In Situ Synthesis of A MoSi 2 /SiC Composite Using Solid State Displacement Reactions
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IN SITU SYNTHESIS OF A MoSi2/SiC COMPOSITE USING SOLID STATE DISPLACEMENT REACTIONS C. H. HENAGER, JR.*, J. L. BRIMHALL*, J. S. VETRANO*, and J. P. HIRTH**
*Pacific Northwest Laboratory, Battelle Blvd., Richland, WA 99352 "**Washington State University, Dept. of Mechanical and Materials Engr., Pullman, WA 99164
ABSTRACT A high-strength in situ composite of MoSi2/SiC was synthesized using a solid state displacement reaction between Mo2C and Si by blending Mo2C and Si powders and vacuum hotpressing the powders at 1350°C for 2 h followed by 1 h at 1700'C. The resulting microstructure consisted of 1-pm diameter R-SiC particles (30 vol%) uniformly dispersed in a fine grained MoSi2 matrix. Transmission electron microscopy was used to study the fine-scale morphology and phase distribution of the composite. Evidence for a small amount of grain boundary glass phase was observed using diffuse dark field imaging. The fl-SiC particles were distributed mainly on grain boundaries and triple points within the MoSi2 matrix. These findings were used to rationalize the observed mechanical property behavior. INTRODUCTION Solid state displacement reactions can be used to produce intermetallic/ceramic matrix composites in situ [1-3]. Interwoven and dispersed microstructures, important for composites, can be produced using displacement reactions [1-4]. The reinforcement phases are produced in situ, an increasingly important idea in composite synthesis because of the potential for low cost processing and improved mechanical properties. Issues of microstructural control and cleanliness can potentially be addressed using displacement reactions in ways that are not possible with other synthesis techniques. A similar approach, usually termed reaction sintering, has been used as a method of synthesizing ceramic composites, but with limited success in producing high-quality structural materials [4]. An example of a ceramic composite produced by reaction sintering is tZrO2 + mullite from ZrSiO4 + alumina [5]. EXPERIMENTAL PROCEDURES Powders of Mo2C (d
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