Joining of SiCf/SiC using polycarbosilane and polysilazane preceramic mixtures

Polycarbosilane (PCS)/polysilazane (PSZ) preceramic mixtures with weight ratios of 100/0, 75/25, 50/50, 25/75, and 0/100 were used as a filler for the joining of SiCf/SiC to obtain high purity SiC at the joining region. SiCf/SiC was fabricated by the electrophoretic infiltration of a SiC-based matrix phase into Tyranno SA3 SiC fabrics followed by hot-pressing at 1750 degrees C under 20 MPa for 2 h in an Ar atmosphere. Microstructural analysis confirmed a sound join without cracks after joining at 1750 degrees C for 2 h under a pressure of 10 MPa. SiC was the only phase remaining at the joint when PCS was used, while a small amount of Si3N4 along with the main SiC were observed in the join using PSZ. The flexural strengths of the butt-joint SiCf/SiC were 120 and 137 MPa for the samples joined using a pure PCS and PSZ at 1750 degrees C, respectively, whereas those joined using the mixture fillers showed relatively lower strength.