Microscopic Characterization of Compound Layers

The properties of the compound layer have a significant influence on the lifetime of nitrided surface layers. In addition to a sufficient thickness, the compound layer characteristics include the phase composition and the porosity. Complex methods such as GD-OES or XRD are already used to qualitatively and quantitatively determine the phase composition of the compound layer. Particularly with regard to the characterization of the pore seam, no method has yet been identified that can be clearly recommended. In this work, the extent to which compound layers can already be characterized with the aid of microscopic examination methods is shown. For this purpose compound layers with varying thickness, phase composition and porosity were formed in the surface area of the material EN31CrMoV9 and EN42CrMo4 by different nitriding processes. It is demonstrated how the phase composition of compound layers can be studied qualitatively by means of special etchants on metallographic cross sections and subsequently quantitatively by image analysis. A more extensive characterization of the pore seam beyond the state of the art could be performed by scanning electron microscopy studies as well as 3D X-ray microscopy.