研究者詳細 - 山下　誠司

論文 - 山下　誠司

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Self lubrication of pressureless sintered SiC ceramics Open Access

Zhang W., Yamashita S., Kita H.

Journal of Materials Research and Technology 9 巻 ( 6 ) 頁： 12880 - 12888 2020年11月

出版者・発行元：Journal of Materials Research and Technology

The self lubrication of SiC ceramics prepared by pressureless sintering was investigated by annealing at different temperatures in air. It was found that low coefficient of friction can be obtained for SiC ceramics by annealing, and the coefficient of friction of SiC ceramics decreased with the increase of annealing temperature. The SiC ceramics with annealing at 1500 °C revealed the best self lubricating property, with the coefficient of friction of 0.4, while the coefficient of friction of SiC ceramics without annealing was as high as 0.7. The SiC ceramics with annealing at 1000 °C can show self lubrication over a long sliding distance without increasing wear. The formation of α-cristobalite on the annealed SiC ceramics can further lubricate SiC ceramics and shorten run in period. Self lubrication mechanism of SiC ceramics with annealing is considered that on the one hand, the formation of silicon oxide layers after annealing can reduce the number of SiC grains directly exposed to the sliding interface in the early stage of the sliding, decreasing the number of hard SiC wear particles formed on the sliding interface; and on the other hand, silicon oxide wear particles generated by the wear of the silicon oxide layers formed by annealing can be used as solid lubricant.

DOI： 10.1016/j.jmrt.2020.09.022

Open Access

Web of Science

Scopus

Effect of counterbody on tribological properties of B<inf>4</inf>C–SiC composite ceramics

Zhang W., Yamashita S., Kita H.

Wear 458-459 巻 2020年10月

出版者・発行元：Wear

Pressureless sintered B4C–SiC composite ceramics were subjected to dry sliding friction and wear against Al2O3, Si3N4 and SUJ2 bearing steel counterbodies at 5 N, 10 N and 20 N. Friction coefficient and specific wear rate were measured, and wear mechanisms were studied. For the B4C–SiC composite ceramics, both the friction coefficient and specific wear rate were dependent on counterbody materials. However, the influence of counterbody materials on friction coefficient and systematic specific wear rate of B4C–SiC composite ceramics was not obvious at high load, which was attributed to the formation of a number of compaction layers on all the worn surfaces of B4C–SiC composite ceramics against Al2O3, Si3N4 and SUJ2 counterbodies. At the same loads, the wear of B4C–SiC composite ceramics sliding against different counterbodies at low load was mainly controlled by the chemical similarity of counterbody, whereas the wear of B4C–SiC composite ceramics sliding against different counterbodies at intermediate and high loads was mainly controlled by the hardness of counterbody.

DOI： 10.1016/j.wear.2020.203418

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Scopus

7-12　人工物製造プロセスのエクセルギー解析

北英紀, 山下誠司, 窪田光宏

日本エネルギー学会大会講演要旨集 29 巻 ( 0 ) 頁： 188 - 189 2020年7月

Tribological Properties of B<inf>4</inf>C Ceramics Prepared by Pressureless Sintering and Annealed at Different Temperatures

Zhang W., Yamashita S., Kumazawa T., Ozeki F., Hyuga H., Kita H.

Tribology Transactions 63 巻 ( 4 ) 頁： 672 - 682 2020年7月

出版者・発行元：Tribology Transactions

B4C ceramics were fabricated by pressureless sintering, and the tribological behaviors of B4C ceramics without and with a postannealing treatment at different temperatures were investigated. It was found that the pores of B4C ceramics prepared by pressureless sintering might cause large fluctuations in the coefficient of friction but did not increase the coefficient of friction. A B2O3 layer was not formed on the B4C ceramics after annealing at 700 °C, whereas an H3BO3 layer was formed on the B4C ceramics after annealing at 1000 and 1200 °C, respectively. B4C ceramics obtained a favorable self-lubricating property after annealing at 1000 or 1200 °C because of the formation of an H3BO3 layer during the annealing treatment. B4C ceramics annealed at 1200 °C exhibited the best self-lubricating properties, with the lowest coefficient of friction of approximately 0.08. The friction and wear mechanisms of B4C ceramics without and with a postannealing treatment are discussed in detail.

DOI： 10.1080/10402004.2020.1734705

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Scopus

Effects of load on tribological properties of B<inf>4</inf>C and B<inf>4</inf>C-SiC ceramics sliding against SiC balls Open Access

Zhang W., Yamashita S., Kita H.

Journal of Asian Ceramic Societies 8 巻 ( 3 ) 頁： 586 - 596 2020年7月

出版者・発行元：Journal of Asian Ceramic Societies

Pressureless sintered B4C and B4C-SiC ceramics were subjected to tests of dry sliding against SiC balls at 5 N, 10 N and 20 N. The effects of load on the respective tribological properties of B4C and B4C-SiC ceramics were studied. Meanwhile, the tribological properties and friction, wear mechanisms of B4C and B4C-SiC ceramics at different loads were compared. Both the friction coefficient and wear rate of B4C ceramics first decreased and then increased with increases in load, while both the friction coefficient and wear rate of B4C-SiC ceramics increased with increases in load. At low load, the B4C-SiC ceramics showeda lower friction coefficient and wear rate. At intermediate load, the B4C ceramics showed a lower friction coefficient, and no difference between the wear rates of B4C and B4C-SiC ceramics was apparent. At high load, the B4C ceramics showed a lower friction coefficient, while the B4C-SiC ceramics showed a lower wear rate. With increases in load from 5 N to 20 N for the B4C ceramics, the wear mechanism changed from adhesive wear to delamination and spalling of tribofilm; for the B4C-SiC ceramics, meanwhile, the wear mechanism changed from surface polishing and mild abrasion to micro-fracture.

DOI： 10.1080/21870764.2020.1769819

Open Access

Web of Science

Scopus

Tribological properties of SiC-B<inf>4</inf>C ceramics under dry sliding condition

Zhang W., Yamashita S., Kita H.

Journal of the European Ceramic Society 40 巻 ( 8 ) 頁： 2855 - 2861 2020年7月

出版者・発行元：Journal of the European Ceramic Society

SiC-B4C ceramic composites with different ratios of SiC to B4C were produced. The relative density, mechanical properties, initial surface characteristics, dry sliding tribological properties against SiC ball and worn surface characteristics of the SiC-B4C ceramics were studied. Results of dry sliding tribological tests showed that, 40 wt. % SiC-60 wt. % B4C ceramic composite had the best tribological properties in SiC-B4C ceramic composites. A relief structure with height difference of 10−30 nm between B4C grains and SiC grains is formed after dry sliding. This relief structure, on the one hand, can reduce real contact area on interface, decreasing adhesion effect, and on the other hand, can fix or trap the wear pieces formed on sliding interface during the dry sliding process, reducing the abrasive wear. However, there is a limit to the beneficial influence of decreased adhesion effect and reduced abrasive wear, and an optimum proportion of relief structure. Pores can also fix or trap some wear pieces, reducing the abrasive wear. Under the condition of strong bonding between SiC grains and B4C grains, the SiC-B4C ceramic composites with higher porosity can obtain better tribological properties. In addition, it is observed by AFM that the depth of scratch on B4C grains is shallower than that on SiC grains. Hence, it is demonstrated by micro scale measurement that the wear rate of B4C is lower than that of SiC in this study.

DOI： 10.1016/j.jeurceramsoc.2020.02.062

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Scopus

Study on friction behavior of SiC-B<inf>4</inf>C composite ceramics after annealing

Zhang W., Yamashita S., Kumazawa T., Ozeki F., Hyuga H., Kita H.

Industrial Lubrication and Tribology 72 巻 ( 5 ) 頁： 673 - 679 2020年6月

出版者・発行元：Industrial Lubrication and Tribology

Purpose: This study aims to investigate the friction behavior of SiC-B4C composite ceramics treated by annealing in air sliding against SiC balls. Design/methodology/approach: The dry sliding tests were performed with a ball-on-disk tribometer in ambient air condition. Analysis of friction coefficient, phase compositions of the surfaces, morphologies of worn surfaces of disks and wear scars of balls and surface profiles of wear tracks for disks were carried out using Raman spectroscope, microscope and surface profilometer. Findings: The results show that a self-lubricating layer with the main composition of H3BO3 was successfully fabricated on the surface of SiC-B4C composite ceramics by the annealing treatment in air. When the mass fraction of SiC is more than that of B4C, SiC-B4C composite ceramics show higher friction coefficients, the values of which are 0.38 for 80 Wt.%SiC-20 Wt.%B4C and 0.72 for 60 Wt.%SiC-40 Wt.%B4C, respectively. SiC-B4C composite ceramics show lower friction coefficients when the mass fraction of B4C is more than that of SiC. The low friction coefficients of 40 Wt.%SiC-60 Wt.% B4C composite ceramics (0.16) and 20 Wt.%SiC-80 Wt.% B4C composite ceramics (0.20) are attributed to the formation of a sufficient amount of H3BO3 layer, rather than the layer of silicon oxides. Originality/value: This study will help to understand the friction behavior of SiC-B4C composite ceramics with different ratios of SiC to B4C treated by annealing in air.

DOI： 10.1108/ILT-08-2019-0350

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Scopus

Progress in tribological research of SiC ceramics in unlubricated sliding-A review Open Access

Zhang W., Yamashita S., Kita H.

Materials and Design 190 巻 2020年5月

出版者・発行元：Materials and Design

Silicon carbide ceramics have many excellent properties, such as high melting point, high strength, high thermal conductivity, high hardness, high stiffness, good chemical resistance, good electrical conductivity and remarkable wear resistance. Therefore, SiC ceramics are useful for various tribological applications. Nevertheless, SiC ceramics usually exhibit poor friction characteristics under unlubricated sliding contacts, which can greatly deteriorate the durability and reliability of a tribosystem. In this work, the tribological research progress of SiC ceramics was summarized based on microstructural characteristics, self-lubrication methods, surface characteristics and external factors. First, tribological performance of SiC ceramics can be improved by controlling microstructural characteristics, such as reducing grain size of SiC ceramics, acquiring elongated SiC grains, reducing the content of grain boundary/intergranular phase, crystallizing amorphous grain boundary phases, hardening intergranular phases, controlling cracks propagation way. Second, good self-lubrication property for SiC ceramics can be obtained by annealing heat treatment, adding the secondary phase or producing porous SiC ceramics. Third, tribological performance of SiC ceramics can be improved by proper surface processing or surface modification, such as proper roughness, surface texture or coating technology. Fourth, tribological performance of SiC ceramics is affected by various external factors. Besides, the research trends of SiC ceramic tribology in future were proposed. This work aims to provide some reference for the design of SiC ceramics with high wear resistance and low friction.

DOI： 10.1016/j.matdes.2020.108528

Open Access

Web of Science

Scopus

Water vapor adsorption on poly(N-isopropylacrylamide) gel cross-linked with N, N′-methylenebisacrylamide

Kubota M., Mochizuki T., Yamashita S., Kita H., Tokuyama H.

Materials Today Communications 22 巻 2020年3月

出版者・発行元：Materials Today Communications

Water vapor adsorption characteristics and the thermosensitivity for vapor adsorption of poly(N-isopropylacrylamide) gel (NIPA gel) cross-linked with N, N′-methylenebisacrylamide (MBAA) (cross-linked NIPA gel) were investigated for application in desiccant humidity control systems. The cross-linked NIPA gels were prepared via copolymerization of NIPA monomers and MBAA monomers, which were used as crosslinkers, at various reagent concentrations and polymerization temperatures in the range of 283–323 K. The water vapor adsorption isotherms of NIPA homopolymer, MBAA homopolymer, and cross-linked NIPA gels were obtained at adsorption temperatures in the range of 298–323 K using a volumetric gas adsorption apparatus. The water vapor adsorptivity of the cross-linked NIPA gel increased with increasing MBAA monomer concentration and decreasing NIPA monomer concentration. NIPA homopolymer under dry conditions showed weak thermosensitivity for water vapor adsorption between 298 and 313 K. Meanwhile, MBAA homopolymer showed almost no change in water vapor adsorptivity above adsorption temperatures of 298 K. The cross-linked NIPA gels had a similar thermosensitivity to NIPA homopolymer, but its sensitivity might be shifted to higher temperature than NIPA homopolymer. Thermosensitivity of the cross-linked NIPA gel was effective in improving polymer water adsorptivity, necessary for desiccant humidity control systems; however, the adsorption performance of the polymer gel systems investigated require further improvements before practical application will be possible.

DOI： 10.1016/j.mtcomm.2019.100804

Scopus

A study on formation mechanisms of relief structure formed in situ on the surface of ceramics

Zhang W., Yamashita S., Kumazawa T., Ozeki F., Hyuga H., Norimatsu W., Kita H.

Ceramics International 45 巻 ( 17 ) 頁： 23143 - 23148 2019年12月

出版者・発行元：Ceramics International

The formation mechanisms of relief structure formed in situ on the surface of B4C–SiC ceramics were studied. The hardness difference between B4C and SiC is one of the formation conditions of relief structure. SiC grains are subjected to a preferential wearing owing to their lower hardness as compared to B4C grains, resulting in the difference of wear rates between B4C grains and SiC grains. Clean, no gap grain boundary in the B4C–SiC ceramics, which can make B4C grains and SiC grains bond firmly protecting them from pulling out, is another formation condition of relief structure.

DOI： 10.1016/j.ceramint.2019.08.008

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Scopus

Influence of surface roughness parameters and surface morphology on friction performance of ceramics Open Access

Zhang W., Yamashita S., Kumazawa T., Ozeki F., Hyuga H., Kita H.

Journal of the Ceramic Society of Japan 127 巻 ( 11 ) 頁： 837 - 842 2019年11月

記述言語：英語出版者・発行元：公益社団法人日本セラミックス協会

Influence of both surface roughness and surface morphology on frictional behavior of ceramics during run-in period under dry sliding was investigated simultaneously. Similar average surface roughness (Ra = 0.01-0.02 μm) was produced for the three ceramics: monolithic boron carbide ceramics, boron carbide-silicon carbide composite ceramics and monolithic silicon carbide ceramics. Surface roughness parameters show some influence on friction processes, however, surface morphology is considered as a more important competitive factor. Lower friction coefficient during run-in period and shorter sliding distance up to the steady state condition were observed for the B4C-SiC composite ceramics, which has a different surface morphology from those of monolithic B4C ceramics and monolithic SiC ceramics.

DOI： 10.2109/jcersj2.19124

Effect of nanorelief structure formed in situ on tribological properties of ceramics in dry sliding

Zhang W., Yamashita S., Kumazawa T., Ozeki F., Hyuga H., Kita H.

Ceramics International 45 巻 ( 11 ) 頁： 13818 - 13824 2019年8月

出版者・発行元：Ceramics International

Nanorelief structure formed on the surface of B 4 C–SiC ceramics by an in-situ method is reported. The nanorelief structure formed by the in-situ method, which differs from the relief structure produced by laser treatment, results from preferential wearing of SiC particles, which have lower hardness, by free diamond particles and mixed wear particles of B 4 C and SiC during polishing and sliding, respectively. The effect of the nanorelief structure formed by the in-situ method on the sliding dry friction against a SiC ball is examined using a pin-on-disk tribometer. A comparison of dry sliding of the B 4 C–SiC composite ceramics with nanorelief structure to that of SiC ceramics without nanorelief structure reveals that B 4 C–SiC composite ceramics have a lower coefficient of friction and a significantly lower specific wear rate than the SiC ceramics. Worn surface analysis indicates that the nanorelief structure does not disappear after a dry sliding test. The depth of the nanorelief structure formed by the in-situ method ranges from 10 to 40 nm. The friction and wear results are associated with the nanorelief structure formed by the in-situ method.

DOI： 10.1016/j.ceramint.2019.04.078

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Scopus

P-7-1 廃棄物を利用したグリーンコンポジットの作製ならびにエクセルギー解析に基づく環境負荷評価

鶴見和幸, 山下誠司, 窪田光宏, 北英紀

日本エネルギー学会大会講演要旨集 28 巻 ( 0 ) 頁： 286 - 287 2019年7月

Progress in pressureless sintering of boron carbide ceramics–a review

Zhang W., Yamashita S., Kita H.

Advances in Applied Ceramics 118 巻 ( 4 ) 頁： 222 - 239 2019年5月

出版者・発行元：Advances in Applied Ceramics

Boron carbide (B4C) ceramics has many outstanding performance, such as extremely high hardness, low density, high melting point, high elastic modulus, high thermoelectromotive force, high chemical resistance, high neutron absorption cross section, high impact and excellent wear resistance. Therefore, B4C ceramics can be used in various industrial applications, such as lightweight ceramic armour, high temperature thermocouples, neutron absorber, reactor control rods in nuclear power engineering, polishing media for hard materials, abrasive media for lapping and grinding, and wear resistant components (blasting nozzles, die tips and grinding wheels). Pressureless sintering is the method with industrialised application value for B4C ceramics, however, it is impossible to sinter pure B4C ceramics to high densities without additives by pressureless sintering. So sintering additives must be used to promote the densification of B4C ceramics. The different sintering additives used to promote the densification of boron carbide will be described in this review, including carbon additives, metallic additives, oxide additives, non-oxide additives, combined additives and rare earth oxide additives. Finally, the recent research trends for sintering methods and sintering additives of B4C ceramics will also be proposed.

DOI： 10.1080/17436753.2019.1574285

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Scopus

Fracture analysis of porous SiSiC ceramics with anisotropic three-dimensional network structure Open Access

Himoto I., Yamashita S., Kita H.

Journal of the Ceramic Society of Japan 127 巻 ( 5 ) 頁： 295 - 303 2019年5月

記述言語：英語出版者・発行元：公益社団法人日本セラミックス協会

The fracture mechanism and reliability of typical dense ceramics can be statistically analyzed using a Weibull distribution as a basis for device design. However, it is not understood if the Weibull distribution can even be applied to highly porous ceramics. In this study, porous Siliconized Silicon Carbide (SiSiC) ceramics with anisotropic three-dimensional network structures in a porosity range of 7192% were fabricated and subjected to a fracture analysis using the results of three-point bending tests. Observations of fracture behavior during the bending tests were conducted using a high-speed camera, image analysis of stress distribution, and observation of crack distribution inside the partially damaged specimens using X-ray computed tomography. The results indicate non-linear behavior with multiple peaks in the loaddisplacement curves. In this regard, the fracture mechanism of the porous SiSiC ceramics was intrinsically different from the brittle fracture of dense ceramics and did not appear to be based on the weakest-link model. However, the Weibull distribution was found to be applicable to the bending strength of the porous ceramics with a confidence coefficient of 0.90. This was because although strain and cracks were generated sporadically during loading, the catastrophic fracture of the porous SiSiC ceramic specimens occurred with a macroscopic crack opening at the bottom of the test specimens, almost the same as a Mode I crack opening in dense ceramics. Furthermore, graded three-layer structures can be formed integrally using the proposed novel replication method with uniaxial pressing, taking the plateau of the stressstrain curve of the template polyurethane foam into account, providing a kind of damage tolerance owing to the sporadic generation and sequential propagation of cracks, manifested as the multiple peaks shown in the loaddisplacement curves.

DOI： 10.2109/jcersj2.18209

P-5-1 異形シェル型セラミック蓄熱体の開発とコンパクト蓄熱システムへの適合性評価

赤埴達也, 山下誠司, 窪田光宏, 北英紀

日本エネルギー学会大会講演要旨集 27 巻 ( 0 ) 頁： 292 - 293 2018年8月

P-6-1 中空セラミックス構造体の活用によるコンパクト蓄熱槽の開発

関井裕哉, 赤埴達也, 山下誠司, 窪田光宏, 北英紀

日本エネルギー学会大会講演要旨集 26 巻 ( 0 ) 頁： 314 - 315 2017年

Design of Heat Emission Controlled Spherical Container Constructed with Skeletal Ceramic Units Based on Heat Transfer Analysis 査読有り

Iori Himoto, Seiji Yamashita, Hideki Kita

JOURNAL OF CHEMICAL ENGINEERING OF JAPAN 49 巻 ( 9 ) 頁： 850-863 2016年9月

Heat press molding of open-celled porous Si-SiC ceramics consisting of skeletal strut via gelcasting with flexible and thermosetting polyurethane resin

Himoto I., Yamashita S., Kita H.

Advanced Powder Technology 27 巻 ( 3 ) 頁： 948 - 958 2016年5月

出版者・発行元：Advanced Powder Technology

A novel powder processing method for the fabrication of thin open-celled porous siliconized silicon carbide (Si-SiC) ceramic substrates is reported. Green SiC-carbon (C) substrate is first formed via a newly developed gelcasting method, using an organic-solvent-based slurry comprised of submicron SiC and nanometer C powders, along with a flexible and thermosetting polyurethane resin, based on the replica method with polyurethane foam as a template. Subsequently, the flexible semi-wet green substrate is uniaxially compressed under heating for molding to a set thickness; this is possible because of its thermosetting property (heat press molding). Although the slurry viscosity is highly sensitive to fine fluctuations in the powder volume concentration (PVC; 0.45-0.48), the PVC criterion for homogeneous powder solidification and improvement in the green SiC-C strut quality is determined to be 0.46. At 0.48 PVC, it is confirmed that the formed green SiC-C struts reproduce the template morphologically with a high correlation coefficient of 0.96 for the average strut thickness. As regards the open-celled sintered Si-SiC substrate (thickness: 6 mm), the Si-SiC strut appears to be skeletal with a triangular vertical cross-section, which can be successfully warped or twisted without cracking; furthermore, the mechanical strength is evidently improved via the heat press molding.

DOI： 10.1016/j.apt.2016.02.031

Scopus

Heat Press Molding of Open-celled Porous Si-SiC Ceramics Consisting of Skeletal Strut via Gelcasting with Flexible and Thermosetting Polyurethane Resin 査読有り

Iori HIMOTO, Seiji YAMASHITA and Hideki KITA

Advanced Powder Technology 27 巻 ( 3 ) 頁： 948-958 2016年

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