Development of Preparation Processes for CNT/Si 3 N 4 Composites Cs. Balázsi a , F. Wéber a , Zs. Kövér a , Z. Kónya b , I. Kiricsi b , L. P. Biró c , P. Arató a a Ceramics and Composites Laboratory, Research Institute for Technical Physics and Materials Science, Budapest, Hungary, b Department of Applied and Environmental Chemistry, University of Szeged, Rerrich Béla tér 1., H-6720 Szeged, Hungary, c Nanotechnology Department, Research Institute for Technical Physics and Materials Science, Budapest, Hungary. Keywords: carbon nanotubes, silicon nitride, mechanical properties Abstract. Silicon nitride based composites with different amount (1, 3 and 5 wt%) of carbon nanotubes have been prepared. Optimisation of the manufacturing processes has been conducted to preserve the carbon nanotubes in composites and to avoid damaging during high temperature processing. The first results show that carbon nanotubes have a good contact to the surface of silicon nitride grains. With increasing the carbon nanotube content a lower densification rate was obtained together with the deterioration of the mechanical characteristics of composites. In the case of 1wt% and 3 wt% carbon nanotube addition the increase of pressure resulted in increase of bending strength. It was found that microstructure features achieved by properly designed sintering parameters are the main responsible factors for the strength improvements. Introduction Carbon nanotubes (CNTs) have been reported to possess exceptional mechanical and electrical properties [1-5]. Therefore, it is expected that the addition of CNTs will radically improve the quality of different matrices, such as polymer, metal and ceramic. So far, only modest improvements of properties were reported in CNTs reinforced silicon carbide [6] and silicon nitride matrix composites [7], whereas a noticeable increase of the fracture toughness and of electrical conductivity has been achieved in CNTs reinforced alumina matrix composites [8,9]. Another research group have found for these composites rather low increments in toughness in the classical sense, but resistance to indentation (contact) damage [10,11]. The CNTs placed to the grain boundaries in alumina which can provide shear weakness under indentation could explain this phenomenon. In order to get the full use of the benefits provided by CNTs it is crucial to achieve a good dispersion of CNTs in the ceramic matrix. Retaining the CNTs un-attacked in the composites and to optimise the interfacial bonding between CNTs and matrix are the further requirements. In this way the toughening effects characteristic to micron-scale fibre composites could be explored: crack bridging by CNTs, CNT pullout on the fracture surfaces and crack deflection at the CNT/matrix interface [12]. This study is focusing on preparation processes to tailor the microstructure of carbon nanotube reinforced silicon nitride-based ceramic composites. Development of the processes has been conducted to effectively disperse the CNTs in the matrix. Importance was given to temperature-pressure-holding time relation to preserve the carbon nanotubes in composites and to avoid damaging during high temperature processing. An appropriate bonding between carbon nanotube and silicon nitride have been also monitored. Morphological, structural observations, as well as characterisation of mechanical properties will be presented. Key Engineering Materials Vol. 290 (2005) pp. 135-141 online at http://www.scientific.net © 2005 Trans Tech Publications, Switzerland Licensed to University of Toronto Library - Toronto - Canada All rights reserved. No part of the contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net . (ID: 142.150.190.39-08/07/05,16:54:07)