Initial Breakdown Process Research Articles

Evolution of texture in Alloy 80A during initial ingot breakdown

Abstract This paper presents details on the evolution of texture in Alloy 80A during the initial ingot break-down process by means of repeated hot-working (cogging). The ingot was produced by vacuum arc re-melting showing equiaxed and columnar grains. Compression tests were performed with a Gleeble system covering the range of temperatures, strains, and strain rates experienced during processing on an industrial scale. Texture analysis (neutron and electron back-scatter diffraction) was applied to all specimens before and after hot deformation to reflect the thermo-mechanical history. The ingot exhibited a well pronounced -fiber texture of the initial microstructure. Low deformation ratios did not change the type of texture, but the degree of the preferred orientation. High strains partially result in the destruction of the fiber texture and lead to the appearance of additional texture components, such as cube- and Goss-components. With continued deformation, recovery and re-crystallization become pr...

A simple knife-edge design for initial phase optimization in plasma focus

A simple knife-edge design was described that enabled easy optimization and investigation of the initial phase for the plasma focus devices. It enhanced the initial breakdown process along the insulator surface by allowing free adjustment or fine-tuning of the insulator length and by forming a sharp knife-edge with effective field emission. The plasma pinching was much improved with neutron yield equal or above that predicted by the scaling law. This knife-edge design is especially suitable for the optimization of medium and large-scale plasma focus devices where it would be otherwise rather difficult to modify the insulator configuration directly.

Activation of pure Al in an indium-containing electrolyte — an electrochemical noise and impedance study

The activation of aluminium in an acidic indium-containing electrolyte has been studied using electrochemical noise measurements. The average pit-growth rate, measured under freely corroding conditions, was comparable in the presence and absence of indium. However, pit growth times were considerably higher in the presence of indium. The initial breakdown process followed a pseudo-first order process with a rate constant almost a factor of two greater in the case of the indium-containing solution. Analyses of the current–noise data in the frequency domain yielded spectral noise plots, which agreed well with impedance spectra measured under similar conditions. Good agreement was also obtained between R n , which is defined as the ratio of the standard deviation in the potential noise signal to the standard deviation of the current noise signal, and the zero frequency limit of the impedance.