MICROSTRUCTURES AND PROPERTIES OF INFILTRATION OFSiC PREFORMS WITH IRON SILICIDE MELTS

Spontaneous infiltration of SiC preforms with Fe_xSi_y (Fe₃Si , Fe₅Si₃ and FeSi) melts was employed to produce fully dense ( > 96.5 % theoretical density) SiC/ Fe_xSi_y composites1 The phases , microstructures and mechanicalproperties were studied by using conventional materials characterization techniques including X-ray diffraction , optical microscopy , scanning electron microscopy , etc. A key issue behind the whole study is the dissolution and precipitation of SiCin Fe_xSi_y melts during infiltration. The dissolution of SiC in Fe₃Si melts leads to carbon precipitation and phase changes( Fe₃Si disappeared and Fe₅Si₃ and FeSi formed) . However , Fe₅Si₃ and FeSi infiltration gives no carbon precipitation , butSiC sintering , particle coalescence and grain growth. Extra-large SiC single crystals are found in fine SiC (0.5μm) infiltrated by Fe₅Si₃ . The phase equilibrium of Fe-Si-C system is quantitatively analysed at 1873 K using CHEMSAGE. SiCsolubility and the condition for SiC precipitation rather than C in Fe-Si melt are determined. Mechanical properties including micro-hardness , bending strength and Weibull modulus of all infiltrated samples were tested and analyzed on the basisof phase and microstructure observations.