Influence of Plasma Power and Oxygen-Containing Process Gases in Active Screen Plasma Nitrocarburizing with Carbon Solid Source*

Abstract Plasma nitrocarburizing by means of active screen technology using an active screen made of carbon fiber-reinforced carbon was carried out by varying the power at the active screen and using oxygen-containing fresh gas components (O2, CO2) in the N2:H2 plasma using the example of the quenched and tempered steel AISI 4140 (42CrMo4). The investigations focused on the analysis of the process gas by means of laser absorption spectroscopy, the evaluation of the produced compound layers with regard to structure and phase composition, as well as the resulting properties. It was shown that by varying the process gas atmosphere, the structural composition of the compound layer and the concentration profiles of nitrogen and carbon can be specifically influenced. The high concentrations of carbon-containing compounds in the process gas resulted in complete suppression of γ’-Fe4N formation, but cementite was detected in the lower part of the compound layer. The addition of oxygen-containing fresh gases and the resulting change in process gas composition suppressed cementite formation. The results suggest that, in particular, high powers at the carbon active screen and the simultaneous addition of oxygen-containing gases results in the generation of nitrogen-rich, single-phase ε-compound layers.