HREM identification of "one-dimensionally-disordered" polytypes in the SiC (CVI) matrix of SiC/SiC composites

Sylvie Schamm-Chardon (1) , Annie Mazel (1) , Dominique Dorignac (1) , Jean Sévely (1)

1 CEMES - Centre d'élaboration de matériaux et d'études structurales

The matrix of SiC/SiC composites has been observed by electron energy loss spectroscopy (EELS) and high resolution electron microscopy (HREM) from both the chemical and the structural point of view. In this material, columnar growth and radial arrangement around the fibres of the reinforcement are typically observed for the crystal of the matrix. The ratio, Si/C = 1, of these crystals has been checked. The cubic structure of some of them has been identified through their diffraction patterns. High resolution experiments were performed to recognize the structure of the others polytypes, which are characterized by a disorder in the direction of the tetrahedral layer stacking. For this reason, they are called, "one-dimensionally-disordered" polytypes. The PHILIPS CM30-ST point resolution (0.19 nm) enables the projected SiC structure to be recognized so that the degree of disorder in this polytype can be estimated. The interpretation of the experimental images was based on comparison with simulations.

2014 La matrice de carbure de silicium des composites SiC/SiC a été examinée d'un point de vue chimique et structural par spectroscopie de pertes d'énergie d'électrons (EELS) et par microsco-pie électronique à haute résolution (MEHR). La croissance colonnaire des cristaux de la matrice et leur distribution radiale par rapport aux fibres qui constituent le renfort sont caractéristiques de ce matériau. La st0153chiométrie des cristaux a été vérifiée (Si/C = 1). La structure cubique (polytype 3C) de certains d'entre-eux a été identifiée à l'aide des diagrammes de diffraction. Dans le cas d'autres cris-taux, dits "polytypes de désordre unidimensionnel", l'imagerie haute résolution s'est avérée nécessaire pour mettre en évidence la désorganisation dans la direction d'empilement des couches de tétraèdres. La résolution ponctuelle, 0,19 nm, du microscope PHILIPS CM30-ST, fonctionnant à 300 kV, permet de reconnaître la structure projetée de SiC et d'évaluer le degré de désordre dans ces polytypes. La simulation numérique des images nous a permis d'interpréter sans ambiguité nos clichés expérimentaux. Abstract. 2014 The matrix of SiC/SiC composites has been observed by electron energy loss spec-troscopy (EELS) and high resolution electron microscopy (HREM) from both the chemical and the structural point of view. In this material, columnar growth and radial arrangement around the fibres of the reinforcement are typically observed for the crystal of the matrix. The ratio, Si/C = 1, of these crystals has been checked. The cubic structure of some of them has been identified through their diffraction patterns. High resolution experiments were performed to recognize the structure of the others polytypes, which are characterized by a disorder in the direction of the tetrahedral layer stacking. For this reason, they are called, "one-dimensionally-disordered" polytypes. The PHILIPS CM30-ST point resolution (0.19 nm) enables the projected SiC structure to be recognized so that the degree of disorder in this polytype can be estimated. The interpretation of the experimental images was based on comparison with simulations. Microsc. Microanal Microstruct. 2 (1991) Classification Physics Abstracts 61.16D-81.15H FEBRUARY 1991, PAGE 59 1. Introduction.

Domaines: Physique [physics]

Sylvie Schamm-Chardon, Annie Mazel, Dominique Dorignac, Jean Sévely. HREM identification of "one-dimensionally-disordered" polytypes in the SiC (CVI) matrix of SiC/SiC composites. Microscopy, Microanalysis, Microstructures, 1991, 2 (1), pp.59-73. ⟨10.1051/mmm:019910020105900⟩. ⟨hal-01745071⟩