Oxide Scale Adherence Mechanisms and the Effects of Yttrium, Oxide Particles and Externally Applied Loads on the Oxidation of NiCrAl and CoCrAl Alloys
Abstract
Studies have been performed to examine the effects of yttrium, oxide dispersions, fabrication conditions and externally applied loads on the oxidation of Ni-15Cr-6Al (wt. %) and Co-25Cr-6Al (wt. %) alloys at 1000-1200 degrees Celsius in air. External layers of alumina were developed on all of the alloys during oxidation and growth of these scales was controlled by diffusion of oxygen along their grain boundaries. The growth rates and mechanism for the alumina scales were not dependent upon alloy fabrication condition, yttrium, or oxide dispersions. Alumina scales spalled, during cooling, from alloys which did not contain yttrium or oxide dispersions. Voids were developed at the alumina-alloy interfaces during oxidation but they did not substantially influence spallation since the stresses generated during cooling exceeded the interfacial bond strengths. Yttrium and oxide dispersions improved the adhesion of alumina by providing vacancy sinks and by causing the development of macro- and micropegs at the alumina-alloy interfaces which mechanically keyed the scales to the alloys. Fabrication conditions which produced the most homogeneous distribution of yttrium or oxide dispersions within the alloys were the most effective procedures for improving the alumina scale adherence. Externally applied loads did not affect the growth rates of the alumina scales. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1975
- Accession Number
- ADA024104
Entities
People
- C. S. Giggins
- F. S. Pettit
Organizations
- Pratt & Whitney