Effect of Sulfur Removal on Scale Adhesion to PWA 1480

摘要

A commercial superalloy, PWA 1480, was annealed in hydrogen at 1000 deg C to 1300 deg C in order to remove a 10 ppmw sulfur impurity. This treatment was very successful above 1200 deg C, resulting in residual sulfur contents below 0.1 ppmw": The degree of scale adhesion in subsequent 1100 deg C cyclic oxidation tests was inversely related to residual sulfur content. Control of adhesion by desulfurization 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/polishing were not successful, in contrast to previous studies on NiCrAl.