Effect of chopped Si–Al–C fiber addition on the mechanical properties of silicon carbide composite

Silicon carbide (SiC) composites containing 0–50 mass% of chopped Tyranno Si–Al–C (SA) fiber (mean length: 214 lm (SA(214)), 394 lm (SA(394)), and 706 lm (SA(706)) were fabricated using the hotpressing technique at 1800 C for 30 min under a uniaxial pressure of 31 MPa in Ar atmosphere. The maximum flexural strength of the SiC composite was 344 MPa for 30 mass%of SA(706) fiber addition, whilst the maximum fracture toughness was 4.7 MPa m1/2 for 40 mass% of SA(706) fiber addition. Increasing the mean fiber length from 214 to 706 lm decreased the flexural strength from 380 to 281 MPa for 30 mass% of fiber addition, whilst the fracture toughness increased from 3.4 to 4.7 MPa m1/2 for 40 mass% of fiber addition. Through use of a treated SA(706) fiber containing an approximately 100 nm surface layer of carbon, the fracture toughness further increased to 6.0 MPa m1/2 for 40 mass% of fiber addition; this value was more than twice that of the monolithic SiC ceramic and is believed to be the highest so far achieved for this type of SiC/SiC composite containing chopped fibers