Abstract
Interrelation between superplastic deformation and internal friction was investigated using an Al-Cu eutectic alloy. The increment of internal friction at room temperature due to deformation, ΔQ-1, increased with the amount of strain under non-superplastic deformation conditions, while under superplastic conditions the change in ΔQ-1 was relatively small. Strain amplitude dependence was observed in ΔQ-1 of specimens deformed at lower temperatures or higher strains. An analysis of the strain amplitude dependent internal friction was carried out by using Granato-Lücke theory. It was found that ΔQ-1 was proportional to the dislocation density ∧. It was also found that the strain rate sensitivity of flow stress m (σ=kεm, σ: flow stress, ε: strain rate, k: constant) was proportional to the negative value of ΔQ-1 or ∧. Changing characteristics of ΔQ-1 for various strains and deformation conditions showed a good correspondence to the results of the direct observation of dislocation structures.
These results are consistent with the superplastic deformation mechanism proposed previously, which involves the grain boundary sliding compensated by the diffusional process predominantly and the dislocation motion acting to decrease the m value.
