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Full Record for Micrograph 155

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Micrograph no
155
Brief description
Silica investment casting core
Keywords
ceramic Link to MATTER Glossary entry for ceramic, fused silica, oxygen Link to MATTER Glossary entry for oxygen, silica, silicon Link to MATTER Glossary entry for silicon
Categories
Ceramic
System
SiO2
Composition
SiO2, trace of clay
Standard codes
Reaction
Processing
Lightly sintered to give a glass bond. Since the core size is critical to the application it is made by a near net shape process involving injection moulding of milled fused silica with clay and light liquid phase sintering at 1050 °C to decompose the clay and give a glass bond resulting in <0.2% shrinkage and high tolerance. The core is then impregnated with polymeric resin which enters the porous matrix providing handling strength. It is placed in the casting mould which is preheated to 1000 °C and the Nimonic poured in at 1600 °C. On cooling it is etched away with caustic soda.
Applications
Cores for investment cast Nimonic turbine blades for jet engines providing the cooling path.
Sample preparation
Polished but unetched.
Technique
Reflected light microscopy
Length bar
300 μm
Further information
The milling makes the (light contrast) silica particles angular leaving only a few contact points between them. This sample still contains the polymeric resin. The low thermal expansion of fused silica and subsequent good thermal shock resistance make it ideal for this application.
Contributor
Prof W E Lee
Organisation
Department of Engineering Materials, University of Sheffield
Date
10/05/02
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales