SiCf–SiBC composites: microstructural investigations of the as-received material and creep tested composites under an oxidative environment |
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Authors: | G Farizy J-L Chermant J C Sangleboeuf & J Vicens |
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Affiliation: | LERMAT-ISMRA, FRE CNRS 2149, 6 Boulevard Maréchal Juin, 14050 Caen Cedex, France; LARMAUR, UPRES-JE 2310, Universitéde Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France |
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Abstract: | SiCf–SiBC composites fabricated by Snecma Propulsion Solide (St Médard en Jalles, France) were investigated by SEM and HRTEM in the as‐received state and after creep tests performed in air, in a temperature range 1423–1573 K, under 170 and 200 MPa. These composites are reinforced by Hi‐Nicalon fibres (Nippon Carbon). A pyrocarbon interphase was first deposited on the fibres. The matrix was then deposited on the fibrous preform by several chemical vapour infiltrations (CVI). As a result the matrix is multilayered and based on the Si–B–C ternary system. This matrix is self‐sealing: this is due to the presence of boron inducing the formation of a sealant glass if the material is heated in an oxidative environment. This glass will protect fibres and fibre/matrix interphases against oxidation. Hi‐Nicalon fibres as well as the different matrix layers were studied by HRTEM and EDX. Some investigations were carried out on the creep‐tested specimens in order to characterize modifications observed in the different constituents of the composites, particularly at the interfaces between the matrix layers and at the fibre/matrix interface. It was shown that several matrix layers crystallized during the creep tests. Moreover, a thin silica layer was observed at the pyrocarbon/matrix interfaces. Differences between the behaviour of the same type of material creep tested under neutral atmosphere are discussed. |
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Keywords: | EDX interfaces multilayered matrix SiCf–SiBC transmission electron microscopy |
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