Characterization of interfaces in C fiber-reinforced laminated C–SiC matrix composites

Abstract

Interfacial studies of carbon fiber-reinforced laminated matrix composites (LMCs) of alternating matrix layers of SiC and carbon prepared by forced-flow thermal-gradient chemical vapor infiltration (FCVI) have been undertaken by transmission electron microscopy (TEM). The carbon-carbon interfacial region consistently displayed distinctive features that enabled the microstructures of the fiber carbon, a thin carbon layer deposited as fiber coating, and the matrix carbon to be distinguished. A thin discontinuous layer of relatively lower graphitic degree was observed at the interface of the fiber and its carbon coating, whereas the interface between the fiber coating and the first carbon layer of the matrix displayed a thin, patchy, and partially ordered layer. At the C-SiC interfaces within the matrix, the interface was observed to be well-defined on one side with the c-axis of the pyrocarbon layers nearly perpendicular to the interface, but, at the other end, the interface appeared rough and somewhat diffuse due to the nature of SiC growth during CVI.

Microstructure and mechanical properties of carbon fiber reinforced multilayered (PyC–SiC)n matrix composites

“…4(a)), but it is interesting that no delamination is found between the first PyC layer and the second SiC layer, and between the third PyC layer and the fourth SiC layer. Such phenomenon could be explained by incorporating the TEM analytical results by Appiah [15] and Bertrand [26]. The intervening SiC layers grow onto the oriented PyC layers resulting in a smooth and strong interfaces of PyC 1 /SiC 2 and PyC 3 /SiC 4 , while the PyC layers deposit around the preexisting SiC layers made of large-faceted crystals leading to a rough and weak interface of SiC 2 /PyC 3 (the subscripts denote the sequence of the layers from inside to outside) [15,26].…”

“…Such phenomenon could be explained by incorporating the TEM analytical results by Appiah [15] and Bertrand [26]. The intervening SiC layers grow onto the oriented PyC layers resulting in a smooth and strong interfaces of PyC 1 /SiC 2 and PyC 3 /SiC 4 , while the PyC layers deposit around the preexisting SiC layers made of large-faceted crystals leading to a rough and weak interface of SiC 2 /PyC 3 (the subscripts denote the sequence of the layers from inside to outside) [15,26]. Additionally, the mismatch of coefficient of thermal expansion (CTE) between the PyC and SiC (α SiC = 5 × 10 −6 /K, α C = 1 × 10 −6 /K [27]) causes matrix delamination during the cooling down stage of processing.…”

“…Most investigations show that the multilayered interphases are beneficial to improving mechanical properties, oxidation resistance and neutron irradiation tolerance of composites [7][8][9][10][11][12]. Furthermore, the concept of multilayered structure has been extended to the matrix itself yielding laminated matrix composites (LMCs) [13][14][15], with a view to improving the performance of brittle materials, such as C/C composites.…”

“…Appiah et al [14,15] studied the effect of deposition temperature gradient on microstructural differences of laminated PyC-SiC matrix composites fabricated by forced flow-thermal gradient chemical vapor infiltration (F-CVI), and characterized the detailed interfacial microstructures between the fiber and matrix and the PyC-SiC interfaces within the matrix. Lamouroux et al [16] introduced a multilayer SiC-B-C ceramic matrix to a 2.5D preform by pulsed CVI (P-CVI) and found that the multilayered ceramic matrix could improve the oxidation resistance and thermomechanical behavior of the composites.…”

Microstructure, mechanical properties and reaction mechanism of KD-1 SiCf/SiC composites fabricated by chemical vapor infiltration and vapor silicon infiltration

“…The microstructural investigation was carried out using a JEOL-2010F transmission electron microscope (TEM). The preparation method of specimens for TEM observations followed the procedure described by Appiah et al [10].…”