Study of Adherent Oxide Scales
Abstract
In agreement with previously reported studies involving alumina formers, the bond between a protective chromia scale and a Ni-40 wt. % Cr substrate is intrinsically strong. Segregation of sulfur to this interface weakens that bond. Segregated sulfur has been documented at the scale-metal interface. The sulfur content of the Ni-40 wt. % Cr is more important than yttrium additions regarding scale adherence during cyclic testing. Glow discharge mass spectrometry has been found to reliably and reproducibly differentiate sulfur contents in metal matrices in the low ppm range, i.e. approximately 1 to 50 ppm by weight. In the presence of ambient environments at elevated temperatures, all structural alloys are thermodynamically unstable reacting to form oxide scales. In order for such thermally grown oxide scales to be protective, they must limit the reaction rate between atmospheric oxygen and the substrate alloy. Oxidation rates are limited by scales which exhibit these properties: 1) Slow growth kinetics; 2) Minimal vaporization effects at temperatures of interest; 3) Minimal interaction with molten salts which might be present on hardware surfaces; and 4) Adherence under thermal cycling conditions. For most alloys which form either alumina or chromia scales, the latter most property--oxide scale adherence under thermal cycling conditions-- controls service life. Keywords: Oxidation; Oxide scale adherence; Oxide scale formations; Minor element effect; Sulfur.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 15, 1989
- Accession Number
- ADA205799
Entities
People
- J. G. Smeggil
Organizations
- United Technologies Corporation