Temperature-dependent elastic and anelastic behavior of silicon-based fiber-reinforced silicon carbide ceramic matrix composites

Temperature-dependent elastic and anelastic properties of silicon-based fiber-reinforced silicon carbide ceramic matrix composites were determined by establishing continuous flexural vibrations in the material at its lowest resonance (eigen) frequency. Anelastic behavior as a function of temperature was determined by observation of the time-dependent amplitude free decay of the sample. The elastic modulus of all the materials studied decreased with increasing temperature, with the exception of carbon fiber-reinforced silicon carbide (C/SiC). Elastic behavior between ceramics is similar up to 600°C, above which material behavior differentiates. Melt-infiltrated composite materials exhibited the greatest modulus decrease to only 88% of its room temperature value at 1200°C. Anelastic strain-independent behavior of composites and monoliths display constant internal friction from room temperature to 400°C. Above 400°C, internal friction differentiates depending upon fabrication method. The highest internal friction occurs in Slyramic fiber-reinforced melt-infiltrated silicon carbide (SiC/SiC) with a value of 200×10−4 in units of logarithmic decrement (log dec). With the high-temperature background removed, an energy absorption peak with a height of 100×10−4 log dec is observed centered at 800°C.