Dislocations and mechanical properties of MgO-Al{sub 2}O{sub 3} spinel single crystals
MgO{center{underscore}dot}nAl{sub 2}O{sub 3} spinel single crystals can be deformed plastically at high temperatures, displaying a range of interesting features. Stress-strain curves often exhibit strong work hardening followed by prominent work softening due to glide and climb processes. The critical resolved shear stress (CRSS) at a given temperature decreases dramatically, by almost 2 orders of magnitude, with increasing deviation from stoichiometry, i.e., as n increases from 1 to 3.5. The CRSS is proportional to exp({minus}T/T{sub 0}) and to [V{sub c}]{sup {minus}2}, where T is the temperature in kelvin, T{sub 0} a characteristic temperature, and [V{sub c}] the concentration of charge-compensating cation vacancies. The Burgers vector is 1/2{l{underscore}angle}110{r{underscore}angle}, and slip can occur on {l{underscore}brace}111{r{underscore}brace} and {l{underscore}brace}110{r{underscore}brace} planes. Slip on {l{underscore}brace}111{r{underscore}brace} planes is believed to occur between the Kagome cation layer and the adjacent anion layer. Slip on {l{underscore}brace}110{r{underscore}brace} planes is slightly easier (and has a higher T{sub 0}), because the planes are more widely separated. The temperature dependence of the CRSS can be explained in terms of the Peierls stress for partial dislocations, either in terms of a steep and high Peierls potential or in terms of temperature and stress-dependent kink diffusion. The dependence of CRSS on [V{sub c}]{sup {minus}2} can be explained in terms of kink nucleation at cation vacancies.
- Research Organization:
- Los Alamos National Lab., NM (US)
- Sponsoring Organization:
- US Department of Energy
- OSTI ID:
- 20005958
- Journal Information:
- Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Journal Issue: 12 Vol. 82; ISSN 0002-7820; ISSN JACTAW
- Country of Publication:
- United States
- Language:
- English
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