Ryuichi Tomoshige

Effect on addition of titanium diboride to titanium carbide produced by the SHS/shock consolidation method

Abstract Preparation of TiC compacts and TiC/TiB2 composites with high density was attempted by the SHS shock consolidation method. Titanium, activated charcoal and boron carbide powders were used as raw materials. Density and hardness values of the TiC compacts obtained increased with increasing the C/Ti molar ratio. The maximum values of the density and the hardness were 4.72 Mg m−3 and ∼31.5 GPa, respectively. However, TiC/TiB2 composites tended to decrease the density and the hardness as increasing TiB2 content.

High-temperature-shock compaction of ceramics/silicide composites produced by combustion synthesis

Abstract Preparation of TiC/Ti–Si composites with high density was carried out by combining self-propagating high temperature synthesis (SHS) with the underwater-shock consolidation technique. For preparing the composites, three kinds of powders (titanium, graphite and silicon) were ball-milled in the molar ratio of Ti:Si:graphite=1:1:1 to 5:1:1. The SHS reaction was initiated by passing an electric current through a tungsten coil, after which an explosive charge was detonated. The detonation wave proceeded into the water was used for densification of the synthesized, porous Ti–Si–C system composites, which were under high temperature due to the exothermic nature of the SHS reaction. As a result, three kinds of silicides (TiSi 2 , Ti 5 Si 3 and Ti 5 Si 4 ) and two kinds of ceramics (TiC and SiC) were detected by XRD. The densities and micro Vickers hardnesses of the shock compacts decreased with increasing silicon content. Microstructural observations revealed that the interaction between TiC and Ti 5 Si 3 grains affected the inhibition of grain growth.

Study of Phase Transformations in Heat Treatment of HVOF Thermally Sprayed WC–17Co Coating

In this work, WC-17Co powder was thermally sprayed onto mild steel using HVOF spray technique. The coated specimen was heat treated at 1100°C in a vacuum chamber and was then studied by using transmission electron microscopy (TEM). Post heat treatment resulted in recrystallization of the amorphous phase, formed during thermal spraying, into low carbon eta phase like Co6W6C. TEM results of the heat treated specimens showed that these new nucleated eta phases had very clear crystallographic structure without any crystalline defects. Heat treatment could also transform high carbon carbides like WC and W2C in the as sprayed samples to high carbon eta phases like Co3W3C. High density of dislocations and staking faults noticed in TEM of these phases might be an indication of possible shear mechanism in formation of these carbides.

Phase Transformation of Powdered Material by Using Metal Jet

The various techniques of phase transformation of the material have been proposed by many researchers. We have developed several devices to generate the ultrahigh pressure by using high explosive. One of them uses metal jets. It is expected that the ultrahigh pressure occurs by the head-on collision between metal jets, because the velocity of the metal jet is very high. By mixing a powdered material with metal jets, the pressure of the material becomes high. The purpose of this study is to transform the phase of the powdered material by using this high pressure. The powders of the graphite and hBN were applied. The synthesis to the diamond and cBN was confirmed by X-ray diffraction (XRD). In this paper, the mechanism of the generation of the ultrahigh pressure is explained and the results of the observation of the powder by using scanning transmission electron microscope (STEM) are reported.

Generation of Ultrahigh Pressure and Application of Ultrahigh Pressure to Formation of Diamond from Graphite Powder

The purpose of our research is to generate the ultrahigh pressure by using high explosive and to transform a phase of a material. The extremely high impulsive pressure generator that has been developed by us uses the head-on collision between metal jets. Because the velocity of the metal jet is very high, the ultrahigh pressure will generate. If a powdered material is mixed to metal jets, it is expected that the material is transformed to a high pressure phase by this ultrahigh pressure. A graphite powder was used to synthesize a diamond. The existence of the diamond was confirmed by X-ray diffraction (XRD). In this paper, the mechanism of the generation of the ultrahigh pressure is explained and the results of the observation of the powder by using scanning transmission electron microscope (STEM) are reported.

Interfacial Microstructure of Titanium Nitride – Titanium Diboride Composite Synthesized by Hot Shock Compaction

Interfacial microstructure of TiN-TiB2 composite, which was synthesized by hot shock compaction combined explosively shock condolidation and self-propagating high-temperature synthesis, was investigated by transmission electron microscopy (TEM). In the TiN-TiB2 composite included 60mol% TiN, an experimentally measured average grain size of the both TiN and TiB2 was approximately 500nm, and it decreased rather than those of the raw powders. By the conventional TEM observations, we clarified that there was a specific orientation relationship between cubic TiN and hexagonal TiB2. The high resolution electron microscopy (HREM) observations revealed that the TiN/TiB2 interphase boudnaries were atomically flat. We also observed grain boundaries of the composite and found that no secondary phases such as amorphous phase and precipitates were observed at the grain boundaries in the composite.

Advanced Materials Synthesis and Microstructural Characterization Using Explosive at Sojo University

In the research center for advances in impact engineering established in Sojo university, advanced materials have been synthesized by using shock wave and their microstructure has been investigated. An extremely high shock pressure and a dynamic hot compaction technique were developed, and the synthesis of the advanced materials and composites was succeeded. Transmission electron microscopy observations revealed unique microstructures of such materials obtained by our original advanced technique.

Evacuation Effect on Products during Underwater Shock Compaction

Underwater-shock powder compaction on mixture of titanium and aluminum was performed under vacuum or atmospheric pressure. The mixture was held at intervals of 1 to 6 cm from bottom of powder container. Since the mixture was subject to high pressure induced by detonation of explosive, it was launched toward the bottom of container intensively. As a result, consolidated mixtures indicated hard formation of compounds, except for upper area of powder compacts. However, the powder compact consolidated under vacuum, which showed about 93% of theoretical density, indicated high density as that obtained under non-vacuume atmosphere. It was found that evacuation of air from interparticle regions affected the powder compacts. There is little fluctuation in-plane Vickers hardness in the compacts, except for upper region of the product in which Ti-Al intermetallic compound was formed. This means that homogeneous materials could be obtained generally.

Optical Observation of Extremely High Impulsive Pressure Generator Using Collision of High Velocity Metal Jets

A method to generate an extremely high impulsive pressure using a converging metal jet, has been developed as a purpose to achieve the high pressure above 1 TPa. The metal jet is discharged from the collision point, when a metal plate is accelerated by the detonation of an explosive and it collides with a conical concave metal block. The metal jet discharged on the concentric circle of the conical concave fly toward the center while converging and collide on the central axis, and the collided metal jets exhibit the extremely high pressure. In the present investigation, framing photographs were taken using an image converter camera to investigate the phenomenon occurred in the generator. The photographs show that the metal jets are discharged from the collision points between the metal flyer plate and conical concave block, and then, collided at the central axis. The maximum pressure obtained under vacuum was estimated about 0.83 TPa from the velocity calculated from the photographs, and the results were slightly lower than that evaluated theoretically.