Full Record for Micrograph 155
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- Micrograph no
- 155
- Brief description
- Silica investment casting core
- Keywords
- ceramic , fused silica, oxygen , silica, 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-NonCommercial-ShareAlike 4.0 International