Characterization of SiC fiber (SCS-6) reinforced-reaction-formed silicon carbide matrix composites
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Characterization of SiC fiber (SCS-6) reinforced-reactionformed silicon carbide matrix composites M. Singh and R. M. Dickerson NYMA, Inc., Lewis Research Center Group, Cleveland, Ohio 44135-3191 (Received 26 May 1995; accepted 5 October 1995)
Silicon carbide fiber (SCS-6) reinforced-reaction-formed silicon carbide matrix composites were fabricated using a reaction-forming process. Silicon-2 at. % niobium alloy was used as an infiltrant instead of pure silicon to reduce the amount of free silicon in the matrix after reaction forming. The matrix primarily consists of silicon carbide with a bimodal grain size distribution. Minority phases dispersed within the matrix are niobium disilicide (NbSi2 ), carbon, and silicon. Fiber pushout tests on these composites determined a debond stress of ,67 MPa and a frictional stress of ,60 MPa. A typical four-point flexural strength of the composite is 297 MPa (43.1 KSi). This composite shows tough behavior through fiber pullout.
I. INTRODUCTION
In recent years, there has been an increasing demand for high performance and lightweight composite materials for aerospace and other high temperature structural applications. Silicon carbide-based advanced ceramics and composites which show high strength and toughness, oxidation resistance, and high thermal conductivity, have attracted attention for a variety of gas turbine engine applications.1,2 Fabrication of gas turbine components requires a process with near-net or complex shape capabilities. Currently, silicon carbide matrix composites are fabricated by a number of techniques: hot pressing,3,4 polymer pyrolysis,5 chemical vapor infiltration,6 and melt infiltration.7,9 Hot pressing, hot isostatic pressing, and sintering require high temperatures for processing (typically around 1600 –2000 ±C). Also, it is very difficult to attain full density due to the constraint of the fibers, especially in the case of pressureless sintering. In addition, complex and near-net shape requirements are additional problems to overcome. In the polymer pyrolysis process, multiple infiltrations are needed. Further, this process yields microcrystalline and often microcracked matrices.8 Another widely used technique is chemical vapor infiltration (CVI) which is a very slow process requiring a long processing time (often weeks). In addition, CVI cannot yield full density; composites typically have 10 –15% residual porosity.8 In the SILCOMPTM and other related processes, which are based on molten silicon infiltration, there is very little control over green body porosity, and thick interface coatings are required to prevent molten silicon attack.7,9 From the above, it is clear that the majority of current composite processing techniques are either expensive or have limitations in complex shape and near-net-shape fabrication. Therefore, it is necessary 746
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J. Mater. Res., Vol. 11, No. 3, Mar 1996
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to develop a processing approach that has near-net and complex
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