Transient creep in fine-grained polycrystalline Al 2 O 3 with Lu 3+ ion segregation at the grain boundaries
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Yuichi Ikuhara Engineering Research Institute, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Taketo Sakuma Graduate School of Frontier Sciences, Department of Advanced Materials Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan (Received 15 May 2000; accepted 18 December 2000)
The creep deformation in fine-grained polycrystalline Al2O3 is highly suppressed by the addition of 0.1 mol% LuO1.5. The transient creep behavior in Lu-doped Al2O3 was examined at the testing temperature of 1250–1350 °C, and the data were analyzed in terms of the effect of stress and temperature on the extent of transient time and strain. The experimental data on the transient creep in Lu-doped Al2O3 showed good agreement with the prediction from a time function of the transient and the steady-state creep associated with grain boundary sliding as well as an undoped one. The difference in the transient creep between Lu-doped and undoped Al2O3 can also be explained by the retardation of grain boundary diffusion due to the Lu3+ ions segregation in the grain boundaries.
I. INTRODUCTION
In polycrystalline alumina, high-temperature creep deformation often occurs by diffusional flow.1–8 The predominant deformation mechanism in Al2O3 with a grain size of less than about 10 m is grain boundary diffusion creep at temperatures of 1100–1400 °C and the applied stress of less than 100 MPa,2–5 and the grain boundary sliding contributes dominantly to high-temperature creep deformation in polycrystalline alumina with a grain size of less than about 2 m at 1400 °C.2,7 Transient creep has been observed in fine-grained Al2O3 as well as metallic materials.6,9 We examined the transient creep associated with the grain boundary sliding of high-purity polycrystalline Al2O3 with an average grain size of 0.9 m.10 To explain the observed transient creep, a time function of creep strain was proposed from a two-dimensional model based on grain boundary sliding for fine-grained, single-phase materials. The observed transient behavior in high-purity, fine-grained alumina can be explained in terms of the time function at temperatures between 1150 and 1250 °C.
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J. Mater. Res., Vol. 16, No. 3, Mar 2001 Downloaded: 03 Apr 2015
It is also striking that high-temperature creep resistance in fine-grained polycrystalline Al2O3 is highly improved by a small amount of dopant cation, such as 0.1 wt% ZrO211 or Y2O3 or Lu2O3, even on the level of 0.05 mol%.12–14 High-resolution electron microscopy/ energy dispersive spectroscopy (HREM-EDS) analysis revealed that the dopant cation does not form the second phase precipitations but segregates in the vicinity of grain boundaries in Al2O3. It is possible to explain the improved creep resistance in terms of the suppression of grain boundary diffusion of Al3+ ions by the segregation of dopant cations. However, the dopant effect has only been discussed in a s
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