Kazuki Hiro

Stagnations of increasing trends in negative pressure with repeated cavitation in water/metal Berthelot tubes as a result of mechanical sealing

To investigate effects of mechanical sealing on negative pressures in water/metal tube Berthelot systems, trends in negative pressure are observed through runs of temperature cycles below 90°C in two systems made of metals having small amounts of gas inclusions. The first system is a pre-degassed all-stainless-steel tube/plug system. The steel is a special product for vacuum engineering. The second is the same tube sealed with plugs made of silver solidified one-dimensionally in a vacuum furnace. A new type of trend, stagnation for intermediate cycles is found in both systems so long as sealing distortion of each plug is small in amount. The stagnation period for the first system is longer than that for the second one. A metallurgical mechanism of a gas-being-replenished crevice model is proposed: distorted parts of metals undergo heat-treatment during runs of temperature cycles, and the heat-treatment enhances the rates of impurity gas transports to crevices on the metal surface where cavitation occurs, and the transport causes the stagnation for cycles during which the rates are still high.

Effects of gas transports in metals on negative pressures in water in Mo/Cu Berthelot tubes

Two series of trends in negative pressure with cavitation in water were observed by the Berthelot method using single- and poly-crystalline molybdenum tubes sealed with single-crystalline copper plugs by repeating runs of temperature cycles at rates of 70-100 cycles/day between 50 and 98 °C, where a run means successive cycles with the same water. The first series were observed while both tubes and plugs were pre-degassed, and the second after exposure of the both tubes alone to N2 gas. The all-single-crystalline-metal tube in the pre-degassed state yielded a steady increase from -120 to -140 bar (1 bar0.1 MPa) in the initial 1250 cycles. After its gas exposure the single-crystalline tube yielded a trend having an initial peak of -160 bar followed by a steady fall to -110 bar in the first run, and recovered the capability of yielding a trend levelling around -165 bar throughout the sixth run after a total of about 5000 cycles. In any run cavitation occurred within about ±12 bar around the current average. In contrast, the poly-crystalline Mo tube in the pre-degassed state yielded widely-scattered negative pressures; the higher envelope increased gradually to -140 bar while lower envelope remained to be about -40 bar in the second run to a total of initial 4000 cycles. After similar gas exposure of the tube alone, the deteriorated capability of the poly-crystalline tube was recovered only to -120 bar after a total of 1.2×104 cycles. The results form qualitative evidence of the crucial effects of impurity gas transport in metal bulks on trends in negative pressures of water in metal tubes. The thermodynamic and metallurgical causes of the time consumption for achieving high negative pressure in liquid/metal Berthelot tube systems are discussed.

Temperatures of maximum density in a pressure range from 15 MPa to −15 MPa generated for water in a metal Berthelot tube

Water exhibits anomalous thermodynamic properties. For example, the specific heat capacity of water is at minimum at 36°C under atmospheric pressure. In order to investigate phase diagrams including thermodynamic meta-stable states, which are important to elucidate the anomalies, the temperatures of maximum density (TMDs) were estimated in a pressure range from +15 MPa to −15 MPa on the basis of data of temperatures and pressures measured for various densities of water in a metal Berthelot tube. The TMDs in the negative pressure region were not on an extrapolation of an equation of state for water. The trend was similar to that not observed by a Berthelot method of glass spiral capillaries but calculated from molecular dynamics computer simulations.

Phase Diagram of Thermotropic Liquid Crystal Including Negative Pressure Region Generated in Metal Berthelot Tube

Phase diagrams including absolute negative pressure regions of thermotropic liquid crystals give useful information on science and technology. A phase diagram was depicted for ca. 40mg of a thermotropic liquid crystal in a pressure vs. temperature (P-T) plane by the Berthelot method using a metal tube. N-I phase transitions occurred even under-10MPa, and a polymorphism of the crystalline phase was observed.

Cutting Performance of Turning Insert with Three-Arcs-Shaped Finishing Edge

In the turning of a shaft with a step of specified corner R, it is important whether the corner radiuses of the turning insert is the same as the specified corner R or lower than it. A turning tool with a large corner radius cannot adapt to cutting a shaft with a step of specified corner R. In this study, the surface roughness, cutting force, and tool wear were experimentally investigated in order to clarify the cutting performance of the turning insert with a three-arcs-shaped finishing edge. The machined surface of the insert with a three-arcs-shaped finishing edge was better than that of the normal insert. The wear progress of the insert with an arc-shaped finishing edge was slightly slower than that of the normal insert. The cutting force of the insert with an arc-shaped finishing edge was almost the same as that of the normal insert.

Observation of Supersonic Jet Using Small Volume High-Pressure Shock Tube

The unsteady supersonic jet and the shock wave injected by the small volume shock tube are experimentally studied in this paper. The experimental was performed by the background oriented schlieren method. The main parameters for the jet are the pressure ratio by the high pressure chamber/ a back pressure 10.9-53.0 and the length of high pressure chamber/diameter ratio 1 and 10. The velocity of the shock wave and supersonic jet were estimated by using the principle of the background oriented schlieren method. The results showed that the influence of the length of the high pressure chamber on the velocity of the jet.

Properties of TaN Coating Film Deposited on WC-Co-Based Cemented Carbide Using Magnetron Sputter Ion Plating

Various methods of surface modification technology are available for yielding high function characteristics such as wear-resistance, lower or higher friction coefficient, corrosion-resistance and thermal-resistance on the surface of the material. Generally, the coating of a hard material like ceramic on the surface of a material is a popular surface modification technology. The physical vapor deposition (PVD) method, which is one of the coating technologies, is widely used because it can be coated at a lower treatment temperature of 470K – 870K. In cutting, e.g. turning, milling, drilling and tapping, coated cemented carbide tools, which have good fracture toughness and wear resistance, seem to be effective tool materials. In this case, the titanium based films (e.g. TiN, Ti(C,N), (Ti,Al)N) are generally used as the coating film. However, the tantalum based films (e.g. TaN, TaC) are not applied as the coating film for cutting tools because the melting point of TaC is higher than that of TiC. Moreover, it is unclear whether TaN coating film can be used as a coating film of WC-Co cemented carbide cutting tools. In this study, to clarify the effectiveness of tantalum (TaN) coating film, we measured the thickness, hardness and scratch strength (critical load measured by scratch tester) of TaN coating film formed on the surface of the substrate which was a cemented carbide ISO K10 by the magnetron sputter ion plating process. The hardened steel ASTM D2 (JIS SKD11) was turned with the TaN and the (Ti,Al)N coated cemented carbide tools. The tool wear of the TaN coated cemented carbide tool was experimentally investigated and compared with that of the (Ti,Al)N coated tool. The following results were obtained: (1) Droplets on the surface of the TaN coating film, which has the K10 substrate, were negligible. (2) The micro-hardness of TaN coating film 2510HV was higher than that of TiN coating film 2090HV, and there was little difference in hardness between the TaN 2510HV and (Ti,Al)N 2710HV. (3) The critical scratch load of TaN coating film over 130N was higher than that of TiN coating film 68N or (Ti,Al)N coating film 73N. (4) In cutting the hardened steel using TaN and (Ti,Al)N coated tools, the wear progress of the TaN coated carbide tool was almost equivalent to that of the (Ti,Al)N coated carbide tool. The above results clarify that the TaN coating film, which is a new type of coating film, has both high hardness and good adhesive strength, and can be used as a coating film of WC-Co cemented carbide cutting tools.

Limitations on achieving negative pressures for water in a Berthelot tube as a result of metallic corrosion

We inserted pieces of metal foils (Al and Au) into a metal Berthelot tube together with water or xylene to investigate whether corrosion of metals limits the achievement of negative pressure. For the test using Al foil with water, the negative pressure rose to -30 bar but diminished almost to zero after 250 cycles, whereas those for all the others increased with the number of temperature cycles. Corrosive reaction of Al with water yielded H2 gas and the resulting increase in the gas concentration in the water enhanced the nucleation probability of cavitation, not on the metal surface but in the solution. In order to attain high negative pressures for water in a metal tube, we should take into account a possible restriction of this achievement of negative pressure by corrosion of metals in contact with water, even though the metals used were well de-gassed beforehand.