Influence of Oxygen Admixture on Plasma Nitrocarburizing Process and Monitoring of an Active Screen Plasma Treatment

The effect of a controlled oxygen admixture to a plasma nitrocarburizing process using active screen technology and an active screen made of carbon was investigated to control the carburizing potential within the plasma-assisted process. Laser absorption spectroscopy was used to determine the resulting process gas composition at different levels of oxygen admixture using O-2 and CO2, respectively, as well as the long-term trends of the concentration of major reaction products over the duration of a material treatment of ARMCO(R) iron. The short-term studies of the resulting process gas composition, as a function of oxygen addition to the process feed gases N-2 and H-2,H- showed that a stepwise increase in oxygen addition led to the formation of oxygen-containing species, such as CO, CO2, and H2O, and to a significant decrease in the concentrations of hydrocarbons and HCN. Despite increased oxygen concentration within the process gas, no oxygen enrichment was observed in the compound layer of ARMCO(R) iron; however, the diffusion depth of nitrogen and carbon increased significantly. Increasing the local nitrogen concentration changed the stoichiometry of the epsilon-Fe-3(N,C)(1+x) phase in the compound layer and opens up additional degrees of freedom for improved process control.

Automated summary

The study explored the effect of controlled oxygen admixture in plasma nitrocarburizing process for carburizing potential control. It was found that oxygen addition led to formation of oxygen-containing species, reduced concentrations of hydrocarbons and HCN, and increased nitrogen and carbon diffusion depth. Additionally, increasing local nitrogen concentration altered the stoichiometry of the compound layer, providing additional degrees of freedom for improved process control.