Composite materials composed of a glass-ceramic matrix and silicon-carbon (SiC) fibers have been recently developed for high-temperature applications.
In the present work, damping properties and the dynamic modulus of unidirectional composites made with SiC-Nicalon fibers and aluminum silicate based matrix (glassy or partially recrystallized) have been studied in a variable frequency torsion pendulum over wide temperature and frequency ranges.
A relaxation peak, characteristic of the vitreous phase, has been observed in specimens with different ratios of the recrystallized phase. The apparent activation energy (Hp = 1.24 eV) and the limit relaxation time (τ0 = 2.10-16s) were found to be constant for all samples.
On every specimen, a decrease of the peak width, accompanied by an increase in the relaxation strength, was observed for measurements at increasing temperatures.
In glassy matrix specimens, the low-frequency damping background has been found to increase abruptly. In the partially crystallized composite specimens, a peak caused by the glassy transition superimposed on to the high-temperature background was also observed.