Image icon  h-BN inclusion in a β-Si3N4 grain

 
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Description: The micrograph shows h-BN inclusion (precipitate) in a β-Si3N4 grain (within a silicon nitride particulate-reinforced silicon carbide composite). 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.
Keywords: boron nitride • ceramic • composite material • silicon carbide • silicon nitride • displacement • indentation • Plasticine
Categories: Science approaches > Deformation & failure > Creep
Science approaches > Microstructure
Processes > Shaping > Powder methods
Properties > Mechanical & thermal > Creep resistance
Testing, analysis & experimentation > Metallography
Scale > Micro
Created by: DoITPoMS, University of Cambridge
Dr K M Knowles, Department of Materials Science and Metallurgy, University of Cambridge
Published by: DoITPoMS, University of Cambridge
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Date created: 01 October 2002
Date added: 21 August 2009
Package: DoITPoMS Micrograph Library
Resource ID: 1580