Masakazu Uchino

Yield properties, phase transition, and equation of state of aluminum nitride (AlN) under shock compression up to 150 GPa

Inclined-mirror Hugoniot measurements were performed on pure AlN polycrystals in the pressure range up to 150 GPa to study the yield properties, phase transition, and equation of state. The Hugoniot-elastic limit (HEL) stress was approximately 9.4 GPa. Above the HEL, the Hugoniot data converged to a static compression curve despite the high thermal conductivity, which indicated that the thermal property is not an important factor in determining the shock yield property. The phase transformation from wurtzite-type (B4) to rock salt-type (B1) structure took place at approximately 19.4 GPa, and was completed by about 75 GPa. The corrected transition pressure at 298 K was 19.2 GPa. Shock velocity (Us) versus particle velocity (Up) relation of the final phase was given by Us=3.27+1.81Up km/s. The Birch–Murnaghan fitting curve of the calculated isothermal compression curve of the B1-type phase roughly coincided with the recent static x-ray diffraction data up to over 100 GPa. The Gruneisen parameter, bulk modul...

Shock compression behaviors of boron carbide (B4C)

Hugoniot measurements on the highly dense, pure B4C polycrystal were performed by the inclined-mirror method to study the elastoplastic transition and to search phase transition. In inclined-mirror streak photographs, the smoothly jagged structure was observed at the free-surface shape in the plastic region. The Hugoniot-elastic limit (HEL) has been determined to be approximately 19.5GPa. In the plastic region, a kink was observed at a particle velocity of around 1.26km∕s. The shock velocity (US)–particle velocity (UP) Hugoniot relations in the plastic region were given by US=3.7+5.4UPkm∕s in the Up range of 0.54–1.26km∕s and US=9.61+0.73UPkm∕s in the Up range of 1.26–4.3km∕s. The S value (0.73) in US=C0+SUP above UP=1.26km∕s is significantly small compared with the result of Vogler et al. [J. Appl. Phys. 95, 4173 (2004)], and was much smaller than those of many oxides and nitrides. This material behaved as an elastoisotropic solid above the HEL and showed a large and linear change in the pressure-density...

Heterogeneous free-surface profile of B4C polycrystal under shock compression

Observations of the free-surface behavior under shock compression by the gapped-flat mirror method were performed on B4C and Si3N4 ceramics to study their shock-yielding properties. Jagged profiles of the moving free-surface in the plastic region, with a special scale of about one mm and a maximum local displacement of a few 10s of μm, were observed for B4C polycrystals. Similar profiles for Si3N4 polycrystals were smooth. Such profiles for B4C polycrystals were also observed in the elastic region. It is suggested that these observations reflect the heterogeneous nature of shock compression in solids, and further indicate that a macroscopic slip system plays an important role in the elastoplastic transition of B4C material under shock compression and decompression.

High-time-resolution streak photographic system equipped with propellant guns for Hugoniot measurement of solids

The high-time-resolution streak photographic system equipped with a powder gun and a two-stage light gas gun has been constructed for the Hugoniot measurement of solids at pressures up to >300 GPa. For this system, a compact rotating-mirror-type streak camera and a long-pulsed dye laser with no Q-switch were produced. A time resolution higher than 1 ns was achieved by using a 2-µm-wide slit of the camera formed using the laser. The shock velocity and particle velocity of steady shock waves of the materials with a shock velocity of ~6 km/s can be measured by the inclined-mirror method with the basic errors of 0.2 and 0.1–0.2%, and 0.2 and 0.35–0.45% for symmetrical and asymmetrical impact, respectively, depending on shock velocity and impact velocity.

Long‐pulsed Nd:YAG frequency‐doubled laser for optical measurements of high‐velocity phenomena

A long‐pulsed neodymium‐doped yttrium aluminum garnet (Nd:YAG) frequency‐doubled laser with no Q‐switch was constructed for optical measurements of high‐velocity phenomena. The laser consists of a doubled‐elliptical pump cavity with a Nd:YAG rod and two xenon flash lamps, an intracavity potassium titanyl phosphate crystal, and a high‐voltage electrical‐pulse source. A narrow‐band‐stimulated emission at the frequency‐doubled 532‐nm wavelength was confirmed by a spectrometer. The delay time from a trigger signal and the effective pulse duration were approximately 40 and 65 μs, respectively. The laser average output power was measured to be larger than 6 kW by a pyroelectric joulemeter. This laser may be used as a flash monowavelength light source, and also as a long‐pulsed single‐mode laser in the visible wavelength region using for example, an intracavity etalon and/or a brewster plate.