Identification of the spinel (Cr,Al)3S4 in the internal sulfidation zone of Al-diffusion coatings

The thiospinel (Cr, Al)₃S₄ has been identified in the internal sulfidation zone of Al-diffusion coatings by electron diffraction in a transmission electron microscope. The Al/Cr ratio of this phase can vary over a rather broad range, obviously dependent on the Al/Cr ratio in the surrounding metallic matrix. The spinel can dissolve significant amounts of Ni and Mo, some Co but only traces of Ti. Increasing Al-content extents its stability to higher temperatures.