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Published online by Cambridge University Press: 25 February 2011
Solid state displacement reactions are being studied at Pacific Northwest Laboratory (PNL) as a method of synthesizing intermetallic and ceramic composites in situ. A high-strength in situ composite of MoSi2/SiC was synthesized using a solid state displacement reaction between Mo2C and Si. Diffusion couples between Mo2C and Si processed at 1200°C revealed the formation of aligned SiC platelets in a MoSi2 matrix. In situ composites were also synthesized by blending Mo2C and Si powders and vacuum hot-pressing the powders at 1350°C for 2 h followed by 1 h at 1700°C. The resulting microstructure consisted of 1-μm diameter SiC particles (30 vol%) uniformly dispersed in a fine grained MoSi2 matrix. Densities of 5.53 g/cm3 were obtained along with a microhardness of 14.2 GPa. Bend bars and chevron-notched bars revealed a strength of 475 MPa and a fracture toughness of 6.7 MPa√m at room temperature. Bend strengths increased to 515 MPa at 1000°C and then decreased to 112 MPa at 1200°C. Measured fracture toughness increased to 10.5 MPa√m at 1050°C.