THE FORMATION OF ALPHA-AL2O3 SCALES AT 1500-DEGREES-C

The growth of Al2O3 scales on beta-NiAl was studied at 1500-degrees-C Oxidation rates, diffusion mechanisms, and microstructures were examined in order to achieve a complete understanding of the scale development. Variation of the Al content within the beta phase field had little effect on the oxidation behavior. Ion-implanted yttrium (2 x 10(16)/cm2) was observed to provide a short-term improvement in scale adhesion but little long-term effect. When doped with Y or Zr, the first 1 mum of alpha-Al2O3 was observed to grow mainly by an inward oxygen growth mechanism. At longer times when the implant was ineffective, microstructural observations indicate a mixed-growth mode.