NATURE OF INDIGENOUS SULFURE SEGREGATED TO THE FREE METAL-SURFACE AND TO THE SCALE METAL INTERFACE

Sulfur segregation to the free metal surface at a Ni-20(wt. %)Cr-12(wt. %)Al alloy has been documented by high temperature scanning Auger electron microscopy. Preferential enrichment of sulfur occurs to the surface of the chromium-rich gamma phase in the two-phase gamma nickel- beta (NiAl) alloy. Electron spectroscopy for chemical analysis (ESCA) studies have indicated that for a free metal surface, i. e. , metal without an overlying thermally grown oxide scale, the surface segregated sulfur correlated with both S** minus **2 and elemental oxide Energy-dispersive X-ray analysis (EDAX) characterization of fractured oxide films thermally grown on the alloy indicated that both a relatively volatile and a refractory sulfur species exist at the scale-metal interface. Elemental sulfur as detected by ESCA has the volatility characteristics for the labile sulfur species found in the scanning electron microscopy (SEM)-EDAX studies.