Short silicon nitride fibers were fabricated by direct nitridation of ferrosilicon in N2 atmosphere, and their structure and possible growth mechanism were characterized and investigated. The rod-like fibers which were α-Si3N4 with a low degree of crystallization and a high aspect ratio had a diameter of about 4 μm and a length close to a few millimeters. Belt-like fibers with a width about 5 μm and a thickness about 1 μm were also found in the nitrides. Scanning electron microscope (SEM), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), and selected area electron diffraction (SAED) investigations indicated that the fibers were single-crystalline α-Si3N4 with few amorphous distributed in the edge region, and the fibers grew by vapor–liquid–solid (VLS) mechanism.
Si3N4-Fe3Si composites were prepared using Fe-Si3N4 as the source of Fe3Si by gas-pressure sintering. By adding different amounts of Fe-Si3N4 into the starting powders, Si3N4-Fe3Si composites with various Fe3Si phase contents were obtained. The microstructure and mechanical properties of the composites were investigated. With the increase of Fe-Si3N4 contents, the content and particle size of Fe3Si both increased. When more than 60 wt. % Fe-Si3N4 were added, the abnormal growth of Fe3Si particles occurred and oversized Fe3Si particles appeared, leading to non-uniform microstructures and worse mechanical properties of the composites. It has been found that Fe3Si particles could toughen the composites through particle pull-out, interface debonding, crack deflection, and particle bridging. Uniform microstructure and improved mechanical properties (flexural strength of 354 MPa and fracture toughness of 8.4 MPa·m1/2) can be achieved for FSN40.
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