Creep in α-Al2O3 thermally grown on β-NiAl and NiAlPt alloys

✍ Scribed by B.W. Veal; A.P. Paulikas; B. Gleeson; P.Y. Hou

• Book ID: 104094063
• Publisher: Elsevier Science
• Year: 2007
• Tongue: English
• Weight: 589 KB
• Volume: 202
• Category: Article
• ISSN: 0257-8972
• DOI: 10.1016/j.surfcoat.2007.05.093

✦ Synopsis

We have measured creep relaxation in α-Al 2 O 3 , thermally grown on stoichiometric β-NiAl, and on βand γ'-phase alloys of Ni-Al-Pt at temperatures between 950-1100 °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 ψ X-ray diffraction technique exploiting synchrotron radiation. For oxides grown on β-NiAl and Ni-Al-Pt samples, we found that strain relaxation rates are comparable to those observed in fine grained α-Al 2 O 3 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 σ n , with n ≤ 2, consistent with a diffusional creep mechanism.