Influence of nitrogen pressure and electrical parameters of a glow discharge on the process of ion plasma nitriding of steel

Abstract

The influence of the working gas pressure on the electrical parameters of the glow discharge and the structure of diffusion hardened layers in the process of ion-plasma nitriding of steel AISI 5140 was investigated. The experiments were carried out in the pressure range of 70–500 Pa, while the power (18 kW), the temperature of the samples (550 °C) and the processing time (6 hours) remained unchanged. The change in gas pressure was accompanied by a change in discharge voltage in the range from 560 to 1800 V and current density from 3.2 to 1.1 mA·cm−2. It is shown that the change in the pressure of nitrogen leads to a change in the energy and density of the particles flows acting on the workpieces. Metallographic and X-ray analysis showed that the surface layers formed at different pressures differ in length, structure, and phase composition. In particular, the maximum width of the diffusion zone of 460 microns was achieved at an operating pressure of 250 Pa The increase and decrease in pressure leads to a decrease in the length of the diffusion zone and an increase in the compound layer to 26 μm.