The creep of sapphire filament with orientations close to the c-axis |
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Authors: | D J Gooch G W Groves |
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Affiliation: | (1) Department of Metallurgy, University of Oxford, UK;(2) Present address: C.E.R.L., Leatherhead, UK |
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Abstract: | Sapphire filament oriented within 2 1/2° of the crystallographic c-axis underwent creep by a mechanism other than slip on the basal planes at temperatures above 1600° C. There was a stress below which creep could not be detected; this decreased from 180 MNm–2 at 1600° C to 65 MNm–2 at 1800° C. The total tensile strain obtained never exceeded 5%. Fracture occurred during a linear stage of creep in which the stress exponent of the strain-rate was approximately 6. The creep mechanism appeared to be slip on {20¯2¯1} 01 T2 (morphological unit cell). A filament in which the c-axis lay at 6° to the filament axis deformed by localized basal slip. The accompanying local latice rotations produced fracture at a small overall strain, usually less than 0.5%. The results demonstrate extreme anisotropy of creep in sapphire crystals. |
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