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DoITPoMS Micrograph Library Full Record for Micrograph 546

Full Record for Micrograph 546

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Micrograph no
Brief description
Delamination cracks seen in h-BN particles subjected to compressive stress in the (0001) planes (within a silicon nitride particulate-reinforced silicon carbide composite)
boron nitride, ceramic Link to MATTER Glossary entry for ceramic, composite material Link to MATTER Glossary entry for composite material, silicon carbide, silicon nitride
Ceramic, Composite
Si3N4-SiC composite
Not specified
Standard codes
To form the composite, hot isostatic pressing in tantalum cans is used, with a boron nitride layer sprayed onto the internal surface of the can (to prevent the tantalum reacting with the SiC).
Sample preparation
High resolution electron microscopy (HREM)
Length bar
10 nm
Further information
The occurrence of BN inclusions results from the introduction of colloidal BN into the hot isostatic pressing process. They are formed from B2O3 present as a thin surface film on the BN particles in the barrier layer. B2O3 will be molten during the pressing process and will diffuse rapidly into the powder compact and react with Si3N4 to form BN. Such inclusions can be related to failure under thermal cycling or creep test conditions (due to cavities and microcracks associated with them), may be grain growth controllers, and may influence crack deflection and slow crack growth at high temperatures. Delamination cracks probably originate during crystal growth or under the subsequent compression or shear stresses.
Dr K M Knowles
Department of Materials Science and Metallurgy, University of Cambridge
Licence for re-use
Attribution-NonCommercial-ShareAlike 4.0 International
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