In recent years, Hard Cyclic Viscoplastic Deformation has become a new effective SPD method for studying the evolution of the structure and properties of Cu-alloys without changing the dimensions of the workpieces up to their destruction during processing at room temperature. Linear compression-tension of the material in the viscoplastic region is carried out in the strain control mode in the range from ε = ±0.2% to ±3% at a constant frequency of f = 0.5 to 2 Hz with a total number of 20–40 cycles in each test series. This method can be used also to improve and stabilize the ultrafine grained microstructure, and also allows you to study changes in the mechanical, physical and functional properties of coarse grained, ultrafine grained, and nanocrystalline metallic materials. Can also to be used to study the stability and viability of metallic materials and predict their suitability over time in harsh environments such as space and military applications.

The development research of Cu–Ti alloys for electrical engineering applications copes with two crucial problems. First, Ti solutes in the Cu matrix result in serious loss of electrical conductivity; second, discontinuous precipitation (DP) results in the deterioration of the mechanical properties of the alloy. In this connection, the effect of isothermal aging in a hydrogen atmosphere on the microstructure of an Mg-doped Cu–Ti alloy, under test conditions of 450°C for 100 h and hydrogen pressure of 0.6 MPa, were investigated using various electron microscopy and microanalytical techniques. During the early stage of aging, the ternary alloy showed almost the same levels of the Vickers hardness as well as the electrical conductivity as those of the binary counterpart without Mg doping. Through this stage, fine needle-shaped metastable β′-Cu₄Ti precipitates were continuously formed, as in the case of the binary alloys subjected to conventional aging in air (or vacuum). After 10 h of aging when the peak hardness was reached, the Vickers hardness and electrical conductivity of the ternary alloy were recorded at more reduced and elevated levels respectively than in the case of vacuum aging. On further aging, the ternary alloy had the β′-precipitates replaced more increasingly by stable TiH₂ precipitates in the matrix than the binary counterpart, resulting in a more rapid increase of electrical conductivity. It is, thus, suggested that the combined treatments of Mg doping and aging in hydrogen atmosphere can affect significantly the microstructures of Cu–Ti alloys to effectively reduce the negative impact of the Ti solutes in matrix as well as of the DP reaction.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 62 (2023) 6–11. Figures 2 and Fig. 3 were interchanged in order from the Japanese one. Figures 5(a) and 6(a) were slightly modified and the figure captions for Figs. 6 and 7 were revised for better readability.

We synthesized an oxygen reduction reaction (ORR) model catalyst surface of Pt(111)/Nb-doped SnO₂(101) (Nb:SnO₂) coherent lattice stacking layers on a Pt(111) substrate and investigated the influence of the surface strain of the Pt(111) layer on ORR activity enhancement. The Nb:SnO₂ lattice stacking layer was synthesized through arc-plasma deposition (APD) of SnNb on Pt(111) in a vacuum chamber (base pressure <10⁻⁷ Pa), followed by thermal annealing at 823 K for 120 min under 1 atm of dry air. The resulting Nb:SnO₂/Pt(111) was then re-introduced into the chamber, and Pt was deposited by using an e-beam deposition method to form Pt/Nb:SnO₂/Pt(111) ORR model catalyst surface. The cross-sectional, atomically resolved HAADF-STEM image of Pt/Nb:SnO₂/Pt(111) clearly shows that the interfaces between the substrate Pt(111)/Nb:SnO₂(101) and the Nb:SnO₂(101)/surface Pt(111) match well and generate a single-crystal Pt(111)/Nb:SnO₂(101)/Pt(111) ORR model catalyst surface. The synthesized catalyst surface showed ca. 3 times higher activity compared with clean Pt(111). It was estimated by in-plane-XRD that 0.6% of compressive strain worked on the surface Pt(111) layer, which was induced by a lattice mismatch between the surface Pt(111) and the underlaid Nb:SnO₂(101). The results suggest that the ORR activity enhancement mechanism of the compressively strained surface Pt(111) lattice can be applied not only to Pt-based alloys of Pt and transition metal elements with smaller atomic radii but also to Pt on ceramic supports, such as SnO₂.

Wires of a Cu–3.8 wt% Zr alloy were produced by conform extrusion followed by wire drawing up to 0.2 mm in diameter (S wire), or by conform extrusion and subsequent annealing during wire drawing up to 0.2 mm (IA wire). The effects of microstructure on the strength and electrical conductivity of the S and IA wires were investigated. The severely drawn S and IA wires had a mixed microstructure consisting of a Cu parent phase with fine grains, fibrous eutectics elongated along the drawing direction, and granular eutectics. The 0.2% proof stress (σ_0.2) and tensile strength (σ_u) of the S and IA wires increased monotonically with increasing drawing ratio (η). The S wire with η = 7.8 exhibited large values of σ_0.2 = 1080 MPa and σ_u = 1320 MPa. The S and IA wires having the mixed microstructure are strengthened primarily by high density of dislocations and grain refinement in the Cu phase and by the presence of fibrous and granular eutectics. The electrical conductivity (E) of the S wire increased in the early stage of wire drawing and then began to decrease, dropping to 42% IACS at η = 7.8. The increase in E is caused by refining of the eutectics, which was formed during casting, toward the granular or fibrous form. The E value of the IA wire after annealing was high, 72%IACS, and then decreased as η increased. Values of E of the S and IA wires with the mixed microstructure was estimated by applying rules of mixtures. The estimated values of E are in agreement with the measured values of E. It is shown that the presence of the fibrous and granular eutectics significantly increases the electrical conductivity.

This Paper was Originally Published in Japanese in J. Japan Inst. Copper 60 (2021) 16–23.

The dependence of mechanical twinning on the crystallographic orientation at the early stage of rolling was investigated. For this purpose, a copper-zinc alloy plate having a sharp {001} texture on the rolling plane (normal direction // 〈001〉) was prepared, and the twinning behaviors during rolling were studied in the grains with orientations of rolling direction (RD) parallel to 〈100〉, 〈210〉 and 〈110〉. The precise examination revealed that grains with RD // 〈110〉 orientation were most prone to twinning among the three crystallographic orientations. Effects of the development of heterogeneous-nano (HN) structure on the tensile properties were also systematically investigated. As the rolling reduction increased from 50% to 70%, the tensile strength increased significantly, and the elongation to failure also increased simultaneously. Considering the microstructural changes, the increase in the strength/ductility balance was attributed to the formation of the HN structure. Further rolling up to 90% resulted in a slight increase in strength and a significant decrease in ductility to about half of the value at 70%. It was suggested that the decrease in the volume fraction of twin domains in the HN structure, instead increase in the other texture components, during the rolling reduction from 70% to 90% complicatedly spoiled the strength/ductility balance.

This Paper was Originally Published in Japanese in J. Japan Institute of Copper 62 (2023) 47–52.

A hot-stamping method was established for manufacturing high-strength automotive parts with good shape fixability. The hot-stamping method has recently been applied to high-performance parts with tailored properties. CAE is indispensable for the design of such parts. To design hot-stamped parts, the forming simulation must be coupled with thermal analysis to consider the effect of temperature on formability. The final shape does not need to be predicted because of its good fixability. However, for high-performance parts with tailored properties, predicting the effect of phase transformations on the final shape is important. A CAE method that considers the phase transformation effects was developed to predict the final shape of the hot-stamped parts. The accuracy of the final shape calculation utilizing the CAE method is also investigated. Hot-stamping experiments were conducted to obtain parts of different shapes via cooling control, and a CAE analysis of the final shape for each experimental condition was conducted. It was clarified that the final shape varied by changing the cooling process and that the results of CAE, including phase transformation, agreed with the tendency for shape change in the cross-section.

This Paper was Originally Published in Japanese in J. JSTP 63 (2021) 52–57. Figure 8 was slightly modified.

A series of impact tests within the temperature range of −180∼20°C were applied to study the low temperature impact behavior and ductile-brittle transition of the 700 MPa nanocluster-strengthened steel. The results clearly demonstrated that temperature had a significant effect on impact properties. As the temperature decreased, the impact absorption energy and shear section ratio were correspondingly reduced, and the micro-morphology was changed gradually from ductile fracture to brittle fracture. The ductile-brittle transition temperature (DBTT) range of was between −80°C and −160°C. The fitting results of the Boltzmann function for the ductile-brittle transition curve were in good agreement with the experimental observations. Specifically, the DBTT was determined to be −110 ± 1°C, which suggested good low-temperature impact toughness. The outstanding low-temperature impact toughness of the test steel is mainly due to its low C content and high Ni content, fine effective grain size (EGS), and a large number of Cu-rich nanoscale precipitates. Furthermore, the effect of temperature on dislocation movement plays a major role in the ductile-brittle transition.

To verify the applicability of glass-fiber reinforced plastic (GFRP) with an unsaturated polyester matrix in manhole environments, we conducted solution immersion tests in a weak alkaline aqueous solution to evaluate degradation characteristics. The test results clarify the effect of accelerated deterioration due to alkali remaining on the sample surface, that diffusion of alkaline ions is slower than that of water, and that the resin-fiber interface preferentially deteriorates due to the diffusion of water. If water diffusion is the dominant factor in the degradation of the flexural strength of a sample, the degradation of the flexural strength can be extrapolated using a power law equation; however, under conditions where the degradation is also accelerated by alkali, it is appropriate to extrapolate by the degree of degradation using a logarithmic equation that fits the measurement results well. The results showed that the flexural strength of hand-layered GFRP with a thickness of 5 mm and 7 layers in an alkaline solution of pH 10 was estimated to decrease by half in 16.3 to 21 years.

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 71 (2022) 237–244.

The tensile and fatigue behavior of an accumulative roll bonded Cu/Nb laminate material was investigated experimentally and numerically by means of crystal plasticity finite element simulations. The material exhibited a slight anisotropy in tensile strength and ductility when deformed either along the rolling or transverse direction. This anisotropy was attributed to the strong crystallographic texture of the Nb phase resulting in a higher stress and strain partitioning when the loading direction was along the transverse direction. Four-point bending fatigue tests were then conducted and revealed apparently higher fatigue life when the tensile axis was aligned with the rolling direction which was attributed to anisotropic texture in the Nb layers leading to longer crack incubation period and lower crack growth rate. The analysis of a fatigue indicator parameter based on the Tanaka-Mura model and the Fatemi-Socie criterion confirmed the longer nucleation period for the rolling direction specimen.

To investigate the effect of the microstructure adjacent to the grain boundaries on the mechanical properties and hydrogen embrittlement susceptibilities in the Al–Cu base 2219 alloy, alloy specimens were solution-treated and then aged at 100°C, 130°C, and the usual aging temperature of 190°C, to control the alloy microstructure in the vicinity of grain boundaries. The slow strain rate technique was conducted on the specimens in humid air and dry nitrogen gas environments to evaluate the effect of environmental hydrogen on them. Transmission electron microscopy was used to measure the grain boundary precipitate size and precipitate-free zone width of the specimens. Thermal desorption analysis was conducted on the gauge sections of the fractured specimens to evaluate the trapping sites and amount of hydrogen desorbed. The specimens aged below 190°C had finer grain boundary precipitates than those aged at 190°C. The test environment did not affect the specimen strength under any of the aging conditions 100°C, 130°C, and 190°C. Some samples had intergranular fractures on their entire fracture surfaces, irrespective of the test environment. The thermal desorption analysis results showed no significant difference between the hydrogen emission spectrum and the amount of hydrogen released within each temperature range. Thus, hydrogen embrittlement does not occur in the 2219 alloy, irrespective of the characteristics of its microstructure adjacent to the grain boundaries.

During automobile crashes, the main behavior of plastics in the vehicle is bending deformation. Because of this, it is important to accurately calculate the edge stress and allowable stress on structural surfaces. For that purpose, it is necessary to consider the distribution of the fiber orientation angle and degree in the plate thickness direction. In a general coupled analysis for injection-molded materials, a material model is created based on the physical properties obtained from an arbitrary test piece. Therefore, even if the orientation angle in each part to be analyzed is taken into consideration, the degree of orientation is constant in each part, and the degree of orientation distribution in the plate thickness direction is also treated as constant. We tried to improve the accuracy of crash analysis by calculating the edge stress and allowable stress with high accuracy by considering the distribution of orientation angle and degree in the plate thickness direction. For that purpose, we created a model that calculates properties of composite materials from resin and fiber properties, and a process that maps the distribution of orientation angle and degree in the plate thickness direction to each integration point of the shell element in structural molding analysis.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 72 (2023) 675–682.

In laser metal-based powder-bed fusion additive manufacturing, it is important to know the laser absorptivity of metal powder to elucidate or optimize the manufacturing process and numerical simulation. Laser absorptivity depends on the manufacturing process conditions and the circumstances of the additive manufacturing machine. Therefore, we tried to develop a simple method of measuring laser absorptivity under the same circumstances present in the manufacturing process by using a commercially available additive manufacturing machine.

The gas atomization is a production technique of a metallic powder. In this study, the β-solidifying Ti–44Al–6Nb–1.2Cr alloy powder fabricated by gas-atomization was investigated regarding the evolving shape, phase constitution, and chemical distribution as a result of the high solidification rate. The powder showed a spherical shape regardless of its size, indicating no relation of solidification rate to powder shape. However, the small powder (D₅₀ = 36.0 µm) showed less segregation and was composed of β and α₂ dual phases. Whereas, the large powder (D₅₀ = 78.7 µm) is relatively high segregation and composed of almost a single α₂ phase because of the difference in the cooling rates. The findings obtained here demonstrated the understanding of phase transformation during the rapid solidification and continuous microstructural evolution process in the β-solidifying alloy.

The strength and electrical conductivity balances in Cu/martensite (α′) steel multilayered sheets with various volume ratios were evaluated. Furthermore, the measured tensile properties and electrical conductivity were compared with the values estimated from the rule of mixtures, and the reason for the difference between the measured and estimated values was discussed based on the deformation and fracture behaviors. The multilayered sheets exhibited excellent strength-electrical conductivity balances superior to those of conventional Cu alloys, and their strength and electrical conductivity can be controlled over a wide range by changing the volume fraction of α′ steel. The electrical conductivities of the multilayered sheets with different volume ratio were approximately identical to the estimated values based on the rule of mixtures. However, the ultimate tensile stresses of the multilayered sheets with lower volume fractions of the α′ layer were slightly lower than the estimated values. A significant strain concentration occurred within the α′ steel layer in the multilayered sheet with the lowest volume fraction of α′ steel. Furthermore, cracks and/or voids were formed in the α′ steel layers even during the uniform-deformation stage. Therefore, the early fracture of the α′ steel layers caused lower ultimate tensile stresses in the multilayered sheet with low fractions of the α′ steel than the estimated value based on the rule of mixtures.

Calcium phosphate cements (CPCs) with macropores and micropores for high bone regeneration ability are desired. CPCs with macropores and micropores which were prepared by combining porous granules have been reported. In this study, the cement system composed of β-tricalcium phosphate (β-TCP) granules and phosphoric acid solution was selected, and the effects of the characteristics of granules on the microstructures and properties of the cements were examined. The spherical porous β-TCP granules with high porosity and irregular porous β-TCP granules with low porosity were prepared, and they were mixed with a phosphoric acid solution. When the spherical porous granules with high porosity were used, the granules were packed uniformly in the cement, and the size distribution of the macropores formed among the granules was narrower than that of the cement prepared using the irregular porous β-TCP granules with low porosity. The cement with high porosity can be obtained from the spherical porous granules with high porosity. The cement prepared using the spherical granules with high porosity showed lower compressive strength and higher dissolution rate than the cement prepared using irregular granules with low porosity.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 70 (2023) 242–247.

A systematic experiment was performed for four types of welding circuit with different circuit inductances and a common welding coil, where each circuit inductance is given by the sum of a different remaining inductance and a common effective inductance. It was demonstrated that increasing the circuit inductance causes adverse effects on the discharge current, resulting in a long first collision time and a low deformation velocity of the moving sheet. When the circuit inductance increases from 0.0587 µH to 0.2280 µH, the maximum current decreases from 223 kA to 132 kA at a discharge energy of 2.0 kJ. With the decrease in discharge current, the deformation velocity of the sheet decreases from 383 m·s⁻¹ to 164 m·s⁻¹. The higher the circuit inductance is, the lower the deformation velocity of the sheet is. With the lower velocity, the shearing load of the resulting welded sheet further decreases, ultimately leading to joining failure. However, in the circuit with a minimum inductance of 0.0587 µH, it is possible to weld an aluminum alloy sheet to a 1 GPa class high-strength steel sheet. It has been clarified that the decrease in circuit inductance improves the joining property of a welded sheet.

This Paper was Originally Published in Japanese in J. JSTP 63 (2022) 129–136.

The evolution of eutectic Si morphology and microsegregation during homogenization heat treatment at 753 K was examined for Al–Si–Cu–Mg–Ni alloy casting billets. Subsequently, casting billets homogenized at 753 K for 0 s, 7.2 ks, and 28.8 ks were forged, and microstructures and mechanical properties at 473 and 573 K were investigated for the forgings with different sizes of eutectic Si. Spheroidization of eutectic Si and elimination of microsegregation were achieved during the heating process of homogenization heat treatment. The spheroidized eutectic Si then coarsened with the homogenization heat treatment time. The interparticle spacing of the eutectic Si and constituent particles after the forging process increased with the coarsening of Si particles during homogenization heat treatment. In the tensile test at 473 K, the 0.2% proof stress, ultimate tensile strength (UTS), and elongation of the forgings were almost the same regardless of the homogenization heat treatment time, i.e., the size of eutectic Si. On the other hand, forgings made of a billet with a shorter homogenization heat treatment time showed more pronounced work-hardening behavior and higher 0.2% proof stress and UTS at 573 K. The increase in strength was explained by the enhancement of work-hardening associated with the decrease in interparticle spacing, which depends on the Si particle size after homogenization heat treatment.

Creep lifetimes of polycrystalline nickel (Ni) based superalloys with given chemical compositions were predicted using the Larson–Miller parameter (LMP) and chemical composition, which reflects the effects of solid-solution strengthening and precipitation strengthening. Herein, the former effect is denoted as a δ parameter representing the amount of strengthening by multiple elements; the latter effect is a lattice misfit between γ and γ′ phases: ξ. These parameters respectively generate vertical and parallel translations of an LMP plot. The solid solution affects strengthening, i.e., vertical translation. The precipitate affects heat resistance in the alloys, i.e., parallel translation. After the trends were formulated in the first order, the amount of translation was evaluated quantitatively. The prediction worked well in the solid-solution strengthened Alloy 600 and Alloy 617 and in the solid-solution strengthened and precipitation strengthened γ + γ′ TMP alloy. Creep lifetimes of Ni-based alloys and superalloys can be predicted well using the simple formulae.