Effect of Methane Addition on Formation of Plasma Nitrocarburized Layers

Plasma nitrocarburizing is a thermochemical process that can be used to improve the mechanical properties of metal surfaces by enriching them with carbon and nitrogen atoms. The quantity of carbon in the plasma primarily affects the formation of the microstructure of the compound layer. This article presents an investigation of the evolution of the nitrocarburized layers on an iron substrate upon addition of several different concentrations of methane in a gaseous mixture of nitrogen and hydrogen. Scanning electron microscopy and x-ray diffraction analysis were used to investigate the microstructure and phases formed in the treated samples, and optical spectroscopy was used to investigate the species formed in the plasma to understand their involvement in the formation of the layers. The results indicate that the CH+ species is involved in formation and stabilization of the ε-Fe2–3(N,C) phase. © 2016, Springer Science+Business Media New York and ASM International.