Investigation of Hot-Filament and Hollow-Cathode Electron-Beam Techniques for Ion Plating

Abstract

The ion plating process has been generally limited to low-melting materials in past coating applications. In this study, several electron-beam melting techniques have been investigated which provide methods for melting various high-melting-point materials within a glow discharge atmosphere. The magnetically focused hot-filament and the cold-hollow-cathode electron sources have been experimentally studied to evaluate their operational and evaporation-deposition characteristics for the ion plating process. The hollow-cathode electron source emits an intense electron beam and is capable of delivering very high beam power. The gun is made of high melting-point sheets or screens formed into a hollow cylinder or sphere having an aperture to allow the emittance of electrons. It operates in an inert-gas, glow discharge environment such as that of ion plating. Gas pressure is a key processing variable in controlling the mode of operation; the hot-cathode mode operates at high pressures with excellent stability and the cold-cathode mode operates at low pressure and is sensitive to gas pressure variation. The operational characteristics of conventional hot-filament electron-beam guns are also described for this type of application. Evaporation-deposition parameters and techniques for each type of electron source have been determined using various materials. Type 304 stainless steel, titanium, iron chromium-aluminum-yttrium, and other alloys and metals have been successfully deposited and the coatings evaluated. The uniformity and adhesion of the coatings were experimentally investigated and are reported for various source and process conditions.