OXIDATION MECHANISMS OF BETA-NIAL+ZR DETERMINED BY SIMS

The oxidation mechanisms of single crystal Zr-doped beta-NiAl from 800 to 1200 degrees C were determined using primarily secondary ion mass spectrometry (SIMS) imaging and depth profiling. High spatial resolution SIMS imaging provides a means for critically assessing the effects of diffusion through the boundaries of the Various morphologies of alpha-Al2O3 scales that form on beta-NiAl. Transient oxidation occurs by outward Al diffusion through transition Al2O3 scales, theta-Al2O3 in this case, for temperatures from 800 to 1100 degrees C. Steady-state oxidation occurs by counter-diffusion of oxygen inward and both Al and Zr outward through boundaries in the alpha-Al2O3 ridge morphology.