A new accommodation process for high-strain-rate superplastic flow is analyzed from a viewpoint of the relaxation of stress concentrations at triple junctions of boundaries for the alloys and around reinforcement particles for the composites resulting from sliding at boundaries and interfaces. A special process by an accommodation helper such as a liquid phase is required to continue superplastic flow when the stress concentration is insufficiently relaxed by diffusional flow and/or diffusion-controlled dislocation movement under the given deformation conditions. A liquid phase plays an important role as an accommodation helper in the accommodation mechanisms of high-strain-rate superplasticity, that is, in an assistance to relax stress concentrations caused by sliding. However, the presence of a liuqid phase does not always lead to the high-strain-rate superplasticity. The critical conditions such as the optimum distribution, thickness and volume in a liquid phase are discussed based on the observation results by transmission electron microscopy and the cavitation bahvior. Cavitation behavior at various conditions for liquid phases are investigated by a quantitative analysis for a high strain rate superplastic materials. It is suggested from an theoretical analysis that diffusion-controlled cavity growth is limited and the plasticity-controlled cavity growth is dominant when stress concentrations at triple junctions of boundaries and around reinforcements are relaxed by the presence of a liquid phase, so that the cavity growth is significantly slow in a small cavity size range. This view was in agreement with the experimental data of the cavity growth rates.
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