The use of the 18O2‐exposure + SIMS‐based approach to investigate the spallation mechanisms of alumina scales

Abstract Spallation of the protective alumina scale accelerates the oxidation‐induced degradation of ‚alumina formers’︁. Despite of the vast evidence of this process its mechanism has not been elucidated, so far. This paper reports the results of the scale spallation mechanism investigation using a novel 18O2‐exposure + SIMS‐based approach. The FeCrAl‐type alumina‐forming alloys, without and with Zr additions, were subjected to high temperature exposure at 1473 K in 18O2‐rich atmosphere and, subsequently, cooled down in air. The surfaces exposed after spallation were observed using SEM, while high resolution SIMS was used to determine the elemental distributions. The obtained results indicate that: (i) in all cases the spallation occurs according to the adhesive‐mode; (ii) for reactive‐element‐free alloys the scales spalls away at temperatures high enough to enable the re‐oxidation of the exposed surface already during cooling; (iii) for the Zr‐containing alloys the spallation occurs at fairly low temperatures. Two practical implications of the obtained results should be noted: (i) oxide layers and not ‘bare substrate’ result from the scale spallation process during cooling; (ii) the formation of oxide layers during cooling may affect the behaviour of the system during subsequent heating to the reaction temperature.