Papers by Author: G. Smoła

Abstract: The early stages of the scale growth process were studied of two FeCrAl alloys: one synthetic (Fe23Cr5Al) and one commercial (Kanthal APM alloy). In addition, Yttrium was implanted to the Fe23Cr5Al alloy. Oxidation exposures were carried out at 1000°C using two-stage-oxidation exposures in atmospheres containing significantly different amounts of ¹⁸O₂-tracer. The scales were analyzed in terms of SIMS, PLS and SEM. The distribution of oxygen isotopes which corresponded to the location of new oxide formation, the scale phase composition, scale morphology and microstructure were determined which enabled description of the scale evolution on all studied alloys. Similar evolution stages were observed, but minor differences were related to the rate of disappearing of the transient aluminium oxides.

Abstract: The oxidation mechanism of FeCrAl (+RE), RE: reactive elements: Y and Hf) thin foils was studied at temperatures ranging from 1093 K to 1173 K in SO2+1%O2 atmosphere. Materials were subjected to isothermal and thermal cycling exposures as well as to the so-called two-stage-oxidation. In the latter, an oxygen isotope 18O2 was used as a tracer. Starting materials and scales were characterized using Grazing Angle X-Ray Diffraction (GA-XRD), EDX, SEM, XPS and High Spatial Resolution Secondary Ion Mass Spectrometry (HSR-SIMS). The obtained results showed within the studied range of exposure conditions the scales on all the studied alloys grow via outward mechanism typical for transient oxides and not for the -Al2O3 which is consistent with phase composition results and scale morphology and/or microstructure. It was also found that ‘as received’ foils are not bare metals but complex oxide-on-metal systems resulting from their manufacturing procedure. The obtained results are discussed in terms of the diffusion-related transport properties of the scale and of the scale phase composition.