Metallographic characterization of the molybdenum based alloy MHC by a color etching technique

The standard etching reagent for molybdenum–hafnium–carbon alloys – an aqueous alkaline potassium ferricyanide solution – is not applicable for the determination of the different phases in the material. Therefore, the color etching technique according to Hasson [Hasson R. Metallography of molybdenum in color. Microscope 1968;16:329–34.] was applied on a sintered Mo–Hf–C alloy to distinguish between the individual phases. Usually, this etching reagent is used for the characterization of the individual crystal orientations in pure molybdenum. By using this etchant for the MHC alloy, the individual phases appear in different colors. It was shown that the alloy contains carbide and oxide particles. The color code from the optical light micrographs was related to the morphology and the chemistry of the particles. In the course of the study X-ray diffraction, energy dispersive X-ray spectroscopy, electron backscatter diffraction and transmission electron microscopy have been used. Furthermore, it was revealed that the hafnium carbide phase contains a distinct amount of molybdenum.

► A color etching technique was applied to distinguish between individual phases.
► The OLM color code was related to the phases by using XRD, EDS and EBSD.
► In contrast to EDS, the EBSD analysis was able to reveal the Mo2C particles.
► It was shown that the HfC phase contains molybdenum.