Cf/C composites: correlation between CVI process parameters and Pyrolytic Carbon microstructure

F Burgio,L Pilloni,A Brentari,P Fabbri,A Brillante,G Magnani,T Salzillo,M Scafè

doi:10.3221/igf-esis.30.10

Abstract

Chemical Vapour Infiltration (CVI) technique has been long used to produce carbon/carbon composites. The Pyrolytic Carbon (Py-C) matrix infiltrated by CVI could have different microstructures, i.e. Rough Laminar (RL), Smooth Laminar (SL) or Isotropic (ISO). These matrix microstructures, characterized by different properties, influence the mechanical behaviour of the obtained composites. Tailoring the process parameters, it is possible to direct the infiltration towards a specific Py-C type. However, the factors, influencing the production of a specific matrix microstructure, are numerous and interconnected, e.g. temperature, pressure, flow rates etc. Due to the complexity of the physical and chemical phenomena involved in CVI process, up to now it has not been possible to obtain a general correlation between CVI process parameters and Py–C microstructure. This study is aimed at investigating the relationship between infiltration temperature and the microstructure of obtained Py-C, for a pilot - sized CVI/CVD reactor. Fixing the other process parameters and varying only the temperature, from 1100°C to 1300°C, the Py-C infiltration was performed on fibrous preforms. Polarized light microscopy, with quantitative measurements of average extinction angle (Ae), and Raman spectroscopy were used to characterize the obtained Py-C microstructures.

Highlights

The applications of pyrolytic carbon (Py-C) are numerous and range over many fields, such as aerospace, nuclear and medical
Despite the Pyrolytic Carbon (Py-C) anisotropy has been studied since the 60th, there is no clear evidence of a defined correlation between Chemical Vapour Infiltration (CVI) process parameters and obtained Py-C structure
The measured extinction angle values were in the range of 4 to 8 degrees, for all the temperature conditions: this could be an indication of a dark laminar texture [11, 13, 14]

Summary

Introduction

The applications of pyrolytic carbon (Py-C) are numerous and range over many fields, such as aerospace, nuclear and medical. Pyrolytic carbon is mainly produced as matrix phase of carbon/carbon (Cf/C) composites Thanks to their excellent mechanical properties at elevated temperatures, combined with light weight and good frictional performances, Cf/Cs are employed for the fabrication of components, as leading edges, brake discs, exit cones etc., for aerospace field. Despite the Py-C anisotropy has been studied since the 60th, there is no clear evidence of a defined correlation between CVI process parameters and obtained Py-C structure This probably arises from the fact that the parameters, affecting the Py-C chemical vapour infiltration, are numerous and interconnected (gaseous precursors, temperature, pressure, gas flow rates, residence time, methane/hydrogen concentration ratio, etc.) and as a consequence the literature experimental conditions are very variable [9]. The temperature effect on the Py-C infiltration behaviour was investigated

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Conclusion