In the next-generation of turbine engines, improving the heat resistance and reducing the weight are the essential solutions to increasing the thermal efficiency and reducing fuel consumption and CO2 emissions. Silicon-based ceramics (e.g., SiCf/SiC ceramics matrix composites (CMCs) and monolithic Si3N4) are the leading candidates for these applications because of their extreme light weight and superior heat resistance compared to the current Ni-based alloys. The main challenge of the Si-based ceramics is oxidation and volatilization of the silica in the high-temperature combustion gas environment with the water vapor and thereby its rapid recession. The most promising approach is protecting the surface of the ceramic matrix composites from the water vapor attack by an external environmental barrier coating (EBC) layer. Since the early 1990s, a lot of efforts have been made to develop suitable EBCs; however, no single material can satisfy all the EBC requirements. Thereby, the current EBC trends are directed to the development of multilayered EBCs, with different functions as a significant solution to prevent CMC recession and to maximize its performance for next engine generation. This paper discusses the history, current status, and future trends of EBC development not only in the world but also in Japan. Furthermore, it introduces future prospects of fine particle spraying in EBC developments.
This Paper was Originally Published in Japanese in J. Jpn. Thermal Spray Soc. 57 (2020) 76–87.
In accordance with the EU RoHS Directive, the use of Sn–3 mass%Ag–0.5 mass%Cu lead-free solder (SAC305) has become the standard in the manufacturing of electronics. Since SAC305 contains more tin than the conventional tin-lead eutectic solder, erosion of the Fe plating frequently occurs on a hand soldering iron tip and a point soldering machine nozzle. In this study, to extend the life of the Fe plating layer, we investigated the applicability of a composite plating in which Fe is combined with the boron nitride (BN) compounds. We used BN particles as the bulk material, and boron nitride nanotubes (BNNT) as a nanomaterial, to fabricate the regarded composite materials. A solderability test and an erosion resistance test were conducted on the composite plating layer, made of both Fe-BN particles and Fe-BNNTs composites. In the solderability test, the spreading factor of SAC305 on the Fe-BN particle and on the Fe-BNNT composite platings were about the same as, or a little decreased compared to, that of the bare Fe plating. The SAC305 solder was not repelled by either composite plating. In the erosion resistance test, the Fe-BNNT composite plating performed the best, and had the lowest erosion depth. The erosion depths of the Fe-BN particle composite plating and the Fe plating ranged from about 6 to 24 times greater, respectively, than those of the Fe-BNNT composite plating layer, confirming that, in a nanomaterial BNNT-base, composite diffusion of Fe into SAC 305 can be suppressed.
An experimental investigation of static and fatigue strength of double strap joints, using thermosetting and thermoplastic adhesives, between aluminum alloy 6061-T6 and carbon fiber metal laminate (CFML) has been carried out during this research. The static properties of joints, using thermosetting adhesives, were also determined while varying the temperature values. Two types of specimens were prepared: one, using YD-128 epoxy and the other using thermoplastic polyurethane by applying hand layup method. Results of both tensile and fatigue testing indicated better strength for thermosetting double strap joint both in elongation and fatigue cycles. For experimental validation of joints, finite element modeling has also been used during this research. Furthermore, the thermosetting double strap joint with maximum shear strength has been tested under a series of high temperatures. Temperature dependence of thermosetting epoxy adhesive indicated an increase in tensile strength of joint below the service temperature. However, a 50% drop in joint’s shear strength was observed when temperature was raised from 25°C to 60°C. Similarly, an increase in tensile strength of about 8.11% was observed at temperatures between −20°C to 25°C. The mode of failure for all combinations of thermosetting joints is mixed mode and cohesive failure whereas adhesive failure was observed for thermoplastics joints.
Weight reduction in automobiles is an effective way to reduce carbon dioxide emissions. To reduce the weight, adhesive joints made from light materials are expected to be widely used. However, the deterioration evaluation of adhesion in joints exposed to corrosive environments, such as the salt-damaged area, is performed using destructive evaluation methods such as tensile tests.
In this study, to develop a non-destructive method for detecting the deterioration of aluminum/carbon fiber-reinforced plastic lap joints by adhesives, we investigated the change in the electric properties of the joints before and after corrosion tests through electrochemical impedance spectroscopy. It was observed that the impedance and frequency dependence of the dielectric loss tangent of the joints were changed by the corrosion test.
This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 70 (2021) 365–369.
The major objective of the present study was to investigate the creep fracture process of a copper tricrystal having 〈110〉-tilt Σ3, 3, 9 grain boundaries. Creep tests at 0.81 TM (TM: melting temperature on the absolute temperature scale) under 4 MPa tensile stress were carried out for three samples prepared from the same tricrystal. Grain-boundary sliding occurred along only the Σ9 boundary, and the triple junction of the boundaries completely suppressed the sliding. The three samples were in different stages of creep deformation. Creep fracture was initiated by sliding-induced voids along the Σ9 boundary. Grain-boundary damage by the void formation developed into complete separation along the Σ9 boundary, and the Σ9 boundary crack induced surface grooves along one of the Σ3 boundaries, arranged almost perpendicular to the tensile axis. The crack propagation resulted in the final fracture of the tricrystal along the Σ9 and Σ3 boundaries. The formation of cavities in the Σ3 fracture surface suggested that the final fracture occurred in a ductile manner after the neighboring grains were partly separated along the Σ3 boundary.
This study developed an original constant-head permeability apparatus for rocks. This apparatus can freely adjust the confining pressure and hydraulic pressure (hydraulic gradient), and can directly measure the runoff volume using an electronic balance. This apparatus can measure the hydraulic conductivity more accurately than the conventional constant-head method that measures the runoff volume using a measuring cylinder. Second, this study measured the hydraulic conductivity of Inada granite specimens (50 mm in diameter and 40 mm in length) under confining pressure conditions using the constant-head permeability apparatus. The test was performed at 22 ± 1°C in a temperature-controlled room. As result, we found that the hydraulic conductivity of Inada granite, which was measured using this apparatus, is quite similar to that reported by a previous study using transient pulse method. Furthermore, the observed decline in hydraulic conductivity due to the confining pressure is consistent with the observations of the previous study. Therefore, the permeability measurement system used in this study is established and reliable. In addition, this study measured the hydraulic conductivity of various seven intact rocks (granite, basalt, dacite, sandstone, and tuff) under confining pressure conditions using a constant-head permeability apparatus, and we presented how the hydraulic conductivity changes as the confining pressure increases.
This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 71 (2022) 221–227.
Chemical alterations of bentonite are critical factors for the ultra-long-term stabilization of barriers and backfill in radioactive waste disposal. The chemical alterations may deteriorate the properties of bentonite-based materials. However, experimental studies on the effects of chemical alterations on the swelling characteristics and permeability of bentonite-based materials have not been investigated extensively. In this study, the effects of chemical factors on the swelling properties and permeability of bentonite-based materials were clarified based on one-dimensional swelling-pressure, hydraulic conductivity, X-ray powder diffraction patterns, and element mapping images. From the analytical and experimental results, a small amount of K+, Fe3+, and Mg2+ can significantly deteriorate the swelling characteristic and permeability of bentonite-based materials in geological disposal (i.e., cause a decrease in swelling-pressure and an increase in hydraulic conductivity). Therefore, we conclude that it is necessary to pay close attention to the existence of these cations.
This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 71 (2022) 395–401.
Although plasma electrolytic oxidation (PEO) coatings possess high hardness and good adhesion, they usually contain lots of pores and exhibit high friction coefficient. In this work, MoS2 was synthesized via hydrothermal reaction to fill the pores of PEO coatings and improve their tribological performance. Microstructure observation of coatings shows that the porous PEO coating formed on the titanium was basically composed of Al2TiO5, and MoS2 in-situ nucleated and grew on the PEO surface and in the PEO pores. The fabricated PEO/MoS2 composite coating had a dense surface and consisted of two layers: the upper MoS2 surface layer and the under PEO-MoS2 interlocking layer. The tribological tests of coatings revealed that the friction coefficient of the PEO/MoS2 composite coating (below 0.2) was much lower than that of the PEO coating (up to 0.6). The PEO coating failed after a short sliding distance of about 56 m under the normal load of 10 N. In contrast, the PEO/MoS2 composite coating reached a much longer sliding distance up to 1000 m without failure. The excellent tribological performance of the PEO/MoS2 composite coating was attributed to the synergistic action of PEO and MoS2 components.
An effect of surface area and microstructure of Li0.29La0.57TiO3 (LLTO) solid electrolyte on an electrochemical performance of LiCoO2 (LCO) as positive electrode in an all-solid-state Li secondary battery was examined. The surface of LLTO sintered body was machined mechanically by using a pico-second laser and obtained in various forms of LLTO. Then, LCO on the LLTO was prepared from molten salts as a starting material. The microstructural observation confirmed that LCO was formed on the surface of a laser-machined LLTO. A discharge capacity was enlarged with the amount of LCO loading. These results suggest that the LCO formed on LLTO by molten salts was active electrochemically regardless of various shapes of microstructures of the solid electrolyte.
This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 69 (2022) 104–107.
To reduce the electrochemical measurement error of magnesium alloys, surface treatment of AZ91 alloys in 0.1 M NaCl solution at pH = 11 at several potential values were investigated. Scanning electron microscope (SEM) was used to observe the surface conditions. Elemental distribution was investigated using an electron probe micro-analyzer (EPMA). The thickness and chemical composition of the coatings could not be accurately determined from the observations. The electrochemical impedance spectroscopy (EIS) results showed that the electrochemical stability and damage of the surfaces treated at −2.2 V were better than those treated at −1.5 V. This result suggests that surface treatment at −2.2 V prior to polarization test measurements results in smaller experimental errors. For the polarization curve measurements, the surface treatment at −2.2 V was effective to reduce the experimental error. This is also reflected in the standard deviation values for each corrosion property. The standard deviation of the corrosion potential of the surface treatment at −2.2 V was 0.009 V, which was clearly smaller than the standard deviation value of 0.0024 V for the surface treatment at −1.5 V. Therefore, it can be concluded that the surface treatment at −2.2 V reduced the experimental error in the measurement of the polarization curve.
This study aimed to observe the thickening of the S-phase and Sα-phase of various stainless steels subjected to low-temperature direct current plasma nitriding using screen (S-DCPN). Austenitic stainless steel SUS304, ferritic stainless steel SUS430, and duplex stainless steel SUS329J4L were treated using two different screens for comparison, namely, a Ni screen and a steel plate cold commercial (SPCC) screen. Plasma nitriding was performed at 673 K for 300 min under a 75% N2 + 25% H2 atmosphere at 100 Pa pressure of the mixed gas. After nitriding treatment, the samples were examined using X-ray diffraction (XRD) and glow discharge optical emission spectrometry (GD-OES), and their cross-sectional microstructure and surface microstructure were examined using an electron probe micro analyzer (EPMA). Nitrided samples were also subjected to Vickers hardness and pitting corrosion tests. Examination of the SUS304 samples revealed thickening of its S-phase and higher surface hardness and pitting corrosion resistance when nitriding was done with the Ni screen. This was due to excess nitrogen diffusion into the sample due to presence of the Ni screen than with the SPCC screen. In the SUS430 samples, thickening of the Sα-phase was not be observed. When the Ni screen was used during nitriding, higher surface hardness and less pitting corrosion resistance of sample were observed, along with enhanced nitrogen diffusion than the SPCC screen was used. In the SUS329J4L samples, upon nitriding with Ni screen, thickening of the S-phase was observed and surface hardness and pitting corrosion resistance of the sample were higher, which was attributed to the enhanced nitrogen diffusion into the sample than when nitriding with the SPCC screen.
This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 86 (2022) 62–70.
In order to obtain the fracture strain of notched samples, the digital image correlation (DIC) technology is employed in this paper. The values of fracture-related state variables such as stress triaxiality and Lode parameter are obtained through mathematical transformation. The fracture parameters of Lou-Huh ductile fracture criterion (DFC) are calibrated by surface fitting with least square method, and the fracture curve is drawn and applied to the fracture prediction during deep drawing. The reliability of DFC is verified considering fracture stroke and location through tests. The results show that the fracture curve can predict the initiation and location of fracture successfully. Fractures are all predicted in advance under multiple blank holder force (BHF) conditions. Comparison results of finite element (FE) simulation and experiment show that the maximum error of fracture stroke is 12.9% and the fracture locations are generally consistent. The prediction of DFC is partial to safety.
SnO2–Sb2O3 particles, with various Sb2O3 mole fraction (x) ranging from 0 to 1, have been synthesized by a sol-gel method. Tin oxalate and antimony chloride were used as the metal precursors, water as the solvent, citric acid as the pH modifier, and triethanolamine as a stabilizing agent. The effect of the chemical composition of the synthesized catalyst on the photocatalytic degradation of methylene blue (MB) and methyl orange (MO) was evaluated. It was established that a SnO2–Sb2O3 (Sb2O3 mole fraction of x = 0.15) catalyst presents a highly oxidative power to degrade a 20 µM MB solution until 98.60%, using a UV lamp of 254 nm and 6 W. The kinetics of the SnO2–Sb2O3 (x = 0.15) photocatalytic oxidation was monitored as a function of the initial concentration of MO (100, 200, 300, and 400 µM) at different reaction times. It was found that the reaction probably presents a pseudo-first-order kinetic model. The effect of the intensity of the power lamp was studied, finding an increment from 16.32 to 98.42%, for UV lamps of 6 W and 72 and 1200 mW cm−2, respectively. Finally, the effect of temperature (298, 318, 328 and 338 K) was analyzed, and the activation energy from Ea = 7.2 kcal mol−1 was determined.
Nickel is an important strategic metal in the world. As the sulfide ore containing high-grade nickel is increasingly depleted, the laterite nickel ore, which is rich in resources, has attracted people’s attention. In this paper, the reduction roasting-magnetic separation process is used to study the method of preparing ferronickel concentrates from low-grade laterite nickel ore under the action of composite additives (Na2CO3 and CaF2). The research results showed that when the ratio of additives Na2CO3 and CaF2 was 1:7, reduction temperature was 1250°C, reduction time was 60 min, magnetic field strength was 150 mT, and wet grinding time was 12 min, the nickel grade and recovery extent were 8.39 wt.% and 98.54%, iron grade and recovery extent were 67.70 wt.% and 71.73%.