Maskless Control of Local-Nitriding Area with Atmospheric-Pressure Barrier Discharge

Abstract

We demonstrated maskless local-nitriding by utilizing the atmospheric-pressure dielectric barrier discharge (DBD) with the operating gas of nitrogen/hydrogen mixture. First, the electric-field calculation proved theoretically that the DBD extension phenomenon under high temperature is caused by the hirizontal extension of the reduced electric field occurring in the discharge gap. Second, an expectation is deduced from the aforementioned theoretical result that the DBD extension phenomenon can be controlled by the value of the voltage applied to the opposite electrode. This expectation eventually leaded to the actual ignition-area control of DBD in the experiment. Third, the utilization of such DBD, the ignition area of which is under control, to nitriding treatment provided the area-control of the nitrided layer formed on the steel surface. As a consequence, the nitrided area was successfully localized from 400 to 0.8 mm² by decreasing the applied voltage without applying any masks and nitriding stop-off paints where the point electrode of 0.7 mm in diameter is used as the opposite electrode.