ABSTRACT
The results are summarized from a number of investigators who focussed on the effects of sulfur content on scale adhesion. Beneficial effects were observed by using higher purity alloys. Sulfur removal was accomplished by vacuum annealing, hydrogen annealing, and by repeated segregation and polishing. Some degree of improved adhesion resulted in all cases. Hydrogen annealing essentially eliminated spallation for NiCrAl foil and bulk PWA 1480. An adherence map, constructed on the basis the amount of sulfur available for segregation, indicated between 1/4 to 4 monolayers as the boundary between spalling and adherence. Sulfur additions also destroyed adhesion for NiCrAl doped with reactive elements. The preponderance of the data is in concert with a sulfur dominated adhesion mechanism.
