Infiltration of SiC preforms with iron silicide melts: microstructures and properties

Spontaneous infiltration of SiC preforms with FeXSiY (=Fe3Si, Fe5Si3 and FeSi) melts produced SiC/FeXSiY composites with nearly full density (≥96.5% theoretical density). The phases, microstructures and mechanical properties have been studied with conventional materials characterization techniques including X-ray diffraction, optical microscopy, scanning electron microscopy etc. A key issue behind these studies is dissolution of SiC in FeXSiY melts during infiltration. The dissolution of SiC in Fe3Si melt led to carbon precipitation and phase changes (Fe3Si disappeared and Fe5Si3 and FeSi formed). However, Fe5Si3 and FeSi infiltration gave no carbon precipitation, but SiC sintering, particle coalesce and grain growth instead. Extra-large SiC grains and SiC single crystals were found in fine SiC (0.5 μm) infiltrated by Fe5Si3. Phase equilibrium calculations for Fe–Si–C system were performed at 1873 K using chemsage in order to study SiC solubility and the condition for the precipitation of SiC rather than C in Fe–Si melt. Mechanical properties including micro-hardness, bending strength and Weibull modulus of all infiltrated samples were tested and analyzed on the basis of phase and microstructure observations.