Microstructure and high temperature strength of SiC_W/SiC composites by chemical vapor infiltration

SiC_W/SiC composites without an intergranular glassy phase are prepared by the CVI process. The microstructure and high temperature strength of SiC_W/SiC composites are investigated. The high temperature strength of SiC_W/SiC composites depends on the interfacial bonding strength between matrix and whiskers. The matrix is effectively strengthened and toughened by the whiskers, and SiC_W/SiC composites show a constant strength of 475±32 MPa below 1000°C. The flexural strength gradually declines from 475±32 MPa to 208±15 MPa at the temperature from 1000°C to 1500°C due to the decreased whisker-matrix interfacial bonding strength. The interfacial bonding strength is too low to transfer stress from the matrix to the whiskers, and SiC_W/SiC composites show a constant strength of 208±15 MPa at temperatures from 1500°C to 1800°C. The fracture mode of SiC_W/SiC composites changes from the toughened fracture below 1000°C to the brittle fracture above 1000°C.