Investigation of the Synthesis and Internal Structure of Protective Oxide Layers on High Purity Chromium with SIMS Scanning Techniques

The major problem affecting the application of chromium in high temperature processes is the ongoing spallation of the protective oxide layer formed during hot gas oxidation. This resultsin a continuous material erosion. To gain a deeper insight in the spallation and oxidation process a high purity powder metallurgically produced chromium sample was submitted to a two stage hot gas oxidation process. The formed oxide layers were investigated by 3D SIMS and Scanning SIMS. The forming of the protective oxide layer is carried by the diffusion of chromium from the bulk through the already existing oxide layer and the reaction of the diffused chromium with the oxygen from the gaseous phase. In parallel to the growing of the layer an accumulation of impurities at the interface oxide layer- bulk can be observed. The enrichment of trace elements at the interface level (for the investigated sample namely Cl and N) can be explained by the low solubility of these elements in chromium oxide and therefore their inability to diffuse through the already formed protective layer.JRC.(IAM)-Institute For Advanced Material