Densification of Ceramic Matrix Composite Preforms by Si2N2O Formed by Reaction of Si with SiO2 under High Nitrogen Pressure. Part 1: Materials Synthesis

Brice Taillet,René Pailler,Francis Teyssandier

doi:10.3390/jcs5070178

Abstract

Ceramic matrix composites (CMCs) have been designed and developed for extreme operating environments. The aim of the present study is to look for a rapid densification process providing a high level of material performance. The fibrous preform was made of Hi-Nicalon S fibers woven in a 3D interlock weave. The matrix was composed of Si2N2O prepared inside the CMCs by reacting a mixture of Si and SiO2 under high nitrogen pressure (1 to 3 MPa). Silica was either impregnated by slurry or obtained by oxidation of silicon grains inside the preform. The synthesis reaction was initiated by heating the impregnated preform by means of a carbon resistor submitted to Joule effect. Composition, homogeneity and porosity of the formed matrix were studied and interpreted as a function of the experimental parameters (nitrogen pressure, heating rate of the preform) as well as the recorded thermal history of the process. The present results show that the matrix formation is almost completed in less than one minute. Melting of silicon has a major influence on the process. Competition was observed between the formation of Si3N4 and Si2N2O, which could be mainly controlled by the heating rate of the preform and the nitrogen partial pressure.

Highlights

Si2 N2 O gives lower mechanical strength mechanical strength to the Ceramic matrix composites (CMCs) matrix, we focused our work on this compound on the to the CMC matrix, we focused our work on this compound on the grounds of the enhanced grounds of the enhanced protection against oxidation it provides
4 and Si2N2O are in compeAsin already mentioned, thesynthesis
Time–temperature history, nitrogen pressure that reactivity are all factors that may influence the composition of the formed matrix

Summary

Introduction

Ceramic matrix composites (CMCs) have been designed and developed for extreme operating environments [1], such as high temperatures, mechanical stress and oxidizing atmospheres. These materials may be submitted to irradiation. CMCs are lighter than metallic materials: their density ranges between 2 and 3, while Inconel density is as high as 8 kg/m3. These materials are, expensive, partly due to the price of the high-performance fibers used, and because of the densification process of the initial preform. Chemical vapor infiltration (CVI) is a long-lasting process performed at 1000 ◦ C under reduced pressure

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