XTEM and XPS studies of plasma nitrocarburising layers on 0.45% C steel

A characterisation study of the phases formed during nitrocarburising of 0.45% C steel at 540±20°C for 4 h in a d.c. glow discharge was performed by X-ray diffraction, cross-sectional electron microscopy and X-ray photoelectron spectroscopy (XPS). The results show a compact surface layer with columnar morphology composed of γ′-Fe4N and ε-Fe2–3N with some α-Fe existing at the interfaces between columns. There are three different kinds of column, which consist of a mixture of ε with γ′ precipitations, single γ′ and single ε, respectively. A transition layer is present between compound layer and diffusion layer. This layer is mainly composed of γ′ phases with sphere morphology. In the diffusion layer γ′ phases and larger carbides were observed.