Chapter 6. Mechanical Properties of Hot Pressed SiC Platelet-Reinforced MoSi₂

Summary

Mechanical characteristics of two different purity molybdenum disilicide (MoSi₂) intermetalllic matrices reinforced with 20 vol% silicon carbide platelets were studied. Matrices examined had purities of 99.5% and 99.95%. Mechanical properties tested included flexure strength, fracture toughness, and pin shear strength. Mechanical property data were collected between room temperature and 1650°C. At room temperature, flexure strengths were increased by 45% and 98% for the low-purity and high-purity MoSi₂ composites, respectively, when compared to monolithic MoSi₂ Elevated temperature strengths were increased by 142% at 1093°C for the low-purity MoSi₂ composite and 150% at 815°C for the high-purity MoSi₂ composite when compared to monolithic MoSi₂. At temperatures greater than 815°C the low-purity MoSi₂ specimens had higher average flexure strengths than the high-purity specimens. Below the brittle-to-ductile transition temperature, ∼1000°C, both compositions exhibit comparable modes of failure. Above the brittle-to-ductile transition temperature, the modes of failure vary with composition. High-purity composites failed intergranularly while low-purity composites failed transgranularfy. Fracture toughness was dramatically increased when compared to monolithic MoSi₂. Improved fracture toughness was maintained to 815°C and then decreased slightly beyond temperatures of 1093°C. Minimum pin shear strength at room temperature was 54.4 MPa and was maintained to 1093°C before decreasing at higher temperatures. Ultimate pin shear strength values were not measured due to premature failure of the test specimens in three-point bending.