Masahiro Fujita

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.

Single-shot explosive welding technique for the fabrication of multilayered metal base composites: effect of welding parameters leading to optimum bonding condition

Abstract Multilayered metal base composites, mainly reinforced with steel sheets, were fabricated using the single-shot explosive welding technique. Plate velocity change during the collision of multilayered plates within small stand-off distances were analyzed using a one-dimensional finite-difference calculation, and the explosive welding parameters required for good bonding were investigated. Wavy interfaces, which suggest good bonding, were found in the case where properties, such as density, strength and melting point, of the bonded materials were not so different, but excess melting, poor bonding and planar interfacial structure were observed when the properties of the materials used were considerably different. In the case where properties of the materials were fairly different, the weldable condition for good bonding was restricted. In this investigation, the way to regulate the explosive welding parameters for good bonding and the welding mechanisms were discussed, and the mechanical properties of the composites measured by tensile tests were investigated based on the rule of mixtures.

Underwater explosion of spherical explosives

Abstract Underwater explosion of high explosive generates underwater shock waves. This phenomenon has been observed by optical measurement. Propagation histories of underwater shock waves in the range close to explosive have been obtained by processing photographs. In order to obtain pressure distributions of these shock waves, the non-linear curve fitting technique was applied to these histories. Underwater explosions have been simulated by an arbitrary Lagrangian–Eulerian (ALE) method and calculated results agree well with experimental results in both propagation histories and pressure distributions. Therefore, pressure histories can be determined by numerical simulation.

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.

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.

Development of high-temperature shock compression system for consolidating powders by the use of underwater shock-wave assembly

Abstract A new system for high-temperature shock consolidation was developed using a converging underwater shock-wave assembly. The possibilities and difficulties in designing the high-temperature experimental system are pointed out, and the performance of the system is evaluated by some experiments.

Non-ideal detonation of emulsion explosives

Abstract In order to obtain a better understanding of the underwater explosion phenomena related to emulsion explosives, optical measurements using the water tank technique and cylinder expansion test were carried out. Streak photographs were taken using an image converter camera with a usual shadow graph system. Four kinds of emulsion explosives differing in aluminium contents were used in the experiments. These emulsion explosives were placed into copper and PMMA pipes. From the results obtained with the water tank technique, it is recognized that the maximum velocity of underwater shock wave in the case of a copper pipe is about 10% faster than that in the case of a PMMA pipe. From the cylinder expansion test, it is found that the degree of radial displacement of a copper case (Uexp) increases with increased aluminium content and that in the range of more than 10 wt.%, Uexp decreases with increased aluminium content.

The effect of shock pressure on the mechanical properties of some b.c.c. metals

Abstract This paper firstly presents the effect of carbon content (0.06–0.85 wt.%C) on the mechanical properties of steels exposed to weak shock pressure and the effect of grain size (9–80 μm) on the mechanical properties of 0.06 wt.%C steel with the shock pressure treatment. Secondly, the effect of shock pressure on the tensile properties including the ductile-to-brittle transition behavior for sintered chromium (99.8 mass% purity) is investigated. The experimental results confirm that the mechanical properties of some b.c.c. metals are markedly influenced by the shock pressure treatment.