Short Fibre Reinforced RBSN

A new approach was carried out to establish short fiber reinforced ceramic matrix composites (CMCs) by mixing of carbon or SiC fibers, ceramic fillers and a viscous ceramic precursor in a kneader, followed by a forming step via warm pressing. The shear forces applied by mixing technique resulted in fiber shortening and aligning. Fiber orientation was maintained during granulation and transferred to the green body achieved by a warm pressing process. To transform the composite from the polymer into a ceramic state a two-step process was applied where the preforms were first pyrolyzed, followed by a nitridation process to form a reaction bonded silicon nitride (RBSN) matrix. The transformation of the precursor was accompanied by an extensive volume shrinkage, which caused differential shrinkage due to different fiber orientation in granules. Stresses between the granules were built up and caused cracking in the specimen. The following nitridation step formed short fiber reinforced composites with an interesting spectrum of properties. (Author)