Plasma-source ion implantation compared with glow-discharge plasma nitriding of stainless steel

Abstract

Plasma-source ion implantation (PSII) is a promising technology to overcome the line-of-sight limitations of beam-line ion implantation. Among the possible fields of commercial use, nitriding of stainless steels by plasma-source ion implantation seems to be one of the favourites. However, the technology of glow-discharge plasma nitriding (GDPN) is already being used commercially. Therefore, it remains to be determined whether PSII is more suitable to the demands of an industrial technology than GDPN. In particular, the incorporation rate of nitrogen during treatment has to be investigated, as the incorporation rate of nitrogen determines the depth of the nitrided layer for a given treatment time. For nitriding of stainless steel, PSII and GDPN were performed for the same treatment time of 2 h, using the same treatment voltage (700 V) and duty ratio (50%) during the nitriding process. The temperature during treatment was fixed at 380 °C and controlled by an isolated thermocouple. The only difference in the experimental conditions was the pressure, during treatment, of 0.1 Pa in the case of PSII and 500 Pa in the case of GDPN. Pure nitrogen as well as a nitrogen-hydrogen mixture was used as the feed gas. The resulting concentration profiles were determined by glow-discharge optical spectroscopy depth profiling to determine the nitrogen incorporation rate of both nitriding techniques. The surface properties were investigated by wear and hardness measurements. Both technologies yield the formation of a hard nitrided layer with an increased hardness. The highest nitrogen concentration and widest hardened layer was found in the case of PSII, using a nitrogen-hydrogen plasma.