Mechanical spectroscopy of interface stress relaxation in metal–matrix composites

C/Mg–2 wt%Si composites were processed by gas-pressure infiltration of long carbon fibers with molten Mg–2 wt%Si. These composites have specific Young's modulus more than 4 times and damping capacity 10–100 times higher than steels or aluminum alloys. The thermal behavior of these materials was investigated by mechanical spectroscopy. A shear modulus anomaly was observed between 200 and 400 K, which has been attributed to the interface de-bonding of the fibers at low temperature. Thermal stress relaxation at interfaces gives rise to transient damping (T˙ effect), which has been interpreted as being due to hysteretic dislocation motion. It is shown that the hysteretic and reversible motion of dislocations that relax interface stresses is a beneficial factor for high damping capacity and good resistance to fatigue.