Study of the sulfur segregation for a TBC system

The degradation of thermal barrier coatings is closely linked to their spalling resistance, which depends on the stability of the protective oxide scale produced by oxidation of the bond coat. In this context, sulfur is well known to reduce the adherence of the thermally grown oxide on the boundary layer in the TBC systems. So, the aim of the present work is to report experimental results concerning the chemical changes at Al2O3/bond coat layer and Al2O3/superalloy interfaces, namely the effect of interfacial sulfur segregation as a function of the oxidation time, the initial S content and the presence of voids at the alumina/ bond coat interface. Sulfur segregations were identified by SIMS depth profiles and the effect of these segregations discussed according to the types of alloys and heat treatments. SIMS depth profiles and TEM results allowed us to localize the S segregation at the alumina/bond-coat interface and in the bulk of the bond-coat and to differentiate sulfur combing from the superalloy and sulfur trapped in the NiAlPt bond-coat.