T. Kino

Effect of hydrogen on the formation of interstitial loops in hydrogen-irradiated aluminum

Abstract The role of hydrogen atoms in the formation of interstitial type dislocation loops in aluminum irradiated with 15 keV hydrogen ions was investigated by electron microscopy. It was found that the loop density satisfied and Arrhenius relation with the pre-irradiation temperature, yielding an apparent activation energy of about 0.3 eV. Experimental results are interpreted in terms of the mechanism that small hydrogen-vacancy complexes formed by the pre-irradiation of hydrogen ions act as nucleation sites of dislocation loops in the subsequent electron irradiation. A basically identical mechanism seems to be acting in the irradiation with hydrogen ions at room temperature.

Preparation Method of High Purity Aluminum Single Crystals with Low Dislocation Density

The preparation method of high purity aluminum single crystal with low dislocation density has been investigated.The single crystals with dislocation dislocation density 5×102/cm2 have been obtained by the strain-anneal technique using the cooling rate changing method under vacuum. The densities and the Burgers vectors of dislocations were examined by X-ray projection topographs. The temperature range to be cooled very slowly has been determined by calculating the excess vacancy concentration and supersaturation in the specimens. The most optimum condition to obtain single crystals with low dislocation densities is obtained, if the specimens are cooled very slowly between 400°C and 150°C.

In-situ observation of the dynamic behavior of bubbles in aluminum during 10 keV H2+ ion irradiation and successive annealing

The behavior of bubbles in aluminum during 10 keV H2+ ion irradiation and successive annealing was investigated by in-situ observation in an electron microscope. Bubbles were formed by irradiation at 300 K, but no bubbles were observed at 113 and 373 K. After irradiation at 113 K, bubbles were found to be formed during annealing from 113 to 300 K. During annealing from 300 to 498 K, smaller bubbles began to shrink and disappear at a lower temperature in comparison with larger bubbles. From these experiments, the activation energy for bubble shrinkage was found to be about 1 eV, and the binding energy of a vacancy to a bubble was inferred to be about 0.4 eV.

In-situ observation of the migration and growth of helium bubbles in aluminum

Abstract Brownian motion of helium bubbles, their disappearance, and coalescence in high purity aluminum were demonstrated in real time by electron microscopy and the recording of these whole processes on VTR. It was experimentally established for the first time that the mean square of the migration distance of the bubble during the time duration, t , is proportional to t at least for t ≥ 1 min. The growth of the bubble was caused by the coalescence between bubbles during Brownian motion and also by annealing at higher temperature unless the coalescence takes place. A dependence of the diffusivity of the bubble on its diameter and a rapid formation of new bubble by the coalescence of two bubbles seem to be supported through the surface diffusion of aluminum on the bubble surface.

Conversion of hydrogen bubbles to disk-shaped defects in hydrogen irradiated aluminum

Abstract Electron microscopy was carried out on hydrogen bubbles in high purity aluminum. It was found for the first time that small hydrogen bubbles formed by irradiation with 15 keV hydrogen ions at 423 K converted to disk-shaped defects by annealing at higher temperature, depending on the initial concentration of bubbles. The many beam lattice image of the defects suggested that they mostly lay over multiple layers of (111) planes, containing characteristic distortions of the lattice on (111) planes. The formation of the disk-shaped defects is interpreted in terms of small hydrogen bubble coalescence during a random migration and collapse on (111) planes, losing their internal pressure, which may be allowed by the formation of aluminum hydride at high temperature.

Effects of solute atoms on the evolution of structural damage in ion irradiated high-purity aluminum alloys

Abstract The evolution of structural damage during 10 keV He ion irradiation and after annealing was examined by in situ observation in an electron microscope, on zone refined aluminum and the alloys doped with 0.1 at% Li, Mg, Si, and Zn. The evolution process depends on the irradiation temperature, ion flux and the solution atom. The main results are summarized as follows: (1) A dislocation loops are formed in the initial stage of irradiation at temperatures below 423 K, but it is not in irradiation at temperatures above 423 K. (2) Bubble formation is retarded by the formation of dislocation loops. (3) Solute effect is most marked at the initial stage of irradiation and in irradiation with low ion flux.

Atomic-resolution images of structural defects on microcrystalline graphite

Abstract Microcrystalline graphites (glassy carbon as a trade name) are polished with emery paper in the diffusion pump oil, cleaned ultrasonically and coated by silicon grease without exposing in air. The sample surface is observed using a scanning tunneling microscope (STM). Atomic-resolution images are obtained including structural defects such as misoriented atomic arrays, vacant lattice sites and extra atomic rows. When the ultrasonic cleaning time is longer, bubble-like and amorphous-like structures are revealed.

Evolution of structural damage in aluminum alloys irradiated with helium ions

Abstract Microstructural evolution in pure Al and alloys during He+ ion irradiation and subsequent annealing was examined by in situ observations. Irradiation was performed over a wide temperature range from 17 to 473 K with fluxes of 3 × 1017 and 6 × 1016 m−2 s−1. In pure Al and alloys irradiated at lowtemperature and subsequently annealed, the number density of interstitial loops and bubbles is higher for a higher ion flux. For high temperature irradiation, the corresponding densities are higher at a lower flux irradiation. Also, the density of bubbles depends largely on the irradiation temperature for high flux irradiation of pure Al and alloys doped with 0.1 at.% Si or Mg.

In-situ observation of structural changes in aluminum during He+ and H2+ dual-ion beam irradiation

Abstract The dual-ion beam irradiation facility at JAERI, which allows in-situ observation, was used to investigate the main factors influencing bubble formation in aluminum. Irradiation employed both (1) single ion beam irradiations with He+ and H2+ and (2) simultaneous He+ and H2+ ion irradiations at room temperature. It was found that both vacancy production rate and gas atom injection rate were important in determining the bubble nucleation, number density and sizes.

Improved High-Temperature X-Ray Lang Camera

A high-temperature X-ray Lang camera which has very slow translational speed without multiscanning is designed to observe slowly changing phenomena using a conventional X-ray source. A single-scanned topograph of a nearly perfect aluminum crystal taken by this camera indicates an annihilation profile of interstitial-type dislocation loops grown as vacancy sources due to a temperature rise.