Plasma Studies in Vacuum ARC Remelting

The visible and uv plasma emissions from a metal vapor arc were studied during vacuum arc remelting of 165 mm diameter Inconel 718 electrodes using emission spectroscopy. Internal energy distributions of a number of emitting species were characterized and found to be approximately described by Boltzmann statistics. Analysis of the data yielded distribution ''temperatures'' ranging from 5400 K to 8200 K for the neutral atomic arc species, whereas values of 12,200 K and 17,000 K were obtained for singly ionized species. These values illustrate that the arc is not in a state of local thermodynamic equilibrium. The excited state densities of various arc constituents were measured and it was found that highly volatile alloy trace components, such as Mn and Mg, were present in the arc in disproportionately high concentrations. These data suggest that the vaporization and subsequent ionization of highly volatile trace materials may play an important role in carrying current between the electrodes.