This paper examines an aluminum oxide coating plasma-sprayed onto a substrate made of high-quality stainless steel by means of light microscopy, X-ray diffractometry, and scanning and transmission electron microscopy (TEM). The aim is to determine the phases that form preferentially at the transition. It is observed that high amount of corundum phase was found in a plasma sprayed white alumina coating. XRD phase analysis of the coating indicated that all three major alumina phases were present: alpha-, gamma-, and delta-aluminum oxide. Further development in the field of TEM sample preparation is required in order to obtain larger electron-permeable surfaces, since it is not clear whether the alpha-aluminum oxide found at the transition is in the form of a spatter or a grain introduced by sandblasting. Paper includes a German-language abstract.