High-temperature viscoelastic mechanism for SiC fibers to elucidate creep and recovery behaviors

Mastering the high-temperature creep behavior of SiC fibers plays pivotal role in designing reinforced ceramic matrix composites. Creep viscoelastic behavior is activated at higher temperatures due to complicated interactive coordination between grain interiors and grain boundaries. This study investigated the tensile creep behaviors at different generations of SiC fibers under conditions of various stress and temperatures. The creep recovery behaviors after unloading exhibits the viscoelastic nature, which comes from the possible motion of amorphous phase near massive grain boundaries. It is driven by the release of elastic energy of the grain boundary, evidenced by frequency shifts in Raman spectroscopy. Then classical diffusion creep theory is modified to a viscoelastic model incorporating physical parameters such as the elasticity, viscosity, and threshold stress for SiC fibers. The proposed equations have been well supported by creep test results. The viscosity and elasticity parameters decrease with increasing temperature, the latter being more sensitive. 3rd generation fiber exhibits higher viscosity and elasticity, explaining better creep resistance. The model can evaluate the elastic and plastic contributions and predict creep results at higher temperatures. This work helps to understand high-temperature SiC fiber creep, and to guide optimizing fiber-reinforced composites.