Creep in alpha-Al(2)O3 thermally grown on beta-NiAl and NiAlPt alloys

摘要

We have measured creep relaxation in alpha-Al2O3, thermally grown on stoichiometric beta-NiAl, and on beta- and gamma'-phase alloys of Ni-Al-Pt at temperatures between 950-1100 degrees C. Creep was monitored using in-situ measurements of strain relaxation in the oxide following the sudden imposition of a stress. A stress was imposed by abruptly changing the sample temperature, exploiting the thermal expansion difference between oxide and substrate. The in-plane elastic strain was obtained using a sin(2)psi X-ray diffraction technique exploiting synchrotron radiation. For oxides grown on beta-NiAl and Ni-Al-Pt samples, we found that strain relaxation rates are comparable to those observed in fine gained alpha-Al2O3 bulk ceramics, when bulk results are extrapolated to the lower temperatures examined here. When Hf was added to the Ni-Al-Pt alloy, creep rates in the thermally grown oxide were substantially slowed. Creep rates at stress levels of 100 MPa, or less, are proportional to sigma", with n <= 2, consistent with a diffusional creep mechanism. (c) 2007 Published by Elsevier B.V.