Calculation of elastic wave velocity using digital rock models is a powerful method to understand physical properties of rocks. However, one difficulty of the approach is to construct a proper digital model due to the uncertainty by the segmentation process of X-ray CT image. Recently, the segmentation-less method has been proposed to avoid the uncertainty, and has shown to be useful in application to Berea sandstone. In this study, we assessed the method through the application to Shirahama sandstone in addition to Berea sandstone, and confirmed whether the method can be applied to other types of sandstones. We also applied and compared two different rock-physics models to obtain elastic properties of a digital rock model. Our results showed that the segmentation-less method can be successfully applied to Shirahama sandstone as well as Berea sandstone. However, when the pore diameter of rock sample is smaller than the spatial resolution of CT image, we found that a correction is required when mapping the CT number to a density. Our results would be useful when applying the segmentation-less method to other types of sandstones.

This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 71 (2022) 235–242.

A good strength-toughness combination is difficult to be obtained in welded joint of low carbon low alloy steel. In this work, a new idea was proposed to improve the strength and toughness of welded joint by strengthening effect of Cu precipitation and toughening effect of retained austenite. The results show that a multiphase microstructure consisting of ferrite, martensite-austenite island, retained austenite as well as precipitates was obtained in welded metal of Cu-free and Cu-containing steel, while the retained austenite and precipitates were found in fine grained heat affected zone (FGHAZ) and coarse grained HAZ (CGHAZ). It is noted that Cu addition changed the ferrite from polygonal-like to acicular-like, increased amount of retained austenite and promoted the Cu-rich precipitates. Accordingly, a better combination of strength, ductility and toughness was achieved in welded joint of Cu-containing steel. Cu-rich precipitates and strain-induced martensitic transformation of retained austenite maintained high strength in welded joint. Meanwhile, high toughness was ascribed to strain-induced martensitic transformation of retained austenite, acicular ferrite and high angle grain boundary.

Under the conditions of deformation temperature of 900∼1200°C and strain rate of 0.01∼10 s⁻¹, the single pass isothermal compression test of CF170 maraging stainless steel was carried out on the Gleeble-3800 thermal compression simulator, and its flow stress curve was measured. Based on the Arrhenius model and Avrami model, the flow stress model considering strain compensation and dynamic recrystallization volume fraction model were established according to the flow stress curve. The results showed that the dynamic recrystallization of CF170 steel occurs in advance compared with other steels, and the relationship between the critical strain of dynamic recrystallization and the peak strain is ε_c = 0.44 ε_p. CF170 steel is sensitive to the deformation temperature and strain rate. The temperature required for complete dynamic recrystallization is relatively low at a low strain rate. In addition, although the flow stress curve does not show the characteristics of dynamic recrystallization under the high temperature and high strain rate, partial dynamic recrystallization still occurs. In addition, the hierarchical relationship between the martensite and austenite was analyzed by Electron Back-Scattered Diffraction. The results showed that a prior austenite grain is divided into multiple martensite packets, subsequently a packet is divided into several martensite blocks.

In this paper, the deformation law of box-shaped parts drawing was analyzed, and the mathematical expression for calculating the critical fracture blank holder force (BHF) was deduced. In order to determine the fracture parameters of 08Al sheet, notched specimen tensile tests were conducted, the full-field strain of the specimens from deformation to fracture was obtained by the digital image correlation (DIC) technology. The evolution law of the stress triaxiality and Lode parameter with plastic deformation was obtained, and the fracture parameters of the modified Mohr-Coulomb (MMC) fracture criterion were fitted by the least squares method. The finite element (FE) simulation model coupled with MMC ductile fracture criterion was established to simulate the fracture behavior of sheet. The reliability of theoretical calculation was evaluated by FE simulation and experiments under various process conditions. The results demonstrated that the prediction of the critical fracture BHF by theoretical calculation and FE simulation were both partial safety predictions and all fracture earlier than the tests. In the theoretical calculation, when the flange shrinkage rate was 0.19, the critical BHF was the smallest, and the error was 17.5% compared with the tests, the theoretical calculation was closer to the test results. The theoretical calculation and FE simulation coupled with ductile fracture criterion provide a reference value for predicting the critical fracture BHF and intelligent control in actual production.

Continuous SiC fibers were used to toughen tungsten in this work. The composites were prepared by hot-press using W powders sintered from 1500°C to 1900°C for 1 h with 20 MPa pressure. Phases changes, microstructure, mechanical and thermal properties of composites were examined. Besides, the kinetics between SiC and W was also studied. The stress-strain curve had pseudo-ductility at room temperature, except for 1900°C sintered samples due to complete damage of fiber. Thermal conductivity was calculated from two directions: in-plane and through-plane directions (parallel and vertical to fiber direction), in which through-plane direction display higher thermal conductivity than other direction. Besides, severe reaction was verified between SiC and W, and the reaction rate increased 18 times when temperature increased from 1500°C to 1700°C. Therefore, it is suitable to use SiC fiber to reinforce W to ameliorate the brittleness with limited reaction between fiber and matrix.

The relation between microstructure and creep property of austenitic heat-resistant cast steels with and without Nb addition under the condition of repeated vacuum carburizing and quenching was investigated. Cr-carbide scale is formed on the sample surface by a carburizing reaction, resulting in the depletion of Cr in the matrix adjacent to the scale. A carburized layer consisting of various fine carbides is observed below the Cr-depleted layer, and the carburized layer depth is suppressed by Nb addition. When process of vacuum carburizing and quenching is repeated, formation of voids caused by heating and rapid cooling is more remarkable in primary Cr carbides than in primary Nb carbides. As the carburized layer depth increases, creep rupture time of both cast steels shifts to the shorter time side; however, Nb addition is effective for extending creep rupture time at 1303 K.

This Paper was Originally Published in Japanese in J. JFS 94 (2022) 235–244.

Optimal deposition parameters for the aerosol deposition of a β-SiAlON coating and the microstructure change of an EBC after heat exposure in air are investigated. Dense and crystalline SiAlON coating having developed texture, where the (0001) plane is declined approximately 10° from the coating plane is formed. The deposition rate increases with the gas flow rate when the rate is ranging from 12 to 16 L/min. Further increase of the gas flow rate decreases the deposition rate. Regarding the 15 µm thick mullite coating deposited on SiAlON substrate heat exposed at 1573 K over 30 h, delamination of the coating occurs due to the oxidation of SiAlON. 30 µm thick mullite coating prevents the oxidation. As for the EBC deposited on Si–SiC substrate, delamination occurs at Si–SiC/SiAlON interface by the oxidation of SiC during heat exposure at 1573 K. At the bonded region during heat exposure, SiAlON prevents the mullite coating to become (SiO₂+mullite) two-phase state by supping Al to the mullite. Residual Si at the substrate moves to SiAlON and mullite coating under heat exposure at 1673 K. Structure of EBC is maintained by using SiC substrate in which the Si will not move to the coating during exposure.

This Paper was Originally Published in Japanese in J. Japan Thermal Spray Soc. 57 (2020) 88–96.

Cold compaction is an essential step of the powder metallurgy process, which is cost-effective in the manufacturing industry. In the present study, the compaction of pure iron powder is investigated. A MATLAB code is developed to create a representative volume element with a given size distribution, number of particles, and initial relative density. The finite element analysis is performed by implementing an ABAQUS/Explicit python script. Multi-particle finite element analysis of compaction is employed to analyze the deformation of the particles into the green body. The effects of loading path, geometry configuration, and wall friction on punch force, axial and transverse stresses, strains, and yield surface are discussed. The results indicate that wall friction affects the load, stress state, and yield surface. It was found that, with the increase of the wall friction from 0.0 to 0.2, the compaction force increases by 14.70%. Also, the difference between the upper and lower RVE face forces increases from 1.01% to 16.27%. Changing the loading path from the compression to the hydrostatic compaction decreases the compaction force by 57.7% in upper and 65.75% in lower RVE faces, while the axial stress decreases by 27.70% and the transverse stress increases by 40.41%. The volume strain of compaction is smaller by 35.33% than that of hydrostatic compression.

Crude copper with a high content of impurities derived from secondary raw materials, known as black-copper, cannot be used in the conventional electrorefining process because of passivation. The current industrial process for black-copper, which involves a combination of high-temperature acid dissolution under pressure, and subsequent electrowinning, results in high power consumption. In this study, the basket electrolysis method was investigated as an alternative process for black-copper. Basket electrolysis experiments were performed using black-copper alloy samples shaped into shot of diameter 2.5 mm. The anodic dissolution behaviors with respect to the connection between the anode and the supporting conductor, anode shape, number of anodes, and anode composition, i.e., with and without Ag, were investigated. Relatively high anodic dissolution ratios, i.e., greater than 70%, were obtained in all cases when multiple-shot anodes with 10 or more shots were used. The anode film formed on the black-copper surface is thought to contribute to the maintenance of electrolysis by providing ion-conducting paths via electrolyte-filled pores, and electron-conducting paths via metal particles. This enabled application of the basket electrolysis method.

CeNF/Al-based composites were prepared using CeNFs collected by a non-woven aluminum filter, followed by hot extrusion to obtain plates. Gel-like CeNFs were collected by an aluminum non-woven filter and compacted by a warm press to obtain a compressed form with a lighter specific density than pure aluminum. The compressed forms were hot extruded to fabricate bars and plates. Both bars and plates were observed in the macro-and microstructural morphology and XRD measurements. They were not significantly carbonized to graphite only, which was inferred to be present as CeNF under the present experimental conditions. Microstructural observations show that CeNFs are aggregated and present in the pores/cracks between the Al filters in the compressed forms. Al filters and CeNF aggregates were more finely mixed when the material was fabricated into hot extruded plates with a higher extrusion ratio. The maximum tensile strength of the CeNF/Al composite extruded plate was about 1.5 times higher than pure aluminum. In addition, the extruded plates could be cold-rolled by about 30%, and the maximum tensile strength of the extruded sheets was found to be about twice that of pure aluminum.