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

SiCW/SiC composites without an intergranular glassy phase are prepared by the CVI process. The microstructure and high temperature strength of SiCW/SiC composites are investigated. The high temperature strength of SiCW/SiC composites depends on the interfacial bonding strength between matrix and whiskers. The matrix is effectively strengthened and toughened by the whiskers, and SiCW/SiC composites show a constant strength of 475A plus or minus 32 MPa below 1000A degree C. The flexural strength gradually declines from 475A plus or minus 32 MPa to 208A plus or minus 15 MPa at the temperature from 1000A degree C to 1500A degree 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 SiCW/SiC composites show a constant strength of 208A plus or minus 15 MPa at temperatures from 1500A degree C to 1800A degree C. The fracture mode of SiCW/SiC composites changes from the toughened fracture below 1000A degree C to the brittle fracture above 1000A degree C.