Zhijun Cheng

Design, Fabrication, and Properties of High Damping Metal Matrix Composites—A Review

Nowadays it is commonly considered that high damping materials which have both the good mechanical properties as structural materials and the high damping capacity for vibration damping are the most direct vibration damping solution. In metals and alloys however, exhibiting simultaneously high damping capacity and good mechanical properties has been noted to be normally incompatible because the microscopic mechanisms responsible for internal friction (namely damping capacity) are dependent upon the parameters that control mechanical strength. To achieve a compromise, one of the most important methods is to develop two-phase composites, in which each phase plays a specific role: damping or mechanical strength. In this review, we have summarized the development of the design concept of high damping composite materials and the investigation of their fabrication and properties, including mechanical and damping properties, and suggested a new design concept of high damping composite materials where the hard ceramic additives exhibit high damping capacity at room temperature owing to the stress-induced reorientation of high density point defects in the ceramic phases and the high damping capacity of the composite comes mainly from the ceramic phases.

Phase transition process in oxide-ion conductor β-La2Mo2−xWxO9 assessed by internal friction method

The oxygen ion diffusion and phase transition in La2Mo2−xWxO9 (x=0, 0.25, 0.75, 1.0, and 1.4) have been investigated by the internal friction method. In addition to the low-temperature relaxation peak associated with oxygen ion diffusion, an internal friction peak of phase transition type is observed around 350°C in all tungsten substituted La2Mo2O9 compounds. Based on the behavior of this peak and the ionic conduction properties, the mechanism of this peak is suggested to be associated with a transition from static disordered state to dynamic disordered state of oxygen ion distribution in anion sublattice that most probably results in a transition of the ionic conduction from the Arrhenius type to the Vogel-Tamman-Fulcher type.