A.S. Ulrich, T. Kaiser, E. Ionescu, R. Riedel, M.C. Galetz
Oxidation of Metals (2019), DOI: 10.1007/s11085-019-09926-w
To reduce scale spallation, scale volatilization, and nitrogen embrittlement in Cr-based systems, reactive elements such as Y, Zr, Hf, La, and Ce were introduced as oxide dispersions into pure chromium. In addition, Hf coating systems were investigated. One was a Hf sputter layer with varying thickness, and the other one a Hf-containing precursor ceramic, i.e., SiHfBCN, which may be considered as suitable material for environmental barrier coating applications. Oxidation tests at 1050∘C in synthetic air for 50 h were carried out using thermogravimetric analysis. The samples were analyzed via X-ray diffraction, optical microscope, electron microprobe analysis, and scanning electron microscope. All reactive elements led to a decrease in total mass gain after oxidation compared to pure Cr, with Y and Zr showing the strongest effect. Improvements in oxide attachment, oxide growth rate, volatilization rate as well as nitridation resistance were observed. Concerning these experiments, Y showed the most promising results. Concerning Hf, coating systems, especially SiHfBCN, showed a higher effect on improving the oxidation resistance. The reason for this outcome might be that not only Hf is active in the precursor ceramic layer. A more complex oxide layer has formed, which consisted of not only Cr2O3 but also of Hf and Si oxides. This layer prevents the material from any nitridation under the selected oxidation conditions.