied for penetrating tool friction stir incremental forming to compare the forming limit in height without sheet fracture. A truncated cone was formed using 200 mm × 200 mm × 2 mm commercial pure aluminum (JIS: A1050-O) sheets. After the cone was formed, the forming limits in height when employing penetrating tool friction stir incremental forming with alternating tool paths were compared with those formed with one-way tool paths. A tool rotation rate for forming of 1000 rpm, tool feed rate for forming of 1000 mm/min, and wall angle of 45° were used. The forming limit in height with alternating tool paths was approximately 30 mm and the limit in height for one-way tool paths was less than 10 mm. Volume change per unit length in radial direction for both formed sheets with alternating and one-way tool paths were calculated such that the improvement of forming limit in height could be examined. The volume change per unit length observed with alternating tool paths was smaller than for that with one-way tool paths, which means that a more uniform material distribution was achieved when penetrating tool friction stir incremental forming was employed with alternating tool paths.

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Two SmCo₅ intermetallic compounds were made by using the raw material made through strip and book casting technique. The strip casting was performed on relatively low speed, whereas book casting was done in an indigenously made mold. The other processing parameters like ball milling time, sintering and heat treatment temperatures for both systems were kept constant. X-ray diffraction analysis revealed the presence of Sm₂Co₇ phase in book casted sintered samples whereas, no such peak was detected in case of strip casted sintered samples. Results of Differential thermal analysis, revealed the presence of Sm₅Co₁₉ phase in strip casting sintered samples, which has relatively higher intrinsic coercivity. Magnetic properties of strip cast sintered samples and book cast sintered samples demonstrated that the strip cast sintered samples had high coercivity i.e. 1940 kA/m as compared to the book cast sintered samples, further the strip cast sintered samples show more magnetic stability than book casted sintered samples. The samples tested at high temperature showed that strip casted sintered samples are more stable than book cast sintered samples.

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We succeeded in obtaining amorphous Si–Ge thin films containing ∼6 nm nanocrystals by means of a vapor deposition. The thermal conductivity was controllable using the particle size of the nanocrystals, and a very small value of thermal conductivity ∼1 W/mK was obtained with an averaged particle size less than 6 nm. The electron transport properties were improved using Au-doping to form impurity levels near the valence band top, and B-doping to control the Fermi level. With the effect of this co-doping technique and nano-structuring, we estimated obtaining ZT = 1.38 at 1100 K.

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Mg-clad Al materials with a Ni foil interlayer were successfully prepared by vacuum roll bonding at a 450°C rolling temperature and 25% reduction, and the effects of the Ni foil interlayer on the interfacial properties were investigated. The clad materials with the Ni foil interlayer only formed the Mg₂Ni intermetallic compound with a 0.9 µm thickness on the Mg–Ni interface, which was smaller than that of the intermetallic compounds (Al₁₂Mg₁₇ of 1.77 µm and Al₃Mg₂ of 7.76 µm) formed on the Al–Mg interface without the interlayer. The bonding strength of the interface increased from 0.79 MPa to 10.46 MPa. The growth characteristics of the Mg₂Ni intermetallic compound on the Mg–Ni interface after heat treatment were investigated. The growth activation energy of Mg₂Ni was 157.24 kJ/mol, which is higher than that of Al₃Mg₂ which mainly affects the Al–Mg interfacial bonding strength. Therefore, the thickness of the Mg₂Ni was thinner and the interfacial bonding strength was greater after the vacuum roll bonding.

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In this study, we studied the elementary volume (EV) size in pore scale simulations of flow in sphere packs and evaluated existing drag models in wide porosity range. The sphere packs in different porosities were modeled with the discrete-element method. Through a parametric study, we confirmed that as the EV size grows large, the simulated values of porosity, permeability and hydraulic tortuosity nearly converge to their respective constants. This trend agrees well with previously reported experimental and numerical results. Using the EV size determined by the parametric study, we simulated the inertial flow in sphere packs of porosity range between 0.3 and 0.95. We found that the simulated drag force disagreed drastically with the existing drag models for high porosity range. Accordingly, we improved the Di Felice equation suitable in high porosity range.

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Present paper shows a simple method for obtaining hardness data required for predicting the hardness values of carburized-quenched steel parts using carburized quenching simulations. Conventionally, the relationship between cooling rate and hardness values is evaluated by preparing specimens with various carbon concentrations and performing quench tests. In new method, Jominy end-quench test with only one specimen is used to obtain carburized-quenching hardness data that reflects the effect of carbon concentration. Finally, a comparison was made between simulated results and measured values of the effective case depth after carburizing-quenching of a cylindrical steel specimen. A good agreement between experimental and simulated results was confirmed.

 

This Paper was Originally Published in Japanese in J. Jpn. Soc. Heat Treat. 58 (2018)164–168. Figures 1–11 were slightly modified.

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Single phase intermetallic RENi₂Si₂ (RE = Y, La) nanoparticles were successfully prepared at as low as 600°C in molten LiCl–CaH₂ system. The BET surface areas were 40.0 m²/g and 14.4 m²/g corresponding to the particle sizes of 26.0 nm and 65.5 nm for YNi₂Si₂ and LaNi₂Si₂, respectively. The improved surface areas are much higher than those prepared by a conventional arc-melting of <2 m²/g. The novel preparation approach presented in this study is a simple scalable chemical method and shown to be applicable to prepare some rare earth metal doped intermetallic nanoparticles by directly reducing the oxide precursors.

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The traditional manufacturing of short fiber reinforced composites by liquid processes require preform manufacturing using inorganic binders. However, conventional preform manufacturing techniques using inorganic binder are nontrivial procedures requiring high-energy inputs for binder sintering process. A novel alternative fabrication process without preform manufacturing was developed for carbon short fiber (CSF) reinforced Al based composite by low-pressure infiltration method. The volume fraction of CSFs in the composites was 10 vol%. Two kinds of CSF/A1070 composites were compared in this paper, one is manufactured with preform manufacturing technique (with SiO₂ binder) and the other is fabricated without preform manufacturing. The microstructures of both the specimens were observed for defects in the composite. In the CSF/A1070 composite obtained from the new manufacturing process, defects by aggregation of CFSs were reduced. Furthermore, compared with the CSF/A1070 composite by preform manufacturing with SiO₂ binder, the relative density of the CSF/A1070 composite obtained from the new manufacturing process is also observed to increase from 96.6% to 97.8%. CSFs were randomly dispersed inside the composites obtained through the new manufacturing process. The Vickers hardness of the CSF/A1070 composite obtained through preform manufacturing and the new manufacturing process was 33.5 Hv and 41.3 Hv, respectively. Furthermore, CSF/Al based composites using the A356 and A336 alloy as matrix were also manufactured through the new fabrication method. The Vickers hardness, relative density of CSF/A356 and CSF/A336 alloy composites were 58.8 Hv, 98.5% and 88.4 Hv, 99.0%, respectively.

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In this study, monolithic micro/nanoporous copper is prepared by sintering and dealloying, that is, the micro/nanoporous copper is obtained by chemical dealloying of a sintered microporous Cu–Mn alloy. The porosity and Brunauer–Emmett–Teller (BET) surface area are 68% and 6.77 m²·g⁻¹, respectively. The micropore and nanopore sizes are 2.44 ± 0.48 µm and 69 ± 16 nm, respectively. The mechanical property is investigated by nanoindentation. The hardness and elastic modulus are 282 ± 65 MPa and 8.25 ± 1.63 GPa, respectively. Indentation creep occurs with a creep depth of 44 ± 7 nm. The electrocatalytic property towards the oxidation of methanol and glucose are investigated using cyclic voltammetry and chronoamperometry. The monolithic micro/nanoporous copper exhibits high electrocatalytic activity and stability. The oxidation peak current density in methanol or glucose alkaline solution is 17 or 51 times that of smooth copper.

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