Analysis of damping in particle-reinforced superplastic zinc composites

Abstract

The damping behavior of superplastic zinc (SPZ) particulate composites with up to 42.5 vol pct spherical TiC particles (3 Μm in diameter) was studied in the 25 ‡C to 330 ‡C temperature range using a low frequency torsion pendulum. The observed damping at room temperature was modeled as a combination of a diffusion-controlled dislocation relaxation and a grain boundary relaxation. Addition of TiC produced a lower dislocation damping contribution at room temperature, but this loss was offset by an increased contribution from the grain boundary relaxation. An increase in the elastic modulus was also observed for the composite. The validity of a theoretical model for predicting changes in the grain boundary relaxation peak temperature resulting from the introduction of large nondeforming particles was tested. This study demonstrates that grain sliding in SPZ alloys occurs by cooperative sliding of grain clusters containing three to five grains. The activation energy for this process was found to be 111 kJ/mole (1.15 eV), which is in agreement with previously published values for grain sliding in SPZ. A second internal friction peak at a temperature just below the eutectoid transformation temperature was also observed and this peak was associated with recrystallization.