Abstract
High-temperature creep resistance in high-purity Al2O3 (nominal purity of 99.99%) and Al2O3 doped with 0.05 mol% Lu2O3 was examined by uniaxial compression testing in air at a constant load at temperatures between 1150 and 1350°C and the applied stress range of 10∼200 MPa. The creep resistance was found to highly improve in this temperature range by doping of Lu2O3 into polycrystalline Al2O3 even at the level of 0.05 mol%. The stress exponent was about 2 in the two materials, but the activation energy for creep was different; 410 kJ/mol for undoped Al2O3 and 780 kJ/mol for Lu2O3-doped Al2O3. Lutetium ions were found to segregate in Al2O3 grain boundaries without forming amorphous phase or second-phase particles. The improved creep resistance in polycrystalline Al2O3 due to Lu2O3 doping was attributed to the segregation of Lu ions in Al2O3 grain boundaries probably due to the suppression of grain boundary diffusion. The change of chemical bonding state in grain boundaries with the segregation of Lu ions is supposed by HREM–EELS analysis.
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