Development of near net shaped Si3N4/SiC composites with optimised grain boundary phase for industrial wood machining
The introduction of ceramics into the market of wood cutting tools has failed so far due to the generally low toughness of ceramics which is causing brittle failure of the cutting edge. A feasibility study showed that Si3N4/SiC composites with fine elongated β-Si3N4 grains are a promising material f...
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| Format: | Doctoral Thesis |
| Language: | English |
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Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola"
2011
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| Online Access: | http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-71329 http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-71329 http://www.qucosa.de/fileadmin/data/qucosa/documents/7132/Dissertation%20Claudia%20Strehler%202011.pdf |
| Summary: | The introduction of ceramics into the market of wood cutting tools has failed so far due to the generally low toughness of ceramics which is causing brittle failure of the cutting edge. A feasibility study showed that Si3N4/SiC composites with fine elongated β-Si3N4 grains are a promising material for industrial wood machining and outperform commercial standard tungsten carbide tools in terms of lifetime. However, they were produced by hot pressing followed by very costly diamond cutting and grinding. The costs associated with the above production route are too high for an industrial viability.
In this thesis Si3N4/SiC composites suitable for industrial wood milling are produced by a near net shape processing route including gas pressure sintering. These newly developed tools show less abrasive wear and consequently twice as long lifecycles than commercial standard tungsten carbide tools. Microscopic properties determine the performance of the Si3N4/SiC cutting tools. Therefore, an adequate selection of sintering additives is crucial. 12 wt% sintering additives are included in the composite as a combination of Al2O3 and the refractory oxides La2O3 and Y2O3. Important for the production of effective Si3N4/SiC wood cutting tools is the formation of a partly crystalline silicate phase within the multiple grain junctions during the final treatment by hot isostatic pressing. The use of MgO as a sintering additive for facilitating the densification of the Si3N4 ceramics inhibits the formation of the favourable silicate phase and must be avoided for the production of these wood cutting tools.
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