Abstract
A magneto-plasma-dynamic (MPD) arcjet generator, in which plasma generated is accelerated by the electromagnetic interaction between the discharge current and the magnetic field induced by it, is a simple, efficient, and reliable device suitable for material processing. A quasi-steady MPD arcjet was studied to examine fundamental operational characteristics and plasma features. The MPD arcjet was operated for discharge currents of 3-25 kA with working gases of Ar, H2, N2 and NH3. Three different discharge modes of diffuse, spot and gross erosion existed in the MPD arc, and a qualitative explanation of their nature was presented. As a result, the MPD arcjet was found to produce high-velocity, high-temperature, high-density, large-area plasmas. For applications of MPD arcjets to ceramic coatings, an ablation-type MPD arcjet with a cathode covered with ceramic materials was developed. In 100-shot operations for Ar at 5-10 kA, the ablation rates of the ceramic covers ranged from 1.1 to 7.5 mg/shot. The MPD plasma spraying showed that a dense uniform ceramic film with above 1200 Vickers hardness was deposited. From the XPS spectra, the peak area ratio of Si/Al for the coating film almost equaled that for the raw ceramic material, and the valence numbers of Al and Si did not change. Consequently, the MPD arcjet was found to have a high potential for material processing.
