Papers by Author: Kazuyuki Hokamoto

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Authors: Tatsuya Yamamoto, Masatoshi Nishi, Masahide Katayama, Kazuyuki Hokamoto
Abstract: The mechanism of damage on the structure of an explosion pit which belongs to the Institute of Pulsed Power Science, Kumamoto University is investigated. Investigated is the mechanism of damage on the structure of an explosion pit which belongs to the Institute of Pulsed Power Science, Kumamoto University. Here, three-dimensional model with square opening (door) is used to simulate by numerical simulation. The numerical result with the actual egg-type model implies that firstly the cracks occurred at the corners of the door and grew larger. In addition, the numerically simulated results with a spherical form model are also demonstrated to study on optimizing the design of an explosion pit.
Authors: M. Heydarzadeh Sohi, Shahin Khameneh Asl, Kazuyuki Hokamoto, M. Rezvani
Abstract: Five types of tungsten carbide based powders with different chemical compositions (WC-12Co, WC-17Co, WC-10Ni, WC-10Co-4Cr and WC- 20Cr-7Ni) were deposited onto ST37 mild steel substrate using high velocity oxy fuel (HVOF) spray technique. The feedstock powders and sprayed coatings were studied by using X-ray diffraction (XRD), and differential thermal analyzing (DTA). The results were shown during HVOF thermal spraying, WC-M powders become partially melted before being sprayed on the surface of the substrate with supersonic speed. In these types of coatings, the crystallographic structures are normally non equilibrium, because the cooling rates of the deposited splats are very high due to the cold substrate acting as a thermal sink. These partially melted powders are then rapidly solidified to an amorphous phase. XRD analysis showed that the amorphous phase was existed in all of the as sprayed coatings. The amorphous phase in WC-12Co, WC-17Co and WC-10Ni coatings was transformed to crystalline phases by heat treatment at high temperature. Heat treatment of these coatings at high temperature also resulted in partially dissolution of WC particles and formation of new crystalline phases. In cobalt base coatings, the new phases were eta carbide phases like Co6W6C and Co3W3C but in WC-10Ni coating a NiW intermetallic phase was formed. Heat treatment of WC-10Co-4Cr and WC-20Cr-7Ni coatings did not change the amorphous phases in these coatings. Differential thermal analysis of cobalt containing coatings revealed an exothermic reaction at approximately 880°C. This exothermic reaction may be related to the transformation of the amorphous phase to eta phases. On the contrary, DTA analysis of feedstock powders of these coatings showed an endothermic reaction at approximately 1000°C. DTA analyses of nickel containing cermets also showed similar results. Differential thermal analysis of chromium containing cermets did not show any noticeable exothermic or endothermic reactions.
Authors: Kazuyuki Hokamoto, Yasuhiro Ujimoto, Shunsuke Tanaka, Masahiro Fujita
Authors: Young Kook Kim, Kazuyuki Hokamoto, Shigeru Itoh
Abstract: A shock compaction method using an underwater shockwave is used to consolidate the Cu/graphite and Ni/graphite composites. The copper powder (particle size < 45 m) and nickel powder (particle size < 150 m) were respectively mixed with the graphite powder (particle size < 45 m, purity 99.9%). The propagation phenomenon of underwater shock wave is studied by means of numerical analysis (LS-DYNA 3D) in terms of the magnitude and distribution of shock pressure impinged on the powder surface. The shock pressure of underwater shock wave obtained from shock compaction device is approximately 16 GPa. To make a big size material (ø30mm), we changed the inner size of powder container from ø10 mm to ø30 mm. We confirmed that the consolidation possibility of the big size composite materials (Cu/graphite, Ni/graphite) by the shock compaction method using underwater shock wave.
Authors: Kazuhito Fujiwara, Tetsuyuki Hiroe, Yasuhide Ohno, Kazuyuki Hokamoto, Tatsuya Nakao
Authors: Kazuyuki Hokamoto, Krishnamorthy Raghukandan, J.S. Lee, Masahiro Fujita, Ryuichi Tomoshige
Authors: M. Ahasan Habib, Li Qun Ruan, Ryuji Kimura, P. Manikandan, Kazuyuki Hokamoto
Abstract: The wide use of clad joints in practical application has been inhibited due to the difficulty in welding certain combinations such as tungsten/-copper, molybdenum/-copper and magnesium with aluminum, titanium and stainless steel. These material combinations are generally classified as difficult to weld by conventional material joining techniques due to the vast difference in material properties and the degradation of mechanical properties of the joints. Explosive welding is here a viable alternative technique. Explosive welding is a solid-phase welding process that uses the energy of a detonating explosive to create a strong metallurgical bond. This technique has achieved impressive success in the joining of metallurgically incompatible combinations that are otherwise impossible to join by conventional welding techniques. Though the technique is suitable for joining only thin plates, it is efficient in joining some difficult to join combinations like magnesium with aluminum, titanium and stainless steel. In this paper, the result of welding titanium and magnesium was reported.
Authors: Akio Kira, Kazuyuki Hokamoto, Yasuhiro Ujimoto, Shoichiro Kai, Masahiro Fujita
Abstract: A new method has been developed to generate an extremely high impulsive pressure by using a metal jet that is discharged when a metal collides with another metal. The high pressure is used to synthesize a new material. When a metal plate was accelerated by the detonation of an explosive, it collides with the concentric circle of the conic surface of a conical concave metal block metal jets are discharged from all parts on the concentric circle. The metal jets fly toward the center while converging and collide with each other at the central axis. Because those collide at high-speed pressure becomes extremely high. The flight direction of the converged metal jet changes downward. The metal jet collides with the bottom of the block. A large hole is formed inside the bottom. The formation process of the hole was examined by the observation of the section of the block. A specimen powder that was rubbed to the conic surface is discharged with the metal jet and become the high pressure. The specimen powder is synthesized to a different material. The synthesized material is held inside the formed hole. The existence of cBN was confirmed by the X-ray diffraction of the synthesized material, in the case that BN was used as the specimen powder. Similarly, the existence of diamond was confirmed in the case of graphite powder.
Authors: H. Eskandari, Kazuyuki Hokamoto, H.M. Ghasemi, M. Emamy, S. Borji, Jung Suk Lee
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