Kazuyuki Hokamoto

New explosive welding technique to weld

Various aluminum alloys and stainless steel were explosively welded using a thin stainless steel intermediate plate inserted between the aluminum alloy driver and stainless steel base plates. At first, the velocity change of the driver plate with flying distance is calculated using finite- difference analysis. Since the kinetic energy lost by collision affects the amount of the fused layer generated at the interface between the aluminum alloy and stainless steel, the use of a thin stainless steel intermediate plate is effective for decreasing the energy dissipated by the collision. The interfacial zone at the welded interface is composed of a fine eutectic structure of aluminum and Fe4Al13, and the explosive welding process of this metal combination proceeds mainly by intensive deformation of the aluminum alloy. The weldable region for various aluminum alloys is decided by the change in collision velocity and kinetic energy lost by collision, and the weldable region is decreased with the increase in the strength of the aluminum alloy.

A new method for explosive welding of Al/ZrO2 joint using regulated underwater shock wave

Abstract Thin aluminium plate was welded onto a zirconia ceramic by the use of a newly developed explosive welding technique. A 0.1 mm-thick aluminium plate was accelerated about 800 m s −1 by regulated underwater shock wave and collided with a zirconia plate at a certain collision angle under moderate conditions for explosive welding. The use of a stainless steel cover plate above an aluminium plate and the use of ceramic block next to the ceramic to be welded, were effective in eliminating cracks generated in the ceramic. The use of a ceramic container made from epoxy resin mixed with steel powders was also useful in crack reducton. No separation at the bonded interface was observed at the fracture surface obtained through a bending test in a sample fabricated under moderate conditions.

Optimization of the experimental conditions for high-temperature shock consolidation

The high-temperature shock consolidation technique using converging underwater shock wave assembly has been developed and the experimental conditions in obtaining well-consolidated bulk materials are discussed. A series of experiments are conducted for various difficult-to-consolidate powders by changing the temperature up to 1100°C and the shock pressure up to about 50 GPa. Amount of cracks normally generated under room-temperature experiments could be decreased by using the high-temperature technique proposed here. The result is brought by the following reasons; (1) decreased shock pressure, (2) increased ductility and (3) enhanced surface melting of the powders. The pressure required for the consolidation is strongly related to the hardness of the used powders. The application of high temperature could decrease the hardness, and subsequently decrease the pressure required for the consolidation. Optimization of the conditions necessary for the consolidation and bonding are discussed.

High temperature shock consolidation of hard ceramic powders

Abstract High-temperature shoch consolidation of hard ceramic powders was used as a means to improve bonding between powders and to decrease the number of cracks generated in the consolidated sample. A converging underwater shock-wave assembly was used for the compaction, and TiB 2 , c-BN and their mixed powders were consolidated at various conditions up to 850°C. The positive effects by heating the powders were confirmed by the experiments conducted.

The synthesis of bulk material through explosive compaction for making intermetallic compound Ti5Si3 and its composites

The possibility of synthesizing Ti5Si3 from mixed elemental powders and the fabrication of its composites by explosive compaction is discussed. A new technique using underwater shock waves was developed and it was found to exercise better control over the influencing parameters. Two processes were employed viz., (1) direct shock-induced reaction and (2) explosive compaction followed by heat treatment. The methodology to produce bulk material by the above two processes are reported. Ti5Si3 intermetallic synthesized by the two processes reveals high hardness than commercially available Ti5Si3.

Optimization of process parameters in explosive cladding of mild steel and aluminum

Explosive cladding is best known for its capability to join a wide variety of both similar and dissimilar combinations of metals that cannot be joined by other conventional metal joining techniques. An attempt has been made to optimize, the tensile and shear strengths of an explosive clad interface using fuzzy logic and genetic algorithm. The parameters considered for this study include flyer plate thickness, loading ratio, angle of inclination, and stand off distance. The experimental data was trained and simulated using fuzzy logic and the optimization of process parameters was performed using genetic algorithm. The optimized process parameters were validated using experimental results.

An improved high-temperature shock compression and recovery system using underwater shock wave for dynamic compaction of powders

Abstract A high-temperature shock compression system using converging underwater shock waves has been developed and the performance is under attempted improvement in the present investigation. A maximum temperature of 1100°C was obtained, and the use of PBX explosive with detonation velocity of 8.5 km s−1 gave us the higher shock pressure. Also, scaling up the size of the experimental apparatus especially in the size of explosive made possible an increase in the duration of shock pressure. Small fragments of consolidated diamond powders were recovered due to difficulty of recovery of the new system, but the sample showed very high Vickers hardness above 60 GPa.

Microstructural characteristics of 2124 Al – 40 vol.% SiCp metal matrix composites produced by room temperature shock consolidation and hot shock consolidation

Abstract2124 Al – 40 vol.% SiCp metal matrix composites have been consolidated by room temperature shock consolidation using axisymmetric assembly, and by one-dimensional hot shock consolidation using underwater shock wave assembly. Trimonite powder explosive was used in room temperature consolidation and SEP explosive was used in hot shock consolidation. The thickness of the explosive layer used in room temperature consolidation was 27 mm. The thickness of the water layer employed in the hot consolidation experiments was 15 mm. The hot shock consolidation was carried out at 200°C, 300°C and 400°C. The microstructural variations across the cross section of the room temperature shock consolidated compact and, the effect of the temperature on microstructure and hardness of the hot consolidated composites have been investigated. Microstructural comparison was made between the composites produced by both room temperature consolidation and hot consolidation.

Shock Compaction of Bulk Nanocomposite Magnetic Materials

Dynamic shock compaction offers the potential of fabricating bulk nanocrystalline functional materials via consolidation of amorphous or nanocrystalline alloy powders, while retaining the metastable structure and/or nanograin size of starting powders. In this work, gas-gun impact, double-tube explosion and underwater explosion techniques were utilized to consolidate exchange-coupled R2Fe14B/α-Fe (R=Nd, Pr) hard/soft phase nanocomposite powders. Design of the consolidation fixtures, densification conditions, and starting powder properties allowed control of the final density and the nanoscale structure of the hard/soft magnetic phases in the recovered shock-compacted samples. Highly dense compacts (~99% of full density) were obtained under optimized shock consolidation conditions. Transmission electron microscopy observations revealed complete retention of the nanostructure, which was within 15-25 nm in the final shock-compacted composite magnets. Retention of the nano-scale structure in the shock consolidated compacts ensured exchange coupling between the hard and soft phases, resulting in optimal magnetic properties. In this paper, the unique attributes of the shock-densification process in forming and retaining the nanocrystalline structure, and therefore leading to improved magnetic properties will be described.

An investigation on underwater explosive bonding process

In this paper, we propose a new explosive bonding method for bonding materials by using the underwater shock wave from the explosion of explosives in water. This method is especially suitable to bond the materials with thin thickness and largely dissimilar property. In bonding those materials, the shock pressure and the moving velocity of shock wave on the flyer plate should be precisely managed to achieve an optimum bonding conditions. In this method, the bonding conditions can be controlled by varying of the space distance between the explosive and the flyer plate or by inclining the explosive charge with the flyer plate. We made the experiment of this technique bond the amorphous film with the steel plate. A satisfactory result was gained. At the same time, numerical analysis was performed to investigate the bonding conditions. The calculated deformation of the flyer plate by the action of underwater shock wave was compared with the experimental recordings by high-speed camera under the same conditions. The comparison shows that the numerical analysis is of good reliability on the prediction of the experimental result. Furthermore, the numerical simulation also gives the deformations of the flyer and the base plate, and the pressure and its variation during the collision process.