Chapter 22. Microstructure and Thermal Properties of 2 Directional and 3 Directional C/C Composites
- Rajan Tandon,
- Andrew Wereszczak and
- Edgar Lara-Curzio
Published Online: 27 MAR 2008
Copyright © 2007 The American Ceramics Society
Mechanical Properties and Performance of Engineering Ceramics II: Ceramic Engineering and Science Proceedings, Volume 27, Issue 2
How to Cite
Ozcan, S., Woldemicheal, M., Iqbal, S. and Filip, P. (2006) Microstructure and Thermal Properties of 2 Directional and 3 Directional C/C Composites, in Mechanical Properties and Performance of Engineering Ceramics II: Ceramic Engineering and Science Proceedings, Volume 27, Issue 2 (eds R. Tandon, A. Wereszczak and E. Lara-Curzio), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470291313.ch22
- Published Online: 27 MAR 2008
- Published Print: 1 JAN 2006
Print ISBN: 9780470080528
Online ISBN: 9780470291313
The friction between disk brakes causes significant surface heating and the ability to control the heat dissipation from the friction surface considerably contributes to improved frictional performance. The thermal properties and the microstructure of the 2D randomly chopped pitch fiber and the charred resin matrix with a smooth laminar CVI, and the 3D non–woven ex–PAN fiber reinforced composites with rough laminar CVI matrix have been studied. The microstructure of the investigated composites was characterized using polarized light microscopy (PLM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
Both of the composites exhibited anisotropy in the thermal conductivity measured in temperature interval ranging from 100°C to 1300°C. The 2D–C/Cs exhibited seven times higher thermal conductivity in the “x–y” plane, where fibers are preferentially oriented, when compared to thermal conductivity in the “z” direction perpendicular to the friction surface. The carbon fibers generate a direct thermal pathway and then also provide a pattern for the directional deposition of the CVI carbon. Specific heat capacity of the 3D–C/C increased as a monotonic function of temperature with an endothermal trend. In contrast to 3D–C/Cs, a weak exothermic effect was measured above 800°C for the 2D–C/Cs. The reason for this instability is not exactly known, but it was speculated that it is related to the stability of the charred resin matrix of the 2D composite. It is obvious that the exothermal behavior observed in 2D–C/Cs also contributes to a decrease on thermal conductivity at temperatures higher than 800°C.
Contrary to the 2D–C/Cs, 3D–C/Cs exhibited higher thermal conductivity in z–direction, despite the turbostratic structure of the ex–PAN fibers. This behavior is attributed to their highly crystalline rough laminar structure of CVI matrix and the continuous fiber/matrix interface which creates a non–disturbed thermal pathway. The crucial issues that determine thermal properties of the C/C composites are the crystallite size and the orientation of the 002 basal planes with respect to reinforcing fiber, a good interfacial contact between fiber and matrix, and the fiber architecture.