Creep in protective α-Al_2O_3 thermally grown on β-NiAl

摘要

The authors report systematic measurements of creep relaxation in α-Al_2O_3, thermally grown in air on (100) single crystals of stoichiometric β-NiAl, at temperatures between 950 and 1100℃. Creep was monitored using time dependent in situ measurements of strain relaxation in the oxide following imposition of a stress resulting from a sudden temperature change. The in-plane elastic strain was obtained using a sin~2 ψ x-ray diffraction technique exploiting synchrotron radiation. The authors found that strain relaxation rates were comparable to those observed in fine grained α-Al_2O_3 ceramics when the latter results were extrapolated to the lower temperatures examined here. Creep rates at stress levels of 100 MPa, or less, are proportional to σ~n, with n ≤ 2, consistent with a diffusional creep mechanism.