Observations of reactive element gettering of sulfur in thermally grown oxide pegs

Reactive elements such as yttrium are known to have a beneficial effect on oxide spallation resistance. Yttrium-rich precipitates containing sulfur were detected by scanning transmission electron microscopy in the peg regions of a thermally grown oxide on a commercial NiCoCrAlY bond coat that has seen service in a gas turbine environment. The coexistence of yttrium and sulfur in these pegs provides clear experimental evidence for the widely held hypothesis that sulfur is gettered by reactive elements in bond coats for thermal barrier coatings.