Spark Plasma Sintering of fine alpha-silicon nitride ceramics with LAS for spatial applications |
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| Authors: | Helen Reveron Laurent Blanchard Yann Vitupier Emmanuelle Rivière Guillaume Bonnefont Gilbert Fantozzi |
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| Affiliation: | 1. Université de Lyon, Insa-Lyon, MATEIS CNRS UMR 5510, 20 Avenue Albert Einstein, F-69621 Villeurbanne Cedex, France;2. Thales Alenia Space, 100 Bd du midi BP 99, 06156 Cannes La Bocca, France;3. CNES, Service Structures et Mécanique, BP 1416, 18 Avenue Edouard Belin, 31401 Toulouse Cedex 4, France;1. State Key Laboratory of New Ceramics & Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, People''s Republic of China;2. Tianjin Nitride Advanced Materials Company, Tianjin 300303, People''s Republic of China;3. Materials Science and Engineering Department, University of Ioannina, GR-451 10 Ioannina, Greece;4. College of Engineeing, Peking University, Beijing, China;1. School of Electromechanical Engineering, Guangdong University of Technology, Guangzhou 510006, China;2. State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Shanghai 200050, China;1. School of Metallurgical and Ecological Engineering University of Science and Technology Beijing, Beijing 100083, China;2. State Key Laboratory of Multiphase Complex Systems Institute of Process Engineering Chinese Academy of Sciences, Beijing 100190, China;3. Department of Metallurgy, Graduate School of Engineering Tohoku University, Sendai 980-8579, Japan |
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| Abstract: | Many space systems such as satellite mirrors and their supporting structures require to be made from very low-thermal expansion materials combining both high hydrostability and relatively high mechanical properties. In this study, we have applied the “composite concept” in order to explore the possibility of fabricating near zero thermal expansion silicon nitride based ceramics. Consequently, a negative thermal expansion material belonged to the lithium aluminosilicate family (LAS powder crystallized under de β-eucryptite structure) was introduced in an alpha-silicon nitride fine powder (5 and 20 vol% of LAS) and the resulting composite system was sintered by Spark Plasma Sintering (SPS) at 1400 and 1500 °C. In the case of 20 vol% LAS compositions, relatively well-densified ceramics (94.4% of the theoretical density) were produced without adding any further sintering additive. The addition of yttria and alumina oxides allowed enhancing the densification level up to 98.2% (20 vol% LAS compositions) or from 62.3% up to 96.7% of the theoretical density in 5 vol% LAS materials. Nevertheless, it was impossible to full consolidate silicon nitride/LAS composite ceramics at temperatures lower than the temperature at which β-eucryptite melts, even by using SPS technology. Moreover, because of the relatively low temperatures involved in SPS, the α to β-Si3N4 transformation was avoided, resulting in microstructures composed of fine equiaxed α-Si3N4 grains (<200 nm) and of a glassy phase. Even if the effect of having a very large negative thermal expansion material was lost during the sintering step (because of the β-eucryptite melting), ceramics containing only 20 vol% of LAS-based phase exhibited very interesting values as regards of mechanical properties (strength, hardness, toughness, and Young's modulus), thermal conductivity and thermal expansion coefficient. We discuss in this work why we are so interested in developing dense silicon nitride/LAS ceramics sintered without any further additive addition, even though β-eucryptite is melted during the process and the transformation to the β phase is avoided. |
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