It is well known that severe plastic deformation (SPD) produces ultrafine-grained structures in bulk metallic materials. The SPD process becomes more versatile when it is performed under high pressure as high-pressure torsion (HPT) and high-pressure sliding (HPS). Not only the grain size is more refined but also the process is applicable to hard-to-deform materials such as intermetallics, semiconductors and ceramics, leading to enhancement of functional properties as well as structural properties. The major drawback is that the sample size is small so that the applicability is limited to a laboratory scale and it is an important subject to increase the sample dimensions. This paper presents an overview describing efforts devoted thus far to deal with this upscaling issue.
As an emerging technology, additive manufacturing (also known as 3D printing) is developing rapidly in various fields, which is regarded as one of the important symbols of the third industrial revolution. Here, we introduce its development status, materials and application fields, then analyze its development trends and prospects, which can provide some predictable analysis of the future development direction of additive manufacturing.
Prediction of the glass forming range is of great significance for the preparation of metallic glasses. A new theoretical model that comprises the bond parameter function and formation enthalpy is proposed. The glass forming ranges of Ti–Ni–Zr, Ti–Cu–Zr, and Ti–Cu–Hf systems were predicted by this model. The predicted results are in good agreement with experimental data. The prediction range of this model was compared with that of the subregular model, and was found to be more accurate and provide a better theoretical reference for experimental preparation.
The graphene oxide/silver nanoparticles (GO/AgNPs) composite films were prepared by spin coating combined with electrostatic self-assembly technology, and the reduced graphene oxide/silver nanoparticles (RGO/AgNPs) composite films were finally obtained at 600°C under Ar/H2 atmosphere for 2 h. With the increase of the number of film layers, the absorption characteristic peak intensity of reduced graphene oxide (RGO) also gradually increases, indicating that the composite film grew uniformly. The conductivity of graphene/silver nanoparticles composite films not only increased with the decreased of particle size, but also increased with the increased of self-assembly and spin-coating times. The lowest sheet resistance of RGO/AgNPs28-10 film was only 0.392 kΩ/sq, which showed excellent conductive performance.
The microstructural evolution of the as-cast large size AA2014 aluminum alloy ingot prepared by direct chill (DC) casting during homogenization was investigated by OM, SEM, EDS, DSC, EBSD, TEM and tensile tests. The results showed that serious dendrite segregation and numerous coarse nonequilibrium eutectics existed in the as-cast alloy were dramatically eliminated, while a small amount of Fe-rich phase was still present along the grain boundaries when the alloys were subjected to the optimized two-step homogenization. Compared with the nonhomogenized alloys, homogenization treatment can effectively reduce grain and second phase particles size, and increase the fraction of precipitates and high angle grain boundaries (HAGBs) during the hot deformation and T6 treatment. Besides, recrystallized grains with random orientation are formed due to dynamic recrystallization (DRX) for the alloys with hot deformation and T6 treatment. Additionally, the strength and elongation of the alloys were simultaneously improved with the application of optimum two-step homogenization because of the more homogeneous structures, finer grain and particles size, higher fraction of HAGBs and fine and uniformly distributed precipitates. The suitable homogenization schedule of the AA2014 aluminum alloy is 490°C × 10 h + 530°C × 8 h.
Fig. 12 Microstructure characteristics of the alloys after hot deforming and T6 treatment under different homogenized conditions: (a, a′) as-cast; (b, b′) OTH; (c, c′) THT30
To create a new surface with desired microstructural features, the proportion of constituent phases and grain size should be quantitatively characterized. However, it is difficult for titanium alloy due to its adhesion microstructure. In the present study, a novel image processing method was proposed to characterize the microstructure feature of titanium alloy Ti–6Al–4V. Graham scan algorithm is innovatively applied to identify and separate the isolated and adhesive phases. Using the proposed method, the changes of volume fraction and grain size of beta phases induced by peripheral milling are evaluated. The main conclusions are as follows: the isolated and adhesive phases in SEM images of Ti–6Al–4V are well separated, and the correct recognition rate can reach more than 90%. The total volume fraction of the beta phase on the machined surface is larger than that of the original material, and its value increased with the increase of cutting speed. With the cutting speed increases, the content of isolated beta phase decreases but that of adhesive beta phase increases. Length-diameter ratio of the isolated beta phase induced by machining does not change significantly relative to that of the original material, which values are lies in the range of 1.9 to 2.0.
Microstructure evolution of Ag–28Cu–1Ni alloy during the continuous casting process was simulated based on 3D-CAFE method, and the effect of the mean nucleation undercooling and the distance from the bottom of the ingot to the cross section on the solidification structure were studied. Furthermore, the effects of pouring temperature, heat transfer coefficient and pulling speed on solidification structure were also investigated. The results show that the simulated results are in agreement with the experimental results. The solidification structure consists of four parts, including region of surface fine grain, zone of columnar grain, transition zone of CET (columnar to equiaxed grain transition) and region of center equiaxed grain. The higher the mean undercooling, the larger the columnar dendrite zone. The ΔTv,max = 5 K is determined as an important simulation parameter to simulate the microstructure evolution. As the cross-section increases from the bottom of the ingot, the columnar crystal regions gradually expand. Moreover, lowering the pouring temperature, increasing the heat transfer coefficient or improving the pulling speed have the beneficial effect on grain refinement. Under the optimal process conditions, the largest proportion of equiaxed grains and the finer grain size is present in the solidified structure.
In order to significantly enhance the performance of graphene in metal matrix composites, and avoid the interface reaction via the common method, the powder semi-solid processing (PSSP) technique was successfully used to fabricate a graphene nanoplatelet (GNP)-reinforced Al2024 composite. The blended powders of Al2024 and GNPs were cold-compacted after ball milling and then hot compressed at a semi-solid temperature, and no further hardening was performed. The GNPs were observed to change during the ball milling process, and a uniform dispersion of GNPs in the aluminum (Al) matrix composite was achieved. The microstructure and mechanical properties of the composites were evaluated, and fracture surfaces of the composites were analyzed to investigate changes in performance. Results showed that GNPs have effective interface with the Al matrix, and that Al4C3 was absent. GNP/Al2024 composites showed significant improvement in strength and favorable ductility. Additionally, the supreme tensile strength of the GNP/Al2024 composite could increase to approximately 524 MPa with 1.0 wt% of GNPs, which is about 41.6% higher than that of the Al matrix composite. The effect of GNPs on the mechanical properties of the composites was discussed.
Fig. 10 Tensile fractographs of GNP/Al2024 composites with different GNP content: (a) 0%; (b) 0.5%; (c) 0.8%; (d) 1.0%; (e) 1.5%; (f) high magnification of (e). White arrow-dimple; red circle-tear ridges; purple flash-GNPs.
Face-centered cubic Co-free Cu-containing solid solution concentrated alloys, Cu, CuNi, CuNiFe, Cu0.3NiFeCr, Al0.4CuFeCrNi2 were prepared, and their microstructure, hardness, and tensile strengths were investigated in order to develop a new high entropy alloy with a high irradiation resistance, which is applicable for nuclear reactor components. All the as-cast alloys were identified as single-phase FCC alloys by X-ray diffraction analysis. While, the SEM observation indicated a new Cr-rich phase with Cu-rich phase in the annealed Cu0.3NiFeCr alloy, which is probably due to low solubility of Cr and Cu in the alloy. After annealing at 1076°C for 120 hours, Cu0.3NiFeCr alloy became a single-phase FCC. Mechanical property examinations indicated the highest Vickers hardness, the highest Tensile strength and the smallest elongation in the Al0.4CuFeCrNi2. The results indicate that the Al0.4CuFeCrNi2 alloy would have the potential to be a Co-free high-entropy alloy applicable to nuclear reactor components. In order to improve the elongation of Al0.4CuFeCrNi2, the detailed analysis of fracture surface and the optimization of annealing condition would be needed.
Fig. 1 XRD patterns for the Co-free Cu-containing solid solution concentrated alloys.
In order to realize direct brazing ZrO2 with Al, a kind of sputtering Ni/Al double layer on Al solder surface was used. Results showed that ZrO2 could directly brazed to Al solder with sputtering Ni/Al double layer without interface reaction. And then direct brazing was investigated with the change of brazing temperature. Microstructure and joint strength of brazing seam were analyzed. Results showed that joint strength of brazing seam increased from 68.6 MPa to 121.2 MPa with the increasement of brazing temperature from 680°C to 840°C, when the brazing temperature increased up to 920°C, the joint strength gradually increased to 122.6 MPa. With the joint strength enhancement of brazing seam, the fracture of the joint is gradually transferred from interface to the brazing seam.
Fig. 7 Schematics of removing Al2O3 film from Al foil (a) uncoated Al foil before Al melting (b) uncoated Al foil after Al melting (c) coated Ni/Al double layer on Al foil before Al melting (d) coated Ni/Al double layer on Al foil after Al melting.
The effects of ultrasonic nanocrystal surface modification (UNSM) treatments on the microstructure, mechanical, and corrosion behavior of LZ91 Magnesium–Lithium (Mg–Li) alloy were systematically investigated. The results show that UNSM treatments have greatly positive effects on the mechanical and corrosion behavior improvements. As compared to the bare sample (BS), the near-surface grains were refined and the surface roughness (Ra) of the sample was reduced from 0.514 µm to 0.082 µm; and the maximum hardness and tensile yield strength remarkable increased by 70% and 65.4% after UNSM treatments, respectively. In addition, the corrosion behavior of LZ91 Mg–Li alloy was also improved after UNSM treatments. The mechanical and corrosion behavior improvements can be attributed to the introduced thick hardening layer with low roughness and smaller grains by UNSM treatments.
UNSM treatment diagram and engineering stress-strain curve of LZ91 Mg–Li alloy 1. A hardening layer was successfully induced on the LZ91 Mg–Li alloy by UNSM treatments. 2. The excellent surface roughness (Ra) was obtained after UNSM treatments. 3. Significant enhancement in hardness and strength was observed after UNSM treatments. 4. The corrosion resistance of the LZ91 Mg–Li alloy was improved after UNSM treatments.
The diffusion behavior of interstitial hydrogen in steel should be clarified to reveal the mechanism of hydrogen embrittlement. In this study, we performed molecular dynamics (MD) simulations to elucidate the relationship between various stress conditions and the diffusion coefficients of interstitial hydrogen in body-centered-cubic (bcc) iron. The results reveal that the diffusion coefficients are independent of isotropic stress and exhibit strong anisotropic stress dependence under uniaxial stress along the 〈100〉 direction. The stress-induced deformation of the atomic structure around the octahedral interstitial site (O site) was examined to elucidate the origin of the anisotropy of the stress dependence. Moreover, a model that predicts the activation enthalpy was derived by quantitatively evaluating the deformation around the O site. The activation enthalpy predicted by the model was consistent with the results of MD simulations when the deformation around the O site was not substantial.
This Paper was Originally Published in J. Soc. Mater. Sci., Japan 69 (2020) 119–125. All captions of figures and tables were slightly modified.
Trajectory of hydrogen diffusion in body-centered-cubic iron.
High-entropy alloys (HEAs) are solid solutions with five or more elements in near equiatomic fractions and exhibit excellent mechanical properties. However, the mechanism has not been fully understood yet. Because general grain boundaries (GBs) contain various sizes of atomic free volumes, a deviation of atomic composition at GBs may appear in HEAs by replacing atoms with ones having different atomic sizes to reduce atomic free volumes at GBs. Various equiatomic HEAs with five elements are modeled by a modified Morse (two-body interatomic) potential. Thermal equilibrium GBs at finite temperatures are obtained by hybrid Monte Carlo-molecular dynamics simulations. As results, GBs in HEAs mainly consist of two elements with the minimum and maximum atomic size and the critical stress to emit dislocations from the GBs increases as the deviation of atomic composition becomes large.
This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 69 (2020) 141–148. The caption of Fig. 3 is partly corrected.
Mg–1.5Zr alloy blanks 1.0 mm in thickness, made from cast and rolled materials, were deep-drawn at room temperature and 150°C. The microstructures were examined and deformability evaluated. The grain size of blanks from cast and rolled materials was 40 µm and 15 µm, respectively. The basal texture was confirmed for rolled-blanks, while the microstructures of cast blanks were randomly orientated. The limiting drawing ratio for cast materials was 1.65 at room temperature and 1.75 at 150°C. For rolled-blanks, it was 1.45 and 1.70 at room temperature and 150°C, respectively. The cast-blanks deformed in a similar way at room temperature and at 150°C, exhibiting a decrease in thickness in the punch-shoulder areas and a progressive increase along the side wall toward the rim of the cups. Rolled-blanks tested at 150°C showed the similar trend as cast-blanks and exhibited evidence of dynamic recrystallization in the punch-shoulder areas, contributing to an improvement on the limiting drawing ratio. When the deep-drawing exceeded the limiting drawing ratio, the cast-blanks tested at room temperature and 150°C and also the rolled-banks tested at 150°C fractured in the rim area of the cups, while the rolled-blanks at room temperature fractured from the punch-shoulder areas.
This Paper was Originally Published in Japanese in J. JILM 69 (2019) 101–106.
Fig. 15 EBSD image quality (IQ) maps and IPF images (corresponding locations to IQ maps) of the bottom corner (R section) of the cups formed from rolled-blanks at room temperature and 150°C. Red lines in the IQ maps indicate twin crystals. Circled areas in the IPE image (B150) suggest the presence of sub-grain and grain boundaries within the crystal.
The applications of high-strength martensitic steels in engineering are limited due to concerns regarding delayed fracture. Recent experimental and theoretical studies revealed that the presence of mobile hydrogen moving toward cleavage crack surfaces in these steels plays an important role in delayed fracture. Although the accumulation rate of hydrogen is known to be affected by its concentration and diffusion coefficient, it is still unclear how these properties are influenced by the carbon content in martensitic steel. In this study, we estimated the hydrogen accumulation rate in martensitic steel under different carbon contents (0.395 and 0.787 mass%) and temperatures (300, 700, and 1,000 K) by calculating the hydrogen solubility and diffusion coefficient using computational methods, including density functional theory, molecular dynamics simulation, and finite element method. Results revealed that the hydrogen accumulation rate tends to increase with the carbon content.
This Paper was Originally Published in J. Soc. Mater. Sci., Japan 69 (2020) 134–140. All captions of figures and tables were slightly modified.
Diffusion Coefficient of Hydrogen along c-axis in Martensitic Steel.
In this work, a series of cobalt-doped ceria nanorods have been synthesized coming from two cobalt precursors by the impregnation method, based on ceria nanorods pre-formed by the hydrothermal method. The properties of obtained catalysts were investigated by various techniques, including Brunauer-Emmett-Teller nitrogen physisorption measurements (BET), X-ray powder diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The catalytic activities of as-prepared samples were studied in the deep oxidation of p-xylene at low temperatures (225–300°C). The catalyst characterizations evidenced the crystalline phase formations of CeO2 and Co3O4 with the average crystallite sizes of 17.5–45.8 nm and 11.1–23.4 nm, respectively. The cobalt addition by cobalt nitrate into CeO2 decreased the surface area of CeO2 nanorods (67.9 m2.g−1), in contrast to the increase using cobalt acetate (76.0–82.5 m2.g−1). Co3O4/CeO2 catalysts showed reduction peaks at much lower temperatures than that of pure nanorod ceria. 7.5 mass% Co3O4 supported on nanorod CeO2 catalyst synthesized from cobalt acetate as a type of cobalt precursor with the smallest nanoparticle size and high BET surface area was the most efficient for p-xylene deep oxidation, achieving more than 95% of p-xylene conversion to CO2 at 275°C, and its performance was stabilized for more than 100 hours tested.
Fig. 7 Effects of cobalt precursor (a) and Co3O4 loading (b) on the activity in p-xylene oxidation of catalysts.
We studied the effects of different types of hot-dip coatings and passivation treatments on cross-sectional morphology, adhesion to polyethylene (PE), and bonding energy. The results revealed that the bonding force of a hot-dip Zn–Al coating on a steel strip to PE is 196.3 N. The adhesion of Zn–Al and Zn–Al–Mg to PE before passivation was increased by 84.6% and −31.1% higher than that of Zn and PE. After passivation, the adhesion of Zn–Al and Zn–Al–Mg to PE was increased by 63.8% and −46.6% higher than that of Zn and PE, respectively. Passivation treatment can effectively improve the bonding between hot-dip coatings and PE. The bonding strengths of the hot-dipped Zn, Zn–Al, and Zn–Al–Mg to PE increased by 73.3%, 26.6%, and 33.3%, respectively, following passivation. The application of a silane coupling agent to the passivator formed chemical bonds on the surface of the hot-dip coatings, which improved the adhesion between the coatings and resin. Overall, utilising a hot-dip Zn–Al coating instead of a pure zinc coating (containing 0.01% Al) can improve the adhesion between the coating and PE in steel-strip-reinforced PE spiral-corrugated pipe (MRP), thereby improving the application performance of the MRP.
In regard to spot welding of manufactured products like automotive parts, it is common practice to join three steel sheets having different grades and thicknesses and subjected to different kinds of surface processing. In such a case, it is more difficult to set the welding conditions than in the case of joining two sheets of the same grade and thickness. The present study aimed to determine by investigation the optimum welding conditions for spot-welded joints consisting of three stacked steel sheets of the sort supposed to be applied in fabricating actual auto components. Furthermore, the effect of zinc plating (i.e., hot-dip galvanizing) on the outer sheet on spot-welding characteristics—which is becoming a serious manufacturing problem—was investigated. According to the results of these investigations, as for a three-layer spot weld, the fused part of the welded joint (i.e., “nugget”) is distorted to the high-tensile side. This distortion causes a difference in the resistance of the sheets, and the nugget is originated on the high-tensile side of the joint (which has higher resistance) and grows from that point of origin. Although two fracture modes are possible, namely, fracture in the base material or fracture in the weld nugget, fracture diameter and tensile shear strength have a proportional relationship in both cases regardless of the welding conditions. In the case that a zinc-plated (i.e., hot-dip zinc galvanized) steel sheet is used in the sheet stack, tensile shear strength falls and becomes more variable at low welding current. Accordingly, it is necessary to control the welding conditions so as to reduce that tensile-shear-strength variability.
The effects of heat treatment parameters including solid solution temperature, transfer time, delay time, aging temperature and time on mechanical properties and electrical conductivity of Al–4.8Si–1.2Cu–0.5Mg alloy were studied by independently altering variables. The experimental results showed that with the increase of solid solution temperature, the tensile strength gradually increases, and the elongation and electrical conductivity monotonously decrease. There is a little effect on the mechanical properties and electrical conductivity when the transfer time is less than 40 s. As the delay time increases, the tensile strength decreases quickly and then increases continuously while the elongation and electrical conductivity increases rapidly and then decreases gradually. The effects of aging temperature and time on the tensile strength and elongation have the same tendency. The electrical conductivity always decreases with the aging temperature while it presents an upward-downward-upward change with the aging time. When the solid solution temperature is 525°C, the transfer time and delay time are below 20 s and 2 h, and aging temperature and time are 160°C and 3–5 h, the alloy can achieved satisfactory properties.
Fig. 1 Solid solution temperature dependence of tensile strength, elongation and electrical conductivity after experiment scheme No. 1 in Table 1.
This research was aimed to study the effect of fiber orientation and stacking sequence of hybrid tube subjected to axial impact. The specimens were composite AL/GFRP, made of circular aluminum tubes and wrapped with 1, 2 or 3 layers of E-glass/polyester. The specimens were manufactured by hand lay-up technique in vacuum bag. Different ply angles of GFRP fiber which are 0°, 45° and 90° and their combination were applied. Various stacking sequence of GFRP layers were used, forming different types of specimen. Specimens were tested using a vertical impact testing machine with a 30 kg hammer dropped from 2.43 m height to strike the specimens. The results revealed that hybrid tube of AL/GFRP can resist higher impact load than AL tube. The stacking sequence and fiber orientation were found to have influence on failure mode and hence the crashworthiness behavior of specimens. Keeping 90° of fiber ply angle in the outer layer of specimen could to provide highest maximum and also mean loads. The collapse mechanism of each tube was examined in detailed and mode of collapse was also discussed. FEA simulation by ABAQUS® was also used for detailed investigation and compared to experiment. Good agreement was achieved.
NiO/SBA-15 catalysts modified by CeO2 were synthesized and studied for the hydrogenation of CO2-rich gas. Effect of CeO2 promoter on the physicochemical properties of the catalysts was investigated by BET, XRD, Raman spectroscopy, SEM, TEM, H2-TPR and CO2-TPD methods. The 4 mass% CeO2 addition improved reduction and dispersion of Ni, resulting in its higher activity in methanation, reaching CO2 conversion of 90% at 350°C. Furthermore, the performance of the prepared catalysts in methanation reaction was enhanced by adding small amount of CO (1 mol%) in the feedstock.
Fig. 11 CO2 conversion in methanation of mixture of 19 mol% CO2 with 1 mol% CO (case I - dashed lines) and with 1 mol% N2 (case II - solid lines) on Ni4Ce/SBA catalyst.
In this study, we propose a simple approach to accelerate crack initiation in intergranular stress corrosion cracking (IGSCC) of Alloy 600 in a simulated pressurized water reactor (PWR) primary water environment. In addition, we perform three-dimensional crystallographic characterization of the crack initiation by electron backscatter diffraction (EBSD). Initiation of IGSCC of the alloy in the PWR primary environment was realized for a flat tensile specimen in a considerably short time through a slow strain rate test (SSRT). The accelerated initiation was attributed to the asperity of the alloy surface induced by mechano-chemical polishing with colloidal silica suspension before the SSRT was conducted. Following the SSRT, the specimen surfaces were covered with thick oxide films, which prevented EBSD measurements. The sputtering of thick oxide films enabled us to characterize cracks with EBSD, thus yielding important information on IGSCC. Finally, an approach for three-dimensional characterization of crack initiation is discussed.
Fig. 8 (a) Correlation between misorientation angle and grain-boundary-plane angle obtained for cracked random boundary. (b) Correlation between type of cracked CSL boundary and grain-boundary-plane angle.
Electrodeposition of biofunctional molecules is effective in adding biofunction to metals; however, the mechanism of electrodeposition remains unclear. We consider the electrodeposition process of poly(ethylene glycol) (PEG) to the pure titanium surface, in which the termination of both PEG terminals proceeds with NH2 (PEG-diamine; MW: 1000). To elucidate this process, the thickness and mass change of the deposited layer and the electron transfer during electrodeposition was investigated using quartz crystal microbalance (QCM), ellipsometry, and cyclic voltammetry. Consequently, surface electric charge directly influenced the adsorption of PEG-diamine and unmodified PEG molecules. PEG-diamine was attracted to QCM electrode containing Ti (Ti-QCM electrode) and condensed on the surface by cathodic charge, by which electron transfer from PEG-diamine to the Ti surface occurred. Bonding of PEG-diamine with the Ti surface by electrodeposition was strong with no detachment from Ti. PEG-diamine was immediately adsorbed onto the Ti surface by the weak electrostatic force and bonded randomly via this force. Subsequent rearrangement and condensation occurred alongside a electrochemical reaction between the molecules and the Ti surface due to cathodic charge. Consequently, PEG-diamine molecules do not firmly remain on the Ti surface under electrodeposition, but shake near the Ti surface while undergoing repeated ionization and un-ionization.
Al–1.5 mass%Mn was chosen as the base alloy, and 1.0 and 3.3Si were added to the base alloys, keeping the same values in the ΔMk of s-orbital energy level as those of Al–1.5Mn–0.8 and 2.4Mg alloys with superior tensile properties for as-cast applications. The Si addition or increment in the base alloy showed strengthened tensile behavior of the 0.2% proof stress (σ0.2) of 67 MPa and ultimate tensile strength (σUTS) of 160 MPa, although there was reduced in fracture strain (εf) to 9%. The increase and decrease in flow stress and strain, respectively, resulted from the increment in degree of solid solution strengthening by the increase of ΔMk of the alloys. There was a good linear relationship between the nanoindentation hardness or rate of elastic deformation work in the α-Al phase and σ0.2 of the alloys. The dislocation density of Al–1.5Mn–xSi alloys increased linearly as the ΔMk-magnitude increased, compared with that of the base alloy. The behavior in the flow stress variation qualitatively agreed with that of dislocation density. There was a linear relationship between the lattice constant and Mkα in Al–1.5Mn–Si/Mg alloys. As the Mkα changed, the σ0.2 of the alloys also increased and its increment rate was similar in both Si and Mg addition alloys. It may be considered that the trend of change in the lattice constant, σ0.2, work hardening amount and dislocation density was predominantly consistent with that in the Mkα or ΔMkα showing the indication of solid solution hardening level of the α-Al phase, and the effect of difference of third elements such as Si and Mg on their mechanical properties could be ignored in tensile examination procedures in this study.
The mold filling simulation in the casting CAE is used to investigate the filling pattern of molten metal and to predict the casting defect. However, the prediction method of defects caused by unsuitable flow has not been established because the verification of analysis accuracy is insufficient. Especially, the air entrapment during mold filling is very important problem to obtain the sound casting. In this study, the direct observation of mold filling behavior using a water model equipment is carried out. The movement of free surface and the volume change of water are measured from observed filling behavior. The air entrapment is analyzed by quantification method using image processing. It is clear the location of thickness direction and entrainment timing of air varied with the experimental conditions. Further, the mold filling simulation is done using the casting CAE software TopCAST, which has the two-phase flow analysis MARS method. As a result of the analysis, the mold filling behavior of water and the volume of air entrapped almost agreed with experimental result. Although the calculated results have almost the same tendency with experiment, it has some unsuitable results. Therefore, it is necessary to make simulation closer to the real phenomenon by the validation of calculation conditions, and by introducing new algorithm of air movement.
Alloy designs of light-weight high and medium entropy alloys (LW-HEA and LW-MEA, respectively) are discussed in relation to solving the problem of the empirical alloy parameter, ΔHmix, and the difficulties of the fabrication process. The ingots of newly-designed Al–Mg–Li–Ca LW-MEAs were fabricated by the conventional casting process via crucible melting without using a vacuum furnace, and casting under air atmosphere. The ΔHmix parameter is the average value of the mixing enthalpy of ΔHi-j between the two components, i-j, in the multicomponent alloys, and the dispersion of ΔHi-j cannot be evaluated. The parameter δ(ΔHmix) was suggested for the evaluation of the dispersion of ΔHi-j. The Al–Mg–Li–Ca LW-MEAs were designed based on the empirical alloy parameters, including δ(ΔHmix). The alloy ingots of equiatomic AlMgLiCa, non-equiatomic Al2MgLiCa, and AlMgLiCa0.3 were successfully obtained by the conventional casting process. The solidification microstructure of the ingots in the Al2MgLiCa LW-MEA was investigated, with particular focus on the position dependences of the chemical composition, constituent phases, solidification microstructure, and hardness. The present study clarified that LW-HEAs and LW-MEAs containing Al, Mg, Li, and Ca can be obtained by the conventional casting process under air atmosphere, without specific expensive casting equipment.
This Paper was Originally Published in Japanese in J. JFS 91 (2019) 717–729. Minor corrections in abstract, main text, figure and table captions, and references were performed with translation from Japanese to English and proof reading by native speakers. Some references written in Japanese was replaced by the related references written in English: Ref. 11) was changed from “the 24th Committee on casting of Japan Society for the Promotion of Science (JSPS), Subcommittee on casting process, the 20th meeting document, No. 22 (2018) 1–5.” to “Mater. Des. 184 (2019) 108172”. Ref. 41) was changed from “J. Soc. Mater. Sci., Japan 68 (2019) 205–211.” to “Mater. Trans. 61 (2020) 311–317”.
Die-casting is widely applied to the production of automotive components because of its high productivity for manufacturing complex-shaped castings. However, since molten metal is injected into a cavity at high speed and it solidified rapidly under high pressure in this process, many casting defects are liable to occur. Although the most frequent internal defect is gas entrapment, shrinkage porosity also forms in the thick-wall portions of die castings. In order to avoid shrinkage porosity, there is a need to feed adequate molten metal to compensate the shrinkage volume during solidification. Therefore, it is desirable to better understand the feeding behaviors of molten metal under high pressure and rapid cooling conditions in the die casting process. In this study, the permeabilities of Al–Si alloys during the solidification process under die-casting conditions were determined by measuring the pressure transmission of the molten metal from the plunger to the mold cavity so as to obtain the feeding resistance coefficients. The formation of shrinkage porosities in die-castings was proven to be predictable by numerical simulation using the obtained feeding resistance coefficients.
This Paper was Originally Published in Japanese in J. JFS 91 (2019) 529–533.
In this study, the multi-pass high-pressure sliding (MP-HPS) process was applied for grain refinement of Al–3Mg–0.2Sc (mass%) rods with an upsized dimension of 16 mm in diameter. To achieve a homogeneous microstructure throughout the cross-section, the rod sample was rotated with 60° around the longitudinal axis (MP-HPS-R) for three times. A microstructure with an average grain size of 280 nm was developed around the center of the cross-section through the MP-HPS-R process. Superplasticity with total elongations of more than 400% was achieved in the 9 mm diameter range on the cross-section of the MP-HPS-R-processed rod.
This Paper was Originally Published in Japanese in J. JILM 70 (2020) 63–65.
Fig. 3 Hardness variation throughout cross section at center of rod sample after MP-HPS-R processing with sliding distance of 15 mm.
It is predicted that the operating temperatures of next-generation aircraft engines will exceed the present critical temperatures of any of the conventional metallic materials (<1400°C). As a result, it is likely that the application of SiC/SiC ceramic matrix composites (CMC) as primary materials. When exposed to an oxidative environment, SiC forms a protective silica scale. This layer provides additional protection from problems that may occur upon oxidation. It will, however, react with the water vapor formed during the combustion process, creating gaseous silicon hydroxides that will reduce its thickness. This problem has hindered the practical realization of CMC engines in aircrafts. Consequently, environmental barrier coatings (EBCs) are required to protect CMC components from oxidative degradation and thus ensure the reliability of CMC engines. In this study, a new deposition process, namely, the suspension plasma spray (SPS) process, is proposed to form the EBC. It produces much denser coatings by feeding a suspension of particles that are a single micron in size. It was confirmed that the coating structure and composition resulting from the SPS process were largely influenced by the residence time of the suspensions in the plasma flame. Subsequently, the optimum spray conditions were examined and discussed.
This Paper was Originally Published in Japanese in Japan Thermal Spray Soc. 56 (2019) 2–7.
The hot deformation behavior of 0.1C–18Cr–1Al–1Si ferritic heat resistant stainless steel has been investigated in the temperature range of 900–1100°C and the strain rate range of 0.01–1 s−1 employing compressive tests. The obtained results have shown that the volume fraction and average size of the AlN phases and (Cr,Fe)23C6 carbides decrease with increasing strain rate. The deformation activation energy is calculated as 332.306 kJ·mol−1. Based on the analysis of processing map and microstructure, the optimum processing domain for hot deformation is confirmed as the temperature range of 1045–1100°C and strain rate range of 0.06–1 s−1.
Well-defined SiO2-coated Fe nanoparticles with various SiO2 thicknesses from 1.2 to 27.8 nm were successfully prepared by controlling the amount of tetraethyl orthosilicate followed by reduction of the SiO2-coated Fe3O4 nanoparticles with CaH2. The saturation magnetization of the SiO2-coated Fe nanoparticles increased with decreasing SiO2 thickness. The saturation magnetization of the SiO2-coated Fe nanoparticles with a SiO2 thickness of 2.7 nm or more decreased slightly after atmospheric exposure for 192 h, but did not change with longer exposure, whereas that of the nanoparticles with the 1.2 nm SiO2 coating thickness decreased steeply in 24 h, and continued to decrease gradually from 24 h to 1080 h.
This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 66 (2019) 429–433.
The relationship between saturated magnetization and exposure time in air for SiO2-coated Fe particles.
Spherical AgPd alloy powder was prepared through the reaction of metal nitrate and reducing agent. Natural gum Arabic was used as a dispersant. SEM observation showed that as-prepared particles had spherical morphology with narrow size distribution. Powder X-ray diffraction showed that as-prepared powder was crystallized regardless of molar ratio of Ag and Pd and alloyed. Fluorescent X-ray analysis showed that the atomic ratio of Ag and Pd in as-prepared powder was in good agreement with that of starting solution. The particle size (D50) of as-prepared powder was decreased with increasing the reaction temperature and the content of gum Arabic. The D50 increased with increasing starting solution concentration. It was assumed from the change of particle number density that the particle growth was due to the diffusion of Ag and Pd ions from starting solution. The thickness of gum Arabic layer on Ag90Pd10 and Ag40Pd60 alloy particles at gum Arabic content of 2 g/cm3 was 20 nm and 22 nm, respectively and increased to 34 nm and 31 nm, respectively, with increasing gum Arabic content. The specific resistivity of Ag90Pd10 paste was 6.2 × 10−8 Ω·m at 1000°C. The specific resistivity of Ag50Pd50 paste and Ag40Pd60 paste was 2.6 × 10−7 Ω·m at 1400°C.
Fig. 1 SEM images and particle size distribution of as-prepared powder with different atomic ratio of Ag and Pd, (a) Ag90Pd10, (b) Ag50Pd50 and (c) Ag40Pd60.
The effects of deformation heating on hot deformation and processing maps of AA7050 aluminum alloy were investigated by hot compression tests at temperatures ranging from 300°C to 450°C with strain rates ranging from 0.001 s−1 to 10 s−1. The results show that deformation heating results in a decrease in flow stress and an increase in deformation resistance. The processing maps and microstructures exhibit that deformation heating may be responsible for flow instability. Compared to the processing maps of AA7050 aluminum alloy with deformation heating, the optimum hot-working area without deformation heating is smaller, which is determined to be at temperatures of 420–450°C and strain rates of 0.001–0.03 s−1. The main deformation mechanisms are dynamic recrystallization (DRX) and dynamic recovery (DRV).
Fig. 5 Effect of deformation heating on the 3D diagram of power dissipation efficiency and instability diagram of AA7050 aluminum alloy: (a), (c) with deformation heating, (b), (d) without deformation heating.