Study of Adherent Oxide Scales
Abstract
Sulfur is an indigenous impurity present at tramp levels within nickel base alloys. Precipitated sulfides are identified within NiCrA1 and NiCra1Y alloys. Auger studies show that sulfur segregates to free surfaces. Sulfur is identified at the critical oxide scale metal interface. The addition of sulfur as ferric sulfide to NiCrA1+Y causes the alloy to form non-protective oxide scales which readily spall. The addition of sulfur as Yteabium sulfide to NiCrA1+Y causes the normally protective oxide scale to spall. Sulfur causes the oxide scale to spall. Sulfur is present at the scale-metal interface in compounds and elemental form. Based upon the ESCA studies, the approximate steady state composition of the overall sulfur peak is 20 a/o elemental sulfur and 80 a/o sulfide. In summary, a new and different mechanism is proposed. It is proposed that the alumina scale that forms on NiCrA1 alloys are quite adherent. Sulfur in the alloy segregates to and weakens the bonds at the oxide scale-metal interface. The role of the reactive materials which promote oxide scale adherence is to interact with and form stable compounds thereby decrease the migration and concentration of sulfur to the critical oxide scale-metal interface.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 14, 1987
- Accession Number
- ADA187368
Entities
People
- J. G. Smeggil
- N. S. Bornstein
Organizations
- United Technologies Corporation