Extension of Treatable Area in Atmospheric-Pressure Plasma-Jet Nitriding

Abstract

A unique nitriding technique using the atmospheric-pressure plasma jet has been upgraded by extending the treatable area. The previous manner to heat up a steel sample was spraying the thermal plasma jet onto the sample surface, which could maintain the treatment temperature only within a limited area of sample to restrict the treatable area to ca. 300 mm². Here, we first introduced an external heating system to the plasma-jet nitriding to control the treatment temperature of a larger sample. As a result, the treatable area is successfully extended to ca. 6300 mm². Moreover, the lifetime of NH radicals produced by the plasma chemical reaction is found to be long enough to cover the relevant area, implying the importance of NH for plasma-jet nitriding.