The internal friction behavior of Al green power compact duxing the sintering process was studied as a function of temperature. The internal friction measurements were performed from room temperature to 600 °C. Two typical internal friction peaks were detected corresponding to heating and cooling processes, respectively. The heating peak corresponds to a recrystallization process of deformed Al particles, which is influenced by many extrinsic parameters, such as measuring frequency, strain amplitude, heating rate, power particle size and compacting pressure. However, the intrinsic nature of the peak is originated from the micro-sliding of the weak-bonding interfaces between Al particles and increased dislocation density induced in compressing. The cooling peak with the activation energy of (1.64±0.06) eV is associated with the grain boundary relaxation, which can be interpreted as the viscous sliding of grain boundaries. The similar phenomena are also found in the Mg green powder compact.
The damping capacity of the shape memory alloy Cu-20.4A1-8.7Mn （at.%） at room temperature is investigated by an internal friction technique. Results indicate that the alloy exhibits higher damping capacity in the Martensitic condition than that in the austenitic condition due to the latter having lower intrinsic damping capacity and pinning effect coming from the precipitate particles. The maximum damping capacity is obtained in the coexistence condition of Martensite and austenite. The condition can be achieved when processing an isothermal ageing for the as-cast sample at temperatures of 100 ℃- 150 ℃. Three possible mechanisms are considered to account for the maximum damping capacity. They are listed as much increased interfaces between twin boundaries, owing to the thinning of martensitic plates, martensitic transformation induced by the applied stress during internal friction measurements, phase transformation itself based on the coexistence of martensitic and austenitic phases with a macroscopic amount. However, the contribution of the first mechanism is predominant.
