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Proceedings Paper

Factors that influence mechanical failure of sapphire at high temperatures
Author(s): Daniel C. Harris; Frederick Schmid; David R. Black; Ender Savrun; Herb E. Bates
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Paper Abstract

Sapphire's loss of strength between 20 degrees and 1000 degrees Celsius depends on orientation and state of stress. The critical weakness of sapphire occurs in compression along the c-axis of the crystal. In flexure tests of sapphire that is not subject to c-axis compression, the strength actually increases between 20 degrees and 1000 degrees Celsius. Compression on the c-axis causes twinning on rhombohedral crystal planes. When twins on different planes intersect, a crack forms and the specimen is then subject to tensile failure. Doping with Mg2+, Ti4+, or introduction of a TiO2 second phase each doubled the c-axis compressive strength of sapphire at 600 degrees Celsius, probably by inhibiting twin propagation. X-ray topography was employed to investigate the relationship between surface and bulk defects and mechanical strength in sapphire. Low angle grain boundaries were not associated with mechanical weakness. Wide, transverse scratches that are evident to x-rays, but not obvious in optical microscopy, can weaken sapphire. Topography demonstrated that annealing reduces long range strain in polished sapphire.

Paper Details

Date Published: 27 June 1997
PDF: 10 pages
Proc. SPIE 3060, Window and Dome Technologies and Materials V, (27 June 1997); doi: 10.1117/12.277047
Show Author Affiliations
Daniel C. Harris, Naval Air Warfare Ctr. (United States)
Frederick Schmid, Crystal Systems, Inc. (United States)
David R. Black, National Institute of Standards and Technology (United States)
Ender Savrun, Sienna Technologies (United States)
Herb E. Bates, Saphikon, Inc. (United States)

Published in SPIE Proceedings Vol. 3060:
Window and Dome Technologies and Materials V
Randal W. Tustison, Editor(s)

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