Diffusion of helium gas bubbles in gold and copper foils

Helium bubbles were induced in gold and copper foils by ion bombardment and their diffusion studied by observing the rate at which the bubbles diffuse out of the foil and also by measuring the distance they move in a given annealing time. This is the first time such quantitative comparisons have been made. It was discovered that helium bubbles in gold diffuse at a rate 10^-4 to 10^-5 times that predicted by surface diffusion and that helium bubbles in copper diffuse at 10^-5 to 10–2 the predicted rate. It is shown that the nucleation of steps on the faceted surface of the bubbles could satisfactorily account for the abnormally slow bubble diffusion rate. Such a process would inhibit the motion of bubbles in more anisotropic solids like oxides even more. This work is based on a thesis submitted by L. E. WILLERTZ to Carnegie-Mellon University in partial fulfillment of the requirements for the Ph.D. in Metallurgy, 1968.     

Effects of metal vapor on electron temperature in helium gas tungsten arcs

In order to investigate the effects of metal vapor on the thermodynamic property of arc plasma in the welding process, electron temperatures in the pure helium plasma and in the helium plasma during welding in gas tungsten arcs (GTAs) were measured by using the laser scattering method. The experimental results showed that metal vapor led to a significant decrease in the electron temperature compared with that of pure helium GTA plasma. The temperature difference reached 6000 K in the arc fringe at the maximum.     

Heat and metal transfer in gas metal arc welding using argon and helium

This article describes a theoretical investigation on the arc parameters and metal transfer in gas metal arc welding (GMAW) of mild steel using argon and helium shielding gases. Major differences in the predicted arc parameters were determined to be due to large differences in thermophysical properties. Various findings from the study include that an arc cannot be struck in a pure helium atmosphere without the assistance of metal vapor, that a strong electromagnetic cathode force affects the fluid flow and heat transfer in the helium arc, providing a possible explanation for the experimentally observed globular transfer mode and that the tapering of the electrode in an argon arc is caused by electron condensation on the side of the electrode. Formerly Graduate Student, Massachusetts Institute of Technology