High temperature oxidation of beta-NiAlThe oxidation of single crystal beta-NiAl has been studied primarily using electron microscopy. Oriented metastable Al2O3 phases form during transient oxidation at 800 C. Specific orientation relationships exist on all metal orientations studied and are a result of the small mismatch along aligned close-packed directions in the cation sublattices of the metal and oxide. Transformation of the metastable Al2O3 phases at 1100 C results in an oxide morphology described as the 'lacey' structure of alpha-Al2O3 scales. This structure results from impingement of oriented patches of alpha-Al2O3 as the transformation initiates and moves radially parallel to the surface. Scale growth occurs by diffusion along high angle grain boundaries. A drastic reduction in oxidation rate accompanies the change in oxide morphology.
Document ID
19860062528
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Koychak, J. K. (Case Western Reserve Univ. Cleveland, OH, United States)
Mitchell, T. E. (Case Western Reserve University Cleveland, OH, United States)
Smialek, J. L. (NASA Lewis Research Center Cleveland, OH, United States)