High‐pressure sintering of nanocrystalline γ‐A1 2 O 3 has been studied over a temperature range of 923‐1323 K and at a pressure of 1 GPa. The γ‐Al 2 O 3 to α‐Al 2 O 3 transformation temperature changed from 1473 K without pressure to ∼1023 K at 1 GPa. Full density was obtained at 1273 and 1323 K in 10 min. The microhardness value of fully dense α‐alumina with a grain size of 142 nm was found to be 25.3 ± 0.8 GPa. The Hall‐Petch slope for the very fine grain size range is different from that of the coarse‐grained alumina.
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Mishra et al. (1996) studied this question.
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