Controlled Hollow Cathode Effect: New Possibilities for Heating Low-Pressure Furnaces

The uncontrolled hollow cathode effect may arise in dc plasma surface treatment (nitriding, nitrocarburizing, etc.) of steel parts having small-diameter holes or narrow channels. This may cause nonuniform heating of a part or a batch consisting of parts with markedly different surface/mass ratios. It has been noticed that if the hollow cathode effect is made controllable, it becomes suitable for heating in low-pressure or vacuum furnaces. Additional advantages can be obtained by combining the controlled effect of the hollow cathode with “active screen” plasma treatment due to the removal of the negative influence of the formed arc, of the heating nonuniformity, and of edge effect, as well as by controlling the cathode sputtering. Some experimental results on the topic are presented and the possibilities of application of the effect in industry are outlined.