Stress Development and Relaxation in Al2O3 during Early StageOxidation of beta-NiAl [electronic resource].
- Washington, D.C. : United States. Dept. of Energy, 2005.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
- Additional Creators:
- United States. Department of Energy
United States. Department of Energy. Office of Scientific and Technical Information
- Using a glancing synchrotron X-ray beam (Advanced Photon Source, Beamline 12BM, Argonne National Laboratory), Debye-Scherrer diffraction patterns from thermally grown oxides on NiAl samples were recorded during oxidation at 1000 or 1100 C in air. The diffraction patterns were analyzed to determine strain and phase changes in the oxide scale as it developed and evolved. Strain was obtained from measurements of the elliptical distortion of the Debye-Scherrer rings, where data from several rings of a single phase were used. Results were obtained from α-Al₂O₃ as well as from the transition alumina, in this case θ-Al₂O₃, which formed during the early stage. Compressive stress was found in the first-formed transition alumina, but the initial stress in α-Al₂O₃ was tensile, with a magnitude high enough to cause Al₂O₃ fracture. New α-Al₂O₃ patches nucleated at the scale/alloy interface and spread laterally and upward. This transformation not only puts the alpha alumina in tension, but can also cause the transition alumina to be in tension. After a complete α-Al₂O₃ layer formed at the interface, the strain level in α-Al₂O₃ became compressive, reaching a steady state level around -75 MPa at 1100 C. To study a specimen's response to stress perturbation, samples with different thickness, after several hours of oxidation at 1100 C, were quickly cooled to 950 C to impose a compressive thermal stress in the scale. The rate of stress relaxation was the same for 1 and 3.5 mm thick samples, having a strain rate of ≈ 1 x 10⁻⁸/s. This behavior indicates that oxide creep is the major stress relaxation mechanism.
- Published through SciTech Connect.
6th International Conference on the Microscopy ofOxidation, U. of Birmingham, UK, April 4-6, 2005.
Paulikas, A.P.; Veal, B.W.; Hou, P.Y.
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
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