EFFECT OF SULFUR REMOVAL ON SCALE ADHESION TO PWA-1480

A commercial superalloy, PWA 1480, was annealed in hydrogen at 1000 de grees C to 1300 degrees C in order to remove a 10 ppmw sulfur impurity . This treatment was very successful above 1200 degrees C, resulting i n residual sulfur contents below 0.1 ppmw. The degree of scale adhesio n in subsequent 1100 degrees C cyclic oxidation tests was inversely re lated to residual sulfur content. Control of adhesion by desulfurizati on in the absence of reactive elements supports an adhesion mechanism based on oxide-metal bonding weakened by sulfur segregation. Attempts at sulfur purging and improving adhesion by repeated oxidation/polishi ng were not successful, in contrast to previous studies on NiCrAl.